Like many American cities, Lynchburg, Va., faces a combined sewer overflow problem. By following a strategy of performing the least costly work first, the city has made significant progress on reducing overflow volumes while developing a new holistic approach to handle the most challenging aspects of the program.

The Lynchburg public water system is one of the oldest in the country, with the first water pumped from a dam on the James River to a reservoir in 1829. In almost two centuries, the public system has grown to provide water, sewer and stormwater services to 75,000 residents of the city. The department also provides wholesale sewer and water services to nearby Amherst, Bedford and Campbell counties.

Nicknamed The Hill City, Lynchburg takes advantage of its geography with a gravity-fed sewer system, requiring no public lift stations. The system incorporates 450 miles of sewer lines, including the combined sewer segments. Pipes are made of various materials, including clay, concrete, ductile iron and some corrugated metal. The oldest pipes date back more than a century.

The CSO problem primarily affects the James River and its tributaries, which ultimately affects the water quality of Chesapeake Bay.

Survey identifies CSO points

An infiltration/inflow evaluation survey (IIES) conducted between 1974 and 1979 used a computer model provided by the U.S. Army Corps of Engineers to help quantify the extent of the city’s CSO problem. It identified 132 CSO points and offered direction for initial sewer improvement efforts.

Lynchburg invested more than $4 million during the 1980s to close several overflow points and to collect data to help fashion a long-term control plan (LTCP) for CSOs.

The survey was updated in 1989 using more sophisticated computer models to estimate the frequency, volume and pollutant loads of each CSO event under various rainfall conditions. The study also parceled the city’s combined sewer territory into 59 different project areas, ranked according to criteria that included their impact on the James River. The original LTCP was comprised of three components, which included complete separation of the combined system and elimination of all overflow points, interceptor replacement, and rain leader disconnection.

The city formalized its approach to the CSO problem by negotiating a unique consent order with the state Department of Environmental Quality in 1994.

“We refer to it as one of the best consent orders in the country because it has no timeline,” says Timothy A. Mitchell, P.E., director of water resources with the City of Lynchburg. “We were proactive in negotiating with the state and the order is structured on our ability to afford to implement the program.”

The order, the first of its kind to be approved by the Environmental Protection Agency, requires the utility to tie the sewer bill to at least 1.25 percent of the city’s median household income.

Lynchburg soon began to eliminate additional CSO points. The efforts were financed, in part, by a combination of state and local grants and low-interest loans through state revolving funds. An update of the LTCP in 2000 reaffirmed that the three original components were still the best approach to meeting water quality goals.

“Our approach was to pick the low-hanging fruit first,” says Mitchell. “We targeted the most cost-effective ways to minimize CSOs within the budget delineated by the consent order while working to upgrade, maintain and repair the system.”

Sewer system survey

In 2011, the department initiated a $1.2 million sewer system evaluation survey conducted by the city’s consulting engineering firm, Brown and Caldwell. The study placed temporary flowmeters at 30 locations. It also included extensive smoke testing, night flow isolation and manhole inspections.

“The study was aimed at controlling the contributions of the sanitary system to volumes of sewage that could lead to sanitary sewer overflows,” says Mitchell.

“Those include pipe failures and defects, inflow and infiltration problems, and blockages caused by roots, grease and debris. The study provided a lot of good information to enhance the CSO plan.”

The study’s conclusions provided the department with a model on which it based its current sewer Management, Operations and Maintenance program.

The city currently contracts out new sewer construction and replacement, but performs its own repairs. Sewer lines are replaced with PVC pipe and larger interceptors are replaced with ductile iron or concrete.

The city’s Utility Line Maintenance Division maintains and repairs all water and sewer lines, valves, fire hydrants, manholes, inlets and clean-outs, and installs new service connections. It also responds to water main breaks and sewer overflows. The division fields five maintenance and repair crews, while a sixth repairs inlets, meter boxes and manhole tops.

Four wastewater maintenance crews clean and televise sewer lines, manholes and storm inlets. The crews operate two Vac-Con combination trucks and two Ford F-450s used as CCTV camera trucks with camera equipment by RS Technical. Crews televise and clean up to 150,000 feet of sewer line each year.

Lynchburg has, in the past, also contracted with Insituform Technologies, to provide cured-in-place pipe lining, and with A.J. Conner General Contractor, Inc. to line sewers using Ultraliner PVC Alloy Pipeliner by Hydroliner.

