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March 1, 1999 <br /> 38737 004 <br /> Mr. Michael J. Infurna,Jr. Harding Lawson Associates <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> Page 2 <br /> milligrams per liter(mg/L) and 3.5 to 22 micrograms per literectively. At depths of 31 to 34 <br /> feet bgs, TPHg and benzene groundwater concentrations wer 17.0 m and 440 ug/L, respectively. <br /> u <br /> These results suggest that a previously unidentified plume of rondwater may occur beneath the <br /> former UST location and that concentrations are greater than in the shallow groundwater. As discussed at <br /> the meeting, these hydropunch data may due to cross-contamination by impacted borehole water. At the <br /> recommedation of PHS/EHD and the RWQCB, TVG is proposing to construct an additional monitoring <br /> well at the location of the former excavation near the location of HP-2. <br /> SCOPE OF WORK <br /> Additional Monitoring Well <br /> The proposed monitoring well location is shown on the attached site plan. The scope of work includes <br /> the following: <br /> • Drill, log, and sample a soil boring to a depth of approximately 40 feet bgs near the location of HP-2. <br /> ♦ Collect soil samples at 5-foot minimum intervals in each boring. <br /> ♦ Analyze soil samples from approximately 25 and 30 feet bgs for total petroleum$ydrocarbons as <br /> gasoline (TPHg) with EPA Method 8015M and for benzene, toluene, ethylbenzene, and total <br /> xylenes (BTEX) with EPA Method 8020. "* <br /> • Construct monitoring well MW-7 in the soil boring with a screened interval be.tween 30 and 40 feet <br /> bgs. ' <br /> • Develop monitoring well MW-7 after 48 hours. <br /> • Purge and sample monitoring well MW-7 after 72 hours. <br /> ♦ Analyze groundwater sample for TPHg with EPA Method 8015M, for BTEX with EPA Method <br /> 8020, and for the following oxygenates with EPA Method 8260B. <br /> ■ tertiary butyl alcohol (TBA) ' <br /> ■ methyl tertiary butyl ether(MTBE) <br /> ■' -di-isopropyl ether(DIPE) <br /> ethyl'tertiary butyl ether(ETBE) <br /> ■ tertiary amyl methyl ether(TAME) <br /> ■ In addition, at the request of PHS/EHD, 1,2-dichloroethane (DCA), an additive utilized as a <br /> lead scavenger, will be included with the above suite of analytes. <br /> In accordance with Work Plan Addendum, dated January 14, 1998, all wells will be resampled once more <br /> after a minimum of 30 days following the sampling of well MW-7. Samples will be analyzed in <br /> accordance with the approved analytical program. The scheduling of the final round of sampling will be <br /> contingent on the results of the sampling of monitoring well MW-7. If the analytical results of <br />