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' Diamond Lumber-Manteca Quarterly Groundwater Monttonng Page 2 results detected elevated levels of benzene, toluene, ethylbenzene, and xylene (BTEX), and total petroleum hydrocarbons as gasoline (TPH-g) On December 5, 1989, BEI installed three ' groundwater monitoring wells near the former USTs, one of these wells reportedly being installed in the former tank location The wells were advanced to depths of 25 feet, with soil samples collected at 5-foot depth intervals from each boring Elevated levels of BTEX and TPH-g were detected in both the groundwater and soil samples October 1991 SRK was retained by Diamond Lumber to address the potential extent of vertical and lateral contaminant migration from the former USTs On October 5, 1991, SRK collected groundwater samples from the three monitoring wells installed by BEI in 1989 During the site visit, it was discovered that actual location of the monitoring wells significantly differed from the well location maps provided in the BEI reports Analytical parameters for the SRK sampling event included BTEX and TPH-gas Elevated BTEX and TPH-gas concentrations were detected in the monitoring well assumed to be MW-3, while slightly elevated concentrations of these parameters were encountered in wells assumed to be MW-1 and MW-2 The BEI analyses performed in 1989 detected elevated BTEX and TPH-gas concentrations to monitoring well MW-1, and slightly elevated contaminant levels in wells MW-2 and MW-3 Because the observed well locations differed ' significantly with the BEI monitoring well location map, there is a high degree of uncertainty regarding BEI's well designation and corresponding laboratory results November 1991 During November 1991, an SRK Field Hydrogeologist supervised the placement of three monitoring ' wells and two test holes during November 18 through November 21, 1991 Permission to install a fourth monitoring well upgradient from the former USTs was not granted by the Southern Pacific Railroad at the time of the initial investigation The Southern Pacific Rail Road later issued a ' statement to SRK stating that permission to install monitoring wells on their property would not be granted in the future These monitoring wells are designated as SRK-MW1 through SRK-MW3, while the monitoring-,sells installed by BE] are designated as BEI-MW4 through BEI-MWb Figure 1 ' contains the monitoring JOLationS ' During SRK's subsurface soil and groundwater investigation, analytical soil samples were selected during the boring of each monitoring wells and test hole at depths of 15 feet (seasonal high groundwater level) and 30 feet (saturated zone) and submitted to a California certified laboratory The analytical soil parameters included TPH-gas, BTEX and total lead The constituents of BTEX and TPH-gas were not detected in any of the analytical soil samples, however, trace amounts of lead ' were detected in soil samples collected from monitoring well SRK-MW2 at depths of 15 and 30 feet Analytical groundwater parameters also included TPH-gas, BTEX, and total lead TPH-gas was not detected in any of the three monitoring wells The constituents of BTEX were not detected in monitoring wells SRK-MWI or SRK-MW3 while trace levels of bencene and xylene were detected in monitoring well SRK-MW2 Lead was detected in all three monitoring wells l The existing monitoring wells installed by BEI in 1989 were not purged or sampled, since data had been collected during the October monitoring event Steffen Robertson and Ku-sten