In Control of Discharge

Aug. 17, 2004
As DOTs monitor storm water, they need to be aware of the call for more stringent monitoring

About the author: Bloom serves as a senior engineer and water quality compliance specialist for PBS&J, Houston.


Storm water discharge requirements are tightening, and transportation agencies may find themselves pinched if they don’t plan for compliance. Agencies diligently working to reduce storm water pollutants to the maximum extent practicable (MEP) may find themselves facing numeric effluent limits based on total maximum daily load (TMDL) studies. In time, “TMDL” will go from a term principally discussed at storm water and water-quality conferences to part of transportation agencies’ everyday vocabulary.

All storm water dischargers must obtain a National Pollutant Discharge Elimination System (NPDES) permit as outlined in the Clean Water Act. Failure to comply with NPDES permit regulations can result in civil and criminal penalties and exposure to third-party lawsuits. Prior to March 2003 only municipal separate storm sewer system (MS4) operators serving populations over 100,000 had to meet NPDES permitting requirements. Now, in what is termed “Phase II” of the storm water regulations, any MS4 operator located in an area defined by the U.S. Census as “urbanized” must comply as well.

Transportation agencies are not exempted from NPDES permits. Agencies are located within rights-of-way that intersect urbanized areas, and they own and operate storm water facilities, namely culverts and channels.

Load restrictions

Section 303 of the Clean Water Act requires states, territories and tribes (referred to as states) to establish water-quality standards for all streams, lakes and rivers. A water-quality standard includes a use designation, defining beneficial uses of the resource and criteria to protect the designated use. Typical use designations include “contact recreation,” “drinking water supply” or “aquatic life propagation.” Water quality criteria specify safe levels of toxic pollutants, such as dissolved copper, or other requirements, such as dissolved oxygen levels for fish respiration.

Section 303 also requires states to identify waters not meeting water quality standards and then determine a TMDL for each pollutant exceeding standards. A TMDL is a water quality study that determines the maximum amount, called “load,” of a particular pollutant that can enter a receiving water without causing the receiving water to exceed standards. Because impaired waters are receiving an elevated pollutant load, water-quality managers must figure out how to reduce discharge loads to the water body to achieve the TMDL load target. Load reductions can be achieved using voluntary approaches or, more typically, through reissuing NPDES permits.

Unfortunately for MS4 operators, many impaired waters nationwide are located within or near urbanized areas and are impaired by pollutants present in urban runoff. To make matters potentially worse, most MS4 operators are now subject to NPDES permitting, so storm water load reductions required by the TMDL can be achieved directly from MS4 operators by imposing stricter permit conditions. This means that transportation agency MS4 permits will be used as TMDL implementation tools to achieve TMDL-required load reductions. Over time, MS4s, including transportation agencies, will certainly face increased monitoring requirements, increased best management practices (BMP) implementation and possibly specific load reduction targets in the form of effluent limits.

Water rescue

Currently, most MS4 permits contain narrative conditions stipulating that pollutant discharges in storm water must be reduced to meet the MEP standard by implementing BMPs. Many MS4 permits promulgated under the Phase II program are anticipated to contain similar conditions.

However, some recently proposed TMDL implementation plans, particularly in the west, have called for the addition of enforceable effluent limits aimed at improving impaired waters. Highway departments have been named as permittees or have been specifically referenced in these permits.

One noteworthy case is the Los Angeles River trash TMDL. The California Regional Water Quality Control Board proposed this TMDL in 2001. Listed permittees include Los Angeles-area communities and the California Department of Transportation (Caltrans).

As drafted, this TMDL called for revisions to Los Angeles-area MS4 permits to include monitoring requirements for trash and reductions in trash discharge load to zero pounds over 13 years. As might be expected, this TMDL is the subject of litigation, so its final provisions are not known at this time. MS4 operators should track its final outcome to prepare for future implications for their own permits.

Another case of numeric effluent limits placed or implemented in an MS4 permit is found in California’s Lake Tahoe watershed. Municipal MS4 operators (Placer and El Dorado counties and the city of South Lake Tahoe) have been issued MS4 permits with effluent limits on total nitrogen, total phosphate as phosphorus, total iron, turbidity and grease and oil. The limits, included in the Lahontan Regional Water Quality Control Board’s basin plan, apply to “surface runoff which directly enters Lake Tahoe or a tributary thereto.” Pollutants generated by Caltrans are considered by the Lahontan board to be covered under Caltrans’ statewide NPDES permit, although the current Caltrans permit is written to the MEP standard.

In a permit issued by the Oregon Department of Environmental Quality, MS4s discharging to Oregon’s Columbia Slough must meet the waterway’s TMDL for dissolved oxygen, pH, bacteria, toxics and organic compounds. Although the Oregon Department of Transportation was not ultimately named a co-permittee in the Columbia Slough permit, and the transportation agency’s own MS4 permit is written to an MEP standard, the Columbia Slough permit indicates the state’s willingness to move toward benchmark compliance levels.

Other MS4 permits that include numeric waste load allocations or limits include the Hickory Run permit in Washington, D.C., with oil and grease numerically regulated, and the Washington State Department of Ecology’s North Creek fecal coliform TMDL.

Time to track

While there are only a handful of permits now incorporating numeric effluent limits, the trend is somewhat worrisome. TMDLs are beginning to transform MS4 permits by shifting them from the MEP standard to numeric effluent limits. This shift will almost certainly increase transportation agency compliance costs, but it is likely to happen gradually.

MS4 operators appear to have adequate time to plan compliance approaches, participate in TMDL development and implementation planning at the watershed level and study the effectiveness of BMPs for their jurisdictions. Because numeric limits come hand-in-hand with monitoring and reporting requirements, MS4 operators will benefit from planning and implementing enhanced monitoring and reporting tools as this trend continues over the next five to 10 years. Transportation agencies can choose from a wide range of effective systems for collecting field data, tracking illicit discharges, managing data and reporting to regulators. Web-based applications based on agencies’ existing geographic information systems appear to be the most comprehensive, and most simply interfaced, means of meeting the future’s more stringent requirements.

NPDES storm water permits are likely to change as TMDLs are developed and implemented. But transportation agencies still have time to participate in the TMDL process and create innovative programs to track and reduce the effect of urban runoff on receiving waters and to reduce pollutant loads.