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1 reduce hydrocarbon migration, at least one additional trench would be needed downgradient • The expense of a groundwater pump and treat system would be added to trenching costs • In Situ Oxidation. The technical applicability for in-situ oxidation b addition of oxidizing Pp Y Y reagents such as Fenton's reagent or oxygen releasing compounds (ORC) has had mixed results ' Application of Fenton's reagent typically heats groundwater to its boiling point which creates offgasing at the surface The effects of other compounds that may be produced during in-situ oxidation (i e , oxidation byproducts) are not well documented Because there is an ' apartment and a commercial building present adjacent to the site, chemical oxidation is not considered as a viable option Application of ORC would be ineffective at this site due to the submerged hydrocarbons at the site and the reduced soil permeability, which limits the delivery of ORC to the residual hydrocarbons ` • Groundwater Pump and Treat System The effectiveness of groundwater pump and treat systems is, in general, a function of site-specific hydrogeologic properties Of particular ' interest at the site is the historical groundwater elevation over time As presented in the hydrographs (Appendix B), groundwater has risen significantly over time A review of these hydrographs reveals an approximately 25-foot rise in groundwater elevations over time at the site from—30 55 feet msl in October 1992 to —5 24 feet msl in June 2001 During this rise in groundwater elevations, the residual hydrocarbons become entrapped in the soil matrix A discussion by C W Fetter (Fetter 1993) of how hydrocarbons can become entrapped in soils after a significant rise in groundwater elevation and how the relative permeability of water and hydrocarbons is significantly reduced under these conditions is presented in Appendix K Below is an excerpt During simultaneous flow of two immiscible fluids, part of the available pore space will be filled with one fluid and the remainder will be filled with the other fluid Figure 5 5 ' (Appendix K) shows possible fluid-saturation states for water and oil with different ratios of each and both water-wet and oil-wet circumstances Because the two fluids must compete for space in which to flow, the cross-sectional area of the pore space available for each fluid is less than the total pore space This leads to the concept of relative permeability Relative permeability is the ratio of the intrinsic permeability for the fluid at a given saturation ratio to the total intrinsic permeability of the rock and sediment A relative permeability exists for both the wetting and the nonwetting phase Figure 5 6 shows the two-phas c-permeab ility curves for both wetting and nonwetting liquids The irreducible water saturation is the water content at which no additional water will ' flow In Figure 5 6, water is the wetting fluid, and the irreducible water (wetting-fluid) saturation is shown on the left side Thus water won't flow at all until the irreducible wetting fluid saturation, S,,,,, is exceeded The nonwetting fluid won't begirt to flow until the residual nonwetting-fluid saturation, S,,,,,,, is exceeded This is shown on the right side of Figure 5 6 For a two-phase oil-water system, if the water content is less than the ' G\Pia,ectSV}942%MASTERIWP%Rd0801\Lert]Ja 8