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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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