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2. The vacuum imposed by the landfill at the closed well will be measured again after 24 hours. 3. The distance from the well that is off to the nearest on-line well will be determined. If the well that is off indicated the presence of vacuum, then the minimum ROI for that well will be noted as the distance to the closest on-line well. 4. After that measurement is recorded, the vacuum to that well will be restored to the vacuum prior to the test and another well will be selected for testing similarly. This procedure will be repeated for all wells. Minimum and maximum values of ROI will be determined for each well using the above testing protocol. If vacuum is detected at the test well following 24 hours of being offline, then the radius of influence extends from the adjacent wells to the test well and the ROI will be at least the distance to the closest well. This also indicates that as long as LFG methane concentrations do not exceed 50% methane, no additional extraction wells are needed in the particular test area. If the vacuum reading at the test well is found to be zero following 24 hours of offline time, then it can be assumed that the test well is at the edge of adjacent wells' radii of influence. Then it can be determined that the ROI of the closest well is no more than the distance to the closest well. If the vacuum reading at the test well is found to be greater than zero (positive pressure), then it can be determined that the ROI from the adjacent wells is less than the nearest well. This test will determine if additional wells within the existing wellfield would be beneficial and will allow an estimate of the maximum ROI. The County can then use the estimated ROI to estimate what areas outside of the wellfield should have additional wells installed in Phase 2. It should be noted that the ROI of a well is affected by: • Well design — the wells at FSL were designed for maximum area of influence by being deeply drilled and by moistening and compacting the well bore backfill soil in lifts. • Well depth — the wells at the FSL were drilled to near the bottom of the refuse. ® Cover soil thickness, compaction and soil type — thicker, less permeable cover will allow the application of more vacuum at the wells heads before significant break -through occurs, thereby improving the area of influence of each LFG well. Water Board Question: What criteria were used to select the proposed well design, especially the depth and length of the screen? County Response: The existing LFG extraction wells were screened closer to the surface of the refuse mass to better control surface emissions, which they are successful in doing. Since there is evidence of LFG Foothill Sanitary Landfill 8 Department of Public Works, Solid Waste Division Revised Engineering Feasibility Study County of San Joaquin — December 19, 2014