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hydraulic communication between the shallow aquifer and the' deeper aquifer has been observed in the area (URS, 1999). 2:2 Extent of Source Area it Several investigations were performed to define the lateral and vertical extent of contamination II. at the site. TPHg and benzene are the predominant contaminants. These compounds are � detected in the vicinity of the former UST sites and have the Ij ery similar distribution in soils and groundwater. Soil and groundwater contamination does not extend 11 off-site and is localized onsite. 3� 2.2.1 Soil The lateral extent of TPHg is bounded by the existing monitoring well MW-14A, former monitoring wells MW-4 and MW-10, and soil boring SB-17 (Figure 3). The monitoring wells pilot borings and soil borings sample in the surrounding area either contained no TPHg and benzene or contained very low levels, with maximum values;of 3.1.mg/kg for TPHg in MW-14 and 2.4 mg/kg for benzene in MW-1. The vertical TPHg extent ranges from 9 m(30 ft)bgs to 14 in (46 ft )bgs. During the 1987 installation of MW-4, the TPHg concentration was 1,100 m Ig/kg and the benzene concentration i was 7.7 mg/kg at 9.1 in (30.5 ft) bgs. During the1992 installation of MW-10, at 14 in (46 ft)bgs, the TPHg concentration was 270 mg/kg and the benzene concentration was 4.4 mg/kg. In 1993, when MW-14 and SB-17 were installed, TPHg concentrations of 11.2,000 mg/kg and 350 mg/kg, !j respectively, were detected at 13.5 in (45 ft)bgs. Benzene concentrations for MW-14 and SB-17 were 1.6 mg/kg and 4.7 mg/kg, respectively at 13.5 in (45 ft) bgs. Figures 4, 5 and 6 present the vertical limits of TPHg in soil. I' During the 2001 installation of MW-14A, soil analytical results included TPHg detected at 13 concentrations ranging from 0.9 to 6.3 mg/kg. BTEX was detected at concentrations ranging from 0.008 to 0.75 mg/kg for benzene, 0.007 to 1.0 mg/kgfl r toluene, 0.012 to 0.16 mg/kg for ethylbenzene, and 0.078 to 0.73 mg/kg for total xylenes (Geocon, 2001). 2.2.2 Groundwater Currently, 11 wells are included in the quarterly groundwatr monitoring program. TPHg and benzene concentrations in groundwater associated with the groundwater data available in November 2001 are presented in Figure 3. it SacDP-N:Lsw.DPM21PR.MJ803W20422b.&C 2-2 {Oi020"0 -b