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There are slightly different shaped type curves for a range of a values over <br />several orders of magnitude. A value of storage coefficient (S) for the aquifer <br />can be obtained by the relationship: <br />::• 2 <br />r <br />a = 2 S <br />r <br />c <br />::_ where rs is the radius of the well screen or open hole. Determination of S by <br />this method is of questionable reliability and should only be used if a good <br />correlation with S values is obtained with other methods. <br />The second method of analysis used is that of Ferris and Knowles (1954). <br />This method involves plotting s (head above static water level; same as H used <br />in the previous method) versus 1/t on arithmetic scales. The data should fall <br />on a straight line as s approaches zero and time approaches infinity at the ori- <br />gin of the graph. Transmissivity is calculated using the s and 1/t values from <br />any point along this straight line by the equation: <br />T = V <br />4'rst <br />• where V is the volume of the slug and consistent units are used. For example, <br />if V is in gallons, s in feet, and t in days, then T in gallons per day per foot <br />(gpd/f t) width of the aquifer can be determined. Storage coefficient (S) can <br />not be estimated by this method. <br />Both the Cooper et. al. and Ferris and Knowles methods assume full pene- <br />tration of a confined aquifer. The total gravel pack zone below the static water <br />level or open hole below water level in each well is assumed to be the total aqui- <br />fer thickness. 1Vhere the gravel packed length was not indicated, length of per- <br />forated casing was used for aquifer thickness. Confined conditions exist in most <br />of the wells with the possible exceptions of the two wells with shallow depths to <br />water (wells SOM 1-H and SOM 22 H-1). In SOD1 1-H, the change in head induced by <br />the slug is sufficiently small. compared to the aquifer thickness that no problem <br />in data interpretation results from these assumptions. In SOM 22 H-1, a thin <br />relatively high permeability zone at the water table creates boundary effects <br />that are difficult to interpret. <br />• <br />s ESA Geotechnical Consultants <br />