The CWA Framework

Water Quality Restoration Implementation Process

In impaired watersheds that have a TMDL in place, Maryland regulates both wastewater and stormwater discharges through discharge permits. TMDLs assign pollutant loads through a Wasteload Allocation (WLA) for permitted sources and Load Allocation (LA) for non-permitted sources, e.g., most agricultural activities. Surface water discharge permits are required to be consistent with any and all applicable WLAs. TMDLs also require a margin of safety to ensure the WLA and LA will be met.

Wasteload Allocation (WLA) Implementation

For municipal and industrial wastewater permits, consistency with TMDL WLAs generally entails the direct incorporation of assigned WLAs and associated concentration and flow limits into a permit. For some wastewater permits, there may be additional requirements to ensure compliance with WLAs and effluent limits, such as the development of Pollutant Minimization Plans when WLAs are exceeded, which try to identify sources of the pollutants within the sewer-shed, particularly for toxic substances. Additionally, as a state requirement, facilities are required to develop and submit to MDE a Capacity Management Plan when facilities reach 80% flow capacity. Broadly speaking, as a result of the Chesapeake Bay TMDL and associated WIPs, MDE has a “no new discharge” policy. If a local jurisdiction or entity is looking to acquire a permit for a new facility or new discharge, the allocation must come from some other facility, or ways to offset the new pollutant load must be identified. Further information related to MDE’s Wastewater permitting program can be found HERE. These permits are renewed every five years and can include additional pollution limits or special conditions if prior permits fail to restore WQSs.

For stormwater permits, consistency with TMDL WLAs is achieved via the implementation of BMPs. Since 1) stormwater permits (with the exception of industrial stormwater and construction stormwater) can encompass thousands of outfalls thereby making compliance monitoring difficult, and 2) there is always some probability that an effluent limit will be exceeded because stormwater loads are rainfall driven; therefore, end-of-pipe limits are not assigned to stormwater permits. Rather, compliance with stormwater permits is ensured via the implementation of BMPs, both for restoration and mitigation in response to new and existing development. Most MS4 permits require permitted local jurisdictions and state and federal facilities to implement BMPs where there is currently little or no SWM. The same principles apply to the incorporation of WLAs into permits for regulated industrial stormwater discharges. Phase I MS4 permittees are also required to develop TMDL implementation plans that specify how, when, and at what cost applicable stormwater WLAs will be achieved. Further information regarding Phase I and II MS4 permits as well as industrial stormwater permits can be found at the links below. Specifically, the BMP manuals that govern permit compliance are included at these web links.

MDE has also developed guidance documents and modeling tools to assist local jurisdictions in the development of their permit-required implementation plans and subsequent TMDL progress reporting. This includes pollutant specific guidance and Maryland’s TMDL Implementation Progress and Planning Tool, which is a spreadsheet model that applies unit loads, BMP efficiencies, and delivery factors from the Phase 6 Chesapeake Bay watershed model that MDE created for Phase I MS4s to use for their nutrient and sediment TMDL implementation plans. These materials can be found on MDE’s TMDL Data Center website HERE. For technical assistance or guidance on using these tools, please contact MDE’s TMDL coordinator at or (410) 537-3818.

Stormwater Law

All jurisdictions, whether regulated under a CWA stormwater permit or not, are required to implement Maryland’s Stormwater Law for new development and redevelopment (Environment Article, Section 4-201 et. seq.​). Maryland’s first SWM regulations went into effect in 1985. The regulations were updated in 2000, 2010, and 2019. The latest requirements are termed Environmental Site Design (ESD). ESD regulations specify that all new development must hydrologically function like “woods in good condition,” which is assessed based on runoff curve numbers specified in USDA-NRCS hydrologic models. Maryland’s Stormwater Design Manual can be found HERE. Specific requirements for new development can be found in Chapter 5 of the manual. MDE also encourages additional water quantity management and comprehensive watershed planning in flood prone watersheds (whether prone to nuisance flooding or large-scale flood events). Within the WRE, jurisdictions should identify recurrent flooding areas in local watersheds and carefully evaluate whether climate change and planned development will exacerbate those conditions; if so, changes to the land use plan or other measures should occur (see the Flood Management Process section).

