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quirements pursuant to Section 66310 of Title 22 NON-HAZARDOUS WASTES CAN of this code." [In July 1991,§66310 of Title 22 of THREATEN WATER QUALITY CCR was repealed and replaced with §66260.210.] DOMESTIC WATER The second art of this definition pertains to those WELL UNLINED p p SURFACE IMPOUNDMENT wastes granted a variance by DTSC from Class I dis- posal,as discussed above. The first half of the"desig- nated waste"definition includes non-hazardous wastes - which have the potential to impair water quality at the site of discharge. Due to their threat to water quality, "designated wastes"are to be discharged to Class II waste management units which have engineered con- Sufficient tainment features—liners,leachate collection systems Attenuation and caps—which act to isolate the wastes from ground ? and surface waters. The Chapter 15 regulations,how- ever,do not contain guidance on how to interpret the first part of the"designated waste"definition. The purpose of the Central Valley Regional Water Quality V Water Table Control Board staff report,The Designated Level Method- ology,is to provide an interpretation of this definition. 0.005 mg Arsenic/liter of water GROUND It may not be immediately apparent how a non- i Proposition 65 regulatory level i rl WATER hazardous waste could pose a threat to water quality. FLOW A simple example will illustrate this point. Figure 4 shows an unlined surface impoundment which con- Figure 4 tains soluble arsenic at a concentration of 4.5 mg/1. which provide a site-specific indication of the waste's The hazardous STLC for arsenic,the level above which eater quality impairment potential. If measured Ion- a liquid waste becomes hazardous under Title 22 of centrations of constituents in a waste exceed these Des- CCR,is 5 mg/1. Therefore,the waste in this example is ignated Levels,the waste is assumed to pose a water not hazardous. The Proposition 65(Safe Drinking Wa- quality threat at the site in question. Because of the ter and Toxic Enforcement Act of 1986)no-significant- site-specific nature of the determination,the same risk level for arsenic is 0.005 mg/l. If natural geologic waste may be classified as"designated"in one loca- materials between the base of the impoundment and tion,but not in another location which provides a the water table are unable to sufficiently filter out or greater degree of protection for water quality. attenuate the arsenic,the Proposition 65 regulatory Designated Levels are calculated by first determin- level will be exceeded,adversely impacting the benefi- ing the bodies of water which may be affected by the cial use of the water for domestic supply. Therefore, waste management activity in question and the present this waste at this site would be classified as a"desig- and probable future beneficial uses of these waters,as nated waste",and the impoundment would have to be shown in Figure 5. Next,site-specific water quality designed to meet Class II containment standards to goals are selected,based on California's water quality isolate the waste from ground water. standards to protect beneficial uses. Finally,the appli- cable water quality goals are multiplied by factors THE DESIGNATED LEVEL METHODOLOGY which account for the magnitude of environmental As shown by the above example,the determination attenuation expected to occur under reasonable worst- of whether a waste poses a threat to water quality must case conditions at the proposed site of discharge. The take into account factors relating to the waste and to result is a set of Soluble Designated Levels for waste the site of proposed discharge. In The Designated Level constituents of concern which are specifically appli- Methodology,this is accorf►plished by determining"Des- cable to both the waste and the site and which,if not ignated Levels",concentrations of waste constituents exceeded,should protect the beneficial uses of waters Central Valley Regional Water Quality Control Board Page 3