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###### Environmental Protection Agency

          - [EPA-R06-OW-2023-0566; FRL-11561-02-R6]

# AGENCY:

Environmental Protection Agency (EPA).

# ACTION:

Notice.

# SUMMARY:

The Environmental Protection Agency (EPA) Region 6 is providing notice of a Revised Designation Decision that storm water discharges from the Los Alamos Urban Area (as defined by the latest decennial Census) and Los Alamos National Laboratory (LANL) property in Los Alamos County and Santa Fe County, New Mexico are contributing to violations of New Mexico Water Quality Standards (WQS) and require National Pollutant Discharge Elimination System (NPDES) permit coverage under the Clean Water Act (CWA). This action is in response to a June 30, 2014, petition filed with EPA by Amigos Bravos entitled “A Petition by Amigos Bravos for a Determination that Storm Water Discharges in Los Alamos County Contribute to Water Quality Standards Violations and Require a Clean Water Act Permit,” and revises the Agency's prior December 16, 2019, designation decision, which was remanded to EPA for reconsideration by the United States Court of Appeals for the Tenth Circuit.

# DATES:

                        The “Revised Designation Decision and Record of Decision in Response to A Petition by Amigos Bravos for a Determination that Stormwater Discharges in Los Alamos County Contribute to Water Quality Standards Violations and Require Clean Water Act Permit Coverage” was signed on December 9, 2024. Please refer to the                         **SUPPLEMENTARY INFORMATION**                         section for additional information.                    

# ADDRESSES:

                        For further information contact Ms. Evelyn Rosborough via email:                         *rosborough.evelyn@epa.gov,*                         or by mail at Ms. Evelyn Rosborough, Environmental Protection Agency, Region 6, Water Division (6WQ-NP), 1201 Elm Street, Suite 500, Dallas, TX 75270.                    

# SUPPLEMENTARY INFORMATION:

## General Information

### A. Does this action apply to me?

                    Small Municipal Separate Storm Sewer Systems (MS4s) operated by the County of Los Alamos, the New Mexico Department of Transportation (NMDOT), and Los Alamos National Laboratory (LANL), including Triad National Security, LLC and the U.S. Department of Energy's National Nuclear Security Administration, will be regulated as a result of this action. To determine whether your entity is affected by this action, you should also review the description of EPA's action in Section II.B of this notice and the Revised Designation Decision document available in Docket ID No. EPA-R06-OW-2023-0566 at the Federal eRulemaking Portal:                     *https://www.regulations.gov/​*                     or online via the EPA Residual Designation web page at:                     *https://www.epa.gov/​npdes/​epas-residual-designation-authority.*                     If you have questions regarding the applicability of this action to a particular entity, consult the person listed in                     **ADDRESSES**                     section.                

### B. Summary and Availability of Revised Designation Documents

                    The Regional Administrator of EPA Region 6 has made a revised designation of stormwater discharges from certain MS4s for regulation under the NPDES permitting program pursuant to Section 402(p)(2)(E) and (6) of the CWA and EPA's implementing regulations at 40 CFR 122.26(a)(9)(i)(C)-(D). Those provisions authorize the Agency to designate for regulation stormwater discharges that contribute to a WQS violation or that are a significant contributor of pollutants to waters of the United States, or where controls are needed based on wasteload allocations that are part of total maximum daily loads. This authority is often referred to as “residual designation authority” or RDA. EPA is providing notice of its                           ( print page 5881)                        Revised Designation Decision that storm water discharges from the Los Alamos Urban Area (as defined by the latest decennial Census) and LANL property in Los Alamos County and Santa Fe County, New Mexico are contributing to violations of New Mexico WQS and require NPDES permit coverage under the CWA.                

This Revised Designation Decision revises EPA's prior December 16, 2019, decision designating stormwater discharges from small MS4s operated by the County of Los Alamos, LANL, and the New Mexico Department of Transportation for NPDES permitting. EPA has carefully considered all record information, including stormwater discharge data and other information submitted by Los Alamos County, NMED, LANL, and the Buckman Direct Diversion, NMED's water quality assessments and lists of impaired waters, and supplemental information submitted by LANL and the County regarding EPA's previous 2019 designation decision, as well as the public comments submitted on that decision when it was proposed. EPA also conducted a site visit in September 2022 to examine first-hand the effects of the discharges and waters at issue.

                    Upon reconsideration of the Petition on remand, EPA has determined that stormwater discharges from small MS4s located in the Los Alamos Urban Area as defined by the latest decennial Census and MS4s located on LANL property within Los Alamos and Santa Fe Counties, New Mexico require NPDES permit coverage because the discharges are contributing to violations of NM WQS in waters of the United States. The Revised Designation Decision plus supplementary information, including the response to comments document, relating to it are available in Docket ID No. EPA-R06-OW-2023-0566 at the Federal eRulemaking Portal:                     *https://www.regulations.gov/​*                     or online via the EPA Residual Designation web page at:                     *https://www.epa.gov/​npdes/​epas-residual-designation-authority.*

Dated: December 19, 2024.

Troy Hill,

Director, Water Division, Region 6.

[FR Doc. 2025-01072 Filed 1-16-25; 8:45 am]

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