Water Quality Restoration Planning Process
When monitoring data indicate that WQS are no longer being attained, those waterbodies are listed as impaired (e.g., Category 5) on Maryland’s IR. Impaired waterbodies then require a TMDL, which quantifies the amount of pollution that a water body can assimilate and still meet WQS. The TMDL and water quality restoration planning processes are represented by the orange boxes in Figure 1. In some instances, TMDLs may not be required, and TMDL alternatives may be used if there are more direct measures in place to achieve WQS. Typically these TMDL alternatives involve specific permitting activities that are expected to result in WQS attainment in the absence of TMDL development. While becoming more frequently used, TMDL alternatives are often not the complete solution to multiple source pollution problems.
TMDLs are typically developed using watershed, hydraulic, and/or water quality models that are calibrated to water quality monitoring data and observed flow and account for the different pollution sources or loads in the watershed. MDE scientists and engineers then use those models as a tool to simulate where and how much pollution load reductions are needed to bring the waterbody back into compliance with WQS. TMDLs also consider future growth in WWTP loads, factor in a margin of safety to ensure WQS will be achieved, and need to provide reasonable assurance that the pollution load reductions can be achieved. More information on the TMDL development process can be found HERE. Consult the Water Quality Assessments and TMDLs HERE to determine the water quality status of the watershed in which your planned growth and development will be occurring. Water bodies in orange have TMDLs.
There are over 500 TMDLs for a variety of pollutants in different tidal and nontidal water bodies throughout the state. In preparing the WRE, local jurisdictions should identify where planned growth is occurring in TMDL or impaired watersheds and conduct a pollution risk assessment to estimate any increased stormwater, septic and wastewater pollution loads with proposed land use changes. Any increases in loads should then be compared to the TMDL’s pollution source allocations and in the context of any local pollution reduction programs or trading approaches. Where the trajectory of this assessment indicates overall pollution increases and continued TMDL non-attainment, pollution offsets, trading, or other approaches to achieve WQS should be implemented. This assessment process should also consider wastewater and stormwater system capacity and whether planned growth and development will exceed or approach system design capacity limits. For example, planned growth and development in watersheds with combined stormwater/wastewater systems already experiencing periodic sewer overflows may further impair WQS. MDE’s wastewater permits require municipalities and local governments to conduct capacity management planning when systems reach 80% of their design capacity to ensure that growth takes place without overloading sewerage facilities.
Upon request, MDE’s TMDL program staff can assist with the pollution risk assessment by using existing modeling tools, established pollution loading factors, and/or other science-based methods. The WRE should summarize the results of this assessment and describe how planned growth and development will be consistent with TMDL and WQS attainment. Performing such an assessment in the WRE will help avoid situations where MDE and local delegated authorities are required to issue special permit conditions to restore water quality that delay or restrict development projects late in the process when significant time and money have already been invested.
When a TMDL is determined to be achievable, MDE works with local jurisdictions to implement the TMDL using CWA regulatory tools for permitted point sources as well as stakeholder engagement, incentives and technical assistance programs for unregulated sectors. See the Water Quality Implementation Process section below for more information. If a TMDL cannot reasonably be achieved or other factors prevent achievement of WQSs then a use attainability analysis (UAA) may be considered to determine if a change to WQSs is justifiable. According to the U.S. Environmental Protection Agency (EPA), a UAA is a structured scientific assessment of the factors affecting the attainment of the use. The CWA provides six different factors that may be used to justify such a change. A description of these factors can be found HERE. See the UAA process section below for more information.
To ensure that growth is not an obstacle to achieving a local TMDL, all local governments should track load reductions occurring within the agriculture, wastewater, stormwater (both MS4 and non-MS4) and septic system sectors. The WRE should include a strategy for achieving this objective. Even though agricultural best practice implementation and changes to agricultural loads are not directly part of the WRE requirements, the land use plan and growth strategies should take into account current progress and remaining load reductions needed within the agricultural sector in order to determine the appropriate amount and location of growth within a TMDL watershed.
