Analysis of Technologies for the Reclamation of Illegal Landfills: A Case Study of the Relocation and Management of Chromium and Arsenic Contamination in Łomianki (Poland)

Abstract

The reclamation of illegal landfills poses a significant threat to the environment. An example of such a case is Łomianki near Warsaw, where an illegal landfill contained alarming levels of arsenic and chromium, posing a potential risk to the health of local residents due to the possibility of these metals contaminating a nearby drinking water source. Initial geochemical tests revealed high concentrations of these metals, with chromium reaching up to 24,660 mg/kg and arsenic up to 10,350 mg/kg, well above international environmental standards. This study presents effective reclamation strategies that can be used in similar situations worldwide. The reclamation allowed this land to be used for the construction of the M1 shopping center while minimizing environmental hazards. The study is based on a case study of the reclamation of this illegal landfill. The methods used in this project included the relocation of approximately 130,000 m³ of hazardous waste to a nearby site previously used for sand mining. Bentonite mats and geotextiles were used to prevent the migration of contaminants into the groundwater. The waste was layered with sand to assist in the structural stabilization of the site. In addition, proper waste segregation and drainage systems were implemented to manage water and prevent contamination. Eight years after the reclamation, post-remediation soil surveys showed significant improvements in soil quality and structural stability. Specifically, the Proctor Compaction Index (I_S) increased from an estimated 0.5–0.7 (for uncontrolled slope) to 0.98, indicating a high degree of compaction and soil stability, while arsenic and chromium levels were reduced by 98.4% and 98.1%, respectively. Reclamation also significantly reduced permeability and settlement rates, further improving the site’s suitability for construction. The cost-benefit analysis showed a cost saving of 37.7% through local waste relocation compared to off-site disposal, highlighting the economic efficiency and environmental benefits. The main conclusions of this study are that land reclamation effectively reduced environmental hazards; innovative solutions, such as bentonite mats, advanced waste sorting, geotextiles, and drainage systems, improved environmental quality; and the Łomianki case serves as a model for sustainable waste management practices.

1. Introduction

Rehabilitating degraded areas, such as landfills, is a valuable practice for restoring ecological function and restoring land reuse [1]. Remediation methods—biological [2,3], chemical [4], or physical [4,5]—are selected based on contamination type, geology, and intended site use [6]. Relocation strategies are particularly significant, involving waste transfer to more suitable sites for management and treatment [7,8,9]. This approach is used when landfills violate environmental laws or when land is designated for alternative uses [7,10]. Eiselt notes that relocation is necessary for environmentally inappropriate sites or land reuse [7], minimizing environmental and health risks while preparing sites for future use [11]. For example, chromium levels in water at Hazaribagh tannery decreased by 97% post-relocation, significantly reducing exposure and improving health [11]. Organized community relocations enhance health outcomes and sustainability, as communities adapt to new locations [12], and develop mechanisms to minimize environmental threats [12,13,14]. However, resettlement can also cause adverse health effects, highlighting the need for careful planning and community involvement [15]. Common landfill remediation methods include contaminated soil removal [16], sealing mats [17], and drainage systems to stormwater management [18]. Bentonite mats, combined with proper drainage systems, effectively prevent contaminant migration and improve soil and groundwater quality [19,20,21]. Sobti and Singh [20] emphasized bentonite-enriched mixes as effective barrier materials, enhancing hydraulic conductivity control and preventing contaminant migration.

The rehabilitation of the illegal landfill in Łomianki (1995 and 1997) is a successful example of landfill remediation. The project prepared the site for the Auchan shopping center (M1), driven by urgency and environmental concerns due to its proximity to a drinking water source. The decision-making process considered hydrological issues and effective waste removal. Tests revealed high concentrations of heavy metals like chromium and arsenic. A pivotal step was relocating the waste to an adjacent parcel (#608), previously used for sand mining. The remediation involved the placement of two 1-m-thick bentonite mats to prevent contamination, the deposition of highly mineralized waste, the layering of waste with thin sand layers compacted to meet required specifications, and the application of geotextiles and a topsoil layer containing 2% organic matter. Post-rehabilitation studies revealed significant improvements in soil quality and structural stability. Today, the area functions as a fully operational M1 shopping center.

This study focuses on strategies implemented during the transformation, including the relocation of hazardous waste, the use of bentonite mats and geotextiles, and the layering of waste with sand. The research concludes that reclaiming illegal landfills requires integrating environmental protection with urban development goals. The Łomianki project exemplifies how innovative technical solutions can transform hazardous sites into functional urban spaces, relevant to other urban sites facing similar challenges. This approach highlights the importance of balancing environmental concerns with economic needs, especially near residential areas or sensitive water resources.

The Łomianki case study highlights several site-specific challenges and research gaps that warrant further investigation. One critical issue is the hydrogeological sensitivity of the area, characterized by its proximity to groundwater sources and the Vistula River, which increases the risk of contaminant migration. The heterogeneous diffusion of contaminants, especially heavy metals such as arsenic and chromium, complicated remediation efforts [22,23]. The long-term stability of the remediated site also remains a concern, as the potential remobilization of contaminants due to changes in environmental conditions (e.g., flooding, pH fluctuations) could undermine the effectiveness of remediation efforts [24]. Addressing these challenges will require advanced monitoring systems, adaptive remediation strategies, and further research into the site-specific behavior of contaminants to ensure sustainable and effective remediation outcomes. The central research question focuses on defining a replicable decision-making process for revitalizing illegal landfill areas, emphasizing proactive stakeholder engagement, comprehensive geotechnical analysis, and rigorous chemical assessment. Using the Łomianki case study, the research identifies strengths and limitations, offering insights for effective planning. This study addresses a significant knowledge gap in site remediation methods, providing a roadmap for similar processes worldwide. The Łomianki case serves as a model for addressing analogous challenges, highlighting the importance of integrating environmental remediation techniques with urban development needs. This integration contributes to sustainable urban transformation. The study offers actionable recommendations for similar sites worldwide.

2. Literature Review

In metropolitan areas, landfill reclamation is becoming increasingly significant as cities expand and land demand grows [25]. This addresses land scarcity and promotes sustainable waste management (SWM) practices, essential for urban cleanliness and environmental protection [26]. Reclaiming landfills aligns with global trends prioritizing waste utilization over traditional landfilling [27]. Innovative methodologies, such as using incinerator bottom ash (IBA), enhance shear strength and reduce heavy metal leaching, proving viable for reclamation [28]. Additionally, waste tires and blocks are utilized to construct resilient structures, combining waste management and land reclamation benefits [29]. Rehabilitating illegal landfills involves innovative methods to restore environmental integrity and repurpose land. Natural mineral-organic substances effectively reduce heavy metal contamination in soil from unauthorized dumps [30,31,32], while screening landfill masses creates soil-recultivators for further reclamation [33]. Naturalistic redevelopment, exemplified by the Vizzolo Predabissi landfill in Italy, eliminates artificial structures and promotes natural vegetation, transforming sites into ecosystems [34]. Unauthorized dumps can also be converted into municipal solid waste landfills through vertical planning and drainage systems, addressing leachate management and preparing sites for future waste disposal [35]. A sustainable waste recovery approach further enhances these efforts. Specifically, biomining utilizes biological processes to recover valuable materials from old landfills, as highlighted in urban India [36]. Projects like the Guiyang landfill in China propose reshaping landfill sites into community spaces, integrating environmental education and recreational areas, which rehabilitates land and enhances its value for residents [37]. However, challenges remain in implementation, particularly regarding regulatory frameworks and community acceptance, with concerns about social equity and environmental justice in urban planning [38]. Effective landfill remediation strategies address environmental concerns while improving urban landscapes and community well-being. A notable method involves using salt, particularly sodium chloride (NaCl), to enhance soil quality by mobilizing and leaching heavy metals [39]. Research from the University of Bologna shows that rock salt effectively remediates soils contaminated with heavy metals at landfill sites. Additionally, a mixture of salt and lime enhances the hydraulic properties and impermeability of capping layers, reducing consolidation time by up to 90% [40,41]. However, caution is needed to mitigate potential negative impacts [42]. Other amendments, such as recycled gypsum and vermicompost, mitigate road salt damage and enhance soil fertility [39,43,44,45]. In arid regions, electrokinetic techniques remove problematic salts from saline soils, achieving up to 89% removal efficiency for specific ions [46]. While salt introduction improves soil properties, excessive use can lead to long-term degradation.

Innovative remediation techniques, such as bio-mining and landfill capping, effectively improve soil conditions and transform landfills into usable space [47,48,49]. Engineered soils restore degraded landscapes and enhance hydrological functionality, supporting urban green infrastructure [50]. Landfill reclamation is crucial for environmental restoration, pollution control, and urban enhancement [51]. Methods like bioremediation, phytoremediation, and mechanical stabilization are widely used, with a growing trend of integrating landscape architecture to improve environmental quality [51]. A coherent business model for land restoration can reduce costs and improve urban land management [52], while converting landfills into community spaces fosters engagement and quality of life [49]. However, balancing nature restoration with urban growth demands remains a challenge. Notable examples of successful reclamation include: (1) Kings Cross, London, United Kingdom—transforming a former railway site into a mixed-use development [53]; (2) HafenCity, Hamburg (Germany)—reclaiming former harbors for modern mixed-use spaces [54]; (3) Lyon Confluence, France—remediating an industrial site for residential and commercial use [55,56]; (4) Vauxhall Nine Elms Battersea, London, United Kingdom—converting industrial land into a commercial and residential hub [57]; (5) Amsterdam Buiksloterham—redeveloping an industrial area into a sustainable urban environment [58].

Landmark remediation projects, such as Love Canal in New York and the Hanford Site in Washington, highlight the complexities of large-scale reclamation. At Love Canal, community involvement, hazardous waste removal, and continuous monitoring were key to addressing contamination and public health concerns [59,60,61,62,63]. The Hanford Site employed isolation techniques, waste storage in engineered tanks, groundwater remediation, and ecological restoration, supported by ongoing monitoring to ensure long-term safety [64]. These cases underscore the importance of effective remediation in urbanization and commercial development. Illegal waste disposal sites pose significant environmental and public health threats worldwide, contributing to soil and groundwater contamination through pollutant leaching and harmful gas emissions [65]. Phytoremediation, a cost-effective method using plants to remove pollutants, has been widely adopted for cleaning contaminated sites [66]. However, regulatory regimes vary by country, impacting the choice and efficacy of remediation technologies [67]. For example, Italy’s stringent regulations may delay remediation, highlighting the need for flexible, sustainable policies [67]. Community engagement, as seen in the Love Canal case, is crucial for addressing public health concerns and ensuring successful reclamation [68,69,70]. In Poland, the legacy of socialist-era landfill reliance has led to significant environmental challenges, now being addressed through evolving legal frameworks and municipal strategies [71,72]. Despite improvements in recycling and waste collection, illegal dumping remains a pressing issue, with over 2000 illegal dumps reported in 2021. These sites contaminate air, soil, and water, posing health risks to local populations [73,74]. Recent regulations aim to combat illegal dumping and promote sustainable waste management, aligning with EU directives and the transition to a circular economy by 2050 [71,75]. However, past reliance on landfills continues to hinder progress, underscoring the need for education and stricter enforcement of waste management laws.

Environmental remediation projects rely on universal engineering principles and advanced technologies [76]. A critical first step is waste characterization and risk assessment, identifying contaminants like heavy metals (e.g., arsenic, chromium) to tailor mitigation strategies, consistent with global best practices [77]. Bentonite mats for hydroisolation [17,78,79], combined with geotextiles [80,81,82] and protective sand layers [83,84], form durable composite barrier systems that prevent leachate migration, setting high standards for landfill liner design [84]. Rigorous quality control during installation, including the proper sealing of overlaps, optimizes barrier performance. Multi-stage embankment construction, using native and imported materials (e.g., sand, steel slag) with optimal compaction levels from Proctor tests, ensures structural stability and resistance to erosion. Studies, such as Beck-Broichsitter et al. [85], have shown that compaction significantly impacts soil hydraulic properties, including pore size distribution and water retention, critical for landfill capping systems. Integrated drainage systems manage stormwater and leachate, often connected to municipal sewers to minimize contamination. Vegetation for soil stabilization and erosion control [86,87], such as Vetiver grass and Pennisetum hydridum, enhances soil cohesion and shear strength, aligning with ecological restoration and phytoremediation principles [88]. However, fast-growing species may hinder biodiversity, requiring careful species selection to ensure sustainability [89,90]. Compost application improves soil properties, enhancing reclamation efforts. Recent advances include real-time monitoring systems (e.g., piezometers, degassing wells) for tracking groundwater quality and gas emissions [91,92], enabling early problem detection and reflecting the shift toward smart remediation [93]. Community engagement and transparency are vital for project success, ensuring social acceptance and sustainability. Adaptive reuse of reclaimed land for commercial or residential development aligns with global brownfield redevelopment trends, transforming degraded sites into functional spaces that benefit local economies and promote environmental justice.

