Editor’s Comments: CMOM—What Does It Mean for Stormwater?

Sept. 1, 2001

The rules and regulations that affect your job—maybe even make it easier—aren’t always the ones intended for you. CMOM, which stands for Capacity, Management, Operation, and Maintenance, is a provision under the NPDES Sanitary Sewer Overflow rule. Its intent is to strengthen the requirements for what has been called “probably the most abused of all public utilities due to misuse and neglect,” the sanitary sewer collection system. And although many stormwater managers have plenty to focus on just in assimilating and complying with the NPDES Phase II Stormwater rule, the progress of CMOM also bears watching.

Stormwater managers in regions that have combined sanitary and storm sewer systems already know the problems caused by combined sewer overflows (CSOs). Though the content of a combined sewer system is destined for a wastewater treatment plant, overflows are common during large storms—exacerbated in many cases by an increased volume of stormwater runoff where urban development has increased impervious surface area in the watershed. When they occur, they constitute an immediate public health threat: in some cases outbreaks of illness have been attributed to pathogens in the overflow. Beaches may close, and concerns abound over fish and shellfish in receiving surface waters. Some cities, in the face of such emergencies, take drastic measures, treating the overflows with chemicals such as sodium hypochlorite to prevent the outbreak of human illness, and possibly undermining the rest of the year’s work by harming the aquatic ecosystems they’ve been trying to protect. Although sodium hypochlorite breaks down into sodium chloride, in its original form it is toxic to freshwater fish and invertebrates.

Many cities with combined systems are gradually converting to separate ones, getting rid of the CSO risk and opting to treat stormwater runoff less expensively by means other than treatment plants. While it may seem that stormwater managers in cities with separate storm sewer systems, or MS4s, have escaped the sanitary sewer problem altogether, that’s not entirely true. Illicit connections—sources that discharge anything into the storm sewer system other than stormwater, and especially illicit sewer connections—are still a concern, one that’s addressed under the Phase II stormwater rule. And overflows of the sanitary sewers themselves, while not technically under the “stormwater” jurisdiction, contribute greatly to surface water impairments. When bacterial contamination occurs at a public beach, for example, it falls at least partially to the stormwater organization to determine the source, whether it’s a leaking sewer system, contaminated runoff from livestock operations, wildlife, or some other cause.

This is where CMOM comes in. The rule requires publicly owned treatment works (POTWs) and municipal sanitary sewer collection systems to maintain and manage their systems, to ensure adequate capacity, and, in effect, to prevent sanitary sewer overflows under any circumstances. It also requires permitees to formulate short- and long-term plans to remedy any deficiencies in their systems.

Last January, in the final days of the Clinton administration, EPA Administrator Carol Browner approved the SSO Policy, including the CMOM provision, which was to be published in the Federal Register in preparation for its 120-day public comment period. Before that happened, the Bush administration placed a hold on new regulations, and although the process has been delayed, most permittees have continued preparing as though the SSO Policy will move ahead more or less as written. In many cases preparation includes adding staff and budget as necessary to inventory and assess the entire sewer system. This is good news for managers of MS4s, who won’t have to deal as often with the harmful effects of SSOs, and for the rest of us as well. After all, no matter what their source, once contaminants reach the beach, lakeshore, or river, they’re everyone’s problem.

About the Author

Janice Kaspersen

Janice Kaspersen is the former editor of Erosion Control and Stormwater magazines.