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Selecting Numerical Limits 7 - 20 August 2002 ❖ Tastes and Odors Objective ➢ Taste- and odor-based limits, normally in the following hierarchy ■ California Secondary MCL ■ Federal Secondary MCL • USEPA National Ambient Water Quality.Criterion based on taste & odor • Taste & odor thresholds published by other agencies or from the peer reviewed literature First, select one limit for each of the items above that begins with an arrow(➢). Record your selections in a chart, such as the following: Water Quality Relevant Portion of Ob'ective/Criterion Objective/Criterion Source California Toxics Rule/ Human Health Protection CTR or NTR Concentration Units National Toxics Rule Aquatic Life Protection—CCC CTR or NTR Aquatic Life Protection —CMC CTR or NTR Chemical Constituents Drinking Water MCL (lowest) DHS Numerical Water Quality Objective Basin Plan Beneficial Use Impairment Limit Toxicity Human Health—Drinking Water Human Health—Fish Consumption USEPA, RAWQC Aquatic Life Protection —CCC Aquatic Life Protection—CMC Tastes & Odors Taste & Odor Based Limits Second, select the limit with the lowest concentration.16 The result should be a limit that satisfies all applicable water quality objectives. Where aquatic life criteria vary with hardness, pH, or other factors, aquatic life criteria may be the most restrictive under some conditions while other limits in the above table may be more restrictive under other conditions. Consideration of natural background levels and antidegradation may require further modifications to this selection, as discussed below. Limitations The above algorithms should be applied carefully, considering the factors of each specific case. Automatically selecting numerical limits according to these algorithms will not always generate the most appropriate limit. If specific beneficial uses do not apply, then limits protective of those uses should be eliminated from consideration. It may be appropriate to deviate from the hierarchies listed above in specific cases. We may have information that a particular limit is outdated or is in formal dispute at the agency that originally issued the limit (as was the case with the former PHG for chromium at OEHHA). In another example, a California health-based limit may be less stringent than a comparable USEPA limit. Normally, we would prefer using the California limit over the one from USEPA. However, if the California and EPA limits are based on the same source of toxicologic information and the California limit is higher simply because it was "rounded off' from the EPA limit, it would be logical to use the more precise USEPA limit. It may also be that a risk-management decision prevented the California 16 In the case of aquatic life criteria,both CCC and CMC limits apply,1 as noted above. �