SITE INFORMATION AND CORRESPONDENCE

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Page 3 • • Concern #5 Appendix G contains the computed values of transmissivity and the storage coefficient for the water bearing zone encountered by MW-6. The values are reasonable, when compared to literature values for the lithology of the well . However, as stated in Appendix F, none of the other wells are screened in the same water bearing zone as MW-6. How was the storage coefficient calculated, without an observation well? Was the value only an estimate? If so, the rationale behind it should be included. Answer #5 Even though the pump test indicates that there is no local hydraulic connection between the water bearing zones within the screened intervals of MW-4 and MW-6, the storage coefficient was estimated by assuming that there was zero drawdown from MW-4 which is located 10 feet from MW-6. Concern #6 The reports claims that three separate aquifers exist within the first one-hundred-twenty-five feet below ground surface at the site. Different aquifers must be both hydraulically and chemically separated from one another. I plotted the results of the minerals analysis performed on the samples that were collected in January 1990 on piper and stiff diagrams (see Figures 1 and 2) . The water in each of the wells appear to have similar chemical characteristics. There is less than two feet of head difference between all of the wells. Some of this is due to ground water gradient. It seems unlikely that the wells are in three hydraulically separated aquifers, when the difference between heads is so small . We cannot conclude that the water bearing zones encountered by the wells are hydraulically separated from the results of the pumping test, since there were only five data points collected from MW-1 through MW-3, and MW-5. Also, static water level measurements were not collected on the day prior to the test. It has not been demonstrated that the water bearing zones encountered by the wells are chemically and hydraulically separated from one another by either the pumping test or the chemical data. Therefore, although the wells may be screened in different water bearing zones, there is insufficient evidence to conclude that these zones are separate aquifers or how may different zones exist. Answer #6 I agree with your statement that "there is insufficient evidence to conclude that these zones are separate aquifers or how many different zones exist". It appears more likely that there is one regional unconfined aquifer beneath the site with locally separated water bearing zones. Interbedded silts and clays that were observed during the installation of the wells appear to have created a local barrier to vertical migration.