ARCHIVED REPORTS_1999 - Laserfiche WebLink

Home Browse Search

Austin Road Landfill Appendix D Contaminant Plume Characterization Report Aquifer Test Methods where b is the aquifer saturated thickness and Kx/Kz is the ratio of horizontal to vertical hydraulic conductivity. Assuming an aquifer thickness of 40 feet and a Kx/Kz ratio of 10(which is a typical value for layered deposits),partial penetration of the pumping wells will have an effect on aquifer drawdowns extending approximately 200 feet from each well. This means that results from observation well MW-8 will be affected late during the Recovery-1 and early in the Pumping-1 phases by well EW-1,and results from observation well MW-9 will be affected during the latter part of the Recovery-2 and early part of the Pumping-2 phases by well EW-2. Observation wells MW-6 and MW-7 are located relatively close to extraction wells and so would also be affected by partial penetration effects. They are screened in a deeper aquifer layer than the other wells used in this test,so should be evaluated by a different set of criteria. The water level data from these wells indicates that the overlying shallow zone and deeper aquifer zones screened by these wells are in hydrologic communication. By discounting the intervening aquitard layer,the combined saturated thickness in the vicinity of these wells is at least 60 feet. The greater saturated thickness in these wells means that the pumping wells are screened over an even smaller portion of this combined aquifer interval,at less than or equal to 46 percent,and that the partial penetration effects are even more prominent in these wells. Due to the effects of partial penetration,the _.. resulting T values calculated for wells MW-6 and MW-7 are likely to be lower than the actual aquifer properties. Background water level fluctuation evaluation The final aquifer analysis assumption listed above,that there are no water level fluctuations other than from the pumping well,was evaluated using well -12. This well is located along Austin " Road approximately 2755 feet northeast of well E -1 and 4034 feet northeast of well E -2(Figure 1-2,Table D-1). A Troll water level indicator was installed in this well prior to the pumping test and recorded measurements every half hour prior to,during and after the aquifer test. Analysis of the water level data indicates daily fluctuations in the ground water table surface at this _ background location of approximately 0.1 feet,with an increase in the water table surface of about 0.7 feet over the course of the pumping and recovery tests(figure xx). These trends indicated the need for a linear correction of the measured water level results from the observation wells. The measured drawdown data from the aquifer test observation wells were corrected using changes in water levels from the background well(MW-12)as the basis. Water level changes over time relative to the measured value in the background well at the start of the first aquifer test phase (Recovery-1)were calculated and become the background water level correction. The background correction was then subtracted from the measured drawdown data in each of the onsite observation wells for each test phase. The measured(raw)and corrected water level data for each observation well are shown on plots for each test phase attached to this appendix.The corrected data were used in the aquifer test analyses are described in the next section. CDM Camp Dresser&McKee D-8 _. W:XREPORTSWOCKTOMARLPLUME.9MPPD.WPD CS 010855 City of Stockton 190855-0006