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The storage coefficient (S) defines the volume of water that a unit area of an aquifer can <br />supply per unit change in head in a confined or semi-confined aquifer. Storage <br />coefficient is unitless, and typical values for a confined aquifer range from 10-3 to 10-5. <br />The storage coefficient of an aquifer can be measured by aquifer pumping tests that <br />involve a pumping well and at least one observation well. If the water level in a <br />confined aquifer declines below the confining layer, the aquifer becomes unconfined and <br />the specific yield is then used to determine how much water can be withdrawn per unit <br />decline in head. The specific yield (Sy) of aquifer materials defines the volume of water <br />that a unit area of an unconfined aquifer can supply per unit change in head when <br />drained under the force of gravity. Though this term typically refers to unconfined <br />aquifer conditions, laboratory tests of core samples collected from confined aquifers <br />measure this parameter as if it were unconfined. In this TM, the specific yield refers to <br />only laboratory derived storage coefficient data from core samples collected from the <br />bedrock aquifers under either confined or unconfined conditions. Specific yield is <br />unitless, and typical values range from 0.01 for clay to 0.30 for coarse sand (Freeze and <br />Cherry 1979, Drisco111986). <br />Data Flow Process <br />During this phase, water level data were obtained from HydroBase and newly identified <br />data sets were added to a temporary HydroBase-compatible SPDSS database used for this <br />study. This SPDSS database was queried for aquifer property data and analyzed. The <br />data in this TM are presented in several forms to depict spatial aquifer property trends. <br />The HydroBase-compatible SPDSS database will be submitted to the State's SPDSS <br />project manager at the end of this phase so all new data can be incorporated into <br />HydroBase by the DWR. <br />The following section describes the approach used to collect, analyze, and map aquifer <br />property data for the bedrock aquifers in the Denver Basin Region. <br />1.1 Sources of Data <br />During Phase 1 of the SPDSS, relevant aquifer property data in the Denver Basin <br />bedrock aquifers were gathered from a variety of published and non-published sources <br />as described in the Phase 1 Task 43.2 TM (CDM 2004a) and summarized in Table 1, <br />below. Data collected by CDM during Phase 1 were added to HydroBase, DWR's <br />hydrologic database, and then provided back to CDM by the DWR on August 11, 2005. <br />SPDSS Phase 2 Task 43.2 TM -Final 3 <br />2/ 13/ 2006 <br />