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i <br /> I. <br /> s <br /> Well Data Sheet Instructions(Rev. 11/94) Page 9 <br /> as <br /> If the screened interval is not known at the time the WDS is completed,the field can be <br /> left blank or you may'ente!r"Unknown In this case, staff will need to use the default <br /> screened interval when doing the delineation calculations for the DWSAP assessment. ' <br /> ,. f <br /> Effective Porosity <br /> Effective porosity is used in the calculated fixed radius method for delineation <br /> calculations. Effective porosity is "the volume of the void spaces through which water or <br /> other fluids can travel in a rock or sediment divided by the total volume of the rock or <br /> sediment_" Effective porosity is used to estimate the volume of water that can be pulled <br /> from the pore spaces of the aquifer. Effective porosity is entered in-decimal percent(no <br /> units). <br /> DHS staff may be tempted to use tables-from various geology or hydrogeology textbooks <br /> to estimate porosity for aparticular type of aquifer material (i.e., sand, sand-gravel, sand- <br /> gravel-silt, etc.). USE THESE VALUES WITH CAUTION! Effective porosity is <br /> difficult to estimate and is best left to people trained in the subject. The default value was <br /> selected by the DWSAP technical advisory committee as a reasonably conservative value <br /> for most types of porous media aquifers,without requiring detailed hydrogeologic <br /> studies. Using non-site specific values from a textbook may result in protection zones <br /> that are too small. <br /> If the effective porosity is entered in the WDS the appropriate entry should be made in <br /> the"Actual, Estimated or Default?"column. <br /> If the effective porosity is not known at the time the WDS is completed,the field can be <br /> Ieft blank, or you may enter"Unknown". In this case, staff will need to estimate the <br /> effective porosity when doing the delineation calculations. <br />