Total Maximum Daily Loads (TMDLs)

Page updated on Jun 30, 2016 at 10:12 AM

Although Alexandria’s geographic location means that pollutants in the City's waterways are influenced by upstream activities outside of the City, the City continues its commitment to protect and enhance water quality through many different programs. The City's MS4 stormwater program implements aggressive best management practices to meet National Pollutant Discharge Elimination System (NDPES) and Virginia Pollutant Discharge Elimination (VPDES) requirements. Further, the City’s local Zoning Ordinance and City Code provide a comprehensive regulatory foundation that not only supports the MS4 stormwater program, but proactively targets other non-point pollution sources to minimize or eliminate their impacts.

What is a TMDL? 

Chesapeake Bay Executive Order 

Chesapeake Bay Nutrients and Sediment TMDL 

Meeting the City's Nutrient and Sediment TMDL 

Bacteria TMDL for Hunting Creek, Cameron Run and Holmes Run  

Bacteria TMDL for Tidal and Non-Tidal Four Mile Run 

TMDL for PCBs in Tidal Portions of the Potomac and Anacostia Rivers 

What is a TMDL?

The Clean Water Act (CWA) sets an environmental goal that all waters of the United States be “fishable” and “swimmable.” More specifically, it requires all states and the District of Columbia to establish appropriate uses for their waters and adopt water quality standards to protective those uses. Under section 303(d) of CWA, jurisdictions are required to develop of list of impaired waters every two years. A number of water bodies in the Commonwealth of Virginia have been placed on EPA’s impaired waters list. Once a water body is listed as impaired for a designated use, a total maximum daily load (TMDL) must be developed for that impaired stream or stream segment to address the impairment based on water quality standards. A TMDL represents the maximum amount of a pollutant that a body of water or stream segment may receive and still meet its water quality standards. This has led to TMDLs being issued for stream segments throughout the Commonwealth of Virginia, as well as in the City of Alexandria. Given that the City is a dense urban area, most of the pollutant reductions in these TMDLs focus on stormwater runoff, as well as discharges from the combined sewer system. Permitted point sources, nonpoint source runoff, and wildlife also contribute to these impairments. While the TMDLs will include reductions for permitted discharges, unregulated discharges often do not have reduction targets.



Chesapeake Bay Executive Order 13508

In May 2009, President Obama issued Executive Order 13508: Chesapeake Bay Protection and Restoration that calls on the Federal government to lead a renewed effort and commitment to restore and protect the Chesapeake Bay. Pursuant to this Executive Order, the Federal Leadership Committee (FLC) established under Section 201 and comprised of lead agencies referred to elsewhere in the order, compiled the Section 202 draft reports from the lead agencies, and published the Section 203 Strategy for Protecting and Restoring the Chesapeake Bay Watershed on May 12, 2010. Beginning in 2011, the FLC has published an annual action plan and progress report. This plan leads a renewed and unparalleled effort by the federal government to restore clean water, recover habitat, sustain fish and wildlife, conserve land, increase public access, expand citizen stewardship, develop environmental markets, respond to climate change and strengthen scientific knowledge. It focuses on improving the environment in communities throughout the entire watershed and in its thousands of streams, creeks, and rivers.



Chesapeake Bay Nutrients and Sediment TMDL

Most of the Chesapeake Bay and its tidal waters are listed as impaired because of excess nitrogen, phosphorus, and sediment. These pollutants cause algae blooms that consume oxygen and create “dead zones” where fish and shellfish cannot survive, block sunlight that is needed for underwater bay grasses, and smother aquatic life on the bottom. Nitrogen, phosphorus, and sediment enter the water from agricultural operations, urban and suburban stormwater runoff, wastewater facilities, air pollution, forested areas, and other sources, including onsite septic systems. Despite some reductions in pollution during the past 25 years of restoration due to efforts by federal, state and local governments; non-governmental organizations; and stakeholders in the agriculture, urban/suburban stormwater, and wastewater sectors, have led to some reduction in pollution over the past 25 years. However, there has been insufficient progress toward meeting the water quality goals for the Chesapeake Bay and its tidal waters.

On December 29, 2010, the United States Environmental Protection Agency (EPA) established the Chesapeake Bay Total Maximum Daily Load (TMDL) for nitrogen, phosphorous, and sediment. This TMDL – the largest ever developed by the EPA – sets pollution reductions across multiple sectors for the six Chesapeake Bay watershed states (including Virginia) and the District of Columbia. The TMDL is required under the CWA and responds to consent decrees in Virginia and the District of Columbia from the late 1990s.

During Phase I, the Bay was divided into 92 segments, with each Bay State and the District of Columbia receiving nutrient and sediment allocations for each of the segments. In turn, the States and District were required to complete Watershed Implementation Plans (WIPs) to illustrate how each would meet pollutant reductions in the TMDL. According to the TMDL, these WIPs are in place to provide the proper “reasonable assurance” that water quality standards would be achieved. Final Phase I WIPs were submitted to the EPA November 29, 2010. Phase II of the process further divides the segments into more local sources to further identify reductions by source sector, with the States and District completing Phase II WIPs. The Final Phase II WIPs were submitted to the EPA on March 30, 2012. EPA may revise the current TMDL based on the Final Phase II WIPs and updated modeling that is occurring.

