Sewers under pressure
Which is the correct answer to the following question?
Local governments should fix their sanitary sewer systems because:
a) Sanitary sewer overflows (SSOs) may result in Clean Water Act violations that pose fines reaching $25,000 a day.
b) SSOs can cause sewers to collapse or can create other dangerous situations, such as floods.
c) Cost-effective technology to fix the sewers, as well as help prevent overflows, exists.
If you answered a, b or c, you were correct. And, if those reasons are not sufficient, then know that local governments likely will have to fix their wastewater collection systems because of federal rules requiring it. The U.S. Environmental Protection Agency’s (EPA) SSO control program has been in the works for several years, and, when enacted, the program will require wastewater systems with National Pollutant Discharge Elimination System (NPDES) permits and satellite collection systems that experience SSOs to implement a comprehensive capacity management operations and maintenance (CMOM) program. EPA says that more than 50,000 communities need to fix their aging sewers to control SSOs, the cost of which only will be part of the approximately $450 billion the agency estimates that local governments will have to spend to repair their wastewater infrastructure by 2019.
The triple threats of wet weather, aging sewers and insufficient preventive maintenance continue to cause problems for collection systems, such as systemic basement backups and odors. Addressing those problems and SSOs, as well as handling and treating peak flows and other compliance concerns, can present daunting financial challenges to many communities. However, many communities are using cutting edge, cost-effective advanced processes, including high-rate clarification (HRC) treatment of peak flows, equalization of excess flow and asset management programs, to better focus maintenance efforts and rehabilitation resources.
Managing peak flows
Storm-induced peak flows are one of the key causes of SSOs. When flows overwhelm collection systems and treatment facilities, many communities are faced with untreated overflows and bypasses, leading to environmental pollution and enforcement fines. In late 2003, EPA issued a draft for a national blending policy, which provides a consistent set of guiding principles for wastewater treatment facilities to use when treating all peak wet weather flows while meeting their NPDES permit limits.
HRC, also known as ballasted flocculation, can economically treat the peak flows that most communities experience. HRC blends peak flows with flows that travel the full treatment process prior to discharge. HRC treats 55 gallons per minute per square foot. By comparison, primary clarification operates at one to two gallons per minute per square foot.
Because HRC is a physical rather than a biological process that requires a steady flow, HRC treatment systems can be started in less than 15 minutes and only when needed. An HRC system also is significantly less expensive to build than conventional secondary wastewater treatment facilities because it generally requires as little as one-tenth the amount of land.
HRC treats peak flows to a suspended solids removal rate that is 10 times greater than the clarifier solids removal rate. The process removes 85 percent to 95 percent of solids, reduces biochemical oxygen demand by approximately 60 percent and removes other pollutants.
Bremerton, Wash., built the nation’s first stand-alone combined sewer overflow treatment facility using HRC and ultraviolet disinfection technology in 2001. The city, which generates 1 million gallons per day (mgd) in daily flow, but as much as 14 mgd during rainy weather, installed the system to treat sewer overflows and improve water quality.
During heavy rainfall, Bremerton’s peak flows are diverted to the HRC system, treated and then discharged to ecologically sensitive waters. By using the system, Bremerton has drastically reduced pollutants in its discharges and spent about $35 million less than the cost of expanding its conventional treatment system. “Where costs for expansion are prohibitive, an HRC treatment system for infrequent wet weather discharge is a cost-effective option,” says John Poppe, wastewater manager of Bremerton Public Works and Utilities. Bremerton plans to implement a second HRC treatment unit at the city’s wastewater treatment plant to further reduce the city’s total maximum daily loads.
Other communities also have built HRC systems to bolster their wet weather treatment capacities. St. Bernard Parish, La., a community of 67,000 residents, upgraded its Munster wastewater treatment plant to 20 mgd to treat its increased flows and to comply with permit requirements. A 110-mgd peak flow HRC design, the first EPA-approved HRC parallel treatment system, currently is being constructed at the Fort Worth, Texas, Village Creek wastewater treatment plant.
Storing peak wet weather flows is another way to reduce untreated discharges. The method has proven to be a cost-effective way of handling peak flows without requiring additional treatment or conveyance capacity. Also, by using storage to equalize the flows through the plant, operators can improve treatment effectiveness and streamline operations. As part of an aggressive SSO mitigation plan, Charlotte-Mecklenburg (N.C.) Utilities uses flow equalization at three of its water reclamation facilities and has reduced wet weather overflows in portions of its system by about 90 percent.
Controlling flow in real time also helps prevent SSOs by manipulating changing system flows, or storing or diverting flows to areas of the system with available capacity. Milwaukee currently is implementing a sophisticated approach to real-time control (RTC) of its deep tunnel system for SSO management. The approach uses measured flow levels and rainfall data to predict tunnel inflows. Based on the predicted volumes, the RTC system adjusts inflow control gates to optimize the system’s operation during wet weather and to prevent SSO discharges.
EPA’s draft SSO program requires utilities to routinely evaluate and improve their sanitary sewer systems, which will reduce Clean Water Act violations (untreated discharges), extend the life of the wastewater infrastructure and improve customer service. Through preventive maintenance and rehabilitation programs, utilities will reduce SSOs, basement backups and odor problems over time. In addition, the CMOM program in the pending SSO regulation will require communities to implement an effective maintenance program, establish an asset management plan and address existing sewer system overflows to stay ahead of problems.
