Whether the uranium MCL is met in California depends on what conversion factor is used. Uranium, a kidney toxicant and a radioactive material, is present at elevated concentrations in groundwater in some states. In 1991 the US Environmental Protection Agency proposed a maximum contaminant level (MCL) for uranium in drinking water of 20 μg/L or 30 pCi/L (1.1 Bq/L). In 1992 California adopted an MCL of 20 pCi/L (0.74 Bq/L). Because California regulations permit analysis of uranium by either mass or radiochemical techniques, a reliable factor that converts values from mass to activity is required to determine compliance with the California MCL and any future federal MCL. The conversion factor for groundwater may differ markedly from that of the natural crustal abundance of uranium. This study compared values determined by three mass measurement techniques and two radiochemical techniques. It is suggested that a conversion factor of 0.79 pCi/μg be used to determine compliance with the California MCL.

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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.