Ammonia WQS Variance Tools for Small Communities with Lagoon Wastewater Treatment Systems
In response to needs identified by state co-regulators and lagoon-utilizing communities, the U.S. Environmental Protection Agency (EPA) developed the Small Lagoon Community Economic Streamlining (SLCES) Tool and the Individual Lagoon Tool (ILT) as priority actions under the EPA’s 2022-2026 Lagoon Wastewater Treatment Action Plan, which can be found on the Lagoon Wastewater Treatment Systems webpage. Both tools provide a user-friendly, streamlined way for a state, Tribe, or community to conduct an economic analysis as recommended in the EPA’s Economic Guidance for Water Quality Standards to determine whether a water quality standards (WQS) variance is appropriate for a small community experiencing lagoon system compliance challenges related to ammonia. The EPA’s Applying the EPA’s Economic Analysis Tools to a WQS Variance for Ammonia for Small Lagoon Communities is a technical resource to assist states and authorized Tribes when using the tools’ results to construct a WQS variance.
For assistance when conducting an economic analysis for dischargers other than publicly owned small community lagoons or for a pollutant other than ammonia, please see the Tools to Evaluate Economic Impacts section of the EPA’s Economic Guidance for Water Quality Standards webpage. That section includes spreadsheet tools to help users perform the recommended calculations and analyses.
On this page:
- Small Community Lagoons and CWA Requirements
- Small Lagoon Community Economic Streamlining (SLCES) Tool
- Individual Lagoon Tool (ILT)
- Applying the EPA’s Economic Analysis Tools to a WQS Variance for Ammonia for Small Lagoon Communities
- SLCES Tool and ILT Supporting Documentation
Small Community Lagoons and CWA Requirements
Small communities with lagoon wastewater treatment systems typically serve fewer than 3,000 people and frequently lack the necessary financial and technical resources to comply with Clean Water Act (CWA) based requirements. A 2022 EPA analysis found that about one-quarter of the nation’s Publicly Owned Treatment Works (POTWs) regulated by the CWA’s National Pollutant Discharge Elimination System (NPDES) program (over 4,500 POTWs) are lagoon wastewater systems without advanced supplemental treatment technology.
A lagoon community may be interested in a WQS variance when they are unable to comply with their ammonia water quality-based effluent limit (WQBEL) in an NPDES permit, and available technological and financial assistance is not sufficient to remedy the noncompliance issue, but incremental water quality improvement can still be made.
This recorded webinar explains how the ILT and the SLCES Tool can be used to streamline an economic analysis to demonstrate the need for a WQS variance. The webinar also provides a demonstration of each tool and discusses the EPA’s guidance on developing an ammonia WQS variance, where appropriate, based on the tools’ outputs.
Small Lagoon Community Economic Streamlining (SLCES) Tool
The SLCES Tool streamlines the information collection process for conducting the economic impact analysis for a WQS variance for publicly owned lagoon wastewater treatment systems for ammonia, following the EPA’s economic guidance for WQS. The SLCES tool can evaluate up to 1,000 lagoon communities at the same time with a minimum of user input.
The SLCES Tool User Manual describes how to use the SLCES Tool, and the tool’s assumptions and limitations.
In March 2025, the EPA fixed minor errors in the SLCES Tool and SLCES User Manual. Users who downloaded these files prior to March 2025 may therefore want to download and use the updated versions.
Individual Lagoon Tool (ILT)
The ILT streamlines cost-estimation while allowing the state, authorized Tribe or community to use community-specific information when conducting an economic analysis for a publicly owned lagoon wastewater treatment system requesting an ammonia WQS variance. The ILT may be particularly useful where using the SLCES Tool may not accurately reflect community conditions.
Applying the EPA’s Economic Analysis Tools to a WQS Variance for Ammonia for Small Lagoon Communities
The following implementation document for the SLCES Tool and ILT describes when each tool might be most useful and how to use the tools’ results to construct a WQS variance consistent with the EPA’s WQS regulation.
SLCES Tool and ILT Supporting Documentation
Learn more about how the EPA developed these tools: