ARCHIVED REPORTS XR0010921 - Laserfiche WebLink

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Ms.LoriDuncan,Senior REHS December 3,2002 Mr.Nuel C.Henderson Jr.,R.G j Page: 2 The log for boring 13-2 was reexamined and, based on the subjective notes on the first appearance of contamination, the vertical extent of the contaminated area reduced from 25 feet to 15 feet. The area of contamination is characterized by a single soil sample (B2- 15). A revised and expanded contaminant mass spreadsheet is shown below. A detailed calculation is provided as an attachment. cu ft weight H2O lbs. Gas 0 2600 1300 10,0013 3.4441875 214.9173 150.44211 Benzene 0 0.86 0.43 4.3E-07 0.0011392 0,07108803 0.049761621 Toluene 0 120 60 0.00006 0.1589625 9.91926 6.943482 E benzene 0 51 25.5 0.0000255 0.0675591 4.2156855 2.95097985 r Xylene 0 400 200 0.0002 0.529875 33.0642 23.14494 MTBE 0.068 87 43.568 4.357E-05 0.115428 17.202705328 5.04189373 TBA 10 2.7 1.35 1.35E-06 0.0035767 0.22318335 0.156228345 The revised model was run with similar conclusions results to the modeling reported in May 2002, which reported an exposure risk via the indoor air exposure to contaminant. Run sheets of the computer model are attached, It should be noted that the risk is a result of the cumulative impact of the contaminants. When individual contaminants are analyzed, a risk is not recognized. As pointed out by SJCEHD the current activities at the facility routinely expose workers to the contaminants of concern, which may provide an additional cumulative impact that cannot be modeled. It was the recognition of the added cumulative impacts that was the basis the no further action recommendation. Discussion Review of the laboratory data sheets and borings logs has resulted in a revised mass calculation. The model was rerun using the revised concentrations and values suggested by SJCEHD. As noted by SJCEHD, values used in the modeling tend to be conservative as it is desirable to error on the side of health and safety. Modeling is an attempt to represent and predict the behavior and subsequent exposures and risks posed by a release. Modeling has value when, using conservative values, it can be shown that a release will not cause significant exposures. In this case, where the calculated cumulative contaminant exposure appears to pose a risk beyond that of an individual compound it may be appropriate to conduct a limited soil vapor testing to determine if significant vapor migration is occurring, A work plan for soil vapor sampling to confirm the soil vapor impacts predicted by the model may be appropriate. The above represents our best professional opinion as to environmental conditions at this site. These opinions were derived using data at hand, and standards of care common to i �