Bobbi Larson, Executive Director of CASA Provides Advice on El Nino Preparedness

With El Nino approaching California this season, we asked Bobbi Larson, Executive Director of California Association of Sanitation Agencies (CASA), for tips and advice for our members and agencies on how best to prepare for El Nino. In particular, what to do after a Sanitary Sewer Overflow (SSO). 

Sanitary sewer overflow (SSO) is a condition in which untreated sewage is discharged from a sanitary sewer into the environment prior to reaching sewage treatment facilities. When caused by rainfall it is also known as wet weather overflow.
Frequent causes of SSO spills include:

  • Blockage of sewer lines
  • Infiltration/Inflow of excessive stormwater into sewer lines during heavy rainfall
  • Malfunction of pumping station lifts or electrical power failure
  • Broken sewer lines

What was your experience at CASA with the 1997-98 El Nino? Have we come far in preparing California’s sewer systems for these potential El Nino storms?

Bobbi Larson, CASA Executive Director

Though I was not directly involved in the El Nino event of 1997-98, I do believe that California wastewater utilities are better prepared this winter. The statewide collection system general order (Order WQO 2006-003) requires the development of comprehensive sewer system management plans to address, among other things, adequate capacity to convey base flows and peak flows, including flows related to wet weather events.

In addition, the current focus on climate resiliency had led to greater awareness and preparedness regarding variability in conditions associated with climate change. Agencies must simultaneously plan for drought impacts—not enough water in the collection system– and extreme weather events—too much water all at once.

If El Nino does cause an SSO are you forecasting fines by the Regional Boards? What are their expectations?

The Water Boards’ expectations regarding collection system performance are set forth in the general order. The order requires an agency to take all “feasible steps” to eliminate sanitary sewer overflows (SSOs). In the event that an SSO does occur, the Regional Boards will look to whether the agency acted timely and appropriately to contain and mitigate the impacts of an SSO.

While there have been exceptions, generally I would not expect the Regional Boards to initiate enforcement actions against agencies that have acted in good faith to prepare, yet nonetheless experience system surges, failures or inundations due to heavy rainfall. One of the factors to be considered is whether the discharge was exceptional, unintentional, temporary, and caused by factors beyond the reasonable control of the agency. There are limits to what an agency can do to prepare for heavy rains, and the best plans in the world won’t change the weather.

Each Regional Water Board has region specific enforcement priorities. The coastal regions have tended to focus more on SSO enforcement as a top priority. Large unpermitted discharges to surface waters may trigger an investigation, but if the inquiry demonstrates that the utility acted prudently and reasonably and could not have prevented the violation I would not anticipate enforcement actions for civil penalties.

However, agencies should also be aware of the potential for third party (citizen initiated) enforcement, which is not governed by the State’s enforcement priorities.

Are you advising agencies to do any proactive work or communication with their Regional Board regarding El Nino?

Absolutely. Keeping the Regional Board (and fellow local agencies in the region) in the loop on planning and preparation is key. An understanding of the agency’s program in advance of the event is far more valuable than explaining it all after the fact—after an incident has occurred.

Does the State or Regional Boards have any programs to help agencies prepare for El Nino storms?

The Water Boards do have programs that can help in an emergency. For example, the Water Board has pre-certified certain emergency repairs, such as clearing sedimentation and vegetative growth from channels, under a Corps of Engineers permit to facilitate readiness.

Other agencies, such as the Office of Emergency Services and U.S. EPA Region 9 are also resources for El Nino preparedness.

Perhaps the most useful thing agencies can do is to communicate with one another, share ideas and strategies for being ready—as ready as they can be for something that can’t be precisely predicted.

The City of Montreal last month released 2 billion gallons of raw sewage into the St Lawrence River so it could bypass an interceptor and complete critical repairs. Have you ever heard of a California agency doing this? Would a California agency receive a permit to release raw sewage to complete repairs?

I am not aware of any releases of this untreated wastewater for repair purposes. However, the law and regulations do allow for limited planned bypasses, recognizing that having sound infrastructure is critical to a sustainable sanitation system. Under the regulations, a permittee may seek authority for a planned bypass, which does not cause effluent limitations to be exceeded, if the bypass is for essential maintenance to assure efficient operation.

The Los Angeles County Sanitation Districts undertook a planned bypass several years ago for the purpose of major maintenance on its ocean outfall—but I stress that the wastewater was treated and met all permit requirements. It was simply discharged at a location other than the permitted outfall.

If an unplanned bypass occurs at a treatment facility as a result of El Nino, and agency may be able to establish a bypass defense if it can show that the bypass was unavoidable to prevent loss of life, personal injury, or severe property damage, there were no feasible alternatives to the bypass, and the regional board is notified within 24 hours of the unplanned bypass.

Agencies should review their permit language regarding bypass and may also want to consult with the Regional Board in advance regarding the scope of what would be considered feasible alternatives in the context of El Nino storms.

Does California have the most stringent sewer system management regulations in the nation and, if so, why?

I am not fully conversant with the regulations in all 50 states, but I can say that California’s regulatory system is the most comprehensive of which I am aware. The enforcement presence in California is also greater than in many areas of the country, with the Water Boards, EPA and third party plaintiffs all quite active.

When the general permit was adopted in 2006, the idea of permitting all publicly owned collection systems separately from the treatment works was novel and drew significant interest from our colleagues in other states.

Many agencies in the east and midwest operate combined sewer and stormwater systems, and the focus of regulations and enforcement in these communities has been on upgrading combined systems through both gray and green infrastructure to reduce the discharge of untreated flows to waters during storms.

California agencies have done a commendable job of investing in their systems and embracing the concept of “the collection system of the future.” 95% of agencies covered by the general order have completed and certified their sewer system management plans.

The most recent Water Board compliance report for SSOs confirms a reduction in spills over time as the permit has been implemented. On a day-to-day basis, California’s wastewater agencies are performing at a high standard. The prospect of El Nino storms presents a major challenge and it is in our collective interest to be as ready as we can be.


Thanks Bobbi for the insights!

How is your agency preparing? Or what is your greatest concern about these potential El Nino storms? Tell us in the comments section below…


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Megan Barillo

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