Laserfiche WebLink
2025 Annual Corrective Action Evaluation Report <br /> <br />www.arcadis.com <br />Forward Landfill 2025 Annual CA Eval Rpt_08012025(1) 3 <br />4 Corrective Action Evaluation <br />In accordance with the 2024 MRP Section E.10 (a) (RWQCB 2024), this section discusses TVOC mass over the <br />reporting period compared to the TL and individual well TVOC concentrations at the Site. <br />4.1 Total Volatile Organic Compound Mass Threshold Limit <br />In accordance with the 2024 MRP Section E.10 (a)(i) (RWQCB 2024), this section discusses TVOC mass over <br />the reporting period compared to the TL. <br />Isoconcentration maps of groundwater TVOC concentrations for the reporting period are presented on Figures 1 <br />through 4. Consistent with the Evaluation Procedures Report (Herst 2002), these maps use a contour interval of <br />25 micrograms per liter (µg/L) and do not include contouring for concentrations less than 1 µg/L. The <br />isoconcentration maps presented include all of the available site groundwater monitoring wells. For each quarter, <br />the TVOC mass was estimated using the following procedures: <br /> The TVOC mass between each pair of isoconcentration contours was first estimated by multiplying the <br />average TVOC concentration between those contours by the area of the contour interval, assumed aquifer <br />thickness and porosity. For example, the average TVOC concentration between the 25 and 50 µg/L contours <br />would be 37.5 µg/L. Consistent with the Evaluation Procedures Report, the aquifer thickness was assumed to <br />be 40 feet and the aquifer porosity was assumed to be 0.25. The area of the contour interval is calculated by <br />adding all applicable plume areas associated with each interval and excluding any other intervals contained <br />within those areas. For example, the contour interval between 1 and 25 µg/L will include multiple plume areas <br />at the Site greater than 1 µg/L and exclude the plume area within the 25 µg/L contour, resulting in the area <br />between 1 and 25 µg/L. <br /> The TVOC masses corresponding to all contour pairs on a given quarter's isoconcentration map were then <br />summed to estimate the total, plume-wide TVOC mass for that quarter. <br />Tables 6 through 9 summarize the quarterly TVOC mass estimation calculations for the reporting period; the <br />historical TVOC masses for the facility are summarized in Table 10; and in accordance with 2024 MRP Section <br />E.10 (a)(v) (RWQCB 2024), the corresponding quarterly groundwater potentiometric maps are presented in <br />Appendix A. <br />In accordance with the 2024 MRP Section E.10 (a)(i) (RWQCB 2024), the TVOC mass for each quarter was <br />compared to the TVOC mass TL of 789.5 kilograms (kg). As shown in Tables 6 through 9, the calculated quarterly <br />TVOC mass during the reporting period ranged from a minimum of 141.5 kg to a maximum of 145.9 kg. There <br />were no exceedances of the TL during the reporting period. <br />4.2 Total Volatile Organic Compound Mass Trends <br />In accordance with the 2024 MRP Section E.10 (a)(ii) (RWQCB 2024), this section discusses TVOC mass <br />throughout the reporting period. <br />The estimated TVOC masses for the past four quarters were reviewed for increasing trends. There was an <br />increase in the TVOC mass from third quarter 2024 to second quarter 2025 (three consecutive quarters) due to