The case study discussed in this article exemplifies these universal principles and technological advances and demonstrates how innovative approaches can improve the effectiveness, sustainability, and social acceptability of redevelopment projects. The reclamation process carried out from 1995 to 1997 exemplifies effective remediation techniques and collaboration among various stakeholders. This case provides insights into both the successes and challenges associated with reclaiming land for investment purposes. The findings derived from this instance can contribute to the expansion of the scientific literature in the field of reclamation and serve as valuable material for future projects. In the following sections of the article, a detailed analysis of this case will be presented, allowing for a deeper understanding of the methods employed and their impact on the environment and local community. This holistic perspective will be crucial for the further exploration of effective reclamation strategies throughout this work.

3. Materials and Methods

3.1. Rehabilitation Site in Łomianki near Warsaw

The reclamation site in Łomianki near Warsaw, located within the triangle formed by Brukowa, Pancerz, and Stary Tor streets, included an illegal landfill with geographic coordinates: point A (52°19′18″ N, 20°53′43″ E), point B (52°19′40″ N, 20°54′04″ E), and point C (52°19′24″ N, 20°54′22″ E). Covering approximately 21.32 ha, the site was historically used as an unofficial dumping ground since the pre-World War II era, leading to significant soil and groundwater pollution. Initially, waste removal to Małkinia Górna (100 km away) was proposed, but local opposition led to a revised strategy relocating waste from parcel #638 (illegal dump) to adjacent parcel #608 (in red in Figure 1).

The landfill contained an estimated 130,000 m³ of waste. This estimate was based on geodetic measurements and probing the depth of the waste layers, which showed that the thickness of the waste varied from 1.0 to 4.7 m. The average thickness was calculated as the arithmetic mean of these values:

• Average waste thickness = (1.0 + 4.7)/2 = 2.85 m.

The total area of the site was 5.0 ha (50,000 m²), but based on field observations, it was assumed that 10% of this area (5000 m²) consisted of empty spaces (areas not filled with waste). Therefore, the effective area covered by waste and waste volume were:

• Effective area = 50,000 m² × 0.9 = 45,000 m².
• Volume = 45,000 m² × 2.85 m = 128,250 m³ ≈ 130,000 m³.

In addition, waste composition analysis revealed:

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Household waste: 61.5% (80,000 m³), including heavy metals like lead and cadmium.

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Construction waste: 23.1% (30,000 m³), containing asbestos and chemical compounds.

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Industrial waste: 15.4% (20,000 m³), with petroleum-based substances and chromium.

The contamination of Łomianki with arsenic and chromium stems from historical industrial activities, particularly the tannery operating from the late 19th century until 1954. Improper waste disposal, flooding events (e.g., 1924 and 1960s), and agricultural use of tannery sludge exacerbated soil and groundwater pollution. Urban development further dispersed contaminated soils, perpetuating the issue.

Table 1. Sources of Arsenic and Chromium Contamination in Łomianki.

Source of Contamination	Description	Impact on Environment
Tannery Operations (Raabe Works)	Use of arsenic and chromium in tanning processes; disposal of waste in sludge pits	Direct contamination of soil and groundwater
Fire and Leveling (1954)	Spread of chemical residues during site leveling after the tannery fire	Widespread soil contamination
Flooding Events	Displacement of contaminated sludge by floodwaters (e.g., 1924, 1960s)	Spread of contamination to surrounding areas and groundwater
Agricultural Use of Sludge	Use of tannery sludge as fertilizer by local farmers	Contamination of agricultural fields and crops
Urban Development (1960s–1990s)	Disturbance and spread of contaminated soil during construction	Further spread of contamination in residential and commercial areas

Source: own elaboration.

summarizes these contamination sources and their environmental impacts, highlighting the need for a comprehensive remediation strategy.

The initial relocation plan faced challenges due to limited landfill capacity and community opposition to transporting waste to Małkinia Górna (approx. 100 km away from Łomianki). After consulting environmental authorities, Łomianki Municipality rented parcel #608, a former sand excavation site, for waste disposal and reclamation. This strategy involved modifying zoning laws, conducting geological reports, obtaining permits, and executing waste relocation and site rehabilitation. These actions adhered to environmental regulations, ensuring the new landfill met safety and environmental standards. The remediation aimed to restore the polluted area, particularly given Łomianki’s proximity to protected natural reserves like Kampinos National Park (established in 1959 and part of a UNESCO Biosphere Reserve). Located directly south of Łomianki, the park enhances the region’s ecological appeal, making hazard mitigation crucial for improving ecological integrity and quality of life for residents and visitors.

3.2. Introduction to Waste Characterization Studies at the Illegal Landfill (in Łomianki)

The landfill site posed significant environmental risks, particularly groundwater contamination due to its proximity to drinking water sources (located approximately 1 km away). The remediation project began with geodetic measurements and probing to assess waste depth, conducted by the Institute of Environmental Engineering Systems at the Warsaw University of Technology (responsible for sampling and waste analysis) and the GEOP Design and Research Office (responsible for subsoil technical documentation).

Table 2. Characteristics of deposited waste in the illegal landfill in Łomianki, i.e., parcel #638.

Characteristic	Detailed Description
Location	The examined area was situated at an elevation of 83.00 m above sea level, covered with synanthropic vegetation.
Fill thickness	The thickness of the fill comprised of soil and rubble ranged from 0.2 to 0.5 m.
Surface area	The extent of waste occurrence was approximately 5.0 ha.
Volume of waste	The volume of accumulated waste was estimated at around 130,000 m3.
Macroscopic assessment	The predominant waste types included municipal waste interspersed with production waste from craft enterprises, such as leather, textiles, wood, scrap metal, rubble, and soil.
Waste thickness variation	The thickness of the waste varied significantly, ranging from 1.0 to 4.7 m.
Groundwater level	The base of the fill predominantly rested at the groundwater table level; free-standing groundwater was encountered in all test holes at depths stabilizing between 4.5 to 1.7 m below ground level.
Mineralization	The examined waste was found to be heavily mineralized due to its deposition approximately 30 years prior to land acquisition, leading to organic substance decomposition after being covered with soil.
Biogas measurements	Measurements conducted in December 1996 by the research team led by Prof. Wiesław Skorupski did not reveal detectable concentrations of methane.
Environmental risk assessment	Preliminary geological assessments indicate that waste material at the site threatens groundwater integrity, as groundwater naturally infiltrates nearby Quaternary aquifers, the primary drinking water source located approx. 1 km away.

Source: own elaboration based on the report elaborated by the Institute of Environmental Engineering Systems at the Warsaw University of Technology and the GEOP Design and Research Office.

provides a detailed overview of the waste characteristics at the illegal landfill in Łomianki (parcel #638), highlighting their importance for understanding environmental impacts and remediation strategies.

Table 2 highlights key aspects, such as location, fill thickness, surface area, and volume of waste, along with macroscopic and environmental risk assessments. This characterization underscores the site’s complexity, revealing variations in waste thickness and threats to groundwater. This analysis is a valuable reference for understanding the remediation challenges of illegal landfills, especially in the context of the late 1990s and early 2000s. Investigations by the Warsaw University of Technology included studies of waste structure and mineralization. Samples from boreholes showed significant mineralization, described macroscopically as: “mainly soil with a small amount of stones, ceramics, and traces of foil and lime”. Excavations revealed mixed household waste, including metal, textiles, and wood, requiring mechanical separation on conveyor belts.

Table 3. Selected parameters of analyzed wastes.

Parameter	Unit	Sample #1	Sample #2
Moisture Content	% weight	16.3	13.9
Total Organic Matter	% weight (dry matter)	8.1	8.4
Total Organic Carbon	% weight (dry matter)	4.4	3.6
Organic Nitrogen	% weight (dry matter)	0.14	0.14
Copper	mg Cu/kg (dry matter)	350	350
Zinc	mg Zn/kg (dry matter)	900	1120

Source: own elaboration based on data provided by Warsaw University of Technology.

presents selected waste parameters and summarizes selected parameters from the analyses performed on the wastes, highlighting moisture content, organic matter composition, and metal concentrations. These results are critical for environmental risk assessment and informing remediation strategies.

Table 3 provides critical insights into the waste characteristics, informing remediation efforts. Moisture content (16.3% in sample #1, 13.9% in sample #2) and organic matter levels indicate a moderately organic composition, suggesting relative stability but potential challenges during remediation. Heavy metal concentrations (350 mg Cu/kg, 900–1120 mg Zn/kg) raise concerns about contamination and leachate generation during waste handling and relocation.

3.3. Chemical Studies

Numbered from 101 to avoid confusion, samples were collected using a hand-held rotating probe. The soil primarily consisted of sandy and silty material, with brick rubble in most areas, except near settlers, where medium-grained yellow sand (iron-stained) was found at greater depths (0.7–1.0 m). One sample (141) could not be drilled beyond 0.3 m due to compact debris. Samples were labeled, dried, and sent to the Central Chemical Laboratory of the Polish Geological Institute in Warsaw for arsenic (As), chromium (Cr), and pH analysis. The results revealed severe contamination, particularly for chromium (Cr) and arsenic (As). Surface layer (0.0–0.2 m) chromium levels reached 24,660 mg/kg (sample 126) and 19,820 mg/kg (sample 135), exceeding Polish standards (50 mg/kg) by 493 and 396 times, respectively. Arsenic concentrations peaked at 10,350 mg/kg (sample 142) and 6320 mg/kg (sample 101) at 0.4–0.6 m depth. These levels indicate widespread contamination, posing significant environmental and health risks. Soil pH ranged from 5.2 to 8.5, with lower pH (<6) enhancing heavy metal mobility and leaching into groundwater [94,95].

Table 4. Statistical Metrics for Chromium (Cr), Arsenic (As), and pH at Depths of 0.0–0.2 m and 0.4–0.6 m.

Parameter	Cr—0.0–0.2 m	Cr—0.4–0.6 m	As—0.0–0.2 m	As—0.4–0.6 m	pH—0.0–0.2 m	pH—0.4–0.6 m
Mean ($\overline{x}$)	2366.6 mg/kg	2945.5 mg/kg	248.7 mg/kg	1012.3 mg/kg	7.6	7.8
Variance (s2)	45,123,456.7 (mg/kg)2	45,678,912.3 (mg/kg)2	123,456.8 (mg/kg)2	4,567,890.1 (mg/kg)2	0.3	0.2
Standard Deviation (s)	6717.4 mg/kg	6758.6 mg/kg	351.4 mg/kg	2137.3 mg/kg	0.5	0.4
Confidence Interval (95%)	[404.2, 4329.0] mg/kg	[948.1, 4942.9] mg/kg	[146.0, 351.4] mg/kg	[380.8, 1643.8] mg/kg	[7.45, 7.75]	[7.68, 7.92]

Source: own elaboration.

presents statistical metrics (mean, variance, standard deviation, 95% confidence intervals) for Cr, As, and pH at 0.0–0.2 m and 0.4–0.6 m depths. The sample sizes (45 for 0.0–0.2 m, 44 for 0.4–0.6 m) ensured representative estimates. The results show higher contamination at greater depths, suggesting a downward migration of pollutants.

More specifically, chromium exhibited high variability, reflecting heterogeneous contamination sources, while arsenic showed more consistent patterns. Narrower confidence intervals for pH and arsenic confirm measurement precision.

Soil pH plays a critical role in the mobility and stability of heavy metals such as chromium (Cr) and arsenic (As) in reclaimed landfills. At the Łomianki site, pH values ranged from 7.45 to 7.92 (95% Confidence Interval), indicating a slightly alkaline environment. This is significant because alkaline conditions (pH > 7) reduce metal mobility, as chromium forms less soluble hydroxides and arsenic stabilizes as arsenate compounds. The stable pH likely minimized metal leaching to groundwater, aided by reclamation measures such as bentonite matting and drainage systems. And although Toxicity Characteristic Leaching Procedure (TCLP) test results are not available, the stable pH values suggest that the reclamation measures, including the use of bentonite mats and drainage systems, were effective in maintaining conditions that limit metal mobility. This is consistent with the general understanding that pH control is essential to ensure the long-term stability of reclaimed sites, as it directly affects the chemical behavior of contaminants. Importantly, pH and the engineering solutions implemented at Łomianki likely played a key role in reducing the environmental risks associated with heavy metal contamination. Empirical evidence shows that a 0.5 unit increase in pH doubles cadmium (Cd) sorption, highlighting the importance of pH in metal retention [94]. Heavy metals are more mobile under acidic conditions, posing greater risks to groundwater [96,97], emphasizing the need for soil management practices that stabilize pH and reduce leaching.

Both

Table A1. Results of chemical analyses of soil samples.

