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<br />7A - ATTACHMENT NO.3 <br />Saltworks Proposal- Water Group Summary Report (22 January 2010) Page 34 <br /> <br />The SC can also be used to estimate the transmissivity of the aquifer using a unitless <br />empirical coefficient (Driscoll, 1986). For confined aquifers such as those underlying the <br />Saltworks site, a coefficient of 2,000 is multiplied by the SC to estimate the T value. <br />Using this relationship, the empirical transmissivity of the aquifer underlying the <br />Saltworks site is estimated to range between 2,300 and 5,280 gpd/ft. These values <br />agree well with the values estimated from the pumping test data described above. <br /> <br />Storativity <br />The storativity (S) is the volume of water an aquifer releases from or takes into <br />groundwater storage. The S value is a measure of the confinement of the aquifer, and is <br />measured as a percentage (per unit surface area of the aquifer per unit change in head). <br />High S-values (greater than 0.1 percent or 0.001) represent an unconfined aquifer and <br />low S-values (less than 0.1 percent) are confined aquifers. The S values for the Pacific <br />Shores wells range from 2.57E-04 to 9.78E-05, indicating that the aquifers tapped during <br />the pumping tests are confined. Since S values can only be measured from responsive <br />observation wells during pumping tests, no S values are reported for the Bayport single- <br />well pumping test. <br /> <br />Boundary Conditions <br />A barrier boundary is an aquifer system boundary represented by lower permeability <br />units or other reduced source of water (AGI, 1998). A barrier boundary is revealed <br />during the pumping test with a steepening of the time-drawdown slope and typically <br />represents a change in hydrogeologic conditions some distance away from the pumping <br />well. Review of the time-drawdown plots for the Maggiora (2001) pumping tests show <br />that barrier boundaries were encountered during the test. The exact boundary condition <br />encountered here is unknown, but could indicate bedrock, permeability variations within <br />the aquifer, or nearby pumping wells. <br /> <br />The horizontal distance to the boundary from the pumping or observation wells can be <br />estimated using the aquifer parameters. This calculation indicates that barrier <br />boundaries encountered in the Maggiora tests (2001) range from 367 to 1,329 feet away <br />from the pumping well depending on which observation well is considered. Insufficient <br />hydraulic information exists to determine if these barrier boundaries are the same barrier <br />for each observation well and/or whether the low SC and T values observed for Bayport <br />Well No.1 represents the barrier. Incomplete recovery in the pumping wells after the <br />Maggiora tests (2001) support the presence of a barrier boundary. <br /> <br />Hydraulic Conductivity <br />The hydraulic conductivity (K) is a measure of the ability of water to move in a porous <br />medium. The K value is a more fundamental property of the aquifer rather than the fluid <br />and is estimated by dividing the transmissivity by the aquifer thickness. Since actual <br />aquifer thickness encountered during the pumping test is unknown, the length of well <br />screen is used as an acceptable surrogate. Calculations by the water team yield <br />estimated K values for the site between 14.6 and 76.4 gpd/ft2, with an average K of 38.4 <br />gpd/ft2. This corresponds to aquifer textures of silty sand to sand (Freeze and Cherry, <br />1978) and is consistent with the geologic framework. <br /> <br />Summary of Hydraulic Analysis <br />Results from the hydraulic analysis of near-site wells produced aquifer and well <br />parameters relevant to the Saltworks site as summarized below: <br /> <br />27 <br />