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Gealagt al Thr ua 1AC Page 11 <br /> ' Groundwater Monitoring Report <br /> Project No 425 2 <br /> April 27,2006 <br /> ' 4.4 CONCLUSIONS AND RECOMMENDATIONS <br /> ' Conclusions <br /> 1 Overall, BTEX and TPH-G constituents have peaked in MW-1 and MW-2 and are <br /> showing decreasing concentrations This is likely due to the plume moving off-site to the <br /> ' north and northeast This quarter showed an increase in constituents in MW-2 <br /> 2 BTEX and TPH-G constituents have reached MW-8 and are likely to reach MW-7 and <br /> ' MW-6 by nud- to late-2006 <br /> 3 The dominance of upward vertical flow of groundwater may be the primary reason <br /> contamination is not impacting Zone C and D or the drinking water aquifer <br /> ' 4 Petroleum hydrocarbon concentrations in the groundwater at the site fluctuate with each <br /> monitoring event The residual contamination in soil, up gradient of MW-2, remains a <br /> significant source of impact to the groundwater plume <br /> ' 5 Generally the soil and groundwater testing data suggests that the contaminants have <br /> spread laterally, but not vertically to any great extent into the deeper aquifer horizons <br /> This may be due primarily to the upward flow of groundwater observed at this site It is <br /> ' also observed that the groundwater plume does not appear to be continuing to spread <br /> laterally down gradient The leading edge seems to be stationary, suggesting that if the <br /> high concentrations of contaminants could be further reduced and if oxygen could be <br /> introduced into the subsurface, the contaminant plume should collapse <br /> 6 The domestic wells sampled remain non-detect above laboratory reporting limits for all <br /> analyzed constituents, indicating that the drinking water aquifer has not been impacted <br /> ' Recommendations <br /> The following recommendations are made <br /> ' 1 Continue quarterly groundwater monitoring events <br /> 2 Implement scope of work discussed in GTIs Feasibility and In-Situ Remediation Pilot <br /> Test Work Plan dated June 14, 2005 and approved by SJCEHD in a letter dated <br /> ' September 16, 2005 <br /> a A traffic control plan was required by San Joaquin County Public Works, which <br /> ' caused some time delays <br /> b The installation of infection and observation wells is scheduled to begin between <br /> May 8 and May 10, 2006 Pilot test area gets flooded and bad weather has caused <br /> ' drilling delays during the first quarter 2006 <br /> c Wells will be developed and tested by Mid-May <br /> d Infrastructure will be installed by the end of May <br /> e Pilot test should begin Early-June <br /> f Report of findings should be submitted by Mid-July <br /> 1 <br />