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California Regional Water Quality Control Bo Central Valle y Region Winston H.Hickox Robert Schneider,Chair .. _r Secretary for Gray Davis Environmental Sacramento Main Office Protection Internet Address: http://www.swrcb.ca.gov/rwgcb5 Governor 3443 Routier Road,Suite A,Sacramento,California 95827-3003 Phone(916)255-3000•FAX(916)255-3015 TO: Technical Staff FROM: Jon B. Marshack, D.Env. Redding, Fresno, and Sacramento Staff Environmental Scientist Offices Program Support Unit DATE: 20 August 2002 SIGNATURE: SUBJECT: SELECTING NUMERICAL RECEIVING WATER QUALITY LIMITS' The text at the beginning of the report,4 Compilation of Water Quality Goals provides information on how numerical limits may be used to translate narrative water quality objectives into receiving water limits. Included are recommendations and examples to help users of the report select appropriate limits. However, it appears that staff in the various Regional Board's programs do not select receiving water limits in a consistent manner. In some cases, limits are chosen that do not fully implement all applicable water quality objectives. In other cases, limits are chosen that would not stand up to legal challenge. To increase consistency in the selection of water quality limits, this memorandum recommends the use of default rules or algorithms for selecting numerical limits to comply with water quality objectives and promulgated water quality criteria. These algorithms are based on a few guiding principles designed to support the selection of appropriate water quality based limits. Other policies and regulations, such as the Antidegradation Policy, the Site Assessment and Cleanup Policy, and NPDES regulations require that technology based limits and background levels also be considered in determining the final water quality limits appropriate for a particular situation. Guiding Principles The following principles guide the derivation of the recommended algorithms. To be defensible, receiving water limits should be chosen so as to implement all applicable water quality objectives and promulgated water quality criteria. For each constituent of concern, the process involves three steps: 1) Select a single numerical limit to satisfy each water quality objective or relevant portion thereof.2 2) To satisfy all applicable objectives, select the lowest of the numerical limits from step (1). t This memorandum is not intended to provide guidance on effluent limits,which are derived from water quality based and z technology based considerations using discharge-specific factors and according to applicable regulations and policies. For example,compliance with the narrative toxicity objective for surface water normally involves selection of one limit to protect aquatic life and another limit to protect human health. California Environmental Protection Agency �a Recycled Paper The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. For a list of simple ways you can reduce demand and cut your energy costs,see our Web-site at http://www.swrcb.ca.gov/rwgcb5