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Austin Road Landfill Appendix D Contaminant Plume Characterization Report Aquifer Test Methods The pretest pumping rates were not measured and the EW-1 pumping rate was not measured during the pumping-2 phase(when both wells were operating again),so there is some uncertainty about the appropriate pumping rates for the Recovery-1 phase. Based on the data collected,the average pumping rates for each test phase are as follows: Average Pumping Rate for Each Test Phase Test Phase Well Pumping Rate (gpm) Recovery-1 EW-1 40 Recovery-2 EW-2 160.4 Pumping-1 EW-1 46 Pumping-2 EW-2 154.9 The flow rate measurements were assumed to be sufficiently consistent over each test phase that the average pumping rates given above can be assumed to meet the requirements of constant pumping rates. Partial penetration evaluation pumpingwell screened over a portion of the saturated zone is referred to as a partially penetrating well. Partial penetration creates vertical components of flow within the aquifer near the pumping well during pumping,which leads to relatively larger drawdown adjacent to the well and underestimates of the calculated aquifer T value from affected observation wells(Fettei,1988). The test wells EW-1 and EW-2 are screened over 28.3 foot intervals,from approximately 88.2 to - 116.5 feet below ground surface,respectively(Table D-1). The non-pumping water level in these wells is about 76 feet below ground surface,so the saturated thickness is about 40 feet. Based on the. saturated thickness,the wells are screened over about 70 percent(28/40 ft)of the saturated aquifer thickness. However,when the extraction wells are operating the water surface is drawn down approximately 7-10 feet. This makes the percentage of the aquifer screened by the wells increase to approximately 85.percent of the aquifer saturated thickness. The effects of partial penetration should therefore be relatively minor for potentially affected wells except during times when the water level has risen to near pre-pumping levels. This situation would occur late in the Recovery-1 and Recovery-2 phases and early in the Pumping-1 and Pumping-2 phases. Selecting other portions of these test phases for potentially affected wells would reduce the effects of partial well penetration. Only selected wells for a given test phase will be affected by partial penetration of a pumping well. Walton(1987)provides an equation to estimate the distance beyond which partial penetration effects become negligible in drawdown data from an observation well: distance =1.5*b*(Kx/Kz)" CDM Camp Dresser&McKee D-7 W:\REPORTS\STOCK70MARLPLUME.9"PPD.WPD CS 010854 City of Stockton 190855.0006