What is the Environmental Protection Agency's (EPA) proposed peak wet-weather discharge policy and how will it affect utilities?
Miles: The EPA's policy on the treatment of effluent overflows through peak wet-weather discharge-or wastewater blending-now states that diversions of wastewater around treatment units can only be allowed where there are "no feasible alternatives." Many utilities perform blending in varying degrees as part of their wet-weather management process. As such, the implications of the policy are site specific.
Matthews: Yes, the effects of the policy are really contingent on the utility's existing sewer programs. Some are very developed and in the process of phasing out their use of blending. These will need to demonstrate their alternative treatment or plans for system improvements compliant with EPA. Others may need significant enhancements and must demonstrate the necessity for blending peak flows.
Utilities will be required to perform an in-depth utility analysis of their wastewater treatment plant to the National Pollutant Discharge Elimination System (NPDES) permitting authority, which will decide as to whether the demonstration of "no feasible alternative" has been made. In many cases, this policy will substantially alter the economic analysis of how much sewer rehabilitation should be done in a sewer system.
What should utilities begin doing to prepare for compliance?
Miles: Initially, facility screenings should be conducted to determine the likelihood of making a successful demonstration for the need to blend. This is a cost-effective approach for accurate decision making before launching into a full-scale analysis. The analysis itself, which will be examined by the permitting authority to determine NPDES approval/renewal, will require the utility owner to:
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document current capacities
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estimate the level and frequency of peak wet weather flows
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evaluate treatment technologies
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assess community funding for improvements
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propose a protocol to monitor recombined flows
What kind of technologies and treatment alternatives are available?
Matthews: Findings from the analysis will help determine the most appropriate and efficient treatment strategy. As facility owners resist the presumption that blending is forbidden entirely, the more options they will have. Even well-run systems are pushed to the limit by severe wet-weather events and will need to prepare for those potential exceedances.
Apart from conventional biological methods, utility managers will need to become familiar with physical/chemical treatment techniques and be knowledgeable of their associated operations and maintenance. Infiltration/inflow reduction and equalization storage are conventional techniques to reducing sanitary sewer overflows and managing wet-weather flows, but are expensive and require significant physical space to operate. Physical/chemical options are a much more viable and cost-effective alternative, namely, the use of high-rate clarification. This method employs the ballasted flocculation process which yields benefits, including:
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Compact size: Five to 15 percent the size of conventional treatment trains; ideal for municipalities with limited space
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Quick startup: Storm induced emergency flows reach peak efficiency in less than 20 minutes
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Effectiveness: Removes more than 85-percent total suspended solids, 65 percent biological oxygen demand, and up to 90 percent phosphorus.
Also, unlike conventional biological treatments, ballasted flocculation can treat a wide range of flows without reducing pollutant removal efficiencies when there are large increases in flow
How is CDM helping clients?
Matthews: We have a strong and extensive resume in delivering wet-weather management solutions-spanning from initial utility screenings and treatment plant design and construction, to program training and asset management and consulting. We've provided all services for conducting wet weather management analyses, and our experts have implemented sewer rehabilitation programs and alternative technology for, in lieu, and as part of a utility's need for blending.
Miles: We have performed collection system flow monitoring/modeling of wet weather-flows and hydraulic performance; engineering inspections of assets and process elements; and developed rate studies/models; comprehensive capacity, management, operation, and maintenance programs; asset management programs; and environmental management system programs as well. As the EPA's policy on blending remains a hot topic for the industry, utilities should seek education in treatment alternatives and initiate facility screenings to determine next steps for compliance, and ultimately, for improving water quality.
S. Wayne Miles, P.E., BCEE, is a vice president who leads CDM's infrastructure rehabilitation services group.
Robert L. Matthews, P.E., BCEE, is a senior vice president specializing in the planning of wastewater public utilities projects and national wastewater regulations.