ARCHIVED REPORTS XR0001370 - Laserfiche WebLink

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I ' GROUND WATER DEPTH AND GRADIENT ' According to the map titled Lines Of Equal Depth Of Water Wells-Fall 1996, published by the San Joaquin County Flood 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 Based on cross sections A-A ' and B-B', AGE informally identified five hydrogeologic flow units ' between first encountered ground water and 199 feet as having significant intervals of apparently porous, coarser-grained soil separated by intervals of finer-grained, less permeable soil Hydrogeologic Unit 1 (HU-1)was subdivided unto three sub-units(HU-1 Upper Zone,HU-1 Middle ' Zone and HU-1 Lower Zone) that may not have significant bamers to vertical migration of 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 to contain mostly continuous sand,Hydrogeologic Umt 3 (HU-3)was identified at depths between 140 ' feet and 160 feet bsg to contain mostly continuous sand,Hydrogeologic Unit 4(HU-4)was identified at depths between 160 feet and 175 feet bsg to Iocally consist of sand and Hydrogeologic Unit 5 (HU-5) was identified at depths between 190 feet and 199 feet bsg to locally consist of sand 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 ' The most impacted soil was encountered beneath the former 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 multi-level wells MW-4 through MW-7,only up-gradient multi-level well MW-9 and cross-gradient ' multi-level well MW-8 had low to non-detectable concentrations of petroleum hydrocarbon compounds 1