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Slug Test Results <br /> Stockton Service Center <br /> 1 <br /> On January 26, 1994, rising and falling head slug tests were conducted in <br /> monitoring wells MW-1, MW-8, and MW-9 at the District's Stockton Service Center <br /> I <br /> ' site The purpose of the study was to gather data that would allow the estimation of <br /> the horizontal hydraulic conductivity of the underlying aquifer Slug tests can be used <br /> to determine in situ hydraulic conductivity values from tests carried out in a single <br /> well <br /> Hydraulic conductivities were estimated from slug test data by the Hvorslev <br /> ' method (Hvorslev, 1951, Freeze & Cherry, 1979) The initial analysis by Hvorslev <br /> assumed a homogeneous, isotropic, infinite medium in which both soil and water are <br /> incompressible <br /> A slug test is initiated by causing an instantaneous change in the water level in <br /> a well by suddenly introducing or removing a solid cylinder of known volume The <br /> ' water levels are measured by a data logger at timed intervals as the water level <br /> returns to static conditions The height of the water level immediately after insertion <br /> of the cylinder is defined as ho The height of the water level above the static level <br /> at some time, t, after the beginning of the test is denoted as h The data are plotted <br /> ' by computing the ratio h/ho and plotting that ratio versus time on semilogarithimic <br /> paper, as shown in the example The data are normalized to static water Ievels <br /> Each slug test graph can be divided into three components The first component <br /> of each graph represents the response of the filter pack to the raising or lowering of <br /> the water level Filter pack material at Stockton is composed of relatively high <br /> ' permeability sand, with an estimated porosity of Q 45 (Freeze and Cherry, 1979) <br /> This filter pack causes the water level in the well to quickly respond to changes in the <br /> water table, and is recorded on each graph during the first several seconds of the test, <br /> ' where the slope of the graph is nearly vertical The second component of each graph <br /> ' represents the true response of the aquifer to the slug test This moderate slope is <br /> used to determine hydraulic conductivity in accordance with the Hvorslev Method <br /> The final data points compose the last element of each graph At Stockton, where <br /> ' the aquifer is composed of sand, the final data points are not pertinent, because <br /> aquifer response times are relatively quick The aquifer has nearly returned to its <br /> original level by the time these data are collected <br /> Once the curve has been plotted, a value is determined for the basic lag time <br /> 1 <br />