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Mr. Todd Del Frate PG -2- SECOND 2 - SECOND SEMIANNUAL 2018 GROUNDWATER AND SURFACE WATER MONITORING REPORT, FOOTHILL SANITARY LANDFILL monitoring period. The well will be developed and sampled as soon the access conditions improve. Although some concentrations slightly exceeded the tolerance limits, they are still within the range of historical data. One VOC, trichloroethene, was reported in monitoring well MW -3 during the 3rd Quarter 2018 at a trace level concentration. Two VOCs, 1,1-dichloroethane and trichloroethene, were reported at MW -3 during the 4th Quarter 2018 at trace level concentrations. VOCs were not detected in any other well during the third and fourth Quarter 2018 sampling events. During the second semiannual 2018 3rd quarter monitoring event, water was reported in lysimeter LZ -4. This was the first detection of liquid in the LZ -4 location and a sample was collected. A resampling and verification sampling event was completed on September 5 and 6, 2018. A work plan was submitted to the Regional Board on September 18, 2018 to present the analytical results and propose additional sampling to be completed for the lysimeter. A third sampling event was completed on October 10 and 11, 2018, but LZ -4 did not have enough water to collect a sample. Per the work plan, quarterly monitoring will continue at the LZ -4 location through the third quarter 2019. The August 2018 LZ -4 sample results reported one VOC, acetone at 200 pg/L, above the PQL and an additional eight VOCs at trace concentrations. The September 2018 LZ -4 sample results reported one VOC, acetone at 130 pg/L, above the PQL and an additional five VOCs at trace concentrations. Concentrations reported in September were lower than the initial detections reported in August. By October, the LZ -4 lysimeter did not have enough water to sample. Methane was not reported in the perimeter soil gas wells during the second semiannual 2018 sampling event. As presented in section "COMPLIANCE HISTORY SUMMARY" of this report, a discussion is provided regarding the 4- to 5 -year lag time between corrective actions taken at the surface of the site and observations of responses to those actions within groundwater. Therefore, the additional landfill gas extraction wells and other additional landfill gas extraction efforts taken with the landfill may take several years to produce observable changes in the groundwater beneath the site. However, the number and the concentration of VOCs detected at MW -3 have declined since 2nd quarter 2017. In addition, the enhanced tuning of the LFG wellfield by the County's operator was ordered following the results of the first semi-annual 2017 monitoring event. The CVRWQCB issued a Notice of Violation (NOV) to the Second Semester and Annual 2017 Groundwater Monitoring Report on June 6, 2018. The NOV requested the County to submit a Work Plan by July 16, 2018. The County's July 16, 2018, response is contained in a letter separate from this report. In response to the NOV, two new monitoring wells, MW -4A and MW - 7, were installed during the second semiannual 2018 period.