Many city officials and utility directors are concerned about the costs of SSO compliance and question how communities will pay for it. Increased costs will lead to higher sewer rates, which some residents may be unable to afford.
Currently, many utilities only fix the failing or failed parts of the system, which is costly and potentially dangerous, as, for example, sewer collapses can result. Not only is that type of emergency response expensive, repairs are not long-term solutions and can lead to even larger problems. Preventive maintenance programs are a cost-effective way to improve sewer operations and reduce customer complaints.
San Antonio, Texas, is developing a CMOM plan to reduce the frequency and severity of SSOs and emergency response costs, and to provide a more effective way to notify the public when overflows occur. “Our short-term goal is beginning an aggressive preventive maintenance program in the city, which, in the long term, should reduce customer service problems,” says Jerome Iltis, San Antonio Water System (SAWS) director of water distribution and wastewater collection.
To change from a reactive maintenance program to a preventive and planned one, SAWS increased the frequency of system-wide and closed-circuit TV inspections of the wastewater collection lines, expanded its system-wide flushing program and continued lift station inspections. SAWS also developed standard operating procedures, taught personnel to perform preventive maintenance work at several of its facilities and purchased additional equipment. SAWS’ goal is to achieve 100-percent CMOM compliance within two years.
Raleigh, N.C., is reducing SSOs by focusing on utility performance to determine where improvements could be implemented and system problems solved. By investigating key CMOM areas, the city is identifying ways to improve its sewer system, such as focusing on trouble spots that can be remedied quickly to eliminate dry-weather overflows and budgeting for short- and long-term needs.
The city already has seen substantial improvements in the integrity, operations and overall performance of its wastewater collection system. An annual sewer rehabilitation program eliminated a number of chronic SSO locations, reduced the city’s operations and maintenance expenses, and increased conveyance system capacity.
Raleigh is systematically assessing and rehabilitating its collection system, composed of 50- to 100-year-old vitrified clay pipe. The program addresses major structural defects, including failed joints, pipe sags and damaged lines from nearby construction. Those problems, in conjunction with grease loads and root penetration, require repeated attention from city maintenance crews.
“We can show that rehabilitation at these sites has [reduced] maintenance costs and [eliminated] potential SSOs,” says Jack Moyer, Raleigh’s assistant public utilities director. “[The program] has allowed us to justify increasing our rehabilitation budget steadily over time so we can continue to reinvest in the system.”
Age, chronic maintenance and damage present numerous challenges to collection system efficiency — from discharges and limited capacity to planning and financing sewer rehabilitation. Addressing structural conditions is a major capital expenditure for many communities. However, newer techniques, such as trenchless technologies, are cost-effective, minimize impact to property and lessen the disruptions to communities. Increased investments in sewer rehabilitation programs have helped communities improve system integrity, reduce maintenance costs, improve customer service, and comply with the Clean Water Act and other regulations.
To upgrade its 150-year-old brick combined sewer system, Newark, N.J., used non-invasive, cured-in-place pipe (CIPP) technology. CIPP, a trenchless technology, extends sewer system life by 50 to 100 years and is much less expensive than conventional open-cut replacement. In addition, CIPP allowed Newark to upgrade its sewer system without compromising the historic sewers or disrupting traffic in major thoroughfares.
CIPP uses water to install and invert a felt liner impregnated with polyester resin through existing manholes. Water pressure holds the liner tight against the existing sewer wall; then, the water is heated to activate the resin and cure the new pipe.
Upgrading Newark’s brick sewers lowered long-term improvement costs, improved system performance and safeguarded the public by eliminating potential dangers. Newark’s rehabilitation program, funded by $23 million in EPA grant money, included closed-circuit TV inspection and a geographic information system to assess the sewers’ structural condition and develop repair priorities. The city has rehabilitated more than 20 miles of pipe, including a 108-inch diameter pipe that is the largest CIPP installation in the country.
While the pressure to adjust to new technologies, regulations and customer concerns can make it difficult to plan, much less operate, a wastewater system, addressing the structural condition and maintenance of sewers now will yield significant long-term benefits and capital costs savings. Identifying the problems and their potential solutions is the smart way to avoid being thrown into the regulatory soup that is brewing.
Robert Matthews is senior vice president and Wayne Miles is vice president for Cambridge, Mass.-based CDM. Matthews is based in Fort Myers, Fla., and Miles is in the firm’s Raleigh, N.C., office.
The key elements of a sound CMOM program
Adequate capacity during both dry and wet weather
Effective overall system management, including mapping, maintenance tracking, training and supervision
Efficient operations, as measured in spending, equipment performance and efficiency
Regular system maintenance
You know you have a problem with your sewer system when…
Your customers’ bathtubs are considered “temporary storage.”
Your manhole covers have labels that read, “return postage guaranteed.”
Your sewer maintenance supervisor wins the blue ribbon at the state fair for the largest easement-grown vegetables.
The mayor campaigns on the platform “A backflow prevention valve for every home!”
Your maintenance staff refers to a manhole as “Ol’ Faithful.”