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_.. File No.2070-2 19 December 1991 —\ page 9 -- 3.5 Well Pumping Test Results s A continuous, 24-hours well pumping test was conducted for the Rainbo Bakery site utilizing the existing onsite monitoring wells. MW-1, located in the center of the groundwater contaminant Plume, was utilized as the pumping well. MW-2, MW-3, MW-4, MW-6 and MW-8 were utilized as observation wells. Drawdown of the local groundwater table was continuously measured and recorded in the pumping well and five observation wells during the well pumping test. I { During the well pumping test, MW-4 was the first observation well to be influenced by the pumped _ well at approximately 5 minutes after the start of the test. At approximately 330 minutes after the start of the test, all five observation wells were noted to be influenced by the pumped well. Since �.. the groundwater contaminant plume extcads no farther than any of the five observation wells,the _ 6111 extent of the groundwater contaminant plume was accordingly contained within the zone of influence of the pumped well at approximately 330 minutes after the start of the well pumping test. } Continued pumping resulted in the local groundwater table lowering even further and the zoite of influence of the pumped well expanding farther out laterally. Figure 1 I illustrates the approximate . drawdown encountered in the pumping well and the observation wells at 330 minut_s, 750 minutes, 1020 minutes and 1320 minutes after the start of the well pumping test. At the pumping rate of 6.7 gpm, groundwater inflow to the pumped well was noted to approximately equal the rate of groundwater extraction at approximately 1200 minutes (10 hours) after the start of the test. At this point, d5awdown in the pumped well was approximately 10.36 feet. From the time of 1200 minutes until the end of the test, drawdown in the pumped well r fluctuated between 10.36 feet and I1.64 feet. A spreadsheet was created tabulating the field data obtained from the performance. of the well pumping test. Data incorporated in the spreadsheet included the, distance of each observation well from the pumped well,the drawdown in the pumped well,the drawdown in the observation wells, and the time at which the drawdown measurements were obtained. A copy of the spreadsheet is _ included in Appendix X. Distance-drawdown graphs for each of the five observation wells were created by plotting the data contained in 010 spreadsheet according to the Jacob Straight-Line Method (see C.W.Fetter, 1988 and Driscoll, 1986 for a detailed explanation of the Jacob Straight-Line Method). Aquifer transmissivity and storage coefficient were then extrapolated from the distance-drawdown graphs. The aquifer properties are utilized to predict the performance of groundwater extraction wells. Copies of the five distance-drawdown graphs are included in Appendix XI. Transmissivity is an aquifer property which reprzsents the quantity of water which can be transmitted through the aquifer. It is determined from the distance-drawdown graph based on the i slope of the drawdown line and the pump discharge rate. The five values obtained for the aquifer i transmissivity based on the pumping test data for the Rainbo Bakery site were 6551, 6206,5340, 6206 and 6936 gallons per day per foot of aquifer,thickness, The average value was calculated a; 6248 gallons per day per foot of aquifer thickness. Tha storage coefficient represents the volume of water stored in the aquifer which can be released ANDERSON ]C'71 CONSULTING GROUP