EPA will use NPDES permits and the WIPs as tools to implement the TMDL and provide reasonable assurance that the reductions in the wasteload allocations (WLAs) will be met. These tools, as well as other possible consequences, may be leveraged further if a Chesapeake Bay Watershed State or the District does not meet EPA's expectations or does not demonstrate satisfactory progress toward achieving nutrient and sediment allocations established by EPA in the Chesapeake Bay TMDL. The first two elements of the accountability framework are the WIPs and the two-year milestones. The Bay states had to complete their first set of two-year milestones by December 31, 2011 and second set by January 2014. The TMDL is designed to ensure that all pollution control measures from all source sectors that are needed to fully restore the Bay and its tidal rivers are in place by 2025, with at least 60 percent of the actions from all sectors to be in place by 2017.

The City’s Environmental Management Ordinance (1992) provides for safeguarding of Chesapeake Bay Resource Protection Areas and protects water quality by requiring stormwater quality best management practices (BMPs) for new development and redevelopment. The Erosion and Sediment Control Ordinance (1981) provides the basis of the City’s vigorous plan review and inspection program to address construction site controls. The City's BMP inspection program continues to be aggressive in requiring proper functioning and maintenance of facilities and predates the 2013 Municipal Separate Storm Sewer System (MS4) General Permit requirements. The City also provides education and outreach to schools, interested organizations, and the general public ways to protect the City's water resources. Lastly, the Erosion and Sediment Control Ordinance (1988) is enforced through a vigorous review and construction site inspection program.

The City is committed to protecting local streams, the Potomac River, and the Chesapeake Bay and will continue to search out innovative ways to meet the requirements of the Chesapeake Bay TMDL requirements.
For more information on the Chesapeake Bay TMDL, including fact sheets, frequently asked questions and video clips of previous presentations, visit the EPA Bay TMDL website.

To learn more about the Virginia WIP process, visit the Virginia Department of Environmental Quality's Chesapeake Bay Total Maximum Daily Load website.



Meeting the City's Chesapeake Bay Nutrients and Sediment TMDL 

The City’s TMDL pollution reduction requirement has been incorporated into the City’s 5-year MS4 permit, which details the specific pollution reduction requirements that must be met in order to comply with the Bay TMDL. In order to meet the City’s TMDL, the City will have three full five-year MS4 permit cycles to implement the required reductions (Phase I: 2013-2018; Phase II: 2018-2023; and Phase III: 2023-2028).

Table 1 below provides the overall loads of each pollutant, the required 5% reductions, and the equivalent area treated to meet the 5% goal. A range is given for the acres treated to account differences in the existing land cover and the varying pollutant removal efficiencies for the many different best management practice (BMP) facilities that can be implemented to treat these areas. 

Estimated Chesapeake Bay TMDL Pollutant Reduction Requirements (2013-2028) 

Pollutant Load 

Pollutant Total (lbs/yr) 


Equivalent Acres 





2009 Pollutant Loads (Baseline) 





Total Pollutant Reductions Required (Phases I-III)  




≈ 2220 - 2400  

Phase I*   (2013-2018) 





≈ 120 - 300 

Phase II   (2018-2023) 





≈ 660 

Phase III  (2023-2028) 





≈ 1440 

*Phase 1 reductions are calculated using loading rates from Table 3b of the City’s current MS4 permit and include an additional estimate of the 5% offsets required for new development occurring between July 1, 2009 and June 30, 2014.

Pursuant to the current MS4 permit (2013-2018), the City must complete a Chesapeake Bay TMDL Action Plan that details the means and methods to meet 5% of the total target reductions for nitrogen, phosphorus and sediment from stormwater runoff that must be implemented no later than the end of the current 5-year MS4 permit period (by June 30, 2018). The City's Draft Chesapeake Bay TMDL Phase I (5%) Action Plan  was posted for public comment during June 2015.  The comment-response table is provided below. The final Chesapeake Bay TMDL 5% Action Plan can be found below.

Draft Bay TMDL Action Plan Comment-Response

Chesapeake Bay TMDL Phase I (5%) Action Plan

Ongoing Stormwater Retrofit Projects



    Bacteria TMDL for Hunting Creek, Cameron Run and Holmes Run

    The Holmes Run, Cameron Run, and Hunting Creek TMDLs were finalized on November 2, 2010, with EPA’s Decision Rationale provided on November 10, 2010. MS4 permittees are given wasteload allocations (WLA) under each of the three impairments. There are no individual VPDES permits in either the Holmes Run or Cameron Run watershed. Two facilities, AlexRenew Enterprises Advanced Wastewater Treatment Plant and the City’s Combined Sewer System, have individual VPDES permits authorizing discharge of bacteria to Hunting Creek. Loads associated with MS4 permits are considered part of the wasteload allocations. Seven MS4 permits have been issued in the Hunting Creek drainage area, which include other municipalities, state and federal entities, and public schools. WLAs for stormwater in these areas will be met through the implementation of programmatic best management practices (BMPs). Currently, the City addresses this TMDL by providing education and outreach, opportunities for public involvement and proactive illicit discharge detection The City also has a targeted pet waste education program to reduce bacterial impacts and improve water quality in local streams.

