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connected to water tanks supplied b AeroPure Water Systems, which . � PP Y Y were regularly filled by AeroPure with water from the City of Manteca This temporary solution remained in place until the affected wells were treated by individual domestic well treatment systems, see Secion 223 2 - 16 SQ mher_2000 CPT Drilling and Monitoring Well Installation ' In September 2000, ASE drilled two additional soil borings using a CPT a n d installed five additional groundwater monitoring wells (Figure 3) Groundwater in the shallow zone (less than 19-feet bgs) flowed primarily ' to the north beneath the site at a gradient of approximately 0 001- feet/foot Groundwater in the 55 to 70-feet bgs zone flowed primarily to the south/southeast at a gradient of 0 003-feet/foot Groundwater in the deeper zone (below 100-feet bgs) flowed to the southeast at a gradient of 0 0018-feet/foot ' In general, groundwater samples collected from monitoring wells on the northern portion of the site, north of the USTs and pump dispensers, ' contained the highest hydrocarbon concentrations Monitoring well MW-5 contained 001-feet of free-floating hydrocarbons Groundwater samples collected from recovery wells RW-1 through RW-5 contained up to 140,000 ppb TPH-G, 840 ppb benzene, 18,000 ppb toluene, 4,500 p p b ethyl benzene, 25,000 ppb total xylenes, 8,100 ppb MTBE, 21 ppb tert- ' amyl methyl ether (TAME), 1,100 ppb TBA, and 380 ppb ethanol Groundwater samples collected from all off-site, downgradient monitoring wells screened in the water-bearing zone less than 19-feet bgs contained MTBE concentrations exceeding the DHS MCL for drinking water The highest hydrocarbon concentrations were in the groundwater sample collected from monitoring well MW-13, which contained 2,000 ppb MTBE, 1,000 ppb benzene, 8 0 ppb toluene, 1,100 ppb ethyl benzene, 1,300 p p b ' total xylenes, 8 6 ppb TAME, and 600 ppb TBA Groundwater samples collected from monitoring well MW-16, located near downgradient monitoring well MW-13 but screened in a deeper water-bearing zone 49 ' to 64-feet bgs, contained 26 ppb MTBE, 8 8 ppb TBA, 11 ppb ethanol a n d 58 ppb methanol Although this MTBE concentration exceeds the DHS MCL for drinking water, the concentration still represents a significant decrease in MTBE concentration with depth ' Groundwater samples collected from monitoring well MW-6, dust south of the gasoline USTs, contained 1,100 ppb toluene, 1,200 ppb ethyl benzene • and 7,200 ppb total xylenes Frank's One Stop Workplan — September 2003