ARCHIVED REPORTS_1989 - Laserfiche WebLink

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' 3. HRS FACTORS ' 3.1 OBSERVED RELEASE It appears that an observed release of hazardous materials to groundwater has not been documented at CHSL. Groundwater sampling data ' provided in a SWAT report prepared by EMCON Associates, indicates that the landfill has not had a negative impact on regional groundwater. The presence of a shallow perched aquifer beneath the landfill indicates that a release of hazardous constituents to groundwater is possible. Although the shallow perched aquifer does not serve as a water source ' for the Tracy area, it is connected to a deep aquifer which serves a large target population. There have been instances where hazardous ' substances were accepted at the facility and continued groundwater monitoring will aid landfill officials in assessing future groundwater impacts. Six groundwater monitor wells were installed at CHSL in 1988 as part of ' the Solid Waste Assessment Test to determine the impact of the landfill kcal groundwater. Three of these wells (MW1-3) were intended to ' ;monitor the deep regional groundwater beneath the site and three (MW-4, MW-5, SB-1) were installed to monitor shallow perched groundwater in the site vicinity. For detailed shallow and deep monitor well locations, ' see Figure 3-1. Cross sections of well depths and vadose composition are given in Figures 3-2 and 3-3. Samples from on-site monitor wells were analyzed for metals, organic volatile compounds (VOCs), and organochlorine pesticide/PCB compounds. ' The concentrations of metals in the deep downgradient well (MW-1) were similar to those in the deep upgradient wells (MW-2 and MW-3) (3). Results of shallow and deep groundwater monitoring efforts are listed in Appendix C. In metal analyses of shallow and deep monitor wells, the highest concentrations detected were of those metals that are commonly known to be characteristic of terrestrially derived groundwater: ' calcium, sodium, potassium, and magnesium (3). 3-1 ' sa/tm/chl/si