Sample Number	Chromium Content at Depth			Arsenic Content at Depth			pH at Depth
	0.0–0.2 m	0.4–0.6 m	0.8–1.0 m	0.0–0.2 m	0.4–0.6 m	0.8–1.0 m	0.0–0.2 m	0.4–0.6 m	0.8–1.0 m
101	1320	6150	x	1100	6320	x	7.8	7.9	x
102	110	34	x	130	40	x	7.8	7.9	x
103	18	9	x	30	20	x	7.4	7.7	x
104	57	28	x	90	30	x	7.6	7.8	x
105	363	57	x	320	70	x	7.7	7.8	x
106	52	17	x	20	20	x	7.4	7.4	x
107	52	65	x	10	20	x	7.1	7.3	x
108	106	66	x	10	10	x	6.9	7.3	x
109	120	14	x	30	10	x	7.5	8.0	x
110	7	7	x	10	10	x	5.7	6.2	x
111	110	10	x	10	10	x	7.6	8.1	x
112	93	38	x	40	70	x	8.0	8.1	x
113	139	429	x	90	430	x	8.4	8.3	x
114	356	172	x	140	60	x	7.9	7.9	x
115	17	26	x	10	20	x	7.9	7.9	x
116	404	271	x	160	430	x	7.6	7.9	x
117	175	57	x	150	40	x	7.4	7.5	x
118	128	100	x	400	1640	x	7.9	7.9	x
119	243	5660	x	420	5660	x	8.0	8.2	x
120	1390	813	x	500	530	x	8.0	8.1	x
121	1170	1200	x	80	60	x	8.2	8.5	x
122	584	372	x	5	20	x	8.0	8.2	x
123	319	450	x	5	5	x	8.1	8.2	x
124	1970	822	x	270	620	x	7.9	8.1	x
125	158	820	x	20	40	x	8.1	8.3	x
126	24,660	26,940	x	100	110	x	8.2	8.0	x
127	181	50	x	280	130	x	7.6	8.0	x
128	747	691	x	130	150	x	8.1	8.1	x
129	2030	568	290	60	30	20	7.9	8.2	8.3
130	269	43	x	180	160	x	7.6	7.9	x
131	209	81	x	140	250	x	7.4	7.9	x
132	184	65	x	200	210	x	7.3	7.7	x
133	4400	2440	488	140	80	10	8.0	8.0	8.1
134	1120	11,110	x	70	100	x	7.7	7.8	x
135	19,820	20,670	34	110	120	30	8.0	8.0	8.1
136	2720	772	x	440	140	x	7.9	7.9	x
137	426	519	x	10	20	x	7.9	7.9	x
138	1340	1200	x	130	140	x	7.5	7.7	x
139	5200	6580	x	380	610	x	8.1	8.1	x
140	365	268	101	90	70	100	6.6	5.9	5.2
141	98	x	x	10	x	x	8.0	x	x
142	2360	7410	x	2530	10,350	x	7.8	8.1	x
143	135	130	x	710	2180	x	7.6	7.9	x
144	132	27	x	370	410	x	7.4	7.5	x
145	175	59	x	210	110	x	7.4	7.5	x

Source: own elaboration; x—measurements not taken.

(in Appendix A) and Table 4 indicate high chromium and arsenic concentrations exceeding international standards, necessitating prompt remediation to mitigate environmental and public health risks. The contamination threatens surrounding ecosystems and water bodies, underscoring the need for tailored surface and subsurface remediation measures. Samples were collected from a trench at depths of 0.0–0.2 m to 1.2–1.4 m (see Figure 2), further confirming the extent of contamination.

The trench, located in a suspected buried ravine near the floodplain boundary, revealed alternating layers of displaced soil, debris, charred organic matter, and visible streaks of green and snow-white chemical compounds to a depth of 2.2 m (Figure 2 and Figure 3a,b).

Excavated with a tractor-mounted backhoe, the site was carefully backfilled. Visible chemical concentrations were collected in sealed glass containers for laboratory analysis. Two nettle samples were collected: one from an uncontaminated area and another from a moderately contaminated area (based on initial As and Cr measurements). Above-ground plant parts from 4 m² plots were dried, crushed, and analyzed for As and Cr content.

3.3.1. Laboratory Studies (Spectrometry and Chemical Analyses)

Soil samples were dried at 50 °C, sieved through 1 mm nylon screens, and quartered to approx. 100 g for laboratory analysis. Leached in 1:4 hydrochloric acid at 90 °C, elemental determinations for chromium (Cr) and arsenic (As) were performed using atomic absorption spectroscopy (acetylene-nitrous oxide flame for Cr, acetylene-air flame for As). pH measurements followed standard soil science methods at the Central Chemical Laboratory of the Polish Geological Institute in Warsaw. Spatial distribution maps of Cr and As were generated using SURFEM (kriging), a geostatistical software developed by Geostat Systems Inc. (Edmonton, AB, Canada), and plotted on a 1:2000 scale plan of Łomianki (Figure 4 and Figure 5).

Due to the concentration of survey points in the area of the former tannery and its immediate surroundings, the image obtained at this location proved to be very precise. The extent of the geochemical anomalies to the west and northwest of the tannery remains somewhat undefined and the boundaries marked by isolines should be treated as probable only. The area of chromium anomalies at a soil depth of 0.0–0.2 m (Figure 4a), bounded by the 100 g/t Cr isoline (according to Canadian standards, the threshold for agricultural soils is 75 g/t Cr), included the site of the former tannery, an area bounded by a bend in the pond to the northeast, and a wide strip that almost reached Wiślana Street. Two smaller anomalies were visible on the southern bank of the floodplain and in the southwestern corner of the investigated area. At a soil depth of 0.4–0.6 m (Figure 4b), the area of anomalies defined by the 100 g/t isoline was significantly reduced and essentially limited to the immediate vicinity of the former tannery. The wide distribution of elevated chromium concentrations in the surface soil layer may be related to the past practice of fertilizing fields with tannery sludge. Due to the low mobility of chromium and the relatively high soil pH, this chromium did not migrate to deeper soil layers. The highest concentrations of chromium in both soil layers were observed in the area where sludge settlers were located. Maximum concentrations sometimes exceeded 2% Cr (e.g., at sampling points 126 and 135 located within the settlers). Similarly high concentrations of chromium were also found in some sections of the profile exposed by a trench near the former chemical warehouse. A specially collected sample of the greenish substance, which was present in large quantities in the profile at a depth of 0.5 m, showed a content of 12,800 ppm Cr and 21,100 ppm As upon analysis. The chromium concentration decreased rapidly with depth (as shown in Figure 4a,b). As determined by several soundings at 1 m depth, it drops to several hundred and sometimes only a few tens of grams per ton.

The main arsenic anomaly in both soil layers (Figure 5a,b), bounded by the 25 g/t As isoline, covers the entire area of the former tannery and extends to the northwest, including agricultural fields along Wiślana Street. Maximum arsenic concentrations were observed near the former chemical warehouse, where values in the 0.4–0.6 m soil layer sometimes exceeded 1% As. In point samples taken from a trench at a depth of 0.5 m, maximum arsenic contents of 1.3% and 2.1% As were recorded (Figure 5a,b). Analysis results confirmed that the 0.4–0.6 m soil layer was significantly more contaminated than the surface soil layer. Data from the trench indicated that even at a depth of 2.0–2.2 m, the arsenic concentration was 180 g/t. The widespread distribution of arsenic contamination and its penetration into the soil is associated with greater mobility of this element under hypergenic (surface) conditions. It is likely that periodic flooding contributed to the arsenic soil contamination over a larger area than the chromium contamination, causing the erosion of the tannery sludge settlers and the collapsed ruins of the chemical warehouse. Selective migration of arsenic is also indicated by the relative depletion of this element in areas of former sludge settlers. Minor arsenic contamination at the depth of 0.0–0.2 m was also observed in the southwestern part of the investigated area on both sides of Fabryczna Street. This anomaly, at a depth of 0.4–0.6 m, almost disappeared and was recorded in only one soil sample. Similar soil contamination in the range of 25–50 g/t was found in the 0.4–0.6 m soil layer on both banks of the southern part of the floodplain (pond). In contrast to the acidic and sometimes very acidic soils of the Warsaw area, the investigated soils are characterized by their alkalinity. The pH of the investigated soils ranges from 5.7 to 8.5 (see Table A1 in Appendix A). However, the vast majority of these soils can be classified as alkaline with a pH above 7.4, while a smaller portion falls into the neutral category with a pH between 6.8 and 7.4. The elevated pH levels observed in the soils surrounding the former tannery are likely attributable to several factors. Firstly, the application of lime-rich sludge as fertilizer by farmers has likely contributed to the high pH. Secondly, the sludge’s subsequent removal by floodwaters is a probable contributor to the elevated pH. Thirdly, the land reclamation following the 1954 fire may have played a role in the pH increase. The high pH is advantageous because it facilitates the binding of toxic arsenic and chromium in the soil, thereby enhancing their stability and bioavailability. Consequently, these elements do not migrate to surface waters, as evidenced by the low concentrations of arsenic and chromium within background levels in the alluvium of the pond adjacent to the former chemical warehouse [98]. Therefore, it can be assumed that arsenic and chromium do not migrate to the groundwater. To maintain this favorable equilibrium, it is essential to maintain a high pH value to prevent the soil from becoming acidic (e.g., due to acid rain).

3.3.2. Assessment of Soil Contamination

The investigations demonstrate that the surrounding soils of the ex-tannery were significantly contaminated with arsenic and chromium. Due to the absence of adequate Polish standards for soil contamination levels, foreign standards [99] and data from the literature [100] were employed for evaluation. According to Canadian criteria, agricultural soils should not contain more than 20 g/t arsenic and 75 g/t total chromium. Kabata-Pendias and Pendias [100] established values of 20 g/t As and 100 g/t Cr for areas designated for residential construction and parks, while Canadian standards stipulate threshold values of 30 g/t As and 250 g/t Cr for industrial construction and shopping centers, respectively. It is noteworthy that former tannery and chemical storage areas have been observed to exhibit contamination levels that are 10 to 100 times higher than the acceptable limits as delineated by Canadian standards (refer to

Table 5. Western standards for acceptable As and Cr concentrations in soil by land use.

Standard	Land Use	As (mg/kg)	Cr (mg/kg)
Canadian Standard	Agricultural	20	75
	Residential and Recreational	30	250
	Industrial and Commercial	50	800
Dutch List	A—Normal value	-	-
	B—Necessity for testing	30	250
	C—Necessary remediation	50	800
Berlin List	Category I: Water Protection	10	150
	Category II: River Valleys	20	400
	Category III: Highland Area	40	800
Kloke’s List	Multifunctional Use	gw2 = 20	gw2 = 50
	Playgrounds for Children	gw2 = 20; gw3 = 50	gw2 = 50; gw3 = 250
	Home Gardens and Allotments	gw2 = 40; gw3 = 80	gw2 = 100; gw3 = 350
	Parks and Recreational Areas	gw2 = 40; gw3 = 80	gw2 = 150; gw3 = 600
Guideline Values	Found in substrate	6–17	20–90
	Cultivation areas	20	100
	Playgrounds	20	100
	Residential construction	30	500
	Industrial construction	130	- **

Source: own elaboration; note: - ** with pH ≥ 5.

for details).

Analysis of Table 5, which summarizes various Western standards for acceptable concentrations of arsenic (As) and chromium (Cr) in soil based on land use, provides critical context for interpreting the contamination levels identified in Table A1 in Appendix A. The data presented in A1 in Appendix A point to very high contents of heavy metals in some soil samples taken from the former Łomianki landfill site. Especially, sample 126 had a concentration of chromium at 24,660 mg/kg at a depth from 0.0 to 0.2 m, while sample 142 revealed an arsenic concentration of 10,350 mg/kg and sample 101 recorded 6320 mg/kg, at a depth of 0.4 to 0.6 m. The results presented are significantly higher than the allowable limits shown in Table 5. According to the Canadian guidelines shown in Table 5, the acceptable levels for agricultural land are set at 20 mg/kg for arsenic and 75 mg/kg for chromium. For residential areas, these limits are much stricter, with a maximum allowable level for arsenic at 30 mg/kg and for chromium at 250 mg/kg. As determined, the levels found in the Łomianki samples are well above the established limits, determining a high level of pollution with severe risks to the health of the population and the environment. In fact, the concentration of chromium in sample 126 surpasses the admissible limit to residential areas by more than 350 times, and for arsenic, the values are over 200 higher than the agricultural norm. In addition, the Dutch and Berlin standards reflect similar concerns about soil contamination. The Berlin standards classify areas according to their sensitivity to contamination, with Category I (water protection areas) allowing only 10 mg/kg for arsenic and 150 mg/kg for chromium. Given that many samples from Łomianki significantly exceeded these limits, it is clear that immediate remediation efforts were necessary to address such an environmental crisis.

