Setting IOC Reporting Limits for Drinking Water Compliance—The California Approach

Abstract

Establishing meaningful reporting limits presents one of the more vexing problems associated with chemical monitoring under the Safe Drinking Water Act (SDWA). At very low concentrations, relative errors can be large, leading to an increase in false‐positives and false‐negatives. Even when a pollutant is correctly identified at concentrations in the region of detection, results can be inaccurate and imprecise. The California Division of Drinking Water and Environmental Management, the primacy agency for SDWA enforcement, established a study group to develop a new approach for reporting limits for metals based on the minimum reporting level (MRL) concept. A voluntary interlaboratory study was conducted to determine an appropriate basis for setting MRL values. Forty‐seven drinking water laboratories accredited by the state received a series of prepared solutions containing analytes of interest. Only analytic methods approved by the US Environmental Protection Agency for SDWA compliance monitoring were used. The major determinative of reporting limits was how many laboratories had the capability of producing accurate results at any given concentration. Other practical considerations included the toxicity and occurrence of the elements.