ARCHIVED REPORTS_XR0011317 - Laserfiche WebLink

Home Browse Search

I Wm. J. Hunter & Associates Benzene in MW-5 decreased from 0.4 ug/L in August to ND in January. Ethylbenzene dropped from 1.0 ug/L to ND; toluene also dropped from 1.0 ug/L to ND. Xylene decreased from 8.0 ug/L to ND. TPHg decreased significantly from 635 ug/L in August to ND in January. However, MTBE increased slightly from 68 to 74 ug/L. Benzene, ethylbenzene, & toluene in MW-6 were ND in August & January. Xylene decreased from 0.5 ug/L to ND over the same period. TPHg also decreased from 88 ug/L to ND. MBTE increased slightly from 230 to 270 ug/L. PLATES II through VII are maps showing the approximate lines of equal concentrations of benzene, ethylbenzene, toluene, xylene, TPHg, and MTBE based upon this latest ampling event. They reveal that the placement of the 3 additional wells have defined the limits of BTEX &TPHg contamination. The results of that work is detailed in the WJH report titled "Interim Report Covering Results of Site Investigation.....; dated October 6, 2000. It is apparent from a review of PLATES II through VI that the limits of benzene, ethylbenzene, toluene, xylene, and TPHg have been well defined by the work done to date. The highest levels of contamination of those compounds continue to be • centered around MW-1, which is the closest to the site of the removed UST. Levels decrease downgradient as would be expected. However, the presence of MTBE in MW-4, 5, & 6, increasing to the north, does not fit the pattern established for BTEX & TPHg. As shown on PLATE VII, concentrations of MTBE increase to the north, away from the site of the removed UST. This suggests an offsite source for that compound that has not yet been identified. MTBE was measured only once in the well nearest the tank site, MW-1, in July, 2000, (TABLE I), and that analysis was not confirmed by the lab, and is considered unreliable. PLATE VII indicates that the source for the MTBE is to the north of the property. We believe that a survey of the area to the northwest, north, and northeast of the site should be performed in an attempt to identify other possible sources of contamination. However, we need approval from your department so that we may request authorization from the Cleanup Fund staff before proceeding with that task. We can prepare a detailed workplan if you wish. Please contact our office with your instructions so that we may proceed. We will continue quarterly monitoring until we receive f her ' structions from your office. m. J. r, RG \5�� o GEn�o Wm. J nter & Associates i1 'sem March , 2001 h� 6VIA�J Hu-%� R 0 cc: Valley Wholesale Drug Co. rXr (- CVRWQCB 6 slq� OF CA1§ 2