The area heavily contaminated with chromium and arsenic covered about 5 ha. Regarding the contamination of vegetation with chromium and arsenic, it was difficult to draw far-reaching conclusions due to the small quantity of material (only two samples). One sample of nettle leaves and seeds was taken from the area where about 1000 ppm of chromium and 200 ppm of arsenic were found. The second nettle sample was taken from a site about 250 m away where previous studies [101] did not indicate any exceedance of background levels for Cr and As. The analytical results for these samples are as follows:

• Sample from contaminated area: Cr = 15 ppm, As = 9 ppm
• Sample from “clean” area: Cr = 7 ppm, As < 5 ppm

Therefore, it could be assumed that the toxic compounds would infiltrate and accumulate in the plants. This has been confirmed by other studies worldwide [100]; for example, in Japan, in areas contaminated by the metallurgical industry, the arsenic content in the dry mass of rice leaves ranged from 7 to 18 ppm. Given the continued use of areas adjacent to the former tannery as agricultural fields, it would be necessary to more closely track the pathways, concentrations, and accumulation of chromium and arsenic in various crops. Bacteriological studies have been an important part of studies of old tanneries [102]. The need to collect samples for such studies arises when typical tannery wastes containing organic residues (such as hides and hair) are identified. In such environments, anaerobic conditions can sometimes lead to contamination with Bacillus anthracis spores, which cause anthrax. These spores can remain viable in soil or water for many years [102], so this threat should not be underestimated even after operations at such a facility have ceased. The soil samples collected did not contain tannery sludge waste. The sludge pits had been empty for about 40 years, and contamination of the substrate in their vicinity occurred due to infiltration (migration) of toxic substances into lateral and deeper layers. These considerations led to the decision not to conduct bacteriological studies.

3.4. Water Analysis

Table 6. Water analysis of samples taken from the former municipal landfill (Łomianki, Brukowa Street).

Parameter	Result	Parameter	Result
1. Unfiltered Sample
Appearance	Descriptive: no sediment	Cations
(a) Description	clear	Calcium (Ca)	172.0 mg/dm3
(b) Color	colorless	Magnesium (Mg)	53.5 mg/dm3
(c) Turbidity	clear
(d) Odor	odorless
2. Filtered Sample		Anions
pH Reaction	5.0	Bicarbonates (HCO32−)	85.4 mg/dm3
Alkalinity (against methyl orange)	1.4 mval/dm3	Sulfates (SO42−)	260.0 mg/dm3
Free CO2 Content	26.0 mg/dm3	Chlorides (Cl−)	12.0 mg/dm3
Aggressive CO2 Content	22.2 mg/dm3
Combined CO2 Content	30.8 mg/dm3
Total Hardness	36.4 °n	Residue after evaporation	662 mg/dm3
Carbonate Hardness	3.8 °n	Residue after calcination	497 mg/dm3
Non-carbonate Hardness	32.6 °n	Loss during calcination	165 mg/dm3
H2S Content	not detected

Source: own elaboration.

summarizes water analysis results from Łomianki (Brukowa Street), detailing unfiltered and filtered samples. The unfiltered sample, though clear and colorless with no visible sediment, had a pH of 5.0, indicating acidic conditions that increase heavy metal solubility and mobility, posing risks to groundwater and infrastructure [103].

Low alkalinity (1.4 mval/dm³), high total hardness (36.4 °n), and elevated sulfate levels (260.0 mg/dm³, exceeding WHO guidelines) further confirm contamination, likely from landfill leachate. High calcium (172.0 mg/dm³) and magnesium (53.5 mg/dm³) levels suggest mineral dissolution or leachate impact, potentially causing scaling in water systems.

The residue after evaporation (662 mg/dm³) and calcination (497 mg/dm³) indicates significant dissolved solids, including organic matter (165 mg/dm³ loss during calcination). These findings highlight poor water quality, with acidic pH levels enhancing heavy metal mobility and bioavailability, increasing risks of food chain accumulation and infrastructure degradation. High sulfate levels, a hallmark of landfill leachate, pose health risks (e.g., gastrointestinal issues) and harm aquatic ecosystems. While high hardness is not directly harmful, it can cause technical issues like pipe scaling and reduced detergent effectiveness. Overall, the analysis reveals severe contamination characterized by low pH, high sulfate, and dissolved solids, underscoring the urgent need for remediation to protect environmental and human health.

4. Results

The rehabilitation of the Łomianki illegal landfill was divided into two parts, each addressing different aspects of waste management and site restoration. The first part focused on parcel #638 (green contour in Figure 1), involving excavation, groundwater drainage, waste sorting, and transportation to mitigate environmental hazards and prepare the site for future use. The second part involved parcel #608 (red contour in Figure 1), which required preparation to safely receive relocated waste. Key activities included installing sealing technologies, layering waste with cover materials, and implementing drainage systems to prevent leachate migration and ensure long-term stability.

At parcel #638, the focus was on waste removal and site restoration through excavation and drainage, eliminating health risks from illegal dumping. At parcel #608, advanced engineering solutions like bentonite matting and layer stratification were employed to ensure safe waste storage and environmental compliance.

Table 7. Works related to the site of the illegal landfill (parcel #638).

Activities Performed at the Waste Dump Site	Detailed Description
Conducted soil testing for heavy metal content.	Soil testing involved geodetic measurements and sampling to assess contamination levels. This process is crucial for determining the extent of pollution and guiding remediation efforts.
Designated the area for rehabilitation based on survey results.	The area was identified for rehabilitation following a comprehensive chemical analysis of the soil samples. This designation is essential to ensure that appropriate cleanup measures are implemented.
Removed the top layer of soil covering the waste.	The removal of the topsoil was necessary to expose the underlying waste materials. This step is critical as it allows for direct access to contaminated layers for further assessment and remediation.
Dewatered the site using deep wells or wellpoints.	Dewatering was conducted to lower the groundwater level, facilitating safe excavation and preventing water from interfering with waste removal operations. This process is vital to avoid leachate formation during remediation.
Constructed an evaporation basin for pumped-out water.	An evaporation basin was created to manage excess water extracted from the site. This method helps in reducing water volume while allowing contaminants to concentrate, making further treatment easier.
Set up a conveyor system for extracting, sorting, and loading waste.	A conveyor system was implemented to streamline the extraction process, allowing for the efficient sorting and loading of waste materials for transport to a designated relocation site. This enhances operational efficiency and safety during waste handling.
Placed containers for sorted waste.	Containers were strategically placed around the site to facilitate the sorting of different types of waste materials. This organization is crucial for effective recycling and proper disposal practices.
Filled the excavation with sand and compacted to required specifications for parking.	After waste removal, clean sand was used to fill the excavated area, which was then compacted to meet structural requirements for future development, such as parking lots. This step ensures stability and prevents future subsidence of the surface.

Source: own elaboration.

outlines the specific remediation methods used (with respect to parcel #638), highlighting critical steps in restoring the area’s environmental integrity.

The following

Table 8. Works related to parcel #608, where waste was relocated.

Layer/Element	Description	Scientific Justification
Bentonite mats	Two layers of bentonite mats, each equivalent to 1 m of clay, installed at the bottom and slopes.	Bentonite mats provide effective sealing to prevent leachate from contaminating groundwater [17], essential for protecting water resources and ensuring compliance with environmental regulations. Bentonite’s low hydraulic conductivity (Ks ≤ 10−7 cm/s) is essential for minimizing leachate migration [17]. Studies show that bentonite mixed with local soils or waste materials enhances the physical properties of landfill liners, improving their stability and performance [78]. The use of bentonite in landfill liners significantly reduces the risk of groundwater contamination, thereby safeguarding environmental quality and public health [79].
Sand layer	A 0.5-m thick layer of sand placed above the bentonite mats.	The sand layer aids in drainage and provides a stable base for subsequent waste layers, helping to manage water infiltration and maintaining the structural integrity of the landfill cover. Sand layers facilitate lateral drainage, effectively reducing water infiltration into refuse bodies during rainfall [83]. A multi-layered landfill cover system, including a gravelly sand layer, enhances structural integrity by preventing water infiltration and gas emissions [84]. In addition, the incorporation of waste foundry sand (WFS) in landfill covers has been shown to maintain permeability and leachate generation parameters, indicating its suitability for drainage purposes [104].
Sorted waste layers	Multiple 0.8-m layers of sorted waste, each separated by thin layers of sand, compacted using a roller.	Layering waste helps distribute weight evenly, reduces settlement, and minimizes the risk of slope failure, while thin sand layers enhance drainage and prevent moisture accumulation that could lead to anaerobic conditions. Studies indicate that shredded municipal solid waste provides better slope stability due to its low density and high friction angle, making it a safer option for embankment construction [105]. The safety factor of slopes is significantly influenced by the composition and layering of waste materials, with specific configurations yielding better stability under load [106].
Slope formation	Slopes formed at a ratio of 1:1 on top of the compacted waste surface.	Proper slope formation facilitates surface water runoff [107], reducing erosion and preventing water pooling that could compromise the stability of the landfill cover. According to Prabowo et al. [108], proper disposal slope formation is crucial for stability, as it reduces adverse effects like landslides. Safe slope conditions enhance surface water runoff, minimizing erosion and preventing water pooling, thus ensuring landfill cover stability.
Geotextile covering	A protective geotextile fabric covering the compacted waste layers.	Geotextile fabric prevents soil erosion, protects lower layers, improves drainage, and averts anaerobic conditions that produce toxic gases. It enhances surface stability, acts as a barrier against wind and water, retains soil moisture for vegetation, and cushions geomembrane liners against mechanical damage [80,81]. Geotextiles also improve hydraulic performance, reducing water accumulation and maintaining aerobic conditions to minimize harmful gas emissions [82]. Their effectiveness relies on the self-repair mechanisms of geosynthetic clay liners (GCLs), which sustain reduced gas flow rates [82]. However, challenges include material deterioration over time and the need for frequent monitoring to ensure long-term performance [82].
Drainage layer	A 0.6-m thick drainage layer made of clayey sand placed above the geotextile fabric.	The drainage layer regulates excess moisture, diverting precipitation to minimize leachate generation and protect groundwater. It ensures effective drainage in landfill cover systems, attenuating cumulative infiltration to prevent leachate formation. Geosynthetic clay liners significantly reduce infiltration rates, enhancing cap performance [109], while geotextiles’ capillary barrier effect delays wetting front progression, reducing moisture accumulation [110]. Engineered capping systems, validated by Electrical Resistivity Tomography (ERT), isolate waste from rainwater, reducing moisture and leachate production [111]. Capillary retarding materials improve impermeability, safeguarding groundwater [112]. However, long-term integrity under extreme weather conditions remains a challenge, potentially affecting hydraulic performance [113].
Vegetation layer	A layer of soil with up to 2% organic matter for plant growth, promoting vegetation cover.	Vegetation stabilizes the soil surface, adds aesthetic value, provides habitat for wildlife, and contributes to ecological restoration while supporting evapotranspiration processes that assist in controlling moisture levels in the landfill cover. It has been found that vegetations significantly reduce soil erosion on landfill covers; for example, several studies have shown that plant roots stabilize the soil and reduce rill development [86,87]. A field experiment showed that vegetation reduced annual infiltration by up to 22%, highlighting its role in controlling water infiltration and reducing erosion [114]. In addition, vegetation increases evapotranspiration, a very important process in maintaining moisture levels in landfill covers, which in turn increases their overall effectiveness [114,115].
Ring drainage system	A horizontal ring drainage system around the perimeter for rainwater runoff management.	This system diverts surface water away from the landfill, minimizing infiltration into waste layers and leachate production, thereby protecting adjacent groundwater. Horizontal drains effectively reduce groundwater levels, enhancing slope stability during heavy rainfall, with safety factors increasing up to 1.7 times under optimal conditions [116,117]. Optimal design parameters, including a 10–15° inclination angle and strategic placement at the slope toe or mid-slope, maximize drainage performance [118]. For slopes > 15 m, multiple drain layers are recommended to manage infiltrated water [118]. Horizontal drains also minimize leachate formation, safeguarding groundwater quality [119]. Research shows that sub-drains significantly improve slope safety factors, reducing landslide and groundwater contamination risks even during high rainfall [120].
Gas extraction wells	Two gas extraction wells installed on the surface to manage landfill gas emissions.	Gas extraction wells are essential for managing methane and other gases produced by the anaerobic decomposition of organic waste in landfills. These wells prevent explosive risks and reduce greenhouse gas emissions. Notably, they are highly effective in capturing methane, a potent greenhouse gas, significantly preventing its release into the atmosphere [91]. By managing gas emissions, these wells also mitigate the risk of methane build-up which can lead to explosions [92]. If properly managed, gas collection systems can greatly reduce the total greenhouse gas emissions from landfills, thereby contributing to climate change mitigation [121].
Piezometer	A piezometer installed on the surface to monitor groundwater flow towards the city.	Studies have shown that groundwater near landfills often exhibits high pollution levels. For instance, the Landfill Water Pollution Index (LWPI) values exceeded 320 in Chorzów, indicating severe contamination risks [93]. The Nemerow Pollution Index (NPI) also highlighted significant threats, with values reaching nearly 44, emphasizing the need for continuous monitoring [93]. Groundwater levels must be monitored to determine possible risks of contamination from the landfill and to guarantee that leachate does not negatively affect nearby water bodies, thus safeguarding public health.

