ARCHIVED REPORTS XR0009884 - Laserfiche WebLink

Home Browse Search

lie The contaminant mass in the saturated zone is partitioned in to two phases, the portion adhering to the soil or absorbed phase, and the dissolved phase The adsorbed phase mass is ' calculated by methods very similar to those described above Field and lab data show that contaminant concentration below 45 feet dramatically decrease almost undetectable levels at ' 50 feet Table 2 —Saturated Zone Adsorbed Mass ' Zone Ave TPH Gross Zone Volume(V) Soil Mass(M) TPH Mass Area Thickness =62.Pd.V =M*TPH ' 30-35 Ft 865 ppm 2,135 s f 5 Ft 10,675 c f 1,206,275 lb 1,043 Ib 35-40 Ft 2,450 ppm 3,545 s f 5 Ft 17,725 c f 2,002,925 Ib 4,907 Ib 40-45 Ft 2,321 ppm 4,000 s f 5 Ft 20,000 c f 2,260,000 Ib 5,245 lb TOTAL 11,195 !b ' Where, V=volume of zone in cubic feet ' pd=bulk density of soil= 1 70(corresponds to�=0 35) C=Soil contaminant concentration expressed as a ratio �=effective soil porosity ' Water weighs 62 pounds per cubic foot iDissolved Mass ' The contaminant mass in the adsorbed phase was estimated by dividing the saturated zone into horizontal bands or "zones" based on the winter, 2003 groundwater monitoring event It was assumed that the impacted groundwater Ines between 30 and 45 feet The area of each of the zones was measured using the planimeter method described above It was assumed that the gasoline was evenly distributed throughout the 15 vertical feet between 30 and 45 feet ' below the ground surface The calculation varies somewhat, however, since all dissolved phase contaminant can reside only in the pore spaces, and the substrate is water rather than soil ' The load mass of each zone was then computed using the area and volume of each contour, and the average TPH concentration of each zone was then applied to arrive at the total load ' mass Insofar as the contaminant concentration contour intervals are in logarithmic progression, it was deemed appropriate to assume a logarithmic contaminant distribution over each contour and thus the average value is approximately 27 percent of the maximum ' concentration of each contoured zone For example, if contoured zone between 10 ppb and 100 ppb were being considered, the average value would be 27 ppb in accordance with a logarithmic spread Similarly for contours between 100 ppb and 1,000 ppb, the average ' would be 270 ppb The following table summarizes the volume of each zone and the average contaminant concentration in each 2937 Veneman Ave, #13240 Geo-Phase Environmental Ine Phone(209) 569-0293 Modesto,CA 95356 Fax(209) 569-0295