ARCHIVED REPORTS XR0009996 - Laserfiche WebLink

Home Browse Search

Ceo(agicaCTec(inics Znc. C&B Equipment Page 3 Site Closure Check List Project No.336.2 August 31, 1998 A The calculations were prepared as follows: • The contamination was assumed to extend from four feet below ground surface (bgs) down to 12 feet bgs in center core, field notes indicate a significant decrease in soil contamination between 10 and 15 feet bgs in MW-101. • The contaminant load in the center core was assumes to equal the TPH-G concentration s from the 5 foot sample in MW-101 (2880 mg/Kg). This most likely results in an over estimation of contaminant mass in the soil. -� • Because TPH-G was non-detect in the deeper soil samples, the TPH-G contaminant >I loading for the ring was assumed to equal the detection limit of TPH-G(1.0 mg/L). • The volume of the core is subtracted from the volume of the ring. • The volume of soil is multiplied by the density of the soil (lbs/ft') then by 0.4536 to :. convert from pounds of soil to kilograms of soil. The contaminant load is then multiplied to this number to give the mass of contaminant in milligrams. The contaminant mass in milligrams is then converted to kilograms which is the contaminant mass value one is -1 after. ,__ • The inner groundwater plume was assumed to extend from 6 feet bgs to 15 feet bgs. There is no data to support this, however the soil in this region is highly contaminated so it would be expected that the shallow groundwater in this area would also be impacted to a greater extent. • The contaminant load for the inner groundwater plume was assumed to equal 100 mg/L, a value much higher then has ever been observed at this site. -:-.� • The outer groundwater plume was assumed to extend from 6 feet bgs. to 45 feet bgs, 5 Fj feet deeper then the deepest depth explored. • The TPH-G contaminant load for the outer groundwater plume was assumed to be the average of the twogroundwater samples from MW-101 (0.5 mg/L). + The volume of groundwater in the inner plume was subtracted from the volume of the outer plume. 14. Model Parameters Risk evaluation and fate and transport modeling have not been performed. The data suggests !==1 that this site is low risk so this level of investigation is not needed. 15. Rationale For the following reasons, the conditions at this site should not adversely impact water quality, health or beneficial use of this property. + The tank and primary soil contamination source have been removed. Residual gasoline is present as estimated below. • Groundwater monitoring results show that the contaminants in the groundwater plume have reduced significantly over the past three years. • The estimated mass of contaminants is very small, with only approximately 502 gallons in the soil, most of this is in the top ten feet, and 6 gallons in the groundwater. , I -_JI