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constituent of a solid waste, expressed in milligrams per liter (mg/1) of WET extract, is equal to the water quality goal times the environmental attenuation factor divided by the ten -fold dilution of the test. [Due to differences in the test methods, a 20 -fold dilution factor is used in calculations based on TCLP results.] For the Figure 7 example, the Soluble Designated Level for arsenic is equal to (0.005 x n =10) mg/l of WET extract. Concentrations of constituents in landfill leachate should not be confused with concentrations of constitu- ents in extract from the Waste Extraction Test or the Toxicity Characteristic Leaching Procedure. They are not the same. Concentrations of constituents in leachate are the result of the accumulation of constitu- ents from the waste as moisture migrates through a landfill or waste pile. The ratio of liquid -to -solids is not expected to be large within a landfill. Concentra- tions of constituents in the extract from the WET or the TCLP are the result of specific laboratory procedures where waste constituents are extracted from a solid waste by an extract solution under a large liquid -to - solids ratio necessary to ease sample handling. The extract from the WET or the TCLP is, therefore; not a simulation of leachate, but a means to measure the amounts of waste constituents that may be leached from the waste in a landfill. As stated above, actual landfill leachate is expected to have considerably higher pollut- ant concentrations than WET or TCLP extracts due mainly to this difference in liquid -to -solids ratio. CONTAMINATED SITE ASSESSMENT DTSC has prepared guidance materials which con- tain procedures for performing risk assessments and determining cleanup/mitigation levels for sites con- taminated with toxic substances. The object of these procedures is to prevent toxicologic impacts on hu- mans and other potential "biological receptors of con- cern". While sufficient to cover DTSC's concerns regarding site assessment and cleanup, the procedures in these documents are not designed to fully protect water resources that may be adversely impacted by site contaminants, as required by the Porter -Cologne Water Quality Control Act. Therefore, another methodology must be used by the State and Regional Water Boards to fulfill this need. Comparison of Figures 7 and 8 reveals that the threat posed to water quality by contaminated soils is similar to that posed by wastes in an unlined landfill. Central Valley Regional Water Quality Control Board SOLUBLE DESIGNATED LEVEL FOR A CONSTITUENT OF A SOLID WASTE DOMESTIC WATER UNLINED LANDFILL OR WASTE PILE WELL /"'♦ ( o.00s x n ) mg Arsenic liter of leachate x n mg soluble As / a waste x n m As titer off extract g /from the WET n— FOLD ATTENUATION 0.005 mg Arsenic / liter of water GROUND ( Proposition 65 regulatory level) �j WATER FLOW Figure 7 Therefore, The Designated Level Methodology can be used to calculate Designated Levels for site contaminants which, if exceeded, indicate a threat to the beneficial uses of nearby ground or surface waters. California's water quality standards (from the applicable Water Quality Control Plans) are used to select water quality goals which protect the beneficial uses of waters which could be adversely impacted by site contaminants. At- tenuation factors are estimated based upon site hydro - geologic data and information on the contaminants themselves. Soluble Designated Levels are then calcu- lated by multiplying the water quality goals by the attenuation factors and dividing by the ten -fold dilu- tion of the WET or the 20 -fold dilution of the TCLP (for volatile contaminants). The results are expressed as milligrams of soluble constituent per liter of extract. Soil samples from the site are subjected to the WET and/or TCLP procedure and results are compared with these site- and constituent -specific Soluble Designated Levels. Cleanup or mitigation would be required for soils having extractable concentrations which exceed Soluble Designated Levels. For this type of site assess- ment, the WET procedure is often modified to account Page 7