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California gional Water Quality Control Board <br /> k Central Valley Region ^ <br /> Karl E.Longley,ScD,P.E.,Chair _:✓ <br /> Linda S.Adams 11020 Sun Center Drive#200,Rancho Cordova,Cal iromia 95670-6114 Arnold <br /> Secretaryfor Phone(916)464-3291 •FAX(916)464-4645 Schwarzenegger <br /> EnvironmentalGovernor <br /> http://www.wat ardt.ca.gov/centralvalley <br /> ProtectionI L I <br /> 21 September 2009 u^(�"—u V LP <br /> Mr. Phil Govea, P.E. SEP 23 2099 CERTIFIED MAIL NO. <br /> Deputy Director of Public Works E P RCN&ILNTyEA�jH7008 1140 0002 8805 5056 <br /> City of Manteca m1T�SERVICES <br /> 1001 West Center Street <br /> Manteca, CA 95337 <br /> MODIFICATION OF PROPOSED WASTE DISCHARGE REQUIREMENTS <br /> (NPDES NO. CA0081558), CITY OF MANTECA WASTEWATER QUALITY CONTROL <br /> FACILITY, SAN JOAQUIN COUNTY <br /> Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff has <br /> modified the reasonable potential analysis (RPA) based on a correction related to the <br /> hardness-dependent California Toxics Rule (CTR) metals criteria for the above mentioned <br /> proposed waste discharge requirements (Proposed NPDES Permit). As required in the Policy <br /> for Implementation of Toxics Standards for Inland Surface Waters, Enclosed Bays, and <br /> Estuaries of California (SIP), the proposed RPA for the CTR metals has been modified to use <br /> the minimum observed upstream receiving water hardness to adjust the applicable CTR <br /> metals criteria. The correction results in reasonable potential for silver to cause or contribute <br /> to an in-stream exceedance of the CTR criteria for silver in the receiving water. Consequently, <br /> the correction adds water quality based effluent limitations (WQBELs) for silver to the <br /> Proposed NPDES Permit. <br /> The Proposed NPDES Permit was modified in sections IV.A.1. and 2., Tables 6 and 7, of the <br /> Limitations and Discharge Specifications, and the Fact Sheet, Attachment E, at Section <br /> IV.C.3.d.ix as shown in the newly proposed text below: <br /> Limitations and Discharge Specifications, Sections IV.A.1. and 2., Tables 6 and 7 _ <br /> Effluent Limitations <br /> Parameter Units Average Average Maximum Instantaneous Instantaneous <br /> MonthlyWeekl Dail Minimum Maximum <br /> Silver, Total Recoverable Ng/L 1.1 2.0 <br /> Fact Sheet, Attachment E, Section IV.C.3.d.ix. <br /> ix. Silver <br /> (a) WQO. The CTR contains hardness dependent criteria for silver. <br /> Section 1.3 of the SIP contains the requirements for conducting the RPA <br /> for CTR constituents. Step 1 of the RPA requires that the CTR criteria be <br /> adjusted for hardness, as applicable. In this case, the minimum observed <br /> receiving water hardness was used to adjust the CTR criteria for silver <br /> California Environmental Protection Agency <br /> C,Recycled Paper - <br />