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Selecting Numerical Limits 9 20 August.2002 3) not result in water quality less than applicable water quality objectives. In addition, the policy requires that discharges of waste to high quality waters meet best practicable treatment or control prior to discharge. If reasonably available technology can achieve constituent concentrations that are better than water quality objectives, then the Regional Water Board must require that the lower technology-based concentrations be met. In the NPDES program, this is the same as the requirement that both technology based and water quality based effluent limits be met for each constituent of the discharge. In site cleanup, State Water Board Resolution No. 92-49 affirmed the applicability of the Antidegradation Policy to the process of setting site cleanup levels. Cleanup levels must meet all applicable water quality objectives and must be the lowest concentrations that are technologically and economically achievable. In cases where cleanup technology cannot meet water quality objectives, 92-49 allows Regional Board to establish a containment zone to manage residual pollution. Analytical detection and quantitation limits may provide additional technologic limitations. When the water quality limit is lower than what can be quantified with appropriate analytical methods, the laboratory should be required to submit both detection and quantitation limits and to report trace results (results that are able to be detected but not quantified). For normal analytical work, quantitation limits may be found in the following references: 1. Minimum Levels (MLs), State Water Board,Policy for Implementation of Toxics Standards for Inland Surface Waters, Enclosed Bays, and Estuaries of California (2 March 2000), Appendix 4, http://www.swrcb.ca.gov/iswT. 2. Detection Limits for Purposes of Reporting (DLRs), Department of Health-Services, litt]2://www.dhs.ca.aov/ps/ddwem/chemicals/DLR/dlr- dex htm. Detection and quantitation limits may also be found in the method manuals from USEPA. Not all laboratories are equipped up to run all of the methods contained in these references. 3. Method Detection Limits (MDLs) Practical Quantitation Limits (PQLs), USEPA analytical method documents, htti)://Www.oa.gov/Stindtrds.litml. a. SW-846, Test Methods for Evaluating Solid Waste (also contains water methods) b. Methods and Guidance for Analysis of Water If available methods cannot detect low enough concentrations to determine compliance with the water quality limit, then we have no choice but to assume that the constituent is not present in the sample. Methods with lower detection and quantitation limits may need to be specified for certain situations. The need for the information should balance the higher cost of such methods. For example, more expensive methods could be reserved for confirmation sampling or be required at a lower frequency. Justification The selection of water quality limits for a particular case should be carefully documented. To be defensible,the limit selected for each constituent must be tied back to a numerical or narrative water quality objective from the Basin Plan or to a promulgated water quality criterion from CTR or NTR. Cite the factors used in selecting numerical limits to translate narrative objectives and to address uncontrollable factors and antidegradation. Include specific rationale in the documentation (e.g., that the selected limit is the most recently developed limit, that its use supports and is consistent with guidance from sister California agencies, that it has been peer reviewed, and that it addresses routes of exposure