By Joseph Lynn Tilton

Which came first - storm sewers or sanitary sewer lines? In many instances, storm sewers were constructed first to prevent flooding in rapidly growing cities. It became a matter of convenience to connect the odorous backyard privies to the storm sewer - thus, the advent of the combined sewer system. In other cases, sanitary sewers were built, and as the cities grew, increasing amounts of stormwater runoff were routed into them. In either case, combined sewer overflows (CSOs) occur when the stormwater flow combined with the base sewage flow exceeds the design capacity of the trunk or interceptor sewer.

Given the pollutants associated with stormwater, the question of separation becomes problematic, particularly in densely populated areas. Ultimately stormwater abatement needs to be addressed in much the same way as CSOs are per the stormwater regulations. The cost of CSO treatment needs to include the immediate and ultimate cost of stormwater abatement.

"The important thing to note is that the driving force for regulatory agencies, such as EPA [the Environmental Protection Agency], is the public health concern," reports Peter Moffa, senior vice president for Brown and Caldwell in East Syracuse, NY. Moffa, who has been helping municipalities find effective and affordable solutions for CSOs for almost four decades, points out that actual contact is the primary concern, then aesthetics.

"The common denominator for all wet-weather concerns is the stormwater component, which causes overflows and increases the risk of human exposure to pollutants," he continues. Fortunately, there are many documents out there to help municipal organizations learn how to deal better with CSO woes. These include books, EPA reports, reports by the Water Environment Research Foundation, and numerous articles.

"There's no question human-origin sewage is a real threat," Moffa adds. "Pathogens tend to be species specific, so organisms from humans are a greater threat than animal organisms. It's essential that sewer lines and satellite and central treatment plants be prepared to handle excess flows caused by wet weather. Immediate steps can be taken to improve regulators, sewer lines, and headworks at treatment plants. This is important to meet CSO requirements. It is particularly important to minimize infiltration and inflow in the case of separately sewered systems before addressing treatment needs related to SSOs [sanitary sewer overflows]."

Moffa emphasizes, "As engineers, we can help our clients tailor solutions to the site-specific considerations. We have not done the client a service unless we have identified receiving-water impacts and used-water quality impairments to identify specifically what the client has to do." He further explains that if discharge pipes violate water-quality standards, whether it is raining or the sun is shining, then the community suffers the consequences and legal action from public interest groups, as well as from state and federal agencies.

A major need is for states to develop appropriate wet-weather standards but it will probably fall on municipalities to do the required work. Although a cost is involved, a municipality is in the best position to collect the necessary data - and benefit from the results.

Keeping It Clear

For some communities, the challenge is keeping stormwater out of the sewer system to begin with or at least ensuring that nothing blocks the system. Accumulated debris, organic waste, and trash can seriously impede the system's ability to handle the proper volumes of water. Sandbags and similar devices sometimes are used as filters, but over time they can rot or wear out and become part of the problem. One of the newer items for this purpose makes use of recycled rubber tires and holds out the promise of not only a long life but of never contributing to the problem. Developed under a grant from the California Integrated Waste Management Board, the Eco-Blok has been available since February. "It's an erosion and runoff control device designed to keep water and debris out of the sewer system to begin with," explains Tom Horan, managing partner with Eco-Blok LLC of Thousand Oaks, CA. "It comes in filter and barrier versions."

Horan, who holds an economics degree, notes a number of cities have added it to their arsenal for combating temporary and permanent water runoff challenges. "Unlike sandbags, the Eco-Blok has a long shelf life, which we conservatively estimate at 10 to 15 years. Further, with 30 million tires a year being discarded in California, this is a great alternative to putting old tires into the landfill."

He points out that actual use during storms depends on municipal concerns. "The filter version can be wrapped with a filter cloth to keep fines out of the system. City employees have to monitor those screens during the storm. But the barrier version is 100% solid and is ideal where no water intrusion is wanted." One key use of that version is at construction sites where a temporary barrier is needed to protect the sewer until the contractor has finished with his changes to the landscape.

