Special Topic: Impaired Waters and TMDLs

  • Apr 29, 2010
  • Greg Blanchard
Datasonde Deployment in the East Fork of the Manatee River

An important responsibility of the Natural Resources Department is to work with the Florida Department of Environmental Protection, our partner agencies and estuary programs, in determining whether the County's water bodies meet state water quality standards and the goals of the Federal Clean Water Act. Much of the data used for these determinations comes from the Natural Resources Department's own water quality monitoring programs. Our technical staff also critically reviews every step of the state assessment and designation process and is ready to assist the state in taking those actions to improve water quality in areas falling short of Clean Water Act goals. This is a complex subject, so we've prepared the following general guide to the "Impaired Waters" process.

Background - The Clean Water Act

Section 303(d) of the Clean Water Act

The goal of the Clean Water Act (CWA) is "to restore and maintain the chemical, physical, and biological integrity of the nation's waters" (33 U.S.C §1251(a)). Under section 303(d) of the CWA, states, territories, and authorized tribes, collectively referred to in the act as "states," are required to develop lists of impaired waters. These are waters for which technology-based regulations and other required controls are not stringent enough to meet the water quality standards set by states. The law requires that states establish priority rankings for waters on the lists and develop Total Maximum Daily Loads (TMDLs) for these waters. A TMDL is a calculation of the maximum amount of a pollutant that a water body can receive and still safely meet water quality standards.
How does the 303(d) Impaired Waters and TMDL Program fit into the Clean Water Act?
The CWA includes two basic approaches for protecting and restoring the nation's waters. One is a technology-based, end-of-pipe approach, whereby EPA promulgates effluent guidelines that rely on technologies available to remove pollutants from waste streams. These guidelines are used to derive individual, technology-based National Pollutant Discharge Elimination System (NPDES) permit limits. The other approach is water quality-based and is designed to achieve the desired uses of a water. This approach may ultimately result in more stringent NPDES permit limits. The 303(d) program is at the core of the water quality-based approach and serves to link the water quality goals to the NPDES permit limits.
Water Quality-Based Approach of the Clean Water Act
Water quality standards are the foundation of the water quality-based control program mandated by the Clean Water Act. Water quality standards define the goals for a waterbody by designating its uses, setting criteria to protect those uses, and establishing provisions to protect water quality from pollutants. A water quality standard consists of four basic elements:
  1. designated uses of the waterbody (e.g., recreation, water supply, aquatic life, agriculture)
  2. water quality criteria to protect designated uses (numeric pollutant concentrations and narrative requirements)
  3. an antidegradation policy to maintain and protect existing uses and high quality waters
  4. general policies addressing implementation issues (e.g., low flows, variances, mixing zones)
By adopting water quality standards, states are able to determine which healthy waters need protection, which waters must be restored and how much pollutant reductions are needed. Consequently, these water quality standards set a goal for restoring and protecting a watershed over the long term.
Water quality monitoring provides the data to characterize waters and identify changes or trends in water quality over time. The collection of monitoring data enables states to identify existing or emerging water quality problems and determine whether current pollution control mechanisms are effective in complying with the regulations. The CWA requires that each state monitor and assess the health of all their waters and report their findings every two years to EPA. This list of data and findings is called the 305(b) report or "biennial water quality report."
Under section 303(d), monitoring data as well as other information, must be used by the states to develop a list of "water quality limited segments," i.e., waters that will not meet water quality standards for a particular pollutant even after a technology-based permit is in place. States must develop TMDLs, or Total Maximum Daily Loads, for every water body/pollutant combination on the 303(d) list.
The TMDL calculates the maximum amount of a pollutant allowed to enter a waterbody, also known as the loading capacity, so that the waterbody will meet and continue to meet water quality standards for that particular pollutant. The TMDL allocates that load to point sources, (Wasteload Allocation or WLA), and nonpoint sources (Load Allocation or LA) which include both anthropogenic and natural background sources of the pollutant.
In many cases, the TMDL analysis is the trigger for determining the source(s) of pollutants. A TMDL may contain WLAs only, LAs only, or a combination of both. Under the CWA TMDLs are not self-implementing, meaning EPA cannot enforce implementation of a TMDL once the analysis is complete. Although, if the TMDL WLA requires more stringent permit limits for point sources these must be implemented in the appropriate NPDES permits at the time of their renewal. If the TMDL identifies nonpoint sources of pollutants as a major cause of impairment, states can apply for EPA funded grants, called Section 319 grants. These grants can be used to fund state programs for nonpoint source assessment and control as well as individual projects.
(Source: http://www.epa.gov/owow/tmdl/intro.html, accessed 4/27/10)

