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iTrc i }..4 Page 9 February 6, 1990 Job No.211-71-6 LOCAL HYDROG OL- 70 CONDITIONS w, Based on the well log presented in Ap`zndix A and boring logs and crosa-~°,'tions reported by Du Pont sUt,and Environmental Services(1989b)the Douglas Gas Station site is underTinlhyvicinity of recover;'wQ nterbedded liraws,of na'"�"1' the minor clay at least to a depth of 8D feet below ground level(BGL). silt and minor clay. Between the soil , a depth of 54 feet BGL is composed of interbedded units of sand, , 9 depths of 54 feet and 78 feet BGL,the soil is composed _)f a fine-or medium-grained,poorly graded rand. With unco fined sand unit represents the present water level at approximately 62 feet BGL, this with minor clay was enc�ounred uppermost,'the bo n'±fi oi' aquifer in the area. Below the sandy aquifer, a very stiff sal RW-1 and-uas determined to be at least 5 feet thick. The top of the sary unit will be considered tae base of the uppermost turated thickness of approximately 16 feet. aquifer in the area which has an undisturbed sa A U� 1FER i EST PROCEDURES PHASE 2 s site on A constant discharge aquifer test was performed by Du Pontundf it electric asubrne le pul Services at Lmp at a deptltDecember 5 through$, 1989. The pump test consisted of placing a feet within. the recovery well (RW-1), discharging water at a controlled rate rr undin3pproground-water ound w gallons-per- 7, surface. minute(gpm j for a 24-hour period,and monitoring the vertical changes in the surrounding gr a specially ed Ground water pumped from the well was controlled and mteasured through r occur to to nth 1 ugpm f The water was then — manifold, utilizing valves and a vertical Rotameter flawn discharged to a 21,000 gallon capacity Baler staragtsurface duringghe testing, Yestwater wPrewas ne cured in into two on- sewer n sewer system. Vertical changes in the ground-water site wells(RW-1 and MW-16 j and one off-site well(MW-25)on a regular basis during the test witM�nelectric MW- sounder. Other potential aquifer test monitoring wells in ed free-floating p oducthe vicinity of tTand, therefore,were not monitored _. 6, MW-8, and MW-22) were either dry or contact the 24-hour production phase of the test,recov.ty on a regular basis during the course of the test. Following in each of the wells was monitored for an additional 50 minutes,unt�greae an 90% recovery was observed. The data were later transferred to an IBM PC for further analysis a. graphing. A uifer Test Results - Semi-log drawdown and recovery curves far recovery well RW l and monitoring well MW-16 are presented for • the production and recovery phases of the aquifer test (Appendix B). These curves indicate the influence of pumping from RW-1,and a recharge and barrier soli conditions within the aquifer. During the 24-hour constant discharge pump test, the maximum drawdown in the extra ction weU(R rodu t on well was uexper experienced a maximured to be m 13 feet. Observation well MW=16,-at a distance of 94.6- eet. nom_the-product sustained drawdown of approximately 0 o5reach a nearum steady-state the cond tion. Observationhase of ta test, rawweU MW-25, at a - in wells RW-1 and MW-16 appeared distance of 112.2 feet from the production well,experienced a maximum drop in water level�f O.DG feet during Du Pont Environmental Semees