"Cities can choose whether they want to divert the stormwater or just keep the particulates out because the treatment plant has been designed to handle the extra flow," states Horan.

Integrity Is Essential

Leaks are a potential problem with many older systems, even if they're not actually exceeding their capacity. Cracks in sanitary sewer lines can allow pathogens to seep into groundwater or, if there is a separate storm sewer system that crosses it, into the storm sewer. An actual collapse of a sewer line can greatly reduce capacity as well.

One of the major players in restoring sewer system integrity, ensuring that the system functions as intended, is Pressure Concrete Inc. in Florence, AL, which uses shotcrete, a hose-applied version of concrete. The firm also relines steel culverts with concrete, builds berms 16-18 ft. high, and constructs large-volume, concrete-lined catch basins.

J.L. Culver, who has been with the company for 51 years, comments, "Most of the old brick sewer lines were built in the 1890s, and they were well built, but during the last 30 or 40 years, daily flows have increased dramatically because the cities they serve have grown. Plus, over time there has been soil movement and root intrusion. Then, when it rains, they get a CSO."

That problem involves collapsed ceilings and walls, especially with the brick lines. When the inside of the line is restored with shotcrete, the diameter might be reduced by as much as 4 in., but the smoother surface makes for faster flows, which helps reduce the risk of a CSO when the storm strikes. Relates Culver, "When we're done, the line is as smooth as a shotgun barrel. You get a faster flow. The water is getting out of the area and going where you want it to go.

"We've done a lot of 24- and 36-inch lines for Indianapolis, as well as some up to 84 inches. One of those larger lines involved Washington Street in downtown Indianapolis, running east and west. The city spent several million dollars over a period of time." The company now has another crew in the city working on another trunk line.

"The first step is to work with local and national consulting engineers to determine the most cost-effective way to solve a given city's CSO problems. We actually enter the lines, physically or with video, block by block, and see the problem areas. We also evaluate the laterals to see whether they're broken and also whether any manholes need lining." The company gives a thorough report to the engineers and the cities, along with its own estimate of the cost of repair.

Culver points out that because the work is done underground, traffic control, which is handled by the client city, is much less of a problem than with open trenches. "We can park our shotcrete mixers and pumpers several hundred feet from where our nozzle men are actually working." Off-street parking helps preserve customer access to the adjacent businesses.

A worker actually can maneuver inside a 24-in. line, including placing the reinforcement wire before adding the shotcrete and reducing the diameter to 20 in. "You'd be surprised how much room you have with 24 inches," Culver comments. However, it's necessary to ensure that the workers don't come into contact with sewage. During the repair, the upstream end of the system is blocked and diverted to another manhole 200-300 ft. downstream, thus requiring a tube above ground to divert the flow. Depending on actual flow, the tube can be protected so that traffic is not a problem. "The fact we can control the flow during the repair saves the city a lot of money."

Culver credits the American Concrete Institute and other organizations with helping to develop certification programs. These programs guarantee that those at the end of the hose have the knowledge they need to do the work correctly. "Anyone wanting to become a nozzle man is looking at 20 to 30 days to become certified. How he places the material and the angles he applies the shotcrete are critical." The operator also has an assistant, who learns as he helps handle the hose, which is pumping 300-400 yd./day of concrete at 40 lb. of pressure.

"Once the material is in place, they then give it a float finish. It's like floating slabs, except we don't recommend steel trowel finishes." He also explains that because of the faster cure time than with regular concrete, sewage flow can resume the same day the work in that section of line has been completed.

Headworks Helper

Lowering jumbo drill down the construction shaft

Public health is the chief concern, which is why cities also include devices at the headworks of the treatment plant to help ensure that the plant does its work unimpeded. One such supplier is JWC Environmental of Costa Mesa, CA. "If too many solids get to the treatment plant, it can affect the life of that operation," declares JWC's Fritz Egger. He states that such solids include small animals, condoms, and feminine products. "There have even been snakes in some cases. All of these contribute to the load the treatment plant has to bear."

