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ments pursuant to Section 66310 of Title 22 of this take into account factors relating to the waste and to code." [In July 1991,§66310 of Title 22 of CCA was the site of proposed discharge. In The Designated levet repealed and replaced with§66260.210.1 Methodology, this is accomplished by determining "Designated Levels',concentrations of waste constitu- The second part of this definition pertains to those ents which provide a site-specific indication of the wastes granted a variance by DISC from Class I waste's water quality impairment potential. If mea- disposal,as discussed above. The first half of the sured concentrations of constituents in a waste exceed "designated waste" definition includes non-hazardous these Designated Levels,the waste is assumed to pose wastes which have the potential to impair water a water quality threat at the site in question. Because of quality at the site of discharge. Due to their threat to the site-specific nature of the determination,the same water quality, "designated wastes" are to be dis- waste may be classified as "designated"in one loca- charged to Class II waste management units which tion,but not in another location which provides a have engineered containment features—liners,leachate I greater degree of protection for water quality. collection systems and caps—which act to isolate the wastes from ground and surface waters. The Chap- Designated Levels are calculated by first determining ter 15 regulations,however,do not contain guidance the bodies of water which may be affected by the waste on how to interpret the first part of the"designated management activity in question and the present and waste" definition. The purpose of the Central Valley probable future beneficial uses of these waters,as Regional Water Quality Control Board staff report, shown in Figure 5. Next,site-specific water quality The Designated Level Methodology,is to provide an goals are selected,as discussed above,based on interpretation of this definition. background water quality and California's water quality standards to protect beneficial uses. Finally, It may not be immediately apparent how a non- the most limiting of the applicable water quality goals hazardous waste could pose a threat to water quality. A simple example will illustrate this point. Figure 4 NON-HAZARDOUS WASTES CAN shows an unlined surface impoundment which con- THREATEN WATER QUALITY tains soluble arsenic at a concentration of 4.5 mg/l. The hazardous STLC for arsenic,the level above which DOMEsncWATER UNUNED a liquid waste becomes hazardous under Title 22 of WELL SURFACE IMPOUNDMENT CCR,is 5 mg/1. Therefore,the waste in this example is not hazardous. The Proposition 65(Safe Drinking Water and Toxic Enforcement Act of 1986)nc-signifi- cant-risk level for arsenic is 0.005 mg/l. If natural geologic materials between the base of the impound- ment and the water table are unable to sufficiently filter out or attenuate the arsenic,the Proposition 65 regula- tory level will be exceeded,adversely impacting the Sufficient Attenuation ..: .. . beneficial use of the water for domestic supply. There- 7 q fore, this waste at this site would be classified as a "designated waste",and the impoundment would have to be designed to meet Class II containment standards to isolate the waste from ground water. "ate - a THE DESIGNATED LEVEL METHODOLOGY 0.005 mg Arsedct liter of water GROUND (yrapoYdon 65„gWamy WM) a WATER FLOW As shown by the above example,the determination of whether a waste poses a threat to water quality must Figure 4 Page 10 California's Water Quality Standards