By 2012, the city had eliminated 112 of the original 132 overflow points, reducing almost 80 percent of CSO volume. It had replaced 26 miles of interceptors, disconnected 70 percent of rooftop downspouts, and 36 of 59 priority projects had been completed, designed, or were under construction. Estimated amounts of solid pollutants had also been cut down to size.

The turning point

All the city’s progress, however, also represented a turning point.

The city had already spent $233 million on the CSO program. Funding received from the American Recovery and Reinvestment Act had been exhausted. Increases in the city’s median income had stagnated, and the city’s sewer fund was out of debt capacity. The city became concerned that if it slowed down or halted its CSO program for an extended period of time, it could invite a review of the existing consent order by the EPA, which had ordered sewer rate increases in some cities by 2 percent of median income.

“We were also running out of high-yield projects that could result in significant CSO reductions,” says Mitchell. “And we were closing in on the 4 square miles of our historic downtown where we knew that the cost of CSO construction projects would increase significantly. That, combined with more stringent stormwater requirements, warranted a more holistic look at our water quality programs and goals.”

If the city continued with the same approach, the department estimated that it could expect to pay another $280 million to eliminate the remaining 20 CSO points over an additional 30 years.

Doing things differently

“At that point, we decided we were going to try to do things differently,” says Mitchell. “Instead of settling for the status quo and continuing with our original long-term plan, we invested $3 million on a study by environmental engineering firm Greeley and Hansen that would take a scientific approach to looking at the system holistically. It would look at the goal of meeting water quality standards in the James River and its tributaries within the city, which demonstrate a bacteria  impairment, and develop the best solution by looking at both our CSO and stormwater programs.”

The consultants developed a complex sewer model, installing nine rain gauges and 72 flowmeters, while incorporating information on numerous pollutant sources, 1,700 pipelines and 129 drainage basins.

More than 2,800 water samples were taken from various streams and the James River during four events representing both dry and wet weather. These were used to characterize pollutants and build a complex hydrologic and hydraulic (H&H) model of the river and streams. The study also characterized and quantified non-CSO contributors to pollution, such as agricultural, residential and urban stormwater, which would still need to be addressed regardless of the city’s approach.

More than 50 options were tested using both the H&H and sewer models and evaluated in terms of annual overflow frequency and volume, and water-quality impact as measured by potential pollutant concentrations in the James River and its tributaries. Each scenario was subjected to a cost-performance analysis.

“The consultants worked closely with city staff and the DEQ to ensure that proposed measures would be both feasible and acceptable to regulators,” says Mitchell.

The approach recommended by the study will aim to reduce more than half of current annual overflow at an estimated cost of about $60 million — a savings of $220 million. Additionally, the State of Virginia awarded the city a $30 million grant for half of the remaining program, in part due to the new approach, further ensuring rapid completion of the program.

Major components of the plan include:

• Separating sewers at just five of the remaining overflow points and avoiding the most costly and disruptive downtown projects
• Eliminating two major overflow points in downtown Lynchburg
• Maximizing wet-weather treatment capacity at the wastewater treatment plant, including a new headworks designed to remove additional organics
• Creating an additional temporary flow storage facility at the wastewater treatment plant
• Installing flow regulators to handle combined sewer volumes more efficiently
• Continuing the downspout disconnection program; homeowners receive cash incentives to disconnect downspouts, while businesses are reimbursed based on the volume of stormwater they divert from rooftops (see sidebar)
• Utilizing cost-effective green infrastructure, such as rain gardens and pervious pavement

“By using this multi-pronged approach, we can achieve overall better water quality results in a fraction of the time — within the next decade — and at a significantly reduced cost,” says Mitchell. “When the program is complete, the system may still experience overflows, but it will be overflowing less often, at lower volumes and represent a higher quality of overflow.”

The plan, however, still requires public participation, State Water Control Board approval, and possible EPA approval.

Mitchell says he’s not only confident that the city will move forward on the new plan, he believes the holistic approach to CSOs may be beneficial for many of the 700 U.S. cities facing CSO challenges.

“Undertaking the study that helped devise this solution presented us with some risk, but it’s a risk that paid off,” he says. “I’d advise other cities facing similar CSO and wet weather issues to explore a more holistic approach to achieving their pollution reduction goals.”