SAWS Evolves With SmartCover Sewer Monitoring Technology