Laserfiche WebLink
Slightly different T values were obtained for most wells by the two analy- <br />sis methods. This difference is usually close to a factor of 2 with the higher <br />• T value obtained by the Cooper et. al. method. A factor of 2 is a reasonable <br />correlation for single well tests in low permeability materials. The difference <br />is atributed to the Cooper et. al. method accounting for the water stored in the <br />well and the less elegant Ferris and Knowles method assuming the well to be a <br />line source of injection to, or withdrawal from the aquifer. The T value obtained <br />by the Cooper et. al. type curve method is probably the most representative of <br />actual aquifer characteristics. At large times the importance of well storage <br />becomes negligible, as evidenced in the results from wells SOD1 2-H and SOM 38- <br />H-2. Given the rather consistent difference between the two methods, the Ferris <br />and Knowles method is valuable as a check on the T values obtained in the pre- <br />ferred Cooper et. al. type curve method. As an example, data from well SOM 22 <br />H-1 provide a tenuous fit to the type curve which gives a T=2283 gpd/ft., but <br />relatively good fits of the late test data to the straight line (Ferris $ Knowles) <br />method gives T(ave)-795 gpd/ft. which tend to support the T obtained from the <br />Cooper et. al. method as a reasonable value. <br />C. Limitations <br />• <br />Inherent in any single hole aquifer test are the limitations that a reli- <br />able value of storage coefficient cannot be obtained, and that any well inef- <br />ficiencies or formation disturbances are transferred directly to the test data. <br />These limitations apply to slug tests as well as to tests involving pumping and <br />measuring water level in a single well. With slug tests the volume of water is <br />small and the duration of the test is usually short compared to other aquifer <br />testing methods, therefore the transmissivity determined from the slug test <br />represents responses of the aquifer close to the well. Interpretations in the <br />___ following section of this report have attempted to consider these sources of <br />error in the evaluation of data for each well. <br />:: . <br />s ESA Geotechnical Consultants <br />