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Water Board Question: How will these monitoring wells be designed? County Response: The design depth of each well and corresponding probes are shown below: WELL ID DESIGN TOTAL DEPTH FT. BGS SHALLOW PROBE DEPTH FT. BGS* MEDIUM PROBE DEPTH FT. BGS* DEEP PROBE DEPTH FT. BGS* SG -2A 260 50-70 140-160 240-260 SG -3A 260 50-70 140-160 240-260 SG -4A 195 15-35 75-95 175-195 SG -5A 195 15-35 75-95 175-195 SG -11A 260 50-70 140-160 240-260 *Actual installed depth will be based upon field observations during drilling. The existing wells (SG -2, SG -3, SG -4, SG -5, and SG -11) will be removed during the over- drilling process. The bore hole will then be advanced to the depth of the deepest probe proposed in the above table and the new probes will be installed. Each of the triple -probe well will consist of 1 -inch diameter PVC casing and screen. The bore hole will be approximately 6 to 8 inches in diameter. The monitored interval will be approximately 10 ft. long with approximately 3 ft. of screen. The monitored interval will be separated by cement and 5 ft. -long bentonite seals, see Appendix C, Figure 3. The actual depths and monitored intervals will be determined in the field based on observation by the onsite geologist. The new triple -probe wells will not be located any further from the landfill than the existing single -level wells. SG -1 is a single -probe well that was installed adjacent to MW -3 as part of the EMP in 2003. SG -1 is 255 ft. deep with the borehole sealed with cement from the surface to a depth 247 ft., i.e., only the bottom 8 ft. of well are monitored. Because soil gas containing VOCs are consistently encountered at the 255 ft. depth, we propose that this well be retained. This well provides valuable data, because it is paired with groundwater well MW -3. The remaining single -probe wells will continue to be monitored. Water Board Question: How will these gas probes be monitored? County Response: The probes of the newly constructed soil gas wells will be monitored monthly for one (1) quarter then quarterly thereafter. The monitoring constituents will be the same as the existing wells (VOCs, methane, carbon dioxide, and oxygen). The monitoring will follow the methods shown in the WDR, Table II (Soil -Pore Gas) of the MRP. Foothill Sanitary Landfill 12 Department of Public Works, Solid Waste Division Revised Engineering Feasibility Study County of San Joaquin — December 19, 2014