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WASTE DISCHARGE REQUIREMENTS ORDER R5-2015-0058-01 -16- SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS FOOTHILL SANITARY LANDFILL, INC. FOOTHILL LANDFILL SAN JOAQUIN COUNTY 67. As part of the Water Quality Protection Standard, Title 27, section 20415(b)(1) requires that the Discharger establish a sufficient number of monitoring wells along the landfill Point of Compliance (e.g., downgradient perimeter of unit) for detection and corrective action monitoring purposes. See Standard Monitoring Specification I.29, SPRR. A Point of Compliance well was not installed directly down gradient of LF-1, however, because previous WDRs classified LF-1 and LF-2 (i.e., Module 1 and the future Subtitle D lined expansion modules) as a single landfill unit with a Point of Compliance along its southern perimeter. Given that these WDRs classify the landfill as two separate units, each with its own Point of Compliance along the southern- perimeter of each unit, and that the two landfills were constructed and developed contiguously as a single unit under previous WDRs, the Discharger has adequately demonstrated that it is no longer feasible to install Point of Compliance wells down gradient of LF-1 (e.g., such a well would puncture the HDPE barrier layer separating the units and would likely be unstable due to landfill settlement ). MRP No. R5-2015- 0058 therefore allows for contiguous monitoring of both units along the downgradient perimeter of LF-2 per Title 27, section 20410(e)(3), with LF-1 in corrective action monitoring and LF-2 in detection monitoring. The groundwater monitoring system for both units complies with applicable Title 27 performance standards for detection and corrective action monitoring. See MRP Section A.1. 68. Low to trace concentrations of VOCs, primarily of Trichloroethene (TCE) and 1,1- Dichloroethene (DCE), have been intermittently detected in monitoring well MW-3 adjacent to unlined LF-1 since 1995, indicating a historical release from LF-1. For example, in January 1995, TCE was detected in MW-3 at a concentration of 0.9 µg/L and has been subsequently detected in the well up to 4.0 µg/L (January 1999). TCE was also detected in this well in 7 out of the last 9 semiannual monitoring events conducted at the site through the First Half 2014 and was most recently detected a concentration of 1.4 µg/L. DCE has been historically detected in MW-3 at trace concentrations. Time series plots of VOC monitoring data in MW-3 suggest a moderate increasing trend in MW-3 over the past 5 years. No VOCs have been confirmed in any of the other groundwater monitoring wells at the site. In 2006, the Discharger implemented various corrective action measures (e.g., partial landfill closure, landfill gas extraction) to address the VOC release under Cleanup and Abatement Order (CAO) R5-2004-0706 issued by the Executive Officer (see Finding 127). The monitoring and reporting program of these WDRs requires corrective action monitoring of LF-1 to assess the effectiveness of these measures and groundwater cleanup. 69. No significant exceedances of inorganic parameters have been historically confirmed at the site. The concentration of chloride and total dissolved solids (TDS) detected in MW-3, for example, have historically averaged about 9.5 mg/L and 207 mg/L, respectively, compared to calculated concentration limits of 7.5 mg/L and 260 mg/L using historical monitoring data from background well MW-4. (The slight chloride exceedance could be spatial variability.) The absence of confirmed inorganics impacts to groundwater at the site indicates that the release is likely due to a landfill gas release from the unlined landfill, LF-1.