SITE INFORMATION AND CORRESPONDENCE 1993-1995

Home Browse Search

0 Mr. Robert Doss, P.E. February 3, 1993 Page Two characterization of the groundwater contamination and then must submit a plan outlining the work to be conducted and the schedule to be followed. 5. The downward vertical gradient has apparently allowed the migration of contaminants (PNA's) to the deeper aquifer (Zone C) . This zone is presently monitored by a single well , MW-13 . One sampling event detected total PNA's at 8. 3 ug/1. It may be expected that with the source of contaminants remaining onsite, contaminants will continue to migrate to the deeper aquifer. Additional deep wells are necessary to assess the flow direction and rate and the extent of contamination in the deeper aquifer (Zone C) . MW-13 may not represent the area of highest contamination in Zone C since the direction of flow is unknown. The report must include a discussion describing the extent of characterization achieved and the additional work required. 6. Human health risks from groundwater contamination of the shallow zone has been dismissed largely because of the saline non-potable nature of the water. PG&E must include a discussion in the text concerning the Regional Water Control Board designation of the beneficial use of the groundwater in the area of the site. In 1988 , the State Water Board adopted Resolution 88-63 , the "Sources of Drinking Water" policy. This policy specifies that except under specifically defined circumstances, ground and surface waters of the State are either existing or potential sources of municipal and domestic supply. Those circumstances include those with existing high total dissolved solids concentrations (greater than 3000 mg/1) , low sustainable yield (less than 200 gallons per day for a single well) , waters within agricultural drains, and geothermal waters. By evaluating site specific data, PG&E shall determine whether the beneficial uses of groundwater include municipal and domestic supply according to this policy. 7. Table 4-1 lists the hydraulic conductivities (K) estimated from slug tests. Some of the values seem on the high side for the type of materials present in the screened interval. For example, Well MW-4, which according to Figure 4-3 is screened entirely in clay, has a K value of 3 . 0x10-4 exponent. The slug test may be measuring the conductivity of the filter pack, not the formation. Describe the method used to calculate the K values and discuss the possible influences of the filter pack.