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Chevron Products Company 8 Former Chevron Service Station 95775 301 West Kettleman Lane Lodi, California March 30, 2000 Water level changes caused by barometric pressure were minimal in wells MW -5B and MW -8B, which are screened in the deeper water -bearing zone (>80 feet bgs) during the performance of the constant -rate pumping test No barometric pressure correction was applied for the constant -rate pumping test data of these deep wells Water level changes caused by barometric pressure were evaluated for water level measurements collected in wells MW -1, and MW-14/EX-2, which are screened in the shallow water -bearing zone, and MW -5A, which is screened from 70 to 75 feet bgs Barometric corrections were applied during the evaluation of the constant -rate pumping test data, by estimating the barometric efficiency, calculating a barometric correction factor, and subtracting the barometric correction factor from observation well water levels Barometric efficiency (Be) and the barometric correction factor (Bc) were calculated from late time recovery data for each well using the following relationships Be = AH(t) / AB(t) Bc =Be x AB(t) where, AB(t) is the change in barometric pressure at time t, and AH(t) is the change in head at time t Corrected drawdown data was then plotted with barometnc pressure . curves and uncorrected drawdown data to evaluate the effects of the barometric pressure correction 0 Estimated barometric efficiencies for the unconfined observation were determined to be approximately 72 percent for MW -1 and 80 percent for MW-14/EX-2 No clear relationship could be established between barometric pressure fluctuations and water level fluctuations in wells MW -1 or MW -5 Based on this, correction of data for barometric efficiency was not performed for data collected from MW -1 or MW -5 Barometric efficiency plots are presented on Figures 10 through 12 The barometric pressure changes shown in the figures are in feet H2O Plots of uncorrected and corrected drawdown versus time for observation wells MW -1 and MW-14/EX-2 during the constant -rate pumping test is presented as Figures 13 and 14 To evaluate the effect of regional fluctuations in groundwater levels during the pumping test, water levels were monitored electronically in observation wells during the background phase Background phase pumping data indicate that site water levels fluctuate in the observation wells Based on G -R's continuous momtonng conducted in 1999 and SECOR's observations during background momtonng, these water level fluctuations were most likely attnbuted to the effect of periodic pumping Well 12 Because of the influence of pumping from the mumcipal well, sufficient data over a significant time period (i e, 7 days) could not be collected As such, regional water level (antecedent) trends during the background phase could not be determined [ IChevron1957751Agwfer test\Revised195775Aqutfertestrevised doc