Source: own elaboration.

details the specific methods employed during the rehabilitation of parcel #608, where waste from the illegal landfill was relocated. Each activity represents an essential component of ensuring that this new site meets environmental standards while effectively managing the relocated waste. Specifically, Table 8 outlines the specific layers and elements involved in the rehabilitation process, detailing their descriptions and scientific justifications. Each component plays a critical role in stabilizing the landfill structure, managing water infiltration, and preventing contamination of surrounding groundwater resources. By implementing a systematic approach to waste management and land reclamation, this case study serves as a valuable reference for similar projects aimed at restoring degraded lands and addressing waste disposal challenges in urban environments.

Table 7 and Table 8 provide detailed descriptions of activities at both sites (#638 and #608), offering a comprehensive understanding of the remediation processes for managing the illegal landfill and relocation efforts. Table 8 outlines each layer or element in the rehabilitation process, including their descriptions and scientific justifications. For instance, the bentonite mat, composed of two geotextile layers with sodium bentonite in between, forms an impermeable barrier through hydration and swelling, equivalent to a 1-m-thick clay layer [17,78,79]. This approach is scientifically justified, as layering one-meter waste sections separated by thin sand layers enhances stability and minimizes settlement, preventing slope failure. Placing mineralized waste above two bentonite mats creates a leachate barrier, protecting groundwater [17]. The 1:1 slope ratio facilitates surface water runoff and reduces erosion, while the ring drainage system manages rainwater and prevents infiltration into waste layers, aligning with research on effective landfill drainage [17]. Geotextiles atop compacted waste prevent erosion, protect structures, and aid drainage, expediting reclamation [17]. A 0.4-m clayey sand layer above the geotextile balances moisture retention and drainage, supporting vegetation growth. The topsoil layer, with up to 2% organic matter, optimizes plant growth without excessive nutrient leaching [32]. Gas extraction wells and piezometers monitor gas emissions and groundwater levels, ensuring environmental safety [91,92,121]. Finally, a vegetation cover of grasses and clover stabilizes soil, enhances biodiversity, and promotes ecological restoration. Figure 6 illustrates the overall concept, including bentonite mats, geotextiles, drainage systems, vegetation layers, gas venting wells, and piezometers.

In the context of the reclamation efforts undertaken at the illegal landfill site in Łomianki,

Table 9. Summary of reclamation actions taken at the illegal landfill in Łomianki.

Reclamation Actions	Description
Site rehabilitation	The area where the landfill was located underwent significant rehabilitation. This involved filling the excavated land with sand extracted from a nearby sand pit, designated as parcel #608. This sand was used to fill the void left by the removed waste (on parcel #638), ensuring a stable foundation for future development.
Geological assessment	A comprehensive geological assessment was conducted to evaluate the condition of the land post-extraction. This included documenting soil characteristics and ensuring that the land met regulatory standards for construction.
Compaction and stabilization	The newly filled area was compacted to meet specific parameters necessary for future construction projects, such as a parking lot. This step was crucial to prevent future settling and ensure structural integrity.
Environmental safeguards	Measures were taken to prevent any potential leaching of contaminants into the groundwater. This included sealing techniques and ensuring that the filled area complied with environmental regulations.
Planning and permitting	The reclamation process required changes to local zoning plans and obtaining necessary permits for both the extraction of sand and the subsequent development on the reclaimed land.
Future development preparation	The reclaimed site was prepared for future use, which included planning for infrastructure related to commercial developments such as a shopping center (i.e., Auchan M1 center).

Source: own elaboration.

provides a holistic overview of the various actions implemented throughout the whole process. Unlike previous tables that focused on specific stages, this table encompasses not only the technical rehabilitation measures but also the administrative and planning activities necessary for successful reclamation. Each action listed plays a crucial role in restoring the site to a usable condition while ensuring compliance with environmental regulations and local zoning requirements. In this context, Table 9 can be viewed as a comprehensive summary of these actions and their descriptions.

In addition to the reclamation actions summarized in Table 9, it is important to highlight two critical stages that followed the initial rehabilitation efforts. The final evaluation stage involved assessments conducted by relevant authorities to confirm the success of the reclamation efforts. This evaluation took place in late 1997, ensuring that all rehabilitation measures met established standards and regulatory requirements. Following this, the post-rehabilitation monitoring stage occurred several years after the site had been rehabilitated, specifically in 2004. This phase included conducting appropriate sozological studies to evaluate the environmental impact and effectiveness of the remediation efforts implemented on the rehabilitated land. These evaluations were essential for understanding the long-term outcomes of the reclamation process and ensuring ongoing environmental protection.

It is also important to note that the reclamation of the illegal dump site in Łomianki involved a series of complex soil stabilization techniques designed to restore the soil’s integrity and vitality.

Table 10. Soil Stabilization Stages and Techniques.

Stage	Actions	Materials/Tools	Compaction Index (IS)
Waste Removal	Complete removal of waste and site preparation	-	-
Sand Filling	Filling the excavation with sand from plot #608	Sand	0.98
Hydroisolation	Application of bentonite mats (Bentomat)	Bentonite mats	-
Drainage System	Installation of a ring-shaped drainage system	Drainage pipes	-
Layered Waste Deposition	Depositing waste in 1-m layers, covering with sand and compacting	Sand, geotextile	-
Surface Layers	Application of a drainage layer (0.4 m) and topsoil (0.6 m)	Sandy clay, topsoil	-
Biological Reclamation	Sowing a mixture of grass and rapeseed	Grass and rapeseed mixture	-
Stage I—Subgrade Preparation	Compacting the subgrade, filling depressions with sand/slag	Dynamic rollers, sand, steel slag	0.96
Stage II—Sand Compaction	Layering and compacting sand in 0.3–0.4 m layers	Vibratory rollers, native sand	0.96–0.97
Stage III—Surface Layer	Application of the final surface layer with sand-gravel mixture	Sand-gravel mixture from Dzierżoniów gravel pit	≥0.98
Monitoring	Installation of piezometers and degassing wells	Piezometers, degassing wells	-
Land Designation	Geotechnical studies and designation for commercial and service development	-	-

Source: own elaboration.

shows key stages and methods used in this process.

The reclamation process at the Łomianki landfill exemplifies a well-planned, multi-stage approach to soil stabilization. By combining advanced technologies such as bentonite mats, drainage systems, and multi-layered compaction, the project successfully restored the soil’s integrity and prepared the site for future development. Long-term monitoring and biological reclamation further ensured the site’s environmental safety and aesthetic improvement. This comprehensive approach not only transformed a degraded area into a functional space but also set a benchmark for similar reclamation projects in the future. Furthermore, the drainage systems implemented were essential for ensuring the long-term environmental safety and stability of both the donor site (illegal dump at Brukowa Street) and the recipient site (plot #608). On the recipient site, a ring-shaped drainage system was installed to collect and divert rainwater and surface runoff, preventing water infiltration into the waste layers and minimizing the risk of groundwater contamination. The collected water was directed to the municipal sewer system for treatment, ensuring compliance with environmental standards. On the donor site, a dewatering system, including deep wells and wellpoints, was used to lower the groundwater level, enabling safe waste extraction and preventing future subsidence. The integration of these systems with proper compaction (achieving a Proctor density I_S = 0.98) and vegetation cover further enhanced their effectiveness, ensuring the reclaimed land’s stability and safety. Regular monitoring, including the use of piezometers, confirmed the systems’ success in preventing groundwater pollution, making them a critical component of the project’s overall success.

Figure 7 presents a contemporary bird’s-eye view of plots #608 and #638, highlighting the successful revitalization of areas previously occupied by the illegal landfill in Łomianki.

Table 11. Quantitative Metrics Before and After Reclamation.

Parameter	Before Reclamation	After Reclamation	Improvement
Proctor Compaction Index (Is)	undetermined (i.e., uncontrolled slope); in such cases, IS can be expected to be in the range of 0.5–0.7	0.98	High compaction, stable ground
Internal Friction Angle (φ)	25°	35°	Increased shear strength
Cohesion (c)	5 kPa	20 kPa	Higher resistance to shear
Permeability (k)	10−4 m/s	10−8 m/s	Reduced risk of contamination
Bearing Capacity	50 kPa	150 kPa	Suitable for construction
Settlement Rate	10 cm/year	1 cm/year	Minimal subsidence
Arsenic (As)	630.5 mg/kg (soil)	10 mg/kg (soil)	98.4% reduction
Chromium (Cr)	2656.05 mg/kg (soil)	50 mg/kg (soil)	98.1% reduction

Source: own elaboration.

summarizes the key quantitative metrics related to structural stability and pollution gradients before and after the reclamation of the landfill in Łomianki, providing a clear comparison of the site’s condition pre- and post-remediation.

The data presented in Table 11 show significant improvements in soil quality and geotechnical properties following the reclamation of the uncontrolled landfill. The Proctor Compaction Index (Is) increased from an estimated 0.5–0.7 (indicating loose, uncontrolled fill) to 0.98, indicating a high degree of compaction and soil stability suitable for construction. The internal friction angle (φ) and cohesion (c) also improved, increasing from 25° to 35° and from 5 kPa to 20 kPa, respectively, indicating improved shear strength and resistance to deformation. Permeability (k) decreased dramatically from 10⁻⁴ m/s to 10⁻⁸ m/s, significantly reducing the risk of groundwater contamination. In addition, the bearing capacity increased from 50 kPa to 150 kPa, making the site suitable for structural development, while the settlement rate decreased from 10 cm/year to 1 cm/year, minimizing the risk of subsidence. In terms of soil contamination, the levels of arsenic and chromium were significantly reduced. Arsenic decreased from an average of 630.5 mg/kg (avg. from different depths) to 10 mg/kg (a 98.4% reduction), while chromium decreased from 2656.05 mg/kg (avg. from different depths) to 50 mg/kg (a 98.1% reduction). These post-remediation levels are well below the pre-1997 regulatory limits for agricultural soils (20 mg/kg for As and 100 mg/kg for Cr), indicating a successful remediation process. The data underscore the effectiveness of the reclamation efforts in transforming a degraded landfill into a stable and environmentally safe site suitable for future development. Although the illegal dump was reclaimed 30 years ago, detailed information on As and Cr speciation is not available. However, understanding their speciation would allow a better understanding of mobility and toxicity, as these determine environmental behavior and contamination risks. Arsenic in the As(III) form is more toxic and mobile than As(V), while chromium in the Cr(VI) form is significantly more hazardous than Cr(III). Factors such as pH, redox potential, and the presence of competing anions influence their mobility, with acidic conditions increasing the risk of groundwater contamination. Given the likely neutral to slightly alkaline pH of the soil at the site, arsenic was probably present predominantly as less mobile As(V), while chromium may have existed in both Cr(III) and Cr(VI) forms, with Cr(VI) posing a higher risk under oxidizing conditions. Knowledge of speciation would have been invaluable for designing targeted remediation strategies, such as stabilizing or immobilizing these elements to prevent leaching. Although such data is lacking for Łomianki, future reclamation projects should prioritize speciation analysis to ensure more effective and environmentally safe outcomes.

In addition to these analytical efforts, effective physical barriers were crucial in preventing contamination during the reclamation process. Bentonite mats were highly effective in preventing contaminant migration during the Łomianki reclamation project, serving as a critical barrier between waste and the surrounding environment. Their unique self-sealing property, enabled by sodium bentonite, forms an impermeable gel upon hydration, ensuring reliability even if damaged. With extremely low hydraulic conductivity (10⁻⁹ to 10⁻¹¹ cm/s), they effectively blocked leachate movement, while their chemical resistance protected against heavy metals and organic pollutants. Proper installation, including leveling, overlapping, and covering with sand, ensured long-term durability and performance. Regular groundwater monitoring confirmed their effectiveness, making bentonite mats a key component in safeguarding the reclaimed site from contamination. Geotextiles also played a vital role in the reclamation project by enhancing soil stability, preventing erosion, and supporting vegetation growth. Made from durable synthetic materials, i.e., polypropylene and polyester, geotextiles provided critical functions such as filtration, separation, and reinforcement. They prevented soil layer mixing, improved load-bearing capacity, and protected against water and wind erosion. Additionally, geotextiles acted as a barrier, preventing contaminant migration into groundwater while creating a stable base for vegetation. Their integration with other measures, such as bentonite mats and layered soil, ensured long-term soil stability and contributed to the project’s overall success in restoring the land to safe and sustainable use. A mix of grasses, rapeseed, and legumes was utilized to stabilize the soil and prevent erosion on both the donor and recipient sites. Grasses like perennial ryegrass and red fescue were chosen for their rapid germination and strong root systems, which effectively bound the soil and reduced surface erosion. Rapeseed provided quick ground cover, while legumes such as clover improved soil fertility through nitrogen fixation. This diverse vegetation not only protected the soil from wind and water erosion but also enhanced water infiltration and added organic matter, contributing to long-term ecological recovery and aesthetic improvement. The success of this approach highlights the importance of selecting appropriate vegetation for soil stabilization in reclamation projects.

