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,• 11 March 2002
<br /> AGE-NC Project No. 95-0130
<br /> ' Page 4 of 13
<br /> September 2001 -AGE installed two multi-level ground water monitoring wells(MW-6
<br /> and MW-7) to depths of approximately 142 feet bsg at the site to assess the vertical
<br /> extent of petroleum-impact. Screen intervals were installed at depths between 35 and 45
<br /> feet bsg(Interval A),50 and 55 feet bsg(Interval B),70 and 75 feet bsg(Interval C), 100 and
<br /> 110 feet bsg(Interval D)and between 125 and 142 feet bsg(Interval E). TPH-g and BTEX-
<br /> impacted water was detected from both wells at sampling intervals B, C, D and E at
<br /> ' concentrations as high as 160,000µg/1;MTBE-impacted water was detected from MW-6(B
<br /> and C)and MW-7(B,C and D)at concentrations as high as 420µg/1; 1,2-DCA was detected
<br /> in samples collected from MW-6 (B and C) and from MW-7B at concentrations as high as
<br /> ' 210µg/1. Soil and ground water analytical results are summarized in Tables 2 and 3.Results
<br /> of the September 2001 investigation were reported in Multi-Level Monitoring Well
<br /> ' Installation Report- Third Quarter 2001, dated 01 March 2002,prepared by AGE.
<br /> Between January 1995 and December 2001, twenty-five ground water monitoring events were
<br /> ' performed at the site to monitor dissolved petroleum hydrocarbon concentrations in ground water
<br /> and to characterize ground water flow direction and gradient on the site(Table 3).Generally,TPH-g
<br /> and BTEX was detected in water samples collected from wells MW-1, MW-2, MW-3, MW-6 (A,
<br /> '• B, C,D and E),MW-7 (B, C„D and E),VW-1 (B and C),VW-2 (A and B)and VW-3 (A and B) at
<br /> concentrations as high as 390,000 µg/1 and BTEX compounds as high as 92,000 µg/1. Generally,
<br /> MTBE was detected in the same wells at concentrations as high as 440,000 gg/l;low concentrations
<br /> of tert-amyl methyl ether (TAME), tert butanol (TBA), ethylene dibromide (EDB) and
<br /> 1,2-dichloroethane(1,2-DCA)were detected from wells MW-1,MW-2,MW-3,MW-6(B and C),
<br /> ' MW-7B,V W-I (B and C),VW-2(B and C)and VW-3A on isolated occurrences.Analytical results
<br /> of ground water sampling events performed at the site are summarized in Tables 3.
<br /> 2.4. REGIONAL GEOLOGIC SETTING
<br /> The property is situated within the Great Valley Geomorphic Province of California, a large,
<br /> elongate, northwest trending, asymmetric structural trough. The Great Valley Province has been
<br /> filled with thick sequences of sediment ranging in age from Jurassic to Recent,creating a nearly flat-
<br /> ' lying alluvial plain,extending from the Tehachapi Mountains in the south to the Klamath Mountains
<br /> in the north. The western and eastern boundaries of this province are comprised of the California
<br /> Coast Range and the Sierra Nevada, respectively. Rocks composing the basement complex of the
<br /> ' province have not been completely defined but are believed to be metamorphic and igneous in origin.
<br /> The northern and southern portions of the Great Valley Province have been designated the
<br /> Sacramento and San Joaquin Valleys, respectively.
<br /> Based on the General Soil Map from the San Joaquin County Soil Survey,published by the United
<br /> • States Department of Agriculture Soil Conservation Service in 1992, the site area is within the
<br /> Advanced GeoEnvironmental,Inc.
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