    The City has made tremendous progress in minimizing its combined sewer system discharges and implementing the National CSO Policy. However, some further reductions in CSOs will be necessary to comply with the loadings specified in the Hunting Creek Bacteria TMDL. The City has outlined an efficient and expeditious approach to achieve the additional reductions that will be necessary, in order to demonstrate compliance with the TMDL for the combined area. The City remains in compliance with all of its NPDES permits.

    The City also meets the requirements of the bacterial TMDLs through other various programs. Through its MS4 General Permit and associated Stormwater Program, the City provides education and outreach to pet owners, enforcement of City code that requires owners to pick up after their pets, and screening of storm outfalls during dry weather to detect the presence of illegal connections to the storm drain system. 



    Bacteria TMDL for Tidal and Non-Tidal Four Mile Run

    The Bacteria TMDL for Tidal Four Mile Run was submitted April 21, 2010. The impaired segment is located in the City of Alexandria and Arlington County, and extends from the confluence with the Potomac River at the state boundary to the upstream limit of tidal waters near Mount Vernon Ave. The Northern Virginia Regional Commission (NVRC, 2002) developed a Fecal ColiformTMDL for Non‐Tidal Four Mile Run. The TMDL was approved in 2002, and an implementation plan (IP) for the TMDL was subsequently completed in 2004 (NVRC, 2004). The TMDL for tidal Four Mile Run builds upon the TMDL for the non-tidal river. The TMDL is implemented in stages through best management practices (BMPs) in the watershed. The benefits of staged implementation are:

    • As stream monitoring continues to occur, it allows for water quality improvements to be recorded as they are being achieved; 
    • It provides a measure of quality control, given the uncertainties that exist in any model; 
    • It provides a mechanism for developing public support; 
    • It helps to ensure the most cost effective practices are implemented initially; and
    • It allows for the evaluation of the TMDL’s adequacy in achieving the water quality standard.

    The City also meets the requirements of the bacterial TMDLs through other various programs. Through its MS4 General Permit and associated Stormwater Program, the City provides education and outreach to pet owners, enforcement of City code that requires owners to pick up after their pets, and screening storm outfalls during dry weather to detect the presence of illegal connections to the storm drain system. 



    TMDL for PCBs in Tidal Portions of the Potomac and Anacostia Rivers  

    Submitted September 28, 2007, with minor revisions Oct 31, 2007, the Total Maximum Daily Loads for Polychlorinated Biphenyls (PCBs) for Tidal Portions of the Potomac and Anacostia Rivers in the District of Columbia, Maryland, and Virginia, establishes PCB TMDLs for 28 listed impaired water body segments. The District of Columbia has listed all of the tidal Anacostia and Potomac rivers within District borders (5 segments) for protection of human health related to the consumption of fish and shellfish, which is not supported due to elevated levels of PCBs in fish tissue. The State of Maryland has listed the Potomac River Upper, Middle and Lower Tidal; and the tidal portion of the Anacostia River as impaired due to elevated levels of PCBs in fish tissue and other causes. Virginia has 19 tidal embayments of the Potomac River listed for fish consumption use due to elevated levels of PCBs in fish tissue.

    PCBs are a class of man-made compounds first manufactured in 1929 and used for a variety of industrial applications, including coolants and lubricants in electrical equipment. Other applications included dust control, pesticides, fire retardants, paints and coatings, printing inks, caulking, and wood treatment. There are no natural sources of PCBs.

    New production was banned in 1979 under the Toxic Substances Control Act (TSCA) due to concerns about possible harmful human health effects, although their use in existing equipment was allowed to continue. Although their current commercial use is restricted in the U.S., they continue to be a common environmental contaminant because they don’t break down easily.

    Implementation of the TMDL is generally carried out through the City’s Stormwater Program and MS4 permit. The City performs the following in support of this effort:

    • Standard contaminated land condition for development Special Use Permit’s (SUPs) requiring screening for PCBs as part of the site characterization 
    • Assess municipal properties for sources of PCBs and assign any “high risk” facilities that currently store, or have transferred, transported or disposed of PCBs in a manner that would expose it to precipitation  (none found)
    • Characterize stormwater runoff from “high risk” properties (none found)
    • Cleanup of the Hume-VEPCO Power Substation (complete)
    • Compliance with CSS Long Term Control Plan
    • Developed brochure for developers, business and homeowners