How Water Body Impairments are Identified

How do states and other jurisdictions assess water quality?


Water quality assessment begins with water quality standards. States and other jurisdictions adopt water quality standards for their waters. EPA must then approve these standards before they become effective under the Clean Water Act.
Water quality standards have three elements: the designated uses assigned to waters (e.g., swimming, the protection and propagation of aquatic life, drinking); the criteria or thresholds that protect fish and humans from exposure to levels of pollution that may cause adverse effects; and the anti-degradation policy intended to prevent waters from deteriorating from their current condition.
After setting standards, states assess their waters to determine the degree to which these standards are being met. To do so, states may take biological, chemical, and physical measures of their waters; sample fish tissue and sediments; and evaluate land use data, predictive models, and surveys.
What are "Causes of Impairment"?
Where possible, states, tribes and other jurisdictions identify the pollutants or stressors causing water quality impairment. These causes of impairment keep waters from meeting the criteria adopted by the states to protect designated uses. Causes of impairment include chemical contaminants (such as PCBs, metals, and oxygen-depleting substances), physical conditions (such as elevated temperature, excessive siltation, or alterations of habitat), and biological contaminants (such as bacteria and noxious aquatic weeds).
What are "Sources of Impairment"?
Where possible, states, tribes and other jurisdictions identify where pollutants or stressors (causes of impairment) are coming from. These sources of impairment are the activities, facilities, or conditions that generate the pollutants that keep waters from meeting the criteria adopted by the states to protect designated uses. Sources of impairment include, for example, municipal sewage treatment plants, factories, storm sewers, modification of hydrology, agricultural runoff, and runoff from city streets.
(Source: www.epa.gov/waters/ir/attains_q_and_a.htm, accessed 4/27/10)

What is a "Total Maximum Daily Load" or "TMDL"?

What is a "TMDL"?

A scientific determination of the maximum amount of a given pollutant that a surface water can absorb and still meet the water quality standards that protect human health and aquatic life. Water bodies that do not meet water quality standards are identified as "impaired" for the particular pollutants of concern - nutrients, bacteria, mercury, etc. - and TMDLs must be developed, adopted and implemented for those pollutants to reduce pollutants and clean up the water body.
The threshold limits on pollutants in surface waters - Florida's surface water quality standards on which TMDLs are based - are set forth primarily in rule 62-302, Florida Administrative Code, and the associated table of water quality criteria.
What are the basic steps in the TMDL program? How does it work?
  1. Assess the quality of surface waters - are they meeting water quality standards?
  2. Determine which waters are impaired - that is, which ones are not meeting water quality standards for a particular pollutant or pollutants.
  3. Establish and adopt, by rule, a TMDL for each impaired water for the pollutants of concern - the ones causing the water quality problems.
  4. Develop, with extensive local stakeholder input, a Basin Management Action Plan (BMAP) that....
  5. Implement the strategies and actions in the BMAP.
  6. Measure the effectiveness of the BMAP, both continuously at the local level and through a formal re-evaluation every five years.
  7. Adapt - change the plan and change the actions if things aren't working.
  8. Reassess the quality of surface waters continuously. 
(Source: http://www.dep.state.fl.us/water/tmdl/index.htm, accessed 4/27/10)