Sanitary Sewer Overflow Initiative Cleans Clear Lake

The Clear Lake City Water Authority (CLCWA)From big cities to small villages, water authorities across the country have wastewater collection systems that are reaching or have exceeded their design lives and urgently need extensive upgrading. With a growing population and an aging sewer system that continues to deteriorate, many utilities are becoming increasingly vulnerable to sanitary sewer overflows (SSOs).

The Clear Lake City Water Authority (CLCWA), the largest water district in Texas, faced such a challenge a decade ago when its aging system experienced a number of SSOs.

“The system was more than 60 years old and some of the pipes were starting to fail,” says Lockwood, Andrews & Newnam Inc. (LAN) associate and project manager Kelly Shipley, P.E. “As a result, we were experiencing as many as 20 to 30 SSOs a year.”

Responding aggressively to this challenge, CLCWA, in 2005 voluntarily joined the Texas Commission on Environmental Quality’s (TCEQ) Sanitary Sewer Overflow Initiative to minimize the number of SSOs. To manage this initiative, the water authority hired LAN, a planning, engineering and program management firm headquartered in Houston, as District Engineer to evaluate its sanitary sewer system, schedule requested maintenance and conduct improvements in a cost-effective manner.

Systematic Approach
Created in 1963 by the Texas state legislature, CLCWA provides, operates and maintains waterworks systems, sanitary sewer systems, storm sewer systems and drainage facilities to more than 100,000 people in the cities of Houston, Taylor Lake Village, Pasadena and Webster. Its wastewater collection system, which has a capacity of 10 million gals a day, is comprised of 28 lift stations, 6,000 manholes and 1.1 million lf of sanitary sewers (gravity and force main) varying from 6 to 60 in. To evaluate and rehabilitate such a large system, LAN engineers developed a systematic approach.

“We decided to evaluate a third of Clear Lake’s 136 subdivisions and a third of the sanitary sewer lines and manholes within each subdivision per year,” says Shipley. “We began inspecting the oldest subdivisions and the subdivisions experiencing the most SSOs and assumed these sections would be the most deteriorated. Using the condition assessments and age of the subdivision, we determined a deterioration rate for the remaining subdivisions. By taking this approach, we could make an accurate assumption about the rest of the system and its state of deterioration.”

Installation of cementious spray liner on CLCWA’s60-in. trunk line.The first step was to analyze SSO reports of sewer lines to determine the location, the type and cause of overflow and the number of overflows in a particular line. Lines that experienced a one-time SSO overflow due to factors such as an electrical surge were fixed immediately while lines with recurring problems were moved to a priority list. Next, the team inspected the sewer lines using CCTV to identify grease/fat buildup, blockages, breaks, cracks or other structural deficiencies. Based on the observations, each inspected line and manhole was given a weighted condition assessment rating, ranging from one to five, one being the best and five being the worst. From this rating, a prioritized list of sanitary sewer lines and manholes that required rehabilitation was created based on technical and environmental criteria. Then, the most appropriate and cost-effective method of rehabilitation was selected using an exhaustive value-engineering analysis.
With the majority of the sanitary sewer lines and manholes located in high-residential areas, LAN primarily used trenchless technology to rehabilitate the system.

“We tried to implement trenchless methods as much as we could,” says Shipley. “A large portion of Clear Lake has clay pipe and when it cracks, a domino effect is created down the line. By using trenchless solutions, we were able to give Clear Lake a whole new pipe from manhole to manhole. It also gave us the comfort that we didn’t have to come back in a year to see another problem 5 ft down the main.”

Pipe bursting was the most common trenchless method used, Shipley says, followed by cured-in-place-pipe (CIPP) lining.

“We pipe burst entire sections within a subdivision, especially the ones built in the 1960s,” says Shipley. “We are starting to use different methods as we get to the newer pipes but pipe bursting has been a standard for us for the last eight years.”

As a final step, the rehabilitated lines were inspected again using CCTV and given a new condition assessment rating to ensure the pipe was rehabilitated as intended and did not have additional problems. For each of these steps, the data gathered was input into a Geographic Information System (GIS). Graphical color-coded maps of the sanitary sewer system and its various attributes, such as the length of the line, the pipe diameter, whether the line or manhole was television inspected and rehabilitated and the rehabilitation method implemented were produced from the data. The maps were used to assess the program’s success in minimizing sanitary sewer overflows.

Program Challenges
The scale and complexity of the project created a number of challenges to the project team. Foremost among them was minimizing the disturbance to residents and businesses affected by the repair work.

“We communicated constantly with the homeowners and ensured contractors sent multiple notices to them weeks in advance,” says Shipley. “In case of scheduling conflicts, we rearranged the schedule to make sure homeowners were present during construction. A lot of it was keeping the residents informed and coordinating with them to keep the construction progressing smoothly.”

With many lines buried deep underneath busy intersections or business and residential properties, accessibility was another challenge.

“There was a deep sanitary line that we were trying to fix in a section of Clear Lake with small patio homes,” says Shipley. “Having enough room for a contractor to work in the area and not disrupt anything around it was a huge challenge. To make things more complicated, there were concrete walls we had to maneuver around. We switched the methodology we were using and extended the line a little further so we could get an access point and fixed it.

“Another line we rehabilitated was in the middle of a major street near a commercial driveway. Using trenchless technology really helped us in that project. We CIPP’d that line and the contractor was able to provide access to all the properties along the street.”

Weather was also a challenge, says Shipley.

“We were working on a 60-in. main near a Bayou when we faced adverse weather conditions,” says Shipley. “We had to fix the line before the Bayou’s water level went up because that would have created more problems.”

Program Benefits
Despite these challenges, CLCWA is well on its way to achieving its goals. Over the past five years, the water authority has seen a 16 percent decrease in wastewater influent to its treatment plant, resulting in lower operational costs. The program also has reduced the condition assessment rating of the sanitary lines and increased the overall life of the system.

“In 2004, the sewer system had a condition assessment rating of 2.55,” says Shipley. “Last year, it was 2.11. When you consider over 1 million lf of sanitary lines, this is a significant improvement.”

And most importantly, the number of sanitary sewer overflows has diminished considerably.
“We have reduced the number of SSOs from 20 to 30 to less than five a year,” says Shipley. “Also, these SSOs have occurred less due to storm water infiltration, as was the case before. They happen because of issues like power outages. The program has been a big success.”

Conclusion
SSOs were once a regular annoyance for wastewater treatment operators, businesses and residents living around Clear Lake, but now they are becoming a thing of the past. To date, more than 880,000 lf of sanitary sewer and 3,400 manholes have been inspected and more than 20 percent of the system has been rehabilitated. CLCWA’s proactive efforts has improved its wastewater collection system, increased sewer capacity, significantly reduced the number of SSOs, prevented unnecessary property damage, and provided a clean, healthy environment for its citizens.

Bill Rosenbaum is a senior associate at Lockwood, Andrews & Newnam, Inc. (LAN), a planning, engineering and program management firm.
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