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Beacon Station No 641 September 28, 1998 Stockton,California_ _ _Remedial Testin>: Report ithe MW-2 data, and 0 015 for the MW-4 data Using an assumed aquifer thickness of 25 feet from the boring log for well MW-1, results in an estimated value of hydraulic conductivity (K) of approximately 25 7 feet per day Using an assumed aquifer thickness of 23 5 feet from the boring log for well MW-2, results in an estimated value of hydraulic conductivity (K) of approximately 44 0 feet per day Using an assumed aquifer thickness of 27 feet from the boring log for well MW-4, results in an estimated value of hydraulic conductivity (K) of approximately 38 9 feet per day These values are within the range of values typical for fine-grained sand aquifer materials as indicated by the boring logs for the site Calculations using the groundwater drawdown measurements for the aquifer parameters discussed above are presented in Attachment C A graph of distance vs drawdown, as measured with the automated data loggers in wells MW-1, MW-2, and MW-4 is also included in Attachment C Using the distance-drawdown method for the data and a pumping rate of 9 0 gpm, the calculated transmissivity (T) was 649 5 square feet per day and the calculated storativity (S) was 0 165 Using a saturated aquifer thickness of 27 feet from the boring log for pumping well MW-5, results in an estimated value of hydraulic conductivity (K) of approximately 24 0 feet per day Based upon the above calculations, the range of hydraulic conductivity (K) values between 24 0 and 44 0 feet per day are reasonable, as the aquifer materials encountered beneath the site consist predominantly of silty sand (SM) and fine-grained sand (SP) with semi- confining interbeds of sandy to clayey silt (ML) and sandy to silty clay (CL) The drawdown curves suggest a semi-confined aquifer response to pumping at the site Aquifer Pumping Test Conclusions During March and June 1998, the direction of groundwater flow was calculated to be toward the northwest with gradients of 0 0013 (Quarterly Groundwater Monitoring Report — First Quarter 1995, Horizon, June 23, 1998) and 0 0011 ( uarterly Groundwater Monrtorrn Report-_Second Ouarter 1998, Horizon, July 27 1998) Prior to beginning the pumping for the aquifer testing, depth-to-water (DTW) measui ements were collected from the five groundwater monitoring wells at the site These DTW measurements indicated that prior to pumping, the groundwater flow beneath the site «as to primarily toward the northwest with a gradient of approximately 0 0011 Based upon the above field test data and using time-drawdown and distance-drawdown calculations for observation wells MW-1, MW-2 and MW-4, a saturated aquifer thickness (b) of 27 feet, and an average hydraulic conducts its (K) value of 33 feet per day were used to calculate a theoretical steady state capture zone that would be created by pumping from monitoring well MW-5 at a rate of 9 0 gpm Assuming a uniform flow field of groundwater beneath the site during pumping, the downgradient stagnation point is estimated to be only 1 5 feet northwest of pumping well MW-5, and the maximum width of the capture zone is estimated to be approximately 9 2 feet toward the southeast from pumping; well MW-5, as shown on Theoretical Capture Zone Map at 9 GPM (Figure 7) These calculations are 1641-21 rpt 6 HORIZON ENVIRONMENTAL INC.