3003 COLBY AVE COURTYARD BY MARRIOTT 2021-03-09

I I Estimate of Aerial Extent of Contamination The aerial extent of the contaminated soil was interpolated from the boring and laboratory data. For our estimate, we assumed that the limit of Class 3 contaminated soil was approximately midway between the "contaminated" (i.e., borings where samples were tested and found to be above MTCA cleanup levels) and"clean" (i.e., borings where samples were tested and found to be below MTCA cleanup levels) borings. For the sake of simplicity, we also assumed that the lateral extent of contamination formed a rectangular distribution. The actual lateral extent of contamination almost certainly forms an irregular shape and may include lobes that extend between the "clean" borings. For these reasons, there is a significant amount of uncertainty in our estimate, and the actual lateral extent of contamination may be larger or smaller than that estimated. For estimating the lateral extent of Class 2 soils, we included the entire aerial extent estimated for Class 3 soils plus an area of 40 feet by 40 feet surrounding boring EB-10. Estimated Thickness of Contaminated Soil over the Contaminated Area Class 3 soils were found in two borings,, EB-5 ancLEB77. The thickness of this contaminated zone was approximately 15 feet in boring EB-5 and 20 feet in boring EB-7. For our estimate, we assumed a contaminated soil thickness across the aerial extent of contamination that was equal to the average of these two thicknesses (i.e., 17.5 feet). Because the actual thickness of contaminated soil is reduced to zero at the limits of the contaminated zone, this estimate may be conservatively high. We also assumed a maximum excavation depth of 35 feet. Based on the existing data, it appears that this would include removal of all Class 3 soil, but not all Class 2 soil. Class 2 soils were found in three borings: EB-5, EB-7, and EB-10. The thickness of Class 2 soils at each of these boring locations was estimated to be those soils outside of the Class 3 soil zone that either exhibited detectable concentrations of petroleum constituents below MTCA cleanup levels, or (where no test data was available) where field screening indicated the presence of some petroleum (i.e., odors or elevated PID measurements). The thickness of Class 2 soils across the impacted area was then assumed to be equal to the average thickness encountered in the three borings. Estimation of Trucking Costs The volume of soil in place in the ground is commonly referred to as "bank yardage." During I excavation bulking or fluffing of the soil occurs resulting in increased volume. The volume of excavated soil is typically referred to as "truck yardage." For estimation of trucking costs, we assumed that 1 truck cubic yard = 1.3 bank cubic yards. Trucking costs for disposal of the contaminated soil were estimated assuming a trucking rate of$120 per hour for a 20 cubic yard truck and trailer load and a 1-hour round trip time per truck, including loading and unloading. Weight of Contaminated Soil I The tonnage of contaminated soil was estimated using an assumed soil unit weight of 150 pounds per cubic foot (2.025 tons per bank cubic yard). 2