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M .1 x 090 y�.ey�'. .�3"''a-fir F F { f File No.=070.2 19 December 1991 pate 9 3.5 Well Pumping Test Results A continuous, 24-hour 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, 14W-3, :N4W-4, I11W-6 ar;d MW-8 Nvere utilized as observation wells. Drawdown of the local groundwater table was continuously measured and recorded in the pumping well and rive observation wells during the well pumping test. During the well pumping test, A1W-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 extends no farther.:!:an any of the rive observation wells,the full MUM 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 zone of influence of the pumped well expanding fartker out laterally. Figure 11 illustrates the approximate drawdown encountered in the pumping well and -4,, observation wells at 330 minutes, 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 rase of groundwater extraction at approximately 1200 minutes (20 hours) after the ~tali of the test. At this point, drawdown 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 fluctuated between 10.36 feet and 11.64 feet. A spreadsheet %as created tabulating the field data obtained from the performance of the well` pumpitg test. Data incorporated in the spreadsheet included &e distance of each observation ►veli <. from tie pumped well,the drawdown in the pumped well,the drawdown in thu observation wells, and the time at which she 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 the spreadsheet according to the lacols Straight-Line MedNod (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 emrapolaied from the distance-drawdown graphs. The aquifer properties are utilized to predict the l.rrformance of groundwater extraction wells. Copies of the five distance-drawdown graphs are included in Appendix XI. Transmissivity is an aquifer property which represents the quantity of water which can be transmitted through the aquifer. It is determined from the distance-drawdown graph based on the slope of the drawdown line and the pump discharge rate. The five values obtained for the aquifer ' transmissivity based on the pumpini,1 test uata for the Rainbu Bakery site were 6551, 6206,5340, 6206 and 6936 gallons.per day per foot of aquifer thickness. The average value was calculated as 6248 gallons per day per foot of aquifer thickness. The storage coefficient represents the volume of water stored in the aquifer which can be released ANDERSON I( ,I CONSULTING i `J GROUP LJ .R