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DISCUSSION VOCs The detection of VOCs at MW-3 from March 2000 to October 2001, and the lack of verified detections since that time indicate a transient effect. In an attempt to identify the mechanism of this transient effect, Solid Waste staff interviewed the site operator and past Solid Waste staff. This investigation indicates that an area(approximately 40'x 60') over refuse fill,immediately adjacent to MW-3, experienced ponding in the three winters of 1995-1998. The slope of this area was corrected in the spring of 1998 by regrading, and future ponding was prevented. It is probable that the VOC detections at MW-3 were the result of an increase in LFG production in those portions of the refuse to which moisture intruded, at a location very close to MW-3. This increase in LFG production would increase the movement of LFG through the soil, and with it the potential transport of VOCs. It is speculated that this temporary increased transport was sufficient to cause a temporary impact detected at MW-3. Inorganic Constituents Inorganic constituents were not sampled in the EMP,which was directed to determining the extent of VOC impact. The following discussion addresses past and current data collected from the existing wells. The morgamc constituent data are inconclusive for an indication of contamination by leachate. Apparent inconsistencies and contradictions in the data include: The nitrate concentration at MW-1 shows an increasing trend(Appendix C), however,MW-1 is the up-gradient well. This change shows that natural variations in ' the groundwater occur,not due to the presence of the landfill. If this trend had been seen in a down-gradient well, contamination by leachate would have been incorrectly assumed. Concentrations of inorganic constituents are very low, generally less than 25 mg/1 for any"single constituent. This indicates high-quality water,not impacted. Although a slight increasing trend is seen for chloride and sulfate at MW-3,the Total Dissolves Solids (TDS) concentration appears to be decreasing; since 1996 (Appendix C,Time Series Plot for TDS). Contribution by leachate would cause an increase in TIDS and other inorganic constituents. The decreasing trend in TDS indicates a small and gradual change in the quality of groundwater due to factors other than contribution by landfill leachate. - Concentrations of Sulfate previously found in LW-1,which is up-gradient from MW-3, are higher than those currently found in MW-3. Because the sulfate in the down-gradient well is lower than the up-gradient well,contamination is not indicated. Engineering Feasibility Report 4 Foothill Sanitary Landfill October 30,2003 San Joaquin County Solid Waste