When Congress approved the Clean Water Act in 1972, it required states to monitor their waterways and “from time to time” submit lists of areas that did not meet water quality standards to the EPA. For those “impaired” waterways, the states were to identify the pollutant (or pollutants) that caused the impairment and determine the Total Maximum Daily Load.

A TMDL is a calculation of how much pollution a given area of water can receive and still meet its water quality goal with a margin of safety factored in. A TMDL is required for each pollutant that contributes to the impairment in a given body of water. Therefore, while 20,000 water bodies, or segments of water bodies, are impaired nationwide, about 40,000 TMDLs are needed to address the pollutants.

Although the TMDL rule was on the books, the EPA and states focused their efforts on other areas — such as forcing pollution reductions from factories, wastewater treatment plants and other “point sources” — for years.

Beginning in 1986, and accelerating in recent years, environmental groups began filing lawsuits against the EPA for failing to force states to list all of their impaired waters and develop TMDLs.

As a result, for 17 states — including Pennsylvania, Virginia, Delaware and West Virginia — courts have set timetables for all waterways to be monitored and TMDLs developed. Cases are pending in many other states, including Maryland.

Existing TMDL regulations are often frustratingly vague. How long it should take to develop a TMDL — and whether it had to be implemented — is not spelled out. At the same time, existing rules prohibit any new discharges of the impairing pollutants in any waterbody that is not meeting the water quality standard for those pollutants.

To clarify the issue, the EPA proposed broad new rules last fall and took comments until Jan. 20. The new rules seek to guarantee that TMDLs will be implemented, regardless of where the pollution was coming from. In the past, it was a straightforward calculation to determine the amount of reductions that might be needed from a regulated point source to achieve water quality criteria. But it was unclear what to do when most of the pollution comes from unregulated runoff, or “nonpoint” sources, and few TMDLs involving nonpoint sources have been implemented

Under the proposed new rules, states must develop an implementation plan for a TMDL which includes a “reasonable assurance” that the pollution reductions will be achieved from point sources and nonpoint sources.

For point sources, that means permits would have to be revised to meet TMDL requirements. For nonpoint sources, voluntary actions or local ordinances and zoning requirements may be acceptable, but states would have to show that adequate funding or other mechanisms are in place to achieve the results on a predictable timetable.

If monitoring shows that the goal is not being achieved, the proposed rule says states “may need to establish a regulatory approach” to control runoff. That could mean requiring sources of runoff to have permits, just like factories.

If states don’t take enough actions to control runoff pollution, the rules give the EPA authority to designate certain operations, such as animal feedlots, aquaculture facilities and certain forestry activities as point sources and require discharge permits.

Under the new rules, states would have 15 years to complete TMDLs. The rule calls for an implementation timetable for each new TMDL, but does not set a specific deadline for completing the cleanup.

Until TMDLs are developed, the new rules seek to prevent the further degradation of a waterbody by requiring that any large new — or significantly expanded — discharge source offset its pollution. Offsets may be achieved from either point sources of from nonpoint sources. Generally, the rule proposes that the offsets be 1.5 times greater than the amount of the new discharge.