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`.., <br /> GEOMATRIX <br /> APPENDIX B <br /> Hydraulic Parameters at the Site <br /> The duration for the transport of dissolved-phase petroleum hydrocarbons from the fine- <br /> grained soil beneath Grant Line Road to the monitoring wells can be estimated using the <br /> following equation: <br /> Retardation factor= 1 +Kd * pb/n a <br /> Where: Kd =distribution coefficient=Ko, * fogy <br /> Pb =bulk mass density <br /> n=porosity <br /> Kos =organic carbon-water partition coefficient <br /> fogy =organic carbon fraction of saturated soil. <br /> The retardation factors for BTEX are estimated to range from 4 to 33 using: <br /> • an assumed fogy of 0.01 for the site, <br /> • a range of Kos values for BTEX between 50 and 565 (Gould and Pardus, 1991),b <br /> • an estimated average site porosity of 0.35, <br /> • an estimated Pb of 2.0 grams per cubic centimeter(g/cm3) corresponding to the <br /> porosity(Freeze and Cherry, 1979, page 405). <br /> Using these retardation factors, the residual petroleum hydrocarbons in the fine-grained soil <br /> beneath Grant Line Road are estimated to be removed after a minimum of 4 to 33 pore vol- <br /> umes of groundwater have been purged from this area. Wells MW-6, MW-7, and MW-12 are <br /> estimated to be located approximately 40 feet hydraulically downgradient of the fine-grained <br /> soil area beneath Grant Line Road. Using an average groundwater flow velocity of 0.06 (ft/d) <br /> for the site (Appendix A), the transport of each pore volume of groundwater is estimated to <br /> take approximately 1.8 years to travel the 40 feet from the fine-grained soil beneath Grant <br /> Line Road to the wells. Desorption of the residual petroleum from the fine-grained soil in the <br /> source area is therefore estimated to take 7 to 60 years based on the purging of 4 to 33 pore <br /> volumes from the fine-grained soil area. <br /> Using existing groundwater data from well MW-6, the total remediation duration at the site, <br /> from the time of release in 1987, is estimated to be about 31 years (Figure 3 of the main text). <br /> This estimate is within the 7- to 60-year duration estimated based on hydraulic parameters. <br /> These groundwater data indicate that remediation duration is limited by the transport mecha- <br /> nism of dissolved petroleum hydrocarbons in groundwater due to the hydraulic conditions at <br /> the site. <br /> a Freeze,R.A.and Cherry,J.A., 1979, Groundwater,Prentice-Hall,page 404. <br /> b Gould,W.W., and Pardus,M.J., 1991,Estimation of Groundwater Contamination Potential by Organic <br /> Compounds in Soil:A Spreadsheet Screening Model,Proceedings of the Petroleum Hydrocarbons and <br /> Organic Chemicals in Ground Water: Prevention,Detection,and Restoration;Water Well Journal Publishing <br /> Company,page 345. <br /> 1ADoc_Safe\2000s\C2463\2463 resp RWQCB App B.doc <br />