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          *                       WASHINGTON, D.C.
 ^^Swlp^il^ J^1
                                                                             WSG 151
                                                           Dale Signed: January 25, 2002


                                   JAN x" 5  T302
                                                                                A'ATfB
 MEMORANDUM

 SUBJECT:   Calculation oCJCompIianceforibeNew Arsenic MCL
 FROM;      Cynthwlu Dougherty, Director
              Offic|jfflF Ground Water and Drinking

 TO:          Water Division Directors
              Regions I-X

        ! am writing to clarify calculation of compliance for the new drinking water Arsenic Rule
 promulgated on January 22, 2001,  In 2006, the new regulation will decrease the Maximum
 Contaminant Level (MCI,) for        to ,01 mg/L (or 10 ug/L). Unlike the other fOCs, arsenic
 compliance is based on special provisions written Into the Arsenic Rule.  Compliance with the
 Arsenic Rule is governed by 40 CFR 141.23, which requires reporting arsenic analytical results
 to the nearest 0.001 mg/L, This reporting requirement has the effect of making all measurements
 that are greater tfiiui or equal to .0105 mg/L a violation of the arsenic MCL (after rounding to the
 nearest ,001 mg/L),

        This method of compliance determination is affirmed by our costing    benefit analysis,
 public presentations, and conversations with stakeholders. We are working with other
             offices, with your staff, and wttSi             to identify whether fimhcr
 are necessary to ensure consistent implementation of the new arsenic

        The January 22, 2001 Arsenic Rule includes the following provisions.  These sections
 explain how compliance is calculated,

 *      40 CFR 141,23(i) "Inorganic Chemical Sampling and Analytical Requirements:"
        Compliance with 141,11 or 141.620)) shall he determined based an the unalytiial
        result(s) obtained at each sampling putnt.

        40CfH14J.23(iX4):
        Arsenic xamphng results will he reported to the nearest .001 mg/L.

        Based on these regulatory provisions, an MCL violation is incurred for arsenic  levels at
 or above ,0105 mg/l, or 10,5 j.ig/L,
                               Internet Address (URL) « http./'www epa.gov
             Recyttad/Fteeyc.tabl» * Pnn!«i with Veti^fcttite 0tj R;»s*<»« ^Minimum 30% Postcuctcuinff)

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                                                                          WSG A
                                                       Date Signed: January 25, 2002

      If you have any questions, comments, or           to promote consistent
implementation, please contact me at 202-564-3750, or have your staff contact Ron Bergman at
202-564-3823 or              at 202-564-4656.

      Drinking Water Program Managers,, Regions i - X
            Hill, OGC
      Carrie Wehling, OGC
            Pollins. OF.CA
      Vanessa Leiby, ASDWA

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