Load Allocation (LA) Implementation

TMDLs allocate loads to the non-regulated sector as well the regulated sector, i.e., the LA portion of the TMDL. The LA includes all sources that are not covered under a CWA discharge permit, such as the majority of agricultural operations, septic systems, and non-regulated urban stormwater. Non-regulated urban stormwater includes all municipal stormwater discharges that are not covered by a Phase I or II MS4 permit, e.g., jurisdictions with a population less than 100,000 people and not in a U.S. Census designated urbanized area. Implementing TMDLs in the non-regulated sector is significantly different than in the regulated sector, where allocations, BMPs, and other pollution controls are directly incorporated into permits. Implementation in the non-regulated sector involves significant amounts of stakeholder outreach, planning, technical assistance, and funding to implement water quality restoration practices. For instance, MDA is the lead state agency for TMDL implementation in the agricultural sector. MDA provides a significant amount of technical resources working with individual farms to implement water quality improvement projects. They also provide a significant amount of funding via Maryland’s Agricultural Cost Share program to support the planning and construction of those projects.

One of the main challenges for TMDL attainment and water quality restoration in non-regulated sectors is that there is no restoration requirement for these sectors. This creates a gap where there is no responsible party that performs water quality based planning, implements BMPs, and tracks TMDL implementation progress. In some instances, a unifying planning entity such as an inter-jurisdictional reservoir group or a national estuary program will fill this void. However, these instances are rare and this gap creates a dynamic where the burden for TMDL attainment then falls more heavily on the regulated sectors. The WRE can be key to implementing TMDLs in the non-regulated sector by encouraging local governments to serve as this key planning entity and conduct pollution risk assessments as new growth is planned. Helping to achieve and maintain the LA as growth continues can help avoid future regulatory controls or statewide legislative mandates.

Margin of Safety in TMDLs

Given modeling uncertainty, all TMDLs include a margin of safety that can be explicitly included as a separate allocation or implicitly included via modeling assumptions. Due to this model uncertainty, MDE recommends that local jurisdictions go above and beyond the minimum requirements for SW on new development, BMP implementation for water quality restoration, and WWTP optimization. Maximizing SWM and BMP potential now represents efficient planning, since these models are iteratively revised and updated incorporating the latest science and data. In the near-term, by implementing the maximum feasible SWM designs and number of restoration projects, jurisdictions can reduce long-term costs if future model updates indicate that additional effort is needed to achieve WQS (for example, in recent years the level of effort to achieve the Bay TMDL has been revised higher based on modeled impacts from climate change). As a best practice, the WRE should include strategies for ensuring this higher level of water quality restoration and protection. Jurisdictions should keep in mind that the ultimate goal of TMDL implementation is not to achieve the specified load reductions, but rather to achieve water quality criteria as assessed via water quality monitoring data. Enhanced SWM designs generally involve additional water quality and quantity treatment above and beyond the minimum 2.7” for new development. There are other SWM enhancements as well that could generally be applied, which are described in Section 5 of Maryland’s Stormwater Design Manual. For instance, see enhanced filters in Section M-9. There are also new and innovative techniques that can be applied as well, which generally provide additional nutrient and sediment load reduction benefits, as well as additional reductions for other pollutants, e.g., toxics. Some of these innovative practices can be found on the Chesapeake Stormwater Network’s website. MDE a​nd its partners continue to research new and innovative practices via the Chesapeake Bay Trust’s Restoration Research Grant Program. MDE also encourages BMP implementation in the context of comprehensive watershed planning that seeks to increase stormwater infiltration, green infrastructure, and natural filters and restore natural hydrologic function, while using in-stream restoration and floodplain reconnection techniques as a component of this larger watershed approach. MDE is exploring enhanced crediting and other incentives for these approaches.

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