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Mr Daniel K Barber,P E <br /> ' September 9, 2003 <br /> • Page 10 of 17 <br /> Diesel-Range Hydrocarbons <br /> Diesel-range hydrocarbons are the primary site contaminants of concern in groundwater, as <br /> rdiesel has been detected in the majority of the exploratory borehole and groundwater <br /> monitoring well groundwater (and soil) samples <br /> SITE CONCEPTUAL MODEL AND <br /> RESIDUAL CONTAMINATION DISTRIBUTION <br /> Conceptual Srtc Model Overview <br /> A conceptual model to identify the contaminant pathways is presented here based on a review <br /> of the site soil contamination, soil lithology, hydrology,and hydrochemistry, along with what <br /> is known about the facility's operational history The source of the petroleum hydrocarbon <br /> contamination in the soil and groundwater is the former underground fuel/liquid asphalt <br /> product storage tanks and/or fuel UST pump area The footprint of the 1987 excavation <br /> centered around well MW-1 is the location of the main area of residual contamination, the <br /> former gasoline and diesel UST excavation area along the southern property line is not <br /> lie <br /> a source area The exact footprint of the 1987 excavation near the source of the <br /> contamination is imprecise as no documentation report was found Diesel-range <br /> hydrocarbons were found to be the main contaminants in soil, corroborating the visual <br /> 1 identification of contamination that was removed along with the tank, leaving an excavation <br /> of unspecified depth (see Figure 3) Water level influence on hydrochemistry appears to have <br /> ' some correlation When water levels are higher, the groundwater contamination is generally <br /> slightly higher However, this correlation does not hold true in all cases, and the last three <br /> quarters of groundwater TPHd concentration show more minor percentage variation than <br /> reflected by the water levels <br /> Geometry of Soil Contamination <br /> Petroleum Hydrocarbons <br /> ' Figure 4 shows the residual soil contamination at the site A zone of relatively elevated <br /> residual hydrocarbons (appeanng approximately 5 feet thick) exists in the 30-foot-depth zone <br /> This soil contamination is likely entrained in the higher percentage of clay in the sediments at <br /> this depth, sorbing onto the clays as it migrated down from the apparent seasonal perched <br /> zone above it Three samples—D-17, B-1, and B-2—have elevated concentrations of TPH, <br /> ranging from 14,000 to 30,560 mg/Kg TPHd There is also one deeper sample, at bore C-2, <br /> Mwith a reported 15,500 mg/Kg at a depth of 45 feet bgs Samples were not collected above a <br /> 1 <br /> Stellar Environmental Solutions <br /> ynpRafF,CISV00l/vv hgecUZ0010-UA9�eLaA Cbu�Pryon mdFiW"°iRF.R)RT-SeM+++�43001 dec <br />