SITE INFORMATION AND CORRESPONDENCE

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..u. A04VU110Va00 E:'RMWEST WC 10004 Environmental Mr.Harlin Knoll Resources Page 3 September 2493 Management Pa Oxygenates were first introduced into the analytical program at County request during the April 1998 monitoring event. The data collected during the July monitoring event are consistent with the previous results and suggest that the lateral extent of these constituents has not increased over the past year. Oxygenates were not detected in any of the samples collected from former Tank Site#1. Oxygenate detections in the former Tank Site#2 samples were limited;TBA and MtBE were detected once in samples collected from MW-1A and MW-3A,respectively,at concentrations just above the detection limits. At the County's request, 1,2-DCA was added to the analytical program during the July monitoring event. Detections of this constituent are associated with MW-5(Site#1)and MW-1A,-2A,-3A,and 4A(Site#2). The majority of these detections are fust above the detection limit. The data suggest that the oxygenate and 1,2-DCA distribution patterns are similar, despite the larger number of 1,2-DCA detections relative to those for oxygenates. The apparent discrepancy in detections can be attributed to the significantly lower detection limits available for 1,2-DCA (e.g., an order of magnitude lower than those for the oxygenates). When oxygenates and 1,2-DCA were both detected at a given location(e.g., MW-1A and MW-3A),the detections were comparable. At locations where 1,2-DCA was detected but oxygenates were not,the 1,2-DCA detections were Iess than the oxygenate detection limits. As was the case for TPH/BTEX(see previous discussion),oxygenate and 1,2-DCA concentrations decrease rapidly with distance from the former tank site. The highest concentrations are associated with MW-5 (for Site#2,1,2-DCA only)and MW-1A(for Site#2). Future Activities Based on the results of the July 1999 sampling event,and pursuant to our discussion at the 30 June 1999 meeting,Catellus/ERM have determined that the appropriate course of action is to proceed with preparing the documentation required by the County to support closure of the site (e.g.,the requirements for closure of DIST sites,as specified in Appendix B of the Tri-Regional Recommendations). As discussed above,because we observed no significant changes in the ground water monitoring results,excavation of additional soils containing residual levels of TPH does not appear to be warranted.