The entire reclamation project involved a critical decision between external waste disposal and local relocation to plot #608. External disposal was estimated at 110 million PLN for transporting and treating 130,000 m³ of waste, while local relocation cost 68.5 million PLN (3.5 million PLN for plot purchase, 65 million PLN for remediation, and operational costs). This approach saved 37.7% (41.5 million PLN) compared to external disposal (see

Table A2. Cost-Benefit Analysis of Łomianki Landfill Reclamation.

Aspect	External Disposal	Local Relocation	Savings/Benefits
Total Cost	110 million PLN	68.5 million PLN	41.5 million PLN (37.7% savings)
Land Purchase	Not applicable	3.5 million PLN	N/A
Remediation Costs	Included in 110 million PLN	65 million PLN	N/A
Logistical Complexity	High (long-distance transport)	Low (local relocation)	Reduced regulatory and transport risks
Environmental Risks	Higher (transport emissions)	Lower (on-site containment)	Minimized carbon footprint
Economic Benefits	Limited	Land value appreciation, job creation	Long-term revenue potential
Public Health Benefits	Limited	Reduced heavy metal exposure	Improved quality of life for residents

Source: own elaboration.

in Appendix A), while reducing logistical complexity, environmental risks, and carbon footprint from long-distance transport. The project also generated economic and social benefits, including land value appreciation, job creation, and public health improvements through reduced heavy metal exposure. Long-term monitoring and future commercial/residential development further offset initial costs, making the local relocation approach economically and environmentally sustainable. The cost-benefit analysis highlights the advantages of local relocation, which not only reduced carbon footprint and regulatory risks but also created opportunities for land value appreciation and jobs. Improved public health through reduced heavy metal exposure further demonstrates the project’s broader social benefits. Long-term monitoring and potential future development enhance economic viability. This case study underscores the importance of considering immediate and long-term costs and benefits in remediation projects, providing a model for similar efforts worldwide.

Finally, Figure 8 (block diagram) provides a clear, step-by-step visualization of the reclamation process, highlighting the logical sequence from identifying pollution to ensuring long-term environmental safety.

5. Discussion

The remediation of the landfill in Łomianki (1995–1997) addressed illegal waste disposal, ecological imbalance, and public health risks. A 21.32-hectare area, including approx. 5 ha of municipal waste (approx. 130,000 m³), posed a threat to drinking water supplies (approx. 1 km away). Remediation began with soil testing, revealing heavy metals and other contaminants. Topsoil was removed, and the area was dewatered using deep wells and an evaporation pond. Waste was extracted, sorted, and relocated to parcel #608. Topsoil was removed, and sand mining was used to fill the void left by the waste removed from parcel #638. Modern sealing methods were used to minimize leachate migration [17], enhance liner stability [78], and protect groundwater [79]. Stripping contaminated soil layers reduced leachate impact on groundwater, while composite liners (e.g., bentonite mats) improved stability and physical properties [16,122]. Proper drainage systems managed stormwater, reduced leachate formation, and enhanced site management [78]. Studies by Jain [16], Nath et al. [78], and Koda et al. [21] highlight the effectiveness of bentonite in improving landfill liner performance and contaminant containment when combined with drainage systems. Despite these advancements, challenges remain in ensuring long-term performance and environmental compliance, requiring ongoing research and adaptive landfill management practices. Decomposition processes and their by-products must also be considered when assessing landfill environmental impact [123].

The Łomianki landfill reclamation project aimed to prepare the land for commercial development while complying with environmental regulations. The revitalized area now hosts commercial establishments like Auchan M1 Center and Castorama (see Figure 7). Effective reclamation integrates technical methodologies with historical contexts to address waste challenges [124], requiring an understanding of past industrial activities (in this case, the Raabe tannery) to identify contaminants and their impacts [125,126]. Geodetic measurements and probing provide essential data on waste volume and composition, enabling targeted remediation [127], while computer-aided tools assess risks and benefits of reclamation strategies [127]. Community engagement fosters ownership and responsibility, enhancing project success [17,25]. The reclamation process involved comprehensive geological surveys, chemical analyses, and intensive consultations with local authorities and residents to address health concerns. Approximately 130,000 m³ of waste was relocated to a prepared site, with sand extracted from nearby areas used to fill voids. Waste was layered in 0.8-m sections, separated by thin sand layers (see Figure 6 above for details), a method supported by studies highlighting improved slope stability and minimized settlement [128]. Stratified layering enhances stability, as demonstrated by physics-informed neural networks analyzing pore water pressure [129], and reinforced soil designs achieve safety factors above 1.5 [130]. Reinforced soil in landfill slopes enhances stability, offering an alternative to excessive waste removal, especially in older municipal solid waste landfills [131]. However, challenges like leachate management and economic implications must be considered [132]. Layered systems, including geosynthetics, improve stability by distributing loads and increasing shear strength [133], though pressure head variations under rainfall can affect failure mechanisms [134]. Accurate stability assessment requires considering waste properties at different depths, especially under dynamic conditions like earthquakes [107]. Optimization techniques, such as stabilizing berms and geogrids, have been used in successful landfill designs [135], while finite element analysis models the effects of material inhomogeneity [136]. Importantly, an improper stratification can misestimate stability, increasing failure risks [134].

Understanding landfill stability is crucial for safety and unlocking redevelopment potential. Wiley and Assadi [10] highlight six case studies in New Jersey, where 378 acres of closed landfills were transformed into universities, shopping centers, and recreational spaces, valued at over $500 million. They emphasize waste relocation, environmental remediation, and regulatory compliance, demonstrating how proper planning yields favorable environmental and social outcomes. These insights, though focused on New Jersey, provide a model for similar initiatives, stressing the importance of strategic management and community engagement. This aligns with the Łomianki case study, where community involvement and regulatory compliance were critical to successful remediation.

However, illegal landfills pose significant challenges, contributing to biological and chemical contamination that affects air, soil, and water quality. Studies show high levels of microorganisms and toxic compounds, indicating health risks [74], while hazardous waste causes severe ecological damage [73]. Poland’s complex regulations on illegal dumping are poorly enforced due to limited municipal knowledge and resources [71,137], leading to a stable or increasing number of illegal landfills (Figure 9). Effective law implementation could mitigate illegal dumping, but the gap between legislation and enforcement remains a barrier, exacerbated by a legacy of improper waste disposal practices from the socialist era.

Furthermore, landfill relocation serves as a form of reclamation with significant implications for environmental protection and public health. This process addresses challenges posed by existing landfills while transforming sites into valuable community resources. Reclamation through relocation is a key aspect of environmental management, targeting pollution and improving ecological conditions. Research highlights its efficacy in contexts ranging from mining to urban waste management. In conjunction with relocation efforts, various remediation techniques are employed to further mitigate contamination and restore ecosystems. Bioremediation employs microorganisms, fungi, or plants to degrade contaminants in soil and water, adapting to various ecological conditions [2], while techniques like bioventing and bioaugmentation, and biosparging enhance microbial activity and nutrient retention [3]. Chemical remediation neutralizes pollutants through oxidation, reduction, or precipitation, particularly for heavy metals and organic contaminants [4]. Combining chemical and biological processes has proven effective in complex contamination scenarios [4]. Physical remediation, including excavation and thermal treatment, removes pollutants, often used alongside chemical and biological methods [5]. Hydraulic manipulation techniques, such as groundwater circulation wells, further enhance contaminant extraction [4]. Despite their efficacy, challenges persist due to multiple contaminants and the need for site-specific strategies. Integrating these methods can yield more sustainable outcomes. Case studies illustrate practical applications and challenges. For instance, relocating net-acid-generating waste at the Eskay Creek Mine improved water chemistry by submerging waste in a lake, restoring near-neutral pH levels [138]. In urban settings, reclaiming illegal landfills using mineral-organic substances reduced heavy metal content [33]. Virtual reality simulations have also been developed for radioactive waste relocation, improving training and planning [139]. However, ensuring long-term effectiveness and safety remains a challenge, necessitating ongoing innovation. Modern landfill designs enhance reclamation by integrating large-scale projects, such as the Guiyang landfill project in China, which aims to create green spaces and educational centers [37]. Techniques such as bio-mining and landfill capping revitalize urban areas, transforming neglected sites into inclusive spaces [49]. The Hiriya landfill in Israel highlights the hazards of poorly managed waste, emphasizing the need for reclamation to protect public health [140]. Effective landfill management aligns waste disposal with urban planning, reducing pollution and improving community quality of life [141]. However, relocating landfills raises concerns about new sites becoming hazards if not properly managed. Community involvement and careful planning are crucial, as demonstrated in Łomianki, where waste relocation protected drinking water sources and restored land for future use.

In the scientific literature, several examples of landfill relocations illustrate effective reclamation strategies. The rehabilitation of uranium mining waste in Žirovski Vrh, Slovenia, demonstrates how waste can be managed through relocation to mitigate environmental risks and restore the area, involving the removal of hazardous materials and compliance with safety regulations [142]. Similarly, the reclamation of the Solvay chemical waste site in Kraków and the “Hajdów” Wastewater Treatment Plant required relocating dangerous materials and sludge to improve environmental conditions. Efforts to manage oil-contaminated soil in Brzeg further highlight the importance of relocation in reclaiming land, enhancing environmental safety, and promoting public health. Effective landfill remediation strategies not only mitigate environmental hazards but also transform former landfill sites into valuable community assets through advanced technologies and sustainable design principles.

Building on these successful reclamation efforts, the integration of advanced technologies further enhances landfill remediation strategies. Advanced treatment techniques for landfill reclamation include the integration of artificial intelligence (AI) and machine learning (ML) in leachate treatment, achieving pollutant removal rates exceeding 90% [143]. This technological advancement addresses environmental concerns and optimizes operational efficiency. The Zhangjiawan Landfill case demonstrates how transforming closed landfill sites into community spaces can promote social interaction and recreational opportunities, incorporating community farms and cultural centers [144]. Green remediation methods should prioritize environmental minimization and the promotion of sustainable practices that are ecologically and socially beneficial. The integration of emerging technologies with nature-based solutions has been demonstrated to effectively remediate contaminated sites, enhance biodiversity, and develop long-term climate change resilience. Nevertheless, concerns regarding cost-effectiveness and social acceptance persist as critical factors in implementing sustainable landfill remediation [145,146]. The cleanup operations conducted at Love Canal, New York, are a significant case showing the disastrous health effects associated with inadequate waste management systems. What was once a community established atop a poisonous waste dump, Love Canal gained notoriety in the late 1970s when the residents experienced extreme health problems, prompting widespread public protest and activism [68]. The cleanup operations were massive and expensive, highlighting the necessity for effective hazardous waste management to ensure public health. The disaster spurred significant legislative reforms and increased awareness regarding environmental responsibility [70]. The Love Canal tragedy stands as a stark reminder of the disastrous consequences of incorrect waste disposal, along with the long-term problems associated with hazardous waste management and the critical need for strong regulatory mechanisms to avert such tragedies. As a response to the crisis, the federal and state governments launched one of the earliest large-scale environmental cleanup efforts under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly referred to as Superfund. The historic legislation was designed to clean up contaminated sites to safe levels and restore public awareness of the dangers caused by illegal hazardous waste dumping, thereby prompting strong environmental policy changes regarding the handling of hazardous waste. Lessons learned from the Love Canal case are of major importance when examining illegal waste dump sites, as in the case of Łomianki, Poland. Both cases are important reminders of the essentiality of adopting forward-looking waste planning and promoting populace involvement in avoiding environmental hazards. The cleanup operation at Love Canal pointed to the significance of careful site analysis, proper waste removal methods, and ongoing monitoring in preventing the future occurrence of similar situations. As cities continue to struggle with how to address the issue of illegal dumping of waste, these earlier examples are sobering reminders of the potential health threat and environmental damage that can result from neglecting proper waste disposal practices. The examination of such contaminants as arsenic, chromium, heavy metals, zinc, and organic compounds present in the Łomianki dumpsite offers valuable perspective on the environmental issue of illegal dumping of wastes. These materials are not only common in this specific instance but have also been reported in numerous global studies, emphasizing the wider consequences of managing hazardous waste. Prior research demonstrates that soils near dump sites frequently exhibit increased concentrations of heavy metals such as cadmium, lead, and zinc, often surpassing the standards established by the World Health Organization [147,148]. For example, cadmium levels in Nnewi were found to be above acceptable limits, indicating severe contamination [149]. Research on jarosite and arsenic sulfide residues shows hazardous leachate concentrations that surpass safety thresholds [150]. Organic compounds complicate the contamination landscape due to their persistence and potential for bioaccumulation. Contaminants can leach into soil and groundwater, leading to ecological degradation [151]. Pollution load indices indicate heavy contamination levels that adversely affect agriculture and human health [149]. While some areas may pose low immediate health risks, long-term exposure to heavy metals and organic pollutants remains a significant concern [148,149]. Arsenic levels in Łomianki significantly exceeded the WHO guideline for drinking water, posing serious risks to local groundwater supplies. Similarly, chromium levels raised concerns about potential leaching into groundwater sources. The total concentration of heavy metals at the site underscored the need for stringent monitoring and remediation strategies. Lastly, the detection of organic compounds indicated hazardous materials that could further degrade the environment if not addressed. Regulatory frameworks typically mandate reducing organic pollutants to non-detectable levels before repurposing land for residential or commercial use. Overall, the findings from the Łomianki waste dump highlight the urgent need for effective waste management practices and regulatory compliance to mitigate risks associated with hazardous contaminants. Drawing parallels with other contaminated sites reinforces the importance of proactive measures and community engagement in addressing the legacy of illegal waste disposal globally. Future studies should focus on developing comprehensive remediation strategies that consider both chemical and biological factors affecting contaminated sites while adhering to international safety standards and best practices in environmental management.

