SITE INFORMATION AND CORRESPONDENCE_FILE 2

Home Browse Search

Site Conceptual Model February 15,2008 Harry's Auto Mari Page I 1 of 20 o UHIVIWl4B/C and UI NMIOB/C fall within the arbitrary boundary and are used in the mass calculations o If monitoring well was ND for the last four monitoring events, fifty percent of the reporting limit was used in the calculations • The deep zone is defined by MW1D and has not shown the presence of any analyzed constituent in the last seven sampling events(Figure 16) • Previous groundwater vertical thickness, porosity, and equation assumptions are used below Pounds of 1.2-DCA Core = (685,344 L) * (0.35) * (1.7 mg/L)* (2.2E-6 lb/mg) 0.90 Ibs Outer Ring = (71,026,560 L) 4' (0-35) * (0.0653 mg/L) * ( 2.2E-6 lb/mg) 3.60 lbs Total 1,2-DCA 4.50 lbs Soil Contamination TPHg and BTEX compounds were found in soil beneath the site during the tank pull in 1989, and in subsequent soil borings SB 1 and SB2. Minor levels of TPHg and BTEX compounds were present in soil samples collected from depths of 20 and 30 feet in monitoring well MW4. Low levels of TPHg and BTEX were detected in SB6 from depths of 100 to 110 feet, however, due to the non-detect results above 100 feet it is believed that contamination was dragged down during drilling. 1,2-DCA was the only oxygenate detected in the soil samples collected on site, which was detected at a low level in MW6 at 65 feet below grade. MTBE was not detected in any of the soil samples collected. It is estimated that impacted soil remains beneath the site in two distinct zones, between the depths of 10 feet and approximately 70 feet below grade. A vertically extensive zone, which has a diameter of approximately 40 feet and extends from approximately 10 feet below grade to 70 feet below grade, and a horizontally extensive zone which is elliptical in shape, with a diameter ranging from 65 to 95 feet and extends from approximately 15 feet to 30 feet below grade. The horizontally extensive zone is believed to be a product of historically high water levels, which spread soil contamination out laterally. Evidence for a historically high water table was found in soil borings SBI and SB2 where mottled soil was present from 12 to 25 feet below grade. Additional evidence is found in MW4 where only a smear zone between 20 and 30 feet bags contains petroleum hydrocarbon constituents. The estimated dimensions indicate that approximately 135,000 ft' of soil has been impacted. It is assumed that the soil has density of 100 lbs/ft'. The calculations below assume the average concentration of benzene in the hottest sample location (SB-1) which is nearly double the average in the contaminated zone. Lbs. of contaminant= Volume(ft) * (100 lbs/ft) 4' avg. contaminant concentration (mg/Kg) * (E-6) TPHg = (135,000 ft') * (100 lbs/ft ) * (1,800 mg/Kg) * (E-6) = 24,300 lbs Benzene =(135,000 ft) * (100 lbs/ft') .k (8.2 mg/Kg) 4' (E-6) = 1 I 1 lbs