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able worst-case conditions may be used to estimate provided guidelines for the selection of generic attenu- <br /> attenuation factors for specific waste constituents at a ation factors based on the depth to ground water and <br /> site. Publications such as The California Site Mitigation i the clay content of unsaturated zone soils. <br /> Decision Tree Manual from DT'SC,The Soil Chemistry of <br /> Hazardous Materials by James Dragun, the U. S.EPA Designated Levels for Liquid Wastes <br /> publications Superfund Exposure Assessment Manual, <br /> Water Related Environmental Fate of the 129 Priority Once the water quality goal is selected and an environ- <br /> Pollutants and DRASTIC:A Standardized System for mental attenuation factor is estimated,their values are <br /> Evaluating Ground Water Pollution Potential Using multiplied together to obtain a Designated Level <br /> Hydrogeologic Settings, and the Handbook of Environmen- applicable to the specific liquid waste constituent and <br /> ,at Data on Organic Chemicals by Karel Verschueren site of proposed waste discharge. If the concentration <br /> contain information and/or procedures that can be of a constituent in the liquid waste exceeds this level, <br /> used to assess the fate of chemicals in the environment the waste is classified as a "designated waste"and <br /> and to estimate environmental attenuation factors for Class 1I containment is required if the waste is to be <br /> specific waste constituents and site conditions. Com- discharged to land for treatment,storage,or disposal at <br /> puter models which are applicable to the waste con- this site. Wastes having concentrations below the <br /> stituents of concern and to the site's hydrogeologic Designated Level are assumed not to pose a significant <br /> conditions may also be used. water quality threat at the site and may be discharged <br /> to a waste management unit with less than Class II <br /> If a waste discharger is unable or unwilling to expend containment. <br /> the resources necessary to develop detailed and <br /> specific attenuation factors for the site of waste dis- Due to the constant hydraulic head and mass loading <br /> charge,the Central Valley Regional Water Board has of waste constituents presented by long-term im- <br /> pounding of liquid wastes at a site,most wastes which <br /> SOLUBLE DESIGNATED LEVEL FOR have a quality poorer than that of underlying ground <br /> A CONSTITUENT OF A SOLID WASTE water will eventually degrade water quality. This <br /> occurs as attenuative mechanisms in the vadose zone <br /> WATER DOMESTIC UNLINED LANDFILL OR WASTE PILE become saturated. For this reason,such wastes are <br /> WELL most-often classified as "designated waste"and are <br /> wwsmost-oftentwq;.ww:As/y..m required to be discharged to Class II impoudments. <br /> lrrf,n "ARr.d.w.n <br /> ICY%s�; /irawwLhlr <br /> Soluble Designated Levels for Solid Wastes <br /> (°0°s'n) M„rr As moisture from within a waste or infiltrating rainfall <br /> ~d b percolates toward the base of a landfill,soluble waste <br /> constituents are accumulated and leachate is formed. <br /> Constituents in leachate at the base of a landfill pose a <br /> similar water quality threat to constituents in an <br /> impounded liquid waste. The processes of environ- <br /> mental fate which act to attenuate constituent concen- <br /> trations are the same in either case. Therefore, <br /> W,,,, I Designated Levels may be calculated for leachate <br /> constituents in the same manner as for liquid waste <br /> constituents,as shown in Figure 7. In this example,the <br /> P°roD5 .tm ��y�ss /ftw afi Der caoTN. <br /> q Proposition 65 regulatory level for arsenic(0.005 mg/1) <br /> l wOU <br /> FLOW has been chosen as the water quality goal to protect <br /> ground water at this site for domestic supply,and the <br /> Figure 7 environmental attenuation factor has been estimated to <br /> /on B.Marshack,D.Env. Page 13 <br />