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r 17 June 1996 r AGE-NC Project No 95-0121 Page 5 of 6 ' Laboratory analysis of ground water samples indicated an increase in TPH-g concentrations in monitoring wells MW-3 and MW-4, a decrease in monitoring wells MW-1 and MW-2, little or no ' change in monitoring wells MW-6 and MW-7, and was not detected in monitoring wells MW-5, MW-8 and MW-9 Furthermore, laboratory analysis of ground water samples indicated that concentrations of TPH-d increased in six wells and decreased in three wells r ' Several BTEX constituents continued to be present in ground water samples collected during May 1996,' Of the twenty-six BTEX constituents detected in ground water samples from wells MW-1 through MW-9, concentrations for nineteen analytes increased, while seven analytes decreased Concentrations of benzene detected in MWA through MW-4, MW-6 and MW-7 were above the State of California Maximum Contaminant Levels (MCLS) for drinking water of 1 0 pg1l ' Concentrations of toluene detected in MW-1, MW-3 and MW-7 were above the State of California MCLS for drinking water of 150 pg1l Concentrations of ethyl-benzene detected in MW-3 and MW- 4 were above the State of California MCLs for drinking water of 700 Pg/l ' The overall increased in detectable hydrocarbons at the site petroleum hydrocarbons concentrations may be related to the rise of ground water, causing washing of impacted soil within the capillary fringe or lower vadose zone Furthermore,the ground water surface was between 1 and 10 feet above the top of screen intervals in monitoring wells MW-I through MW-8 Because screened intervals ' are below ground water levels, analytical results from samples collected in these wells may not be representative of actual aquifer conditions ' 5 2 RECOMMENDATIONS 5 Further assessment is required northeast of MW-4 and west of MW-7 to determine the extent of dissolved hydrocarbons in ground water and to monitor possible migration of the plume as a result of ground water migration Additional monitoring wells installed at the site should be"completed ' with a minimum of 30 feet of slotted screen to ensure that ground water does not rise above screened intervals A Remedial Action Work Plan (RAWP) and addendum were submitted to the PHS-EHD in April and May 1996 Upon regulatory approval of the RAWP, installation of the remediation system Ishould commence 6.0. LIMITATIONS Our professional services were performed using that degree of care and skill ordinarily exercised by environmental consultants practicing in this or similar localities The findings were based upon