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. 2_...Z May 1999 Monitoring Well TnStallat�nn In May 1999, ASE installed monitoring wells MW-1 through MW-10 at the site (Figure 3) Monitoring wells MW-1 through MW-6 are screened between 9 and 19-feet bgs to monitor the first water-bearing zone encountered Monitoring wells MW-7 and MW-9 are screened between 55-feet bgs and 70-feet bgs Monitoring well MW-8 is screened between 100-feet bgs and 115-feet bgs Monitoring well MW-10 is screened between 105-feet bgs and 115-feet bgs Hydrocarbons and/or VOCs were detected in groundwater samples collected from all ten monitoring wells The highest concentrations detected were in groundwater samples collected from monitoring wells MW-5 and MW-6 Both of these wells are screened in the first water- bearing zone encountered with the bottom of the zone extending to a depth of no greater than 19-feet bgs Monitoring well MW-5 is located between the USTs and the pump island near West Yosemite Avenue Monitoring well MW-6 is located between the USTs and the site building BTEX concentrations in groundwater samples collected from these two wells exceeded DHS MCLS for drinking water Benzene concentrations in groundwater samples collected from monitoring wells MW-7, MW-8 a n d MW-9, all screened in deeper zones, also exceeded the DHS MCLS for drinking water The groundwater flow direction in the first zone (shallower than 19-feet bgs) was to the northwest at a gradient of between 0 008 to 0 01- feet/foot Not enough wells were screened in the deeper zones to calculate the groundwater flow direction at these depths (since three non- linear points are needed) 2 -fes August 1999 Quarterly Groundwater Monitoring In August 1999, ASE collected groundwater samples from the site groundwater monitoring wells, as well as the on-site drinking water well Free-floating hydrocarbons, believed to be gasoline, were present on the groundwater surface in monitoring well MW-5 A hydrocarbon sheen was present on the groundwater surface in monitoring well MW-6 The analytical results from the remaining wells showed a slight decrease from the initial sampling of these wells The only hydrocarbon concentrations which exceeded DHS MCLs for drinking water were the toluene, ethyl . benzene and total xylene concentrations in groundwater samples collected from monitoring well MW-6, and the benzene concentration in groundwater samples collected from monitoring well MW-7 TPH-D was Frank's One Stop Workplan — December 2000 -4-