Problems Associated with Using Current EPA Approved Total Cyanide Analytical Methods for Determining Municipal Wastewater Treatment Plant NPDES Permit Compliance

Many municipal wastewater discharges currently exceed total cyanide (CN) effluent limitations when based on analytical results from standard EPA methods. The approved EPA methods used to measure CN in wastewater effluent are prone to numerous interferences that are unpredictable and difficult to mitigate. Substantial evidence indicates that these analytical problems are causing many current CN compliance issues, rather than actual high CN concentrations in the treated effluent. The preservative NaOH is required to be added to all samples that cannot be analyzed in less than 15 minutes, and NaOH is itself a proven interference for which there is no specific mitigation technique. Substantial evidence suggests NaOH addition may be unnecessary to maintain sample integrity over typical hold-times prior to analysis. Based on this information, CN measurements made under the current paradigm are likely inaccurate and produce unreliable information for determining NPDES permit compliance.