Air Quality

Water Quality

INCOG's Role
Regional Water Quality Programs
Pollution and Impairment
Total Maximum Daily Loads (TMDLs)
Resources and Links


Energy Management

Metropolitan Environmental Trust (M.e.t.)



Point Source vs. Nonpoint Source
In the past 10 years, wasteload allocation studies have become more complex by adding nonpoint source load assessments. Nonpoint sources are different from the discrete single pipe discharges of point sources that come from a treatment facility. Nonpoint sources have no discrete discharge pipe, and they are from pollutant sources that do not undergo any type of waste treatment. Further, they are usually associated only with rainfall runoff, so under dry conditions, nonpoint sources are usually minimal or non-existent.

Characterizing and calculating nonpoint source loads is very difficult, and the scientific investigations and modeling of nonpoint sources is still actively evolving. Also, most nonpoint sources do not have permit limits and are not regulated. Exceptions are discharges from Confined Animal Feeding Operations (CAFOs) and municipal stormwater systems regulated as Phase I and Phase II permittees.

A study that incorporates point source wasteloads, nonpoint source loads and includes a margin of safety calculation is called a Total Maximum Daily Load (TMDL). TMDLs are now routinely used to set point source discharge permit limits. A TMDL can address bacteria, dissolved oxygen, turbidity, metals, pesticides or any other type of pollutant. However, in Oklahoma the majority of TMDLs have addressed only dissolved oxygen to date. Bacteria TMDLs are beginning to be performed, and within a few years hundreds of pathogen TMDLs across Oklahoma will be completed. Turbidity TMDLs are expected to also be started within a few years.

Since most of these new pathogen TMDLs have a significant nonpoint source component, they will be difficult to implement load reductions. This is for two reasons: 1) most land use related bacteria sources such as cattle production are unregulated nonpoint sources, and 2) many bacteria sources are not associated with human activities at all but are instead from natural background sources.

Future TMDLs for turbidity and pesticides (the other major causes of stream impairment in Oklahoma) will also be difficult to implement reduction strategies, particularly in urban areas. Turbidity in streams is frequently caused by stream bank erosion which is often related to too much impervious surface (e.g. from parking lots, streets and rooftops). Pesticides in urban areas frequently come from individual home use. Control of home chemicals is largely accomplished through public education programs and individuals taking personal responsibility for how they apply and dispose of chemicals.

Rural agricultural nonpoint sources are addressed in a TMDL implementation strategy by deploying voluntary measures. A Watershed Base Plan may be written that identifies the most likely pollutant sources, and agencies such as the Oklahoma Conservation Commission and Oklahoma State University Extension Service can bring resources into the watershed to encourage voluntary pollution reduction projects.

Regulated treatment plant point sources must meet numerical effluent limits. Their discharge permits will have mandatory compliance strategies, and there are stiff penalty provisions for failure to comply. Stormwater permitted cities and counties within TMDL watersheds must implement Best Management Practices (BMPs) to control pollution in runoff.

TMDLs will continue to be an important part of water quality assessment and for implementing effective pollutant control strategies, both in urban and rural settings.