*4.4. Point Source*

The HWMD watershed has a total of 11 WWOs from which 5 were found to discharge less than 1 MGD, and the rest discharged more than 1 MGD. Major PS pollutants identified in this watershed were TLAP and MSW. The TLAP corresponds to the presence of high levels of nitrogen in the watershed, and the MSW corresponds to the presence of high total phosphorus levels. There were 8 TLAPs found upstream of the watershed. Currently, there are 2 active MSW facilities in the HWMD watershed. This watershed has a total of 17 MSW facilities recorded from which 4 are considered closed facilities, 4 are inactive, 2 posted closed, and the rest are not constructed. HWMD watershed covers 13% of MS4s. There are currently 7 MS4s permitted areas within the HWMD watershed. The HWMD watershed has the highest MS4s areas among the other watersheds. Therefore, the HWMD watershed shows severe impact by the PS pollution compared to the other watersheds *Sustainability* **2021**, *13*, x FOR PEER REVIEW 13 of 23 the HWMD watershed shows severe impact by the PS pollution compared to the other watersheds Although the RVD watershed has a greater area compared to the IBWCNF water-

> Although the RVD watershed has a greater area compared to the IBWCNF watershed, it is limited with PS pollution (Figure 5). Five WWOs were identified within the watershed boundaries from which 3 are considered industrial wastewater effluent and 2 domestic. Only 4 TLAPs were found in the RVD watershed. Currently, the City of Edinburg Landfill is an active MSW in the RVD watershed. A total of 4 MSWs were identified in the RVD watershed: 2 not constructed, 1 closed, and 1 post closed MSWs. RVD watershed is considered to contribute to 0% of MS4s, with only 0.3% of the city of Edinburg's MS4 found. This watershed covers almost the entire Willacy County, which is identified as limited in MS4s. The IBWCNF watershed presents 9 WWOs from which 4 are domestic and 5 are industrial wastewater effluent. For instance, only 3 TLAP were found, and 3 active MSWs were identified. These PS pollutants are mainly located upstream of the watershed. As a result, it is important to identify the potential PS pollutants of the downstream area of the Arroyo Colorado Watershed that diverts to the IBWCNF watershed. The IBWCNF watershed has 7% of MS4s permitted areas. The MS4s permitted areas include 11 cities. Consequently, it is important to improve stormwater management within these areas to mitigate PS pollutants. Unlike sanitary sewer systems, MS4 systems do not treat the stormwater collected; instead MS4s are required to develop and implement stormwater management programs (SWMP) that reduce the amount of contaminants that enter the system and prohibit illicit discharges [24]. shed, it is limited with PS pollution (Figure 5). Five WWOs were identified within the watershed boundaries from which 3 are considered industrial wastewater effluent and 2 domestic. Only 4 TLAPs were found in the RVD watershed. Currently, the City of Edinburg Landfill is an active MSW in the RVD watershed. A total of 4 MSWs were identified in the RVD watershed: 2 not constructed, 1 closed, and 1 post closed MSWs. RVD watershed is considered to contribute to 0% of MS4s, with only 0.3% of the city of Edinburg's MS4 found. This watershed covers almost the entire Willacy County, which is identified as limited in MS4s. The IBWCNF watershed presents 9 WWOs from which 4 are domestic and 5 are industrial wastewater effluent. For instance, only 3 TLAP were found, and 3 active MSWs were identified. These PS pollutants are mainly located upstream of the watershed. As a result, it is important to identify the potential PS pollutants of the downstream area of the Arroyo Colorado Watershed that diverts to the IBWCNF watershed. The IBWCNF watershed has 7% of MS4s permitted areas. The MS4s permitted areas include 11 cities. Consequently, it is important to improve stormwater management within these areas to mitigate PS pollutants. Unlike sanitary sewer systems, MS4 systems do not treat the stormwater collected; instead MS4s are required to develop and implement stormwater management programs (SWMP) that reduce the amount of contaminants that enter the system and prohibit illicit discharges [24].

The water quality parameters samples for the north and central watersheds are shown in Figure 6, where the red line represents the screening level according to TCEQ

2000 MPN/100 mL. The existence of high levels of bacteria is caused by a variety of NPS and PS pollution sources such as urban runoff, agricultural lands, ranches, WWO, OSSF, MS4s, and colonias. Ammonia levels in this watershed were below the screening level with 2.7 mg/L as N, which is considered the highest record. In 2018, the TKN levels were the highest compared to the other years with more than 3.0 MGL as N. The presence of TKN in the HWMD watershed, according to the EPA, can be traced to failing septic systems, croplands, and industrial discharges [59]. TP levels barely exceed the screening level of 0.7 mg/L with the maximum value of 0.8 mg/L in 2017. Moreover, the nitrite and nitrate levels found in the watershed are higher than the screening level of 1.95 mg/L [2,60]. Chlorophyll-a levels identified surpassed the screening level of 14 μg/L for the three years [2].

**Figure 5.** Location of potential sources of pollution in the North and Central Watersheds: (**a**) non-point sources and (**b**) point sources of pollution identified in each watershed. **Figure 5.** Location of potential sources of pollution in the North and Central Watersheds: (**a**) non-point sources and (**b**) point sources of pollution identified in each watershed.

*4.5. Water Quality Parameters* 

In 2018, chlorophyll-a had the highest level of 98 μg/L.
