SITE INFORMATION AND CORRESPONDENCE

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Greg K. Vaughn • -7- • 11 May 1988 Deeper Aquifers If the lack of hydraulic interconnection between shallow and deeper water bearing zones is not adequately demonstrated, the requirements of ASC, Section 25208. 8 (f and g) must be satisfied for deeper water-bearing zones. I%. vadose Zone The manner of presentation of some data makes the hydrogeological and chemical characterization of the vadose zone beneath the site more confusing than necessary. Boring logs in Appendix I use non- unique numbers in some cases (2 each of Boring 1, 2 and 3) . All borings should be given unique numbers to avoid confusion. The locations of borings and surface sampling points at the site has not been represented well . All wells, borings and surface sampling locations should be graphically depicted on a single site plan or on several such maps at the same scale. The amount of data collected pertaining to constituent concentrations in the vadose zone would lend itself well to a graphical presentation in the form of cross sections. This was. dene in only a few cases. Bis(2-ethylhexyl) phthalate was detected in soil samples from as deep as 19 feet under the impoundment. Ground water samples should be analyzed to determine whether this constituent has migrated to the water table. The HAR states that nickel concentrations decrease to background at depth, except in SB-20, where concentrations decrease and then increase with depth. Other borings were shallower than. SB-20 and did not reach the depth where nickel concentrations begin to rise, thus it is unreasonable to expect that this phenomenon doesn't occur in locations other than SB-20. The entire thickness of the vadose zone beneath the impoundment has not been investigated. The deepest boring, SB-20, was advanced to a point approximately 10 feet above the water table. The lateral extent of leachate migration from the pond has not been fully investigated, as evidenced by high nickel concentrations in some wall samples. Full characterization of the vertical and lateral extent of leachate affected soils in the vadose zone may take place as a part of closure activities. Characterization of background vadose zone chemistry with respect to metal concentrations is adequate to satisfy the requirements of HSC, Section 25208 . 8 (j ) . Results of background soil sampling for pH, EC, TDs and major ionic constituents (nitrate, sulfate, chloride, etc. ) were summarized in the HAIR. Complete results of these analyses should be included in a PAR amendment.