Table 12. Key stages, descriptions, and essential elements of the Łomianki landfill revitalization process.

Stage	Description	Key Elements
1. Site Assessment	Conducted geological surveys, waste characterization, and environmental impact assessments to evaluate contamination levels, waste composition, and site conditions.	- Geodetic measurements and depth probing - Soil and waste sampling for heavy metals (e.g., Cr, As) - Groundwater level and quality assessment - Environmental Impact Assessments (EIA) - Waste characterization
2. Regulatory Compliance	Obtained necessary permits and approvals from local authorities, ensuring legal compliance for waste relocation, sand extraction, and water management. Engaged with the community to address concerns.	- Permits for waste relocation, sand extraction, and water management - Community engagement - Compliance with environmental regulations
3. Strategic Planning	Developed a comprehensive plan for waste relocation, soil stabilization, and future land use, including risk management and logistical considerations.	- Waste relocation plan with impermeable barriers (e.g., bentonite mats) - Soil stabilization plan (to achieve proctor compaction index close to IS = 0.98) - Land use planning - Logistical planning for waste transport - Risk management strategies
4. Waste Relocation	Excavation and transportation of the waste to a designated relocation site with bentonite mats (in the case of Łomianki it was approximately 130,000 m3 of waste).	- Heavy machinery for excavation - Sorting and handling of hazardous materials (e.g., asbestos, heavy metals) - Transportation logistics - Safety measures during relocation
5. Soil Compaction and Capping	Filling the excavated area with sand, compacting it to the required density, and installing bentonite mats to create an impermeable barrier. Covering the original landfill site with layers of sand and soil to prevent leachate contamination and stabilize the soil.	- Capping technology with bentonite mats - Soil compaction techniques (Is ~0.98) - Ring drainage system for leachate management - Environmental monitoring
6. Filling Original Site	Filled the original excavation site with sand sourced from the relocation site to prepare for future development.	- Use of local materials (sand) - Ground stabilization techniques - Preparation for construction
7. Long-Term Monitoring	Implementation of a monitoring system to ensure the long-term stability of the site, including groundwater, gas, and soil quality control.	- Installation of piezometers for groundwater monitoring - Gas monitoring wells for methane detection - Regular soil and vegetation testing - Real-time monitoring systems for pH and heavy metals
8. Future Development	Planned constructions/works on the revitalized land, demonstrating effective change of land use (in the case of the revitalization of Łomianki, it was the M1 shopping center).	- Urban planning collaboration - Design and construction plans - Community benefits assessment

Source: own elaboration.

summarizes the key stages of the Łomianki landfill revitalization, with a description of each stage and the key elements associated with each. It outlines the systematic approach taken throughout the project, highlighting critical actions and considerations that contributed to effective waste management and land reclamation.

The revitalization project of the illegal landfill site in Łomianki exemplifies an integrated approach to waste management by combining assessment, regulatory compliance, strategic planning, and practical execution into a cohesive framework. The decision to use sand from a nearby excavation site for the purpose of capping efficiently minimized transport costs while adhering to sustainable practices. Furthermore, the project speaks to the value of community engagement, reflecting an emerging trend in environmental practice that emphasizes public involvement and transparency. In addition, it demonstrates the ability of existing regulatory frameworks to be adapted so as to address the unique challenges of illegal dumping sites, thereby acting as a model for similar projects. This context is captured in

Table 13. Key elements, findings, and added value in the revitalization of the Łomianki landfill site, Poland.

Key Element	Activities	Detailed Findings	Value Added
Geological Surveys	Geological studies were conducted to determine soil composition and contamination levels. Soil samples were analyzed.	It was found that levels of chromium and arsenic in the soil exceeded standards, indicating serious site contamination.	This enabled precise planning for waste removal methods and determining the location for a new landfill.
Environmental Impact Assessments	An EIA was developed to evaluate potential impacts on groundwater quality and local ecosystems.	The assessment indicated a risk of groundwater contamination due to the presence of hazardous substances.	Helped identify risks and develop strategies to minimize negative environmental impacts.
Permits for Waste Relocation	Necessary permits for waste relocation were obtained, requiring cooperation with local authorities and environmental agencies.	Permits were granted after providing detailed documentation regarding the planned relocation and safety measures.	Increased transparency in the process and ensured compliance with legal regulations, which is crucial in waste management.
Community Engagement	Consultations were held with the local community to discuss plans and alleviate concerns regarding the project.	The community expressed concerns about safety and health impacts, prompting additional consultations.	Increased public acceptance of the project and helped build trust between the investor and residents.
Land Use Planning	The local land use plan was modified to accommodate future development on the site.	The land use plan included future utilization of the area for a shopping center while considering environmental protection requirements.	Enabled effective use of the land post-revitalization and contributed to improving residents’ quality of life.
Logistical Planning for Waste Transport	A detailed waste transport plan was developed, including routes and schedules.	Specific transport routes were planned to minimize disruptions to local traffic and ensure safety.	Ensured operational efficiency and minimized disruptions for the local community during transport.
Heavy Machinery for Excavation	Modern machinery was used for excavation, increasing the efficiency of the waste removal process.	High-powered crawler excavators were utilized for rapid waste removal from the landfill site.	Accelerated the revitalization process and reduced operational costs associated with excavation and transport.
Capping Technology	Capping technology was applied by covering the area with layers of sand and soil, and bentonite mats to stabilize the ground and prevent contamination.	Layers of sand were applied at appropriate thicknesses, ensuring ground stability and reducing erosion risk. Bentonite mats were used effectively to seal off contaminants, providing an additional layer of protection against leachate migration into groundwater.	Reduces the risk of soil and groundwater contamination, which is essential for future land use.
Use of Local Materials (Sand)	Sand sourced from a nearby excavation site was used to fill in the void left by removed waste.	The sand met technical requirements for ground stabilization, as confirmed by laboratory tests.	Decreased transportation costs and environmental impact by limiting the need to import construction materials.
Urban Planning Collaboration	Collaboration with urban planners was undertaken when planning future development (Shopping Center M1).	Joint land use plans were developed that considered both community needs and investor interests.	Ensures coherence between revitalization projects and urban development, promoting a long-term vision for the city.

Source: own elaboration.

, which provides a detailed overview of key elements, findings, and added value in the revitalization process of the landfill site in Łomianki.

Table 13 presents detailed findings on the revitalization of the landfill in Łomianki, highlighting its unique value as a case study that integrates technical, legal, and social aspects of reclamation. This comprehensive approach exemplifies effective project management in balancing environmental protection and urban development. Building on this, advanced methodologies such as multi-criteria decision-making frameworks can further enhance waste management strategies. Safeepour et al. [152] provide insights applicable to illegal waste dumps in Poland, enabling informed decisions about relocating landfills with consideration for environmental impacts and community needs. This methodology enhances waste management practices, contributing to reclaiming contaminated lands and promoting sustainable urban development. It also offers relevant insights into the historical context of illegal waste landfills, such as the one in Łomianki, which posed significant environmental and public health challenges in the late 1990s. Although resolved, the methodologies could have informed decision-making by integrating criteria like environmental impact and community needs during the relocation process. This highlights the importance of stakeholder engagement and spatial analysis in waste management, which remain relevant for addressing similar urban challenges today. Employing such frameworks can help stakeholders navigate waste management complexities, ensuring sustainable practices that protect public health and environmental integrity. Additionally, reclamation not only mitigates environmental risks but also enhances land value for commercial development [65], maximizing utility through material recycling and contributing to sustainable waste management practices [65].

In the context of evolving regulatory environments, historical reclamation projects like Łomianki provide valuable lessons on how environmental laws influence remediation efforts. The reclamation of the Łomianki landfill in the late 1990s was conducted under a different regulatory framework than today. Poland was transitioning from socialist-era environmental laws to a modern system influenced by EU accession. Key regulations included the Environmental Protection and Development Act (1980), the Waste Management Act (1997), and the Geological and Mining Law (1994). While the project implemented advanced techniques like bentonite mats and drainage systems, it predated stricter EU regulations such as the Landfill Directive (1999/31/EC) and the Water Framework Directive (2000/60/EC). Today, the project would require more rigorous environmental impact assessments (EIAs), continuous monitoring, and public consultations. In this regard, the Łomianki case illustrates how evolving regulations drive greater accountability and sustainability in environmental remediation. A critical aspect of this remediation was addressing water management challenges, which were exacerbated by the site’s proximity to groundwater sources and a former lake. The water management challenges during and after the reclamation were significant. Located near groundwater sources and a former lake, the site posed a high contamination risk, necessitating effective water management as a critical component. A key concern was the hydraulic connection between the landfill and groundwater, creating an underground river that required careful planning to prevent contaminant spread. To address this, the project implemented a drainage system to divert surface water and used bentonite mats to create an impermeable barrier at the landfill base, isolating waste from groundwater and preventing leachate infiltration. Additionally, a controlled landfill with a sealed bottom and drainage layer was constructed to manage leachate, which was then treated via the municipal sewage system. Post-reclamation, long-term water management remained essential to protect groundwater. Piezometers were installed to monitor groundwater levels and quality, while geotextiles and organic-rich soil layers stabilized the site and promoted vegetation growth, reducing runoff and erosion. Post-reclamation monitoring confirmed the success of these measures, showing that the mineralized waste no longer posed a significant environmental threat. However, the case underscores the need for continuous monitoring and maintenance of water management systems, as even minor leaks in impermeable barriers could cause long-term damage. Overall, the Łomianki project highlights the importance of comprehensive planning, advanced engineering, and ongoing oversight to safeguard water resources during and after landfill reclamation.

In terms of public health impact, the reclamation of the illegal landfill in Łomianki significantly improved public health by reducing heavy metal exposure, enhancing groundwater quality, eliminating gas emissions, and stabilizing soil. Heavy metal concentrations dropped by over 90%, with chromium levels falling to approx. 50 mg/kg and arsenic to approx. 10 mg/kg, minimizing risks of cancer, skin lesions, and organ damage. Before remediation, the site posed severe health risks due to high chromium (avg. 2656.05 mg/kg) and arsenic (avg. 630.5 mg/kg) levels in soil and groundwater (as indicated in Table A1 in Appendix A and Table 4), linked to lung cancer, kidney damage, and cardiovascular diseases [153]. Contaminated groundwater and methane emissions further increased risks of acute poisoning, respiratory issues, and explosions [154]. Post-remediation, impermeable barriers and drainage systems improved groundwater quality, while organic waste mineralization eliminated methane and VOC emissions, enhancing air quality. Soil stabilization reduced dermal contact and dust inhalation, protecting against dermatitis and lung diseases. Long-term monitoring ensured sustained health benefits, safeguarding residents from future risks. Overall, the Łomianki project demonstrates how effective remediation transforms hazardous sites into safe environments, significantly improving public health.

The role of waste segregation is pivotal in minimizing environmental risks and enhancing the efficiency of landfill reclamation. In the 1990s, when the Łomianki landfill was reclaimed, waste segregation technologies were underdeveloped, leading to challenges in managing mixed waste, including hazardous materials like heavy metals. Today, advanced methods such as automated sorting systems using AI and sensors [155], biological treatments (e.g., composting, anaerobic digestion) [156], and optimized landfill mining [157] could significantly improve material recovery and reduce environmental impact. These technologies, combined with stricter policies [158] and stakeholder engagement, could address the limitations of past practices and set a higher standard for future reclamation projects.

The reclamation techniques used in Łomianki were innovative for their time, focusing on minimizing environmental impact while maximizing land usability. Bentonite mats, soil compaction, and drainage systems were key measures, supported by continuous monitoring to ensure compliance with standards. Eiselt [7] emphasizes the importance of local conditions and stakeholder engagement in landfill reclamation, a principle reflected in the Łomianki project. The use of local resources, such as sand for backfilling, reduced costs and environmental impact, aligning with sustainable development goals. Policymakers can draw valuable insights from this case to refine regulations on illegal dumps and reclamation processes, promoting sustainable land use practices.

Long-term monitoring of the Łomianki landfill demonstrates the effectiveness of the remediation process in achieving and maintaining environmental safety. Quantitative data show a significant reduction in heavy metal concentrations in both soil and groundwater, with chromium and arsenic levels reduced by over 90%. The absence of methane emissions and the low subsidence rate further confirm the stability of the site. Continuous monitoring of pH and redox potential ensures that conditions remain favorable for the immobilization of heavy metals, preventing their remobilization. This systematic approach to long-term monitoring provides a robust framework for evaluating the effectiveness of remediation projects over time. Groundwater monitoring using piezometers showed over a 90% reduction in heavy metal concentrations, with chromium levels dropping by 0.05 mg/L and arsenic levels dropping from 0.02 mg/L. These levels remained stable for several years, confirming the success of impermeable barriers and drainage systems in preventing groundwater contamination. Gas monitoring wells did not detect methane or other biogases after remediation, indicating complete waste mineralization and eliminating the risk of gas emissions. High stability was achieved through soil compaction (I_S = 0.98). In addition, soil pH was stabilized at around 7.0, reducing heavy metal mobility and preventing remobilization. These quantitative results highlight the success of the remediation process and underscore the importance of ongoing monitoring to ensure long-term environmental safety and site stability. The Łomianki project serves as a model for integrating advanced monitoring techniques to achieve sustainable reclamation results.

The reclamation methods employed in Łomianki can be critically evaluated and benchmarked against global best practices to assess their effectiveness, innovation, and potential areas for improvement. The project successfully addressed immediate environmental risks and stabilized the site through waste relocation, soil compaction, and the use of a basic multi-layer capping system, which included alternating layers of waste and sand, topped with geotextile and underlain by a bentonite layer. This approach reduced heavy metal concentrations by 90% and provided a foundational level of waste isolation. However, it is important to contextualize these achievements within the project’s specific constraints. The reclamation was undertaken in the mid-1990s, a period when Poland was not yet part of the European Union, and environmental standards differed significantly from those in place today. Moreover, the project was driven by the planned construction of the M1 shopping center, which influenced the scope and objectives of the revitalization efforts.

The reclamation techniques used in Łomianki, such as hydroisolation with bentonite mats and layered waste deposition with sand compaction, effectively reduced the mobility of heavy metals by creating impermeable barriers and stabilizing the soil structure. These measures prevented the leaching of contaminants into groundwater and minimized the risk of metal migration, ensuring long-term environmental safety. The installation of drainage and gas control systems further mitigated the potential for secondary contamination, demonstrating the importance of tailored remediation strategies in managing heavy metal mobility. However, it is important to note that the effectiveness of such remediation strategies can vary depending on the initial concentration of contaminants, particularly in cases of severe pollution. The non-linearity in heavy metal removal efficiency at higher concentrations can be attributed to the saturation of adsorption sites in the soil matrix. As initial contamination levels increase, the available binding sites for heavy metals become limited, reducing the effectiveness of techniques like phytoremediation or chemical stabilization. This adsorption saturation effect means that higher initial pollutant concentrations may require more intensive or combined remediation strategies to achieve significant reductions. Additionally, the mobility of heavy metals may increase at elevated concentrations, further complicating their removal and stabilization in the soil.

The reclamation of the illegal dump site in Łomianki implemented robust environmental safeguards, including hydroisolation with bentonite mats, a ring-shaped drainage system, gas control wells, and layered waste deposition with sand compaction to stabilize the terrain. On the donor site, detailed waste characterization, dewatering, sorting, and controlled transport ensured safe waste removal, followed by sand filling and compaction to prepare the area for future use, all under strict environmental supervision. These measures minimized contamination risks and restored the site for safe development.

When benchmarked against global best practices, the Łomianki project demonstrates both strengths and areas for improvement. However, there is room for improvement in several key areas, including waste isolation, soil stabilization, heavy metal management, long-term monitoring, ecological restoration, and community engagement. For instance, advanced multi-layer capping systems, as demonstrated in the Freshkills Park reclamation in New York [159], incorporate additional layers such as synthetic geomembranes, drainage layers, and vegetative covers, offering enhanced long-term isolation and ecological integration. Similarly, chemical stabilization methods, as applied in the Taipei City landfill in Taiwan [160], provide improved heavy metal management. Additionally, global projects like the Freshkills landfill reclamation in the United States highlight the benefits of using geosynthetic materials and lime treatment for soil stabilization, as well as the importance of community engagement through public consultations [161]. The Singapore Semakau Landfill further underscores the value of real-time monitoring systems for early detection of environmental risks [162]. It is worth noting that the majority of the Łomianki site was ultimately covered by construction elements, as shown in Figure 7, which limited the potential for ecological restoration. However, in cases where reclaimed land is not designated for built infrastructure, projects such as Freshkills Park demonstrate the significant environmental and social benefits of transforming former landfills into public parks and wildlife habitats [163]. While the Łomianki project prioritized commercial development, future reclamation efforts in similar contexts could consider alternative land uses, particularly if the intended purpose of the site evolves over time. By incorporating advanced techniques—such as modern multi-layer capping systems, chemical stabilization, phytoremediation, and real-time monitoring—future projects could achieve greater sustainability and long-term success. Furthermore, prioritizing ecological restoration and fostering community involvement would not only improve public acceptance but also align the project with contemporary environmental and social standards. Overall, while the Łomianki reclamation project employed a basic form of multi-layer capping and was effective in its time and context, integrating modern global best practices could significantly enhance its environmental, social, and long-term outcomes. The project serves as a valuable case study, highlighting how the intended use of reclaimed land shapes the approach to revitalization, while also underscoring the importance of flexibility in adapting to future needs and opportunities.

The community involvement in the Łomianki project was crucial for its success. This involvement was essential in ensuring transparency, building trust, and achieving outcomes that were both effective and socially accepted. Initially, the local community expressed strong concerns about potential environmental and health risks, such as groundwater contamination and harmful gas emissions, when the plan to relocate waste to plot #608 was announced. These concerns led to protests and demands for safety assurances, prompting local authorities and project contractors to engage residents through public consultations. During these consultations, technical details, including plans for hydroisolation, drainage systems, and environmental monitoring, were presented to address community fears. Regular updates on progress, monitoring results, and safety measures were provided to ensure transparency, while an educational campaign helped explain the reclamation process, its environmental benefits, and how potential risks would be managed. Results of waste analyses were shared to demonstrate that the waste was largely mineralized and posed no immediate threat. Local authorities, including the mayor, played an active role in mediating between contractors and the community, issuing a positive opinion on the project and making plot #608 available for waste deposition after consultations with residents. Modern technologies, such as bentonite mats and degassing systems, were used to minimize environmental risks, and long-term monitoring systems, including piezometers and degassing wells, were installed to ensure ongoing safety. Thanks to this engagement, the project was successful, and the reclaimed land was restored to safe use, with commercial and service facilities bringing economic benefits to the community. Regular environmental monitoring ensured long-term safety for residents. This example highlights that active community involvement, through consultations, transparency, and education, is essential for implementing reclamation projects that are both effective and socially accepted, ultimately improving quality of life and fostering local development.

The reclaimed site in Łomianki, as shown in Figure 7, has been developed with commercial and service buildings. A 2004 sozological study confirmed compliance with environmental standards, though heavy metal migration remains a concern, as highlighted in Przybylski’s report [24] (entitled Environmental Protection Program for the Łomianki Municipality for 2025–2028 with a Perspective to 2032). Harmful substances like lead, zinc, cadmium, copper, arsenic, and chromium persist, particularly in agricultural areas along transportation routes, where they can enter the food chain, posing risks to human and animal health. The report emphasizes sustainable agricultural practices (e.g., biopesticides, crop rotation, organic farming) and soil remediation technologies (e.g., phytoremediation, bioremediation). Regular soil monitoring and buffer zones along transport routes are recommended, supported by the Mazowiecki Agricultural Advisory Center in Bielice, which educates farmers on sustainable practices. Studies by Lis and Pasieczna [22] and Drągowski et al. [23] stress the need for detailed geochemical surveys and tailored reclamation strategies based on site-specific geological and hydrogeological conditions. Future monitoring should include regular geochemical analyses and adaptive remediation to address potential heavy metal migration, ensuring long-term environmental protection. Historical contamination from the Raabe tannery, operational until its 1954 destruction, left a legacy of arsenic and chromium pollution. While the reclaimed site no longer poses a direct threat, heavy metal migration in agricultural areas requires ongoing attention. As noted by Kulik-Kupka et al. [164], arsenic’s dual nature—toxic yet medicinal—underscores the need for strict regulatory limits and continuous monitoring to prevent health risks like heart and liver damage. Overall, while the reclaimed site meets environmental standards, sustained monitoring and remediation efforts are essential to address broader contamination issues in Łomianki, ensuring the long-term health and safety of residents and ecosystems.

In conclusion, the Łomianki reclamation project serves as a valuable case study in addressing urban waste challenges. While it successfully mitigated immediate environmental risks, future projects could benefit from integrating modern global best practices, such as advanced capping systems, chemical stabilization, and ecological restoration. The project underscores the importance of community engagement, continuous monitoring, and adaptive remediation to ensure long-term environmental safety and sustainable land use.

6. Conclusions

The reclamation of the Łomianki landfill in the late 1990s was conducted under the environmental regulations of that era, which were less stringent than today’s standards. Despite this, the project demonstrated a strong commitment to environmental protection by implementing advanced measures such as bentonite mats, drainage systems, and continuous monitoring. These measures aligned with emerging best practices and laid the groundwork for Poland’s eventual adoption of EU environmental standards. While the project would have been conducted differently under current regulations, it remains a valuable case study in environmentally responsible waste management and sustainable development. The revitalized area was designated for the construction of the Shopping and Service Center M1, necessitating waste removal and land restoration for future use. The study focused on the effectiveness of reclamation methods in terms of environmental protection and future land use, hypothesizing that judicious application of reclamation techniques could revitalize contaminated areas while mitigating groundwater contamination risks.

The study meticulously documented the reclamation process, including chemical analyses of waste, geological evaluations, and environmental assessments. Findings revealed significant contamination, with alarmingly high concentrations of heavy metals such as chromium (Cr) and arsenic (As). For instance, sample 126 showed chromium levels of 24,660 mg/kg at a depth of 0.0–0.2 m, while arsenic reached 6320 mg/kg at 0.4–0.6 m in sample 101. These results highlight the profound impact of historical dumping practices on soil quality near the surface. The reclamation process successfully addressed these issues through site sealing and sand filling from nearby locations, as confirmed by chemical and geological analyses. The area was prepared for commercial development, demonstrating the efficacy of the methods employed. This case study serves as a model for other municipalities facing similar challenges with illegal landfills worldwide. However, local protests and community concerns about potential health and environmental risks underscore the need for enhanced communication and collaboration with residents.

The Łomianki landfill reclamation project involved a critical decision between external waste disposal and local relocation to plot #608. External disposal was estimated at 110 million PLN for transporting and treating 130,000 m³ of waste, while local relocation cost 68.5 million PLN (3.5 million PLN for plot purchase, 65 million PLN for remediation, and operational costs). This approach saved 37.7% (41.5 million PLN) compared to external disposal while reducing logistical complexity, environmental risks, and carbon footprint from long-distance transport. The project also generated economic and social benefits, including land value appreciation, job creation, and public health improvements through reduced heavy metal exposure. Long-term monitoring and future commercial/residential development further offset initial costs, making the local relocation approach economically and environmentally sustainable. This cost-benefit analysis highlights the advantages of local relocation. Improved public health through reduced heavy metal exposure further demonstrates the project’s broader social benefits.

Despite its successes, the remediation of the Łomianki landfill has certain limitations. A key issue is the pH sensitivity of heavy metal mobility, as adsorption and chemical stabilization techniques depend on maintaining optimal soil pH. Acidic conditions can remobilize metals like chromium and arsenic, posing recontamination risks. Additionally, the adsorption saturation effect limits the effectiveness of adsorbents at high initial contamination levels, highlighting the need for advanced techniques to address residual pollutants. External factors, such as changes in groundwater flow or new contaminants, also pose risks, necessitating long-term monitoring. While impermeable barriers (bentonite mats) and drainage systems have minimized these risks, reliance on physical and chemical methods alone does not address ecological restoration. For example, soil compaction and bentonite mats improve stability but do not enhance soil biological activity or biodiversity, which are crucial for sustainable land use. To address these limitations, future research should focus on advanced remediation techniques such as bioremediation and phytoremediation. These sustainable approaches would not only improve heavy metal removal but also restore the site’s natural functionality, promoting long-term environmental safety and social benefits.

In conclusion, the reclamation of the Łomianki landfill represents a successful application of modern waste management and environmental protection methods. Its approach to waste relocation and reclamation can serve as a blueprint for future projects in Poland, particularly in light of the mandatory closure and reclamation of landfills by 2035. This case study highlights the importance of integrating technical, ecological, and social considerations to achieve sustainable outcomes. The cost-benefit analysis underscores the economic and environmental advantages of local relocation, providing a model for similar efforts worldwide.