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Environmental <br /> Mr Harlin Knoll Resources <br /> 27 September 1999 Management <br /> Page 3 <br /> Oxygenates were first introduced into the analytical program at County <br /> request during the April 1998 monitoring event The data collected <br /> during the July monitoring event are consistent with the previous results <br /> and suggest that the lateral extent of these constituents has not increased <br /> over the past year Oxygenates were not detected in any of the samples <br /> collected from former Tank Site #1 Oxygenate detections in the former <br /> Tank Site #2 samples were limited, TBA and MtBE were detected once in <br /> samples collected from MW-1A and MW-3A, respectively, at <br /> concentrations just above the detection limits <br /> At the County's request, 1,2-DCA was added to the analytical program <br /> during the July monitoring event Detections of this constituent are <br /> associated with MW-5 (Site#1) and MW-1A, -2A, -3A, and -4A (Site #2) <br /> The majority of these detections are lust above the detection limit The <br /> data suggest that the oxygenate and 1,2-DCA distribution patterns are <br /> similar, despite the larger number of 1,2-DCA detections relative to those <br /> for oxygenates The apparent discrepancy in detections can be attributed <br /> to the significantly lower detection limits available for 1,2-DCA (e g, an <br /> order of magnitude lower than those for the oxygenates) When <br /> oxygenates and 1,2-DCA were both detected at a given location (e g, <br /> MW-1A and MW-3A), the detections were comparable At locations <br /> where 1,2-DCA was detected but oxygenates were not, the 1,2-DCA <br /> detections were less than the oxygenate detection limits <br /> As was the case for TPH/BTEX (see previous discussion), oxygenate and <br /> 1,2-DCA concentrations decrease rapidly with distance from the former <br /> tank site The highest concentrations are associated with MW-5 <br /> (for Site #1, 1,2-DCA only) and MW-1A (for Site #2) <br /> Future Activities <br /> Based on the results of the July 1999 sampling event, and pursuant to our <br /> discussion at the 30 June 1999 meeting, Catellus/ERM have determined <br /> that the appropriate course of action is to proceed with preparing the <br /> documentation required by the County to support closure of the site <br /> (e g, the requirements for closure of UST sites, as specified in Appendix <br /> B of the Tri-Regional Recommendations) As discussed above, because <br /> we observed no significant changes in the ground water monitoring <br /> results, excavation of additional soils containing residual levels of TPH <br /> does not appear to be warranted <br />