ARCHIVED REPORTS XR0012580 - Laserfiche WebLink

Home Browse Search

Page 10 --� February 6, 1990 Job No.211-71-6 :he course of the test. The minor water level fluctuations observed in MW-25 are small and may or may not have been the result of drawdown due to the pump test, therefore, the data from well MW-25 are not reliable and were not analyzed. The drawdown and recovery data from well RW-1 were analyzed by the Jacob Approximation-Method (Cooper +. and Jacob, 1946)to detennine the aquifer properties of the uppermost unconfined aquifer in the vicinity of the subject site- Due to the large drawdown relative to the original aquifer thickness observed in recovery well RW-1, the drawdown and residual drawdowr data from the recovery well were corrected using the fo:lowing ',• method by Jacob(1944): - s' (s2/2b) i where , s' = Corrected drawdown (ft.) s = Observed drawdown (ft.) b = Original aquifer thickness (ft.) Appendix C contains the calculations used to determine the aquifer properties of the uppermost unconfined aquifer in the vicinity of the subject site. Based on our analysis of tine data from recovery well RW-1,the shallow, unconfined aquifer is predicted to exhibit the following average characteristics: Transmissivity- 170 gal./day/ft. ' Hydraulic Conductivity- 11 gal./day/ft' �'•1: Due to the relatively large distance of 94.6 feet between monitoring well MW-16 and recovery well RW-i,and ,. the low transmissivity predicted for the shallow aquifer at the site, the Jacob Approximation Method could not i. be used to analyze the tranxient portion of the drawdown curve for well MW-16. An attempt was made at . analyzing the drawdown data from well MW-16 using the type curve matching techniques described by Newman k (1975), however, the drawdown curve could not be matched to any of the type curves for unconfined aquifers. Du: to the relatively minor response of MW-16 to the ag7!ifer test and the effects of heterogeneities that probably exist in the natural aquifer system which are riot allowed for in general well hydraulic theory,it is our opinion that reliable aquifer parameters cannot be obtained through the analysis of the drawdown data from - ,,{ well MW-16. - Carmare Zone Analysis s Based on shallow ground-water levels measured at the subject site by Du Pora Environmental Services (1989a) on September 14, 1989,the ground-water gradient in the vicinity of well RW-1 is directed towards the southeast ------ ------- ----:at a-magnitude-of-approximately-0.024-foot-per-foot-(see Figure --7 ,, dimensions under the ground-water gradient that existed across the site on September 14, 1989 are calculated to give a downgradient radius'of 220 feet and a capture zone width of 690 feet(Appendix C). Table B lists the predicted capture zone dimensions for a variety of discharge rates based or a ground-water gradient magnitude , Du Pont Environmental Services