Egger sees screens and grinders at the headworks as a combination to help keep the treatment plant fully functional. "Grinders range in size from 6-inch to 90-inch cutter cartridges. One of our Channel Monsters is able to accommodate a stream flow of up to 60 million gallons a day. It easily handles tree branches 3 inches thick, but we've even used them to grind up couches." Such performances make believers out of treatment plant officials.

As with other equipment, maintenance is essential to make sure that the machine continues to work. "The grinders need to be checked every three to five years, depending on the severity of operation. The machine is serviced to last 10 to 20 years, depending on the amount of grit in the system."

Egger reports that startup takes one day and that treatment plant employees find it relatively easy to use. "Basically they have to do a regular service check of the lower cutters, which are under water most of the time. The upper cutters are not usually engaged until there's a storm event."

In reference to screen size, he notes, "We most frequently supply down to 6 millimeters, which is capable of removing 70% of all solids. A 2-millimeter screen can remove up to 87%. On an ordinary day it's not unusual for a screen to remove 150 cubic feet of solids an hour. This tactic ensures there are no problems where there is no storm. With storms, some cities even get trees and other larger solids, which have to be kept out of the system so they don't damage the equipment or block off the flow."

Solving Overflow Problems in Georgia

Concrete lining of 35-ft.-diameter tunnel construction shaft

On the other side of the coin are those who want to do what's right but need an affordable solution. "More CSOs are being reported due to changing regulations," explains Wayne Haynie, group manager of water, wastewater, and tunneling for the engineering firm Jordan, Jones & Goulding in Norcross, GA. "There are laws from the federal government, mainly the Clean Water Act, as well as state and municipality regulations, that require reporting. Now CSOs that wouldn't have been reported in the past are being reported."

At one time an overflow wasn't reported until it had exceeded 10,000 gal. "Cities could exceed sewer-line capacity because wastewater treatment plants can treat additional volume and not overflow. But when the wet seasons arrive, then that's when the problem starts. In Georgia, just about any overflow must be reported to the state, which has adopted a zero-tolerance policy. If you are subject to overflows, you had better be trying to fix it." The Georgia Environmental Protection Division fines communities for overflows, with the strength of those fines depending on the efforts taken on by communities to conquer their CSOs.

Haynie has been in the field since 1982, and his company has been working with municipalities on CSOs and related problems for the last 45 years. "Our company has designed hundreds of projects, including sanitary sewers to relieve overflows, combined sewer system separations, and private industrial systems - all designed to meet regulatory needs and return the systems to compliance."

Take, for instance, Cartersville, GA, where the cost of sanitary sewer rehabilitation appeared to be prohibitively expensive for this community of 40,000. Haynie explains that the northwest Georgia community had a major sewer through the downtown business district. It had a large drainage area and a 15- to 24-in.-diameter trunk line a mile long. "Because it had some stormwater inflow, the sewer had reached capacity. Also, parts of the system had decayed over time and fallen into disrepair." Jordan, Jones & Goulding spent two years planning and designing for excavating the streets and making the open cuts, as well as some short tunneling and boring. One of the main tactics was video inspection before and after each repair. When the effort was completed, the trunk line had been replaced with a 24-in. line that leads directly to the treatment plant.

"It took a good bit of excavation, but by rehabilitating the system we were able to remove any connections between the storm and sanitary systems that we found, making it as efficient as possible," he continues. Furthermore, the combination of open cuts and tunneling helped reduce the time needed to complete the project.

He comments, "As a community grows, you get more and more connections. The additional growth causes the system to exceed capacity, yet there is no surface space to expand capacity."

