SITE INFORMATION AND CORRESPONDENCE_FILE 2

Home Browse Search

Site Conceptual Model February 15,2008 Harry's Auto Mart Page 10 of 20 o The concentrations used in the calculations are an average of the highest concentration found in each well within the given area over the last four monitoring events o MW5 is outside the estimated extent of the plume and was not included in the 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 (Figure 12) and has not shown the presence of any analyzed constituent in the last seven sampling events(Table 5) • Previous groundwater vertical thickness,porosity, and equation assumptions are used below Pounds of Benzene Core = (2,647,792 L) * (0.35) * (10.2 mg/L)* (2.2E-6 lb/mg) 21.0 lbs Outer Ring = (59,811,840 L) * (0.35) * (0.086 mg/L) * (2.2E-6 lb/mg) 4.0 lbs Total benzene 25.0 lbs MTBE—Groundwater Mass Estimate • The MTBE plume may be commingled between the U-Haul and Harry's Auto Sites • For the purposes of the following calculations the end of the MTBE plume is MW6 • The MTBE plume is divided into two areas: The Core and the Outer Ring o The Core is approximately 145 ft2 area and lies within the 100 ppb contour interval (Figure 13) o The Outer Ring is approximately 9,000 ft2 and represents area between the estimated extent of the plume and the 100 ppb contour interval(Figure 13) o The highest MTBE concentration ever detected in MW1 was used to represent the concentrations in the Core o The only MTBE detection ever found in MW2, and the highest ever detected in the Outer Ring, was used to represent the concentration of the entire Outer Ring • The deep zone is defined by MW 1 D (Figure 14) and has not shown the presence of any analyzed constituent in the last seven sampling events(Table 6) • Previous groundwater vertical thickness,porosity, and equation assumptions are used below Pounds of MTBE Core = (180,682 L) a. (0,35) * (0.14 mg/L)* ( 2.2E-6 lb/mg) 0.02 lbs Outer Ring = (11,214,720 L) * (0.35) * (0.006 mg/L) 'k (2.2E-6 lb/mg) 0.05 lbs Total MTBE 0.07 lbs 1,2-DCA—Groundwater Mass Estimate • The 1,2-DCA plume is commingled between the U-Haul and Harry's Auto Sites • An arbitrary line (Figure 15) between the abandoned Frontier Domestic Well and MW-12B/C is assumed to separate the U-Haul and Harry's Auto plumes. • The 1,2-DCA plume is divided into two areas: The Core and the Outer Ring o The Core is approximately 550 ft2 and is represented by the area within the 1,000 ppb contour interval(Figure 15) o The Outer Ring is approximately 57,000 ft2 and occupies the area between the estimated extent or arbitrary boundary of the plume and the 1,000 ppb contour interval(Figure 15) o The concentrations used in the calculations are an average of the highest concentration found in each well within the area over the last four monitoring events