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constituents,increases in the depth to ground water (thickness of the vadose zone),in the clay content,organic matter content,ion exchange capacity or pH of vadose zone materials, in the ionic strength,viscosity, degradability or octanol/water partition coefficient (the affinity of the chemical for octanol or soil organic matter versus its affinity for water) of the waste constituent,in the concentrations of solvents or other chemicals that can increase the permeability of soils or act as carriers for the constituent,in the steepness of the terrain,and in the rate of flow of ground water will cause the attenuation factor to be larger (greater attenuation) Increases in the net recharge rate (a driving force for movement of waste constituents),in the permeability or porosity of vadose zone materials,in the polarity or volatility of the waste constituent, and in the mass loading of waste constituents will cause the attenuation factor to be smaller(less attenuation as the constituent migrates to ground water). If surface waters are threatened by constituents in a waste,increases in the distance of travel from the site of waste discharge to surface water,in the volatility, reactivity, degradability or octanol/water partition coefficient of the waste constituent,in the concentrations of solvents or other chemicals that can increase the permeability of soils or act as carriers for the constituent, and in the amount of initial dilution that the waste or leachate would receive upon entering surface waters will cause the attenuation factor to be larger. Increases in the steepness of the terrain,in the polarity of the constituent, in the amount of interconnection of ground and surface waters, and in the total constituent loading will lower the attenuation factor. Undoubtedly the most important characteristic that must be evaluated in the derivation of environmental attenuation factors is the relative uncertainty of the data and assumptions used to describe environmental fate processes. The more uncertainty involved in the . estimation of environmental attenuation factors, the more the assumptions being used in their derivation should lean in the direction of underestimating the amount of attenuation expected to occur. In this way, a greater assurance of water quality protection is provided. The degree of uncertainty irahe estimation o€enm onmental-attenuation should also be reflected in the amount of vadose zone and ground—water—monitoring that is required for-a-_ J. waste management unit. Greater uncertainty necessitates a greater monitoring effort to -_ - --- assure that the environmental fate analysis was protective of Nater quality: _ - -- -- - r Note: Because of the great uncertainty in environmental fate analysis,some regulators favor an approach for setting Designated Levels that does not consider any attenuation between the initial leachate or liquid waste and waters of the State. While this approach is surely protective of water quality, it does not appear to be feasible from an economic nor logistic point of view at the present time,since many more wastes would be found to be'designated' - ------- -- -------and would-require Class II or Class I disposal. --- - - - - - - - - Site-and constituent-specific information regarding key environmental fate characteristics f under reasonable worst-case conditions may be used to derive attenuation factors for specific waste constituents at the site. The DHS publication The California Site Mitigation L, Decision Tree Manual.3 the EPA document Water_Related Environmental Fate of the 129 ' E[LO—rity Pollutants 74 The Soil Chemisjjy of Hazardous Materials by James Dragur;$ Handbookof Environmental Data on Or anic Chemicals by Karel Verschueren?r and the .� EPA publication DRASTIC: A Standardized System for Evaluatin Ground Water Pollution Potential U ing H dro Bolo 'c Settings zs contain useful information and LDesignated Level Methodology Page 31