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Kd = Distribution coefficient (1/kg); and Pb = bulk density of soil (g/ml) The following ten (10) VOCs detected at the highest site concentrations in the soil gas on March 2014 were selected for VLEACH modeling to develop SVSLs: • Acetone, detected at a concentration of 140 gg/kg in well SG -6 • Benzene, detected at a concentration of 5 gg/kg in well SG -6 • Freon 11, detected at a concentration of 580 gg/kg in well SG -6 • Freon 12, detected at a concentration of 3,000 gg/kg in well SG -10 • Freon 114, detected at a concentration of 1,000 gg/kg in well SG -10 • m, p -Xylene, detected at a concentration of 9.4 gg/kg in well SG -6 • Tetrachloroethylene, detected at a concentration of 810 gg/kg in well SG -11 • Toluene, detected at a concentration of 160,000 gg/kg in well SG -1 • Trichloroethylene, detected at a concentration of 54 gg/kg in well SG -10 • Vinyl Chloride, detected at a concentration of 1,500 gg/kg in well SG -1 The modeling will be conducted within 30 days of the approval of the EFS. The results of the modeling will be reported to the RWCQB in a brief letter and summary table. The SVSLs produced by the modeling can be used as conservative cleanup thresholds for LFG VOCs in the vadose zone. The results of monitoring of the site's soil gas wells will be compared to the SCSLs as a means to assess the effectiveness of the LFG collection system and as a basis for making adjustments thereto. Water Board Question: Because there is a continuing release at MW -3, the frequency of groundwater monitoring for MW -3 must be revised to now be on a quarterly basis. All wells proposed to delineate the release around MW -3 shall also be monitored quarterly using the constituents in Table I of the MRP. County Response: MW -3 will be monitored quarterly using the constituents in Table I of the MRP. A sample will be collected in December 2014 to commence the quarterly schedule. Water Board Question: The County requested that this be done in phases. Please provide a section that presents your proposed schedule. Please take into account that for an evaluation monitoring program/corrective action program, Title 27 has timeframes that the County must comply with. For instance, CCR Title 27 Section 20425 (b) requires the Discharger delineate a release within 90 Days. If this is not possible, please address this in your document. and also: Water Board Question: During the meeting, we requested that the field work would be completed during the Spring and Summer of 2015. This is only part of the project. The County Foothill Sanitary Landfill 16 Department of Public Works, Solid Waste Division Revised Engineering Feasibility Study County of San Joaquin — December 19, 2014