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Although shifts in the groundwater flow direction are commonly observed at many sites, complete <br /> reversals, such as has apparently occurred at this site, are rare In this case, the reversal is caused by <br /> a greater rise in the static water level in monitoring wells GT-1, -2, and -3 than in any of the other <br /> wells Several explanations for this rise are possible <br /> 1) The seals on these older wells may have deteriorated, allowing rainwater to enter the well bore <br /> and causing the water level to rise above the static level The wells were monitored the day after a <br /> strong rain storm <br /> 2) As illustrated in the Problem Assessment Report, wells GT-1, -2, and -3 lie within a more <br /> permeable, coarse-grained belt of the Riverbank aquifer As a result of the recent rains, these wells <br /> may have experienced a greater recharge along this permeable flow pathway <br /> 3) Much of the apparent reversal in gradient is due to the fact that the least amount of rise occurred <br /> in well GT-5 This well is close to G-1, the Gillies' domestic well If, as previously suspected, <br /> groundwater conditions in GT-5 are affected by pumping from G-1, then the water level in GT-5 <br /> may have been drawn down slightly by the use of G-1 <br /> Because of the uncertainty surrounding the groundwater gradient, we recommend continued <br /> monitoring of the water depths on a quarterly basis <br /> At the present time, nine drums containing purged water and one drum containing soil cuttings are <br /> stored on the site We recommend that these be removed early in 1997 Upgradient has submitted a <br /> cost estimate for transport and disposal and is awaiting pre-approval from the State UST Cleanup <br /> Fund <br /> It is our understanding that San Joaquin County PHS/EHD is currently preparing a written response <br /> to the Problem Assessment Report that was submitted in November 1996 Based on recent <br /> conversations with Mr Steve Sasson, Upgradient anticipates that PHS/EHD will concur with the <br /> conclusion that assessment of the extent of soil and groundwater contamination has been <br /> completed PHS/EHD may request Gillies Trucking to prepare a Corrective Action Plan comparing <br /> the cost and effectiveness of potential cleanup methods and addressing the possibility of drilling <br /> new drinking water wells on the Gillies and Barbot properties We recommend that representatives <br /> of Gillies Trucking and Upgradient Environmental meet to discuss these options after the <br /> PHS/EHD response has been received <br /> 3 <br />