Haynie describes another recent project for Rockdale County, GA. "The original sewer system was installed in the early 1900s, and the downtown business district's line originally went directly to the creek. By the 1950s the city had begun to install sewers that discharged to treatment facilities, but with growth of the town they were soon very undersized. Now Rockdale County is eliminating the original trunk sewer and putting larger 24-inch sewers in the trench, spending about $1 million a year to do so. They are systematically eliminating sewer overflows and are doing it on a pay-as-you-go basis." Naturally this makes it a long-term project, but it does show the state that the county is working to solve its overflow problems. Furthermore, the country is avoiding further long-term debt yet still answering the need for stormwater and sewer separation.

For Speed, Space, and Economy, Try Tunneling

When a community or metro area has run out of space, what's to be done? One solution, borrowed from the mining industry, is to tunnel. After all, most people don't worry about what they don't see, so aesthetics is not a concern here, yet large tunnels can supply an amazing amount of storage capacity. Refik Elibay, director of tunneling services for Jordan, Jones & Goulding, reports that his company has 18 mi. of tunneling projects under construction in various communities. "We're designing 8.5 miles of large bore tunnels in the Atlanta area that will be wastewater related." With an average rainfall of 50 in. a year in Atlanta, CSO control is a particular challenge for that community.

Elibay, who has been a civil engineer for 31 years, reports that one of the greatest benefits with tunneling is the minimal impact on residents or the environment. "Open cuts for laying pipe can be quite destructive. Tunnels avoid that." In addition, weather conditions don't affect work underground nearly as much as they do on the surface. Add to that the difference in traffic control needs and one can see from a community's standpoint why tunneling is a good technique.

Referring to the tunneling scheduled for Atlanta, he states, "The tunnel itself will have 150 million gallons of storage capacity. The city of Atlanta has 19 square miles in the downtown areas with combined sewers. At one time they had two systems, on the east side and one on the west, each with four overflow points. Eighty times a year those overflows got into nearby streams."

Drilling blast holes for the tail tunnel chamber

This was back in the mid-1980s, when the city used eight mini-treatment plants to screen most of the solids, then chlorinated before placing the water and the remaining solids back into the stream. Naturally those living downstream saw the floatables coming from the treatment plants, and environmental groups began attending city council meetings. In addition, increased regulatory pressure made it even more imperative that Atlanta do something about its stormwater problem.

Elibay recalls, "Extra treatment required by EPA made the mini-treatment plant solution no longer feasible. So the city entered into an agreement in 1999 to make a number of improvements to its system. The court mandates that construction begin January 2004 and that the project be completed by 2007." This includes a separate sewer system and a storage system for the stormwater.

During the initial study, Atlanta discovered that the west side of the town could not handle any surface treatment extension. "So they're going to a deep tunnel system," explains Elibay. "Those tunnels will average 300 feet deep and be 24 feet in diameter and 8.5 miles long. After the storm, the flow will be conveyed to the city's R.M. Clayton Treatment Facilities, a new facility just for CSO that can handle 85 million gallons per day. In two days those tunnels will be pumped empty, ready for the next storm event."

This process makes certain that Atlanta not only meets current water-quality standards but exceeds them and has room to grow. It's also designed to handle a 25-year storm and will reduce the 80 overflows to just four. And soon those four also will become history.

Treatment will be ultraviolet disinfection in lieu of chlorination. Elibay explains, "The matter of concern is that chlorination may combine with heavy metals and organic materials and become a toxic substance. Also, those four projected overflows are at an undersized dechlorination facility, so when they've made the switch to ultraviolet, overflows should cease being a problem."

Regarding how the company handles the tunneling, even at 300 ft., without shaking the ground, Elibay explains, "Instead of blasting, we use boring machines for mechanical removal." And at 300 ft. underground, neither noise abatement demands nor unauthorized onlookers are as much of a problem. For the most part, industrial, commercial, and residential members of the community will rely on the media for information on the project's progress.

When it comes to CSOs, solutions do exist. The trick still remains to solve the problems economically, and this is where engineers and contractors working together for the benefit of the client community can make that a reality.

Author Joseph Lynn Tilton is a frequent contributor to Forester Media publications.

SW November/December 2003

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