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I Feasibility Study Report 1140 W Hammer Lane, Stockton, CA The testing program consisted of three separate elements designed to provide complimentary information The first element consisted of static groundwater monitoring to establish initial conditions and to help in the evaluation of water level changes observed during pumping The second element of the test program consisted of a step-drawdown test of well MW-4, designed to provide data on well efficiency and to select an appropriate pumping rate for the longer term tests The third element of the program consisted of conducting a constant rate pumping test on well MW-4 to estimate aquifer formation transmissivity by two methods 1) the Jacob time-drawdown method and 2) the relationship Ibetween specific capacity and transmissivity ' Using the test data, RESNA calculated the estimated value of formation transn-ussivity, based on the ' pumping test, at approximately 11,300 gpd/ft The log for pumping well MW-4 indicates an aquifer thickness of approximately 10 feet RESNA calculated the hydraulic conductivity to be approximately 1,130 gpd/ft2 This value corresponds to the upper to middle range of expected values for sandy aquifers RESNA calculated the radius of plume capture for a hypothetical extraction well constructed similar to the existing monitoring wells using Darcy's law Using the data obtained from the pumping tests and a natural groundwater gradient of approximately 0 003 ft/ft, the estimated radius of influence was calculated to be approximately 20 feet RESNA concluded that the radius of influence would not be acceptable, either in terms of hydraulic control or effective remediation RESNA concluded that a capture zone radius of approximately 100 feet would be necessary to capture the plume using a dedicated extraction well with a diameter of 4 to 6 inches optimally located near MW5 (the well impacted to the greatest extent) The estimated pumping rate required to achieve the capture zone radius is approximately 21,300 gpd or 15 gpm It is unclear, based upon the pumping test, if the shallow aquifer beneath the site would yield 15 gpm over an extended period 1 45 Additional Subsurface Investigation Pursuant to a request by PHS/EHD, Ground Zero advanced additional soil borings at the site to ' investigate the vertical extent of soil contamination in the vicinity of the former USTs and to investigate .� the lateral extent of groundwater contamination north of the former USTs Ground Zero supervised G 11h%taV.ROUNDZE1KNOWLES HAMIREMRT51FemN1ityRLpart dog ' 5