ARCHIVED REPORTS XR0013118 - Laserfiche WebLink

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Ms. Katie Hower �LOMATRIX Chevron Environmental Management Company March 29, 2000 Page 2 station was located. What is the source ofgasoline along the pipeline ifthe pipeline only transported crude oil and heavy fuel oils?" Response: These measurements are from EPA Method 8015M analyses, which quantify all of the hydrocarbons within a specified boiling range against a chosen standard. Crude oil contains low-, medium-, and high-boiling range constituents,and these constituents would be incorporated within a`"TPH as gasoline'or"TPH as diesel"measurement. It does not mean that gasoline or diesel are actually present. A forensic review of the chromatograms or other data is required to determine if gasoline or diesel are present instead of, or in conjunction with, the crude oil. The forensic evaluation of the sample collected from GMX-13,near the southem edge of the site, identified mostly degraded low boiling range petroleum(suggesting mostly weathered gasoline); the forensic evaluation of GMX-6,closer to the pipeline,was a mixture of low and high boiling range petroleum. Because the exact location of tanks or fuel dispensers at the former Mohawk gasoline station or spills or handling practices are unknown, we cannot be sure if the low concentration of gasoline range petroleum in GMX-6 is from the former gasoline station or is merely low boiling range components of the crude oil. Specific comment number 4 - "Geomatrix reports petroleum related hydrocarbons at depths from 8.5 to 12.5 feet bgs. Earth Systems Consultants reports petroleum related constituents down to 15 feet bgs. Borings EB-7 and EB-9 are in close proximity to GMX-7 and GMX-6, respectively. However, the results of the soil analysis are dissimilar. Can these data be explained? The lateral extent of the contamination appears to be adequately addressed. " Response: Page 2 of the Geomatrix report states "petroleum hydrocarbon-stained soil was observed in nine borings...between depths of 6 and 19 feet bgs." The sample depths on Table 1 do not reflect the vertical extent of observed petroleum at the site, they are merely the depths at which a particular sample was collected. Differences in analytical results are not unexpected. Soil samples were collected from EB-7 (TPHc 3400 mg/kg)and EB-9(TPHc 4300 mg/kg)at depths of 9.5 and 15 feet bgs, respectively. Soil samples were collected from GMX-6 (TPHc 12,000 mg/kg) and GMX-7 (TPHc 10,000 mg/kg)at depths of 11.5 and 11 feet bgs, respectively. Soil analytical results vary with depth due to the depth of the release and fluctuations in the depth to water(the crude oil tends to"float"on the water table and"smear'as the water table rises and falls). Soil analytical results also can vary widely with location and small changes in soil type. These results seem to imply that the greatest concentrations of TPHc are at a depth of I 1 to 11.5 feet bgs,which is likely close to the average depth of the water table. The goal of Geomatrix's sampling program was to collect soil samples at the depth most affected by petroleum hydrocarbons (usually close to the water table). s�On apsEasalnoc SafaMDOsb I MOMPomWP-Response-Lv