**Assessing Groundwater Vulnerability: DRASTIC and DRASTIC-Like Methods: A Review**

### **Alina Barbulescu**

Department of Mathematics and Computer Science, Ovidius University of Constanta, 900527 Constanta, Romania; alinadumitriu@yahoo.com

Received: 30 March 2020; Accepted: 8 May 2020; Published: 11 May 2020

**Abstract:** Groundwater vulnerability studies are sources of essential information for the management of water resources, aiming at the water quality preservation. Different methodologies for estimating the groundwater vulnerability, in general, or of the karst aquifer, in particular, are known. Among them, DRASTIC is one of the most popular due to its performance and easy-to-use applicability. In this article, we review DRASTIC and some DRASTIC-like methods introduced by different scientists, emphasizing their applications, advantages, and drawbacks.

**Keywords:** aquifer; DRASTIC; index; groundwater; vulnerability

### **1. Introduction**

In recent decades, water scarcity and its pollution became a major issue all over the world. Preserving the groundwater quality is very important for assuring the drinking water resources, given that billions of people all over the world do not have access to water or suffer from water scarcity [1].

Since 1968, when Margat [2] introduced the concept of groundwater vulnerability, many definitions were proposed for this concept. For example, Hirata and Bertolo [3] defined the groundwater vulnerability as "the property of a groundwater system that depends on the sensitivity of the material in permitting the degradation of the saturated zone by pollutant substances originating from human activities", while the National Research Council [4] defined this term as "the relative ease with which a contaminant (in this case a pesticide) applied on or near the land surface can migrate to the aquifer of interest under a given set of agronomic management practices, pesticide characteristics, and hydrogeological sensitivity conditions".

The intrinsic vulnerability describes the water vulnerability to different pollutants (independent of their nature) resulted from human activities and is related to the hydrological, geological, and hydrogeological aquifer's characteristics. Given that the aquifers have different reactions to the same contaminant due to their physicochemical characteristics, the specific vulnerability shows the groundwater vulnerability to a pollutant (or a group of pollutants), determined by the pollutant's properties, taking into account the time of impact, its intensity, and the interaction between the intrinsic vulnerability components and the contaminant [5,6].

Adams and Foster [7] emphasized that the aquifer vulnerability depends on the properties of the layers situated above the saturated zone to attenuate the pollutants' effect, by retention or neutralization by chemical reactions.

Gogu and Dassargues [6] divided the approaches of assessing the groundwater vulnerability in three groups, as a function of the groundwater protection. The first group takes into account only the soil and unsaturated zone, the second one takes into consideration the groundwater flow and the contaminant transfer to some extent [8], whereas the third focuses on the soil, the unsaturated medium, and the aquifer.

Different approaches are used for estimating groundwater vulnerability. They can be grouped into three categories. The first group is formed by the index-based methods, which take into consideration only the characteristics of soil and unsaturated zone. They are divided into Hydrogeological Complex and Settings methods (HCS) [9]; Matrix Systems [10], approaches based on the combination of two parameters, and Rating Systems [11–13]. They work by building water vulnerability groups using different ratings associated with the physical characteristics of the study media. The second group contains the statistical approaches that assess the groundwater vulnerability through statistical analysis or regression models [14–16]. The third one contains the methods based on simulation, which uses simulation techniques for forecasting the processes related to contaminant transport [17–20]. The index-based techniques have the advantage that they do not depend on data availability or similarities [21].

The procedures that belong to the first and second categories are used for studying the intrinsic vulnerability of large areas [22].

The most used index methods for studying the groundwater vulnerability are DRASTIC [23], GOD [12], AVI rating system [13], DIVERSITY [24], ISIS [11], PRAST [25], SEEPAGE, SINTACS [26–29]. For the karst aquifer, EPIK [5], REKS [30], RISKE [31], RISKE 2 [32], COP and COP + K [33,34], PaPRIKa [35], PI and the Slovene approach [36,37] have been proposed.

Introduced in 1985, DRASTIC is among the most popular approaches used in groundwater vulnerability estimation due to its capability and easy-to-use. In the following, we shall focus on reviewing this method, and some of the DRASTIC-like procedures that aim to improve the performance of the groundwater vulnerability estimation, emphasizing the differences between them. We shall not focus on the methods assessing the groundwater vulnerability for the karst aquifer because of the extensive literature for the general case and the lack of space.

Some classifications of the methods that will be presented in next sections are:

	- a. With general applicability—DRASTIC, GOD
	- b. For specific regions—SINTACS, DRAMIC, DRIST, DRAV
	- c. That considers the land use—DRASTIC-LU, DRASIC-LU, SINTACS-LU
	- d. For urban area—DRAMIC, DRASTICA
	- a. Lithological-oriented—methods assessing the kart aquifer vulnerability [5,29–36] and for the fractured environment (referred in the following by Modified DRASTIC)
	- b. Pollutants' oriented—Pesticide-DRASTIC, Modified Pesticide–DRASTIC, SI DRARCH.

We shall indicate the references to the articles treating these methods in the next sections, together with a description of approaches.

The methods (and corresponding parameters) for groundwater vulnerability assessment discussed in this article are summarized in Table 1.

### **2. DRASTIC**

DRASTIC is a model that considers the main hydrological and geological factors with a potential impact on aquifer pollution. Its acronym stands for D—depth to groundwater, R—recharge rate, A—aquifer, S—soil, T—topography, I—vadose zone's impact, and C—aquifer's hydraulic conductivity [38].

The depth to water table (D) [m] is the thickness of the layer crossed by the pollutant before reaching the aquifer. The aquifer vulnerability is inverse proportional to the depth to the water table.

*Water* **2020**, *12*, 1356


**Table 1.** Methods and corresponding parameters for groundwater vulnerability assessment.
