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Atlantic Richfield Company ARCO 4932 16 E Harding Way,Stockton,CA June 7 2002 • - were monitored in wells EW-1, MW-1, MW-4, MW-6, and MW-7 Groundwater levels were recorded for approximately 24 hours, until the data loggers were removed from the wells on April 4, 2002 Water level data compiled throughout aquifer testing was downloaded from the data-loggers onto a computer, and was later used to determine ' hydraulic properties of the aquifer beneath the site Data Analysis ' Drawdown data from observation wells MW-1 MW-4, MW-6, and MW-7 were analyzed using the Cooper and Jacob (1946) method applied using the AQTESOLV ' software groundwater modeling program The analyzed data were selected after borehole storage effects were considered negligible approximately 115 minutes after pumping began (Hargis, 1979) Groundwater recovery data from extraction well EW-1 ' and observation wells MW-1,MW-4, and MW-7 were also analyzed using the Theis (1935) method of plotting the recovery water levels versus the time that pumping commenced/time that pumping was ceased (tit') on semi-log paper Results of the ' analysis of drawdown data from wells MW-1, MW-4, MW-6,and MW-7 indicated a transmissivity (T) ranging from 1,200 to 5,400 gallons per day per foot (gpd/ft) The Ts ' from extraction well EW-1 and observation wells MW-1, MW-4, and MW-7 were also calculated using the straight-line method described by Theis (1935), which analyzes the late-time recovery water The results of the groundwater recovery data analysis indicated Ts ranging from 1,400 to 11,000 gpd/ft The geometric mean of the T from 7, analysis of the drawdown and recovery data is 3,600 gpd/ft The hydraulic conductivity (K) was calculated by dividing the T at each well by its respective aquifer thickness, ' which ranged from 16 7 feet in well EW-1 to 10 95 feet in well MW-7 The calculated Ks ranged from 0 005 centimeter per second (cm/sec) in EW-1 to 0 046 cm/sec in MW- 7 The geometric mean for K was calculated at 0 014 cm/sec This is consistent with the silts and sands described in the saturated zone on the boring logs (Attachment B) Storativity (S) of the aquifer can be calculated from analysis of the observation well ' data only S ranged from 0 02 to 0 03, with a geometric mean calculated at 0 03 The S values are typical of a semi-confined aquifer system A summary of hydraulic properties determined from aquifer testing is presented in Table 7 Assuming that semi-confined or confined conditions may exist across the site at depths beyond 90 feet bgs, based on soils encountered in deep soil borings SB-1 and SB-2, and ' the boring for deep well DMW-1, a capture zone for pumping well EW-1 was calculated using the Javandel and Tsang(1986) method According to Gorelick et a] (1993), the Javandel and Tsang (9186) method may be applied at sites with semi-confined rconditions based on the following " semi-confined conditions seem to indicate that the delayed yield effects from gravity drainage are insignificant Confined-aquifer ' hydraulics can be applied with reasonable confidence in such cases " Using a discharge rate of 0 59 ft/min (weighted average of pumping rates recorded during the constant- rate pumping test), an average hydraulic gradient of 0 009 ft/ft calculated from all ' I 1ARCO149321ReportslAsmt&Aq&TstRpt doe