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0 0003 gallons of 1,2 DCA The closest well to MW-2 is MW-1 located 40 feet away A potentially impacted volume of groundwater equal to a cylinder with an 80 foot diameter centered at a location halfway between MW-2 and MW-5, and existing in the saturated sandy zone from 72 to 90 feet below grade was used for the basis of calculations For BTEX, the detection limit of 0 5 ugA was used as a worst case concentration, regardless of the fact that these compounds have been non- detectable for over one year The resulting estimate of 0 001 gallons of total hydrocarbon mass remaining in Site groundwater provides a worst case value ' OF 1 2 DCA 4.5 FATE AND TRANSPORT Using the available Site data, estimates of 1,2 DCA travel times in Site groundwater were calculated in the same manner that benzene was evaluated in the September 30, 1994 Closure Report Two ' different soil samples collected from the sandy zone were analyzed for hydraulic conductivity, porosity and specific gravity These ASTM geotechnical laboratory methods were performed by Wallace-Kuhl & Associates Their results are provided in Appendix D of the September 30, 1994 ' Closure Report The results between the soil samples analyzed were comparable indicating a vertical hydraulic conductivity of 1 x 10-4 cm/sec, a porosity of 0 40 to 0 45 and a derived bulk density of 101 lbs/ft Considering the fact that the alluvial deposits at the Site are stratified, the ' measured vertical hydraulic conductivity value was adjusted to an approximate horizontal value by multiplication by a factor of 10 This multiplication factor represents a typical K,/Ki, ratio for medium level" stratification The resulting value is typical of the horizontal conductivity of silty sands and clean, fine sands (Groundwater Manual, 1981) ' Both soil samples were also analyzed for total organic carbon indicating 0 03% to 0% in the samples Using these data and the Kos, (organic carbon partition coefficient) for 1,2 DCA a retardation factor (Rf) for 1,2 DCA in the sandy zone was calculated to be 1 02 The assumptions ' and backup calculations for this fate and transport assessment are provided in Table 8 and described in Appendix G ' Modeling calculations indicate that for a gradient ranging from 0 001 to 0 006, the retarded transport rate of 1,2 DCA in Site groundwater could range from less than 2 7 feet to 16 1 feet per year based ' on the assumption of a continuous and uniform hydraulic gradient Given that the gradient magnitude and direction is documented to vary significantly throughout the year, the actual lateral travel distance of detectable 1,2 DCA from the Site during a typical year would be much less than these estimates suggest ' As mentioned previously, a similar evaluation for benzene fate and transport was performed and presented in the SECOR September 1994 Report The findings regarding this evaluation are revisited in Table 9 and described in Appendix G ' CRC Environmental Risk Managcment Inc SECCR International Inc (SECORO) 16 November 30 1994 N0026 001 01 add