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' GROUND WATER DEPTH AND GRADIENT ' According to the map titled Lanes Of Equal Depth Of Water Wells-Fall 1996, published by the San Joaquin CountyFlood Control and Water Conservation District,the estimated depth to ground water at the property is approximately 20 to 30 feet below surface grade(bsg) The prevailing groundwater flow direction in southern Stockton is generally northeast,although flow directions may vary locally and seasonably Depth to first encountered ground water at the property during the last two quarters has been measured to be approximately 25 feet bsg HYDROGEOLOGIC UNITS IBased on cross sections A-A ' and B-B ', AGE informally identified five hydrologic flow units between first encountered ground water and 199 feet as having significant intervals of apparently I porous, coarser-grained soil separated by intervals of finer-grained, less permeable soil Hydrogeologic Unit 1 (HU-1)was subdivided into three sub-units(HU-1 Upper Zone,HU-1 Middle Zone and HU-1 Lower Zone) that may not have significant barriers to vertical migration of I contaminations Generally, HU-1 Upper Zone was identified at depths between 25 feet (first encountered ground water) and 51 feet bsg, HU-1 Middle Zone was identified at depths between 48 feet and 75 feet bsg, and HU-1 Lower Zone was identified at depths between 60 feet and 90 feet ' bsg, Hydrogeologic Unit 2 (HU-2) was identified at depths between 112 feet and 125 feet bsg, Hydrogeologic Unit 3 (HU-3) was identified at depths between 140 feet and 160 feet bsg, Hydrogeologic Unit 4 (HU-4) was identified at depths between 160 feet and 175 feet bsg and Hydrogeologic Unit 5 (HU-5) was identified at depths between 190 feet and 199 feet bsg HYDROCARBON IMPACTED SOIL AND GROUND WATER Based on the analytical results of soil samples collected during the August and September 2002 investigation and previous subsurface investigations, cross sections illustrating the inferred vertical and horizontal extent of hydrocarbon-impacted soil were constructed hydrocarbon-impacted soil appears to be defined vertically,although the lateral extent of impacted soil is not defined at the site I The most impacted soil was encountered beneath the fonner UST locations,to depths as great as 115 feet bsg ' The most highly impacted ground water appears to be located near the former UST locations Vertically, hydrocarbon-impacted ground water was detected in each of the screened intervals of I multi-level wells MW-4 through MW-7,only up-gradient multi-Ievel well MW-9 and cross-gradient multi-level well MW-8 had low to non-detectable concentrations of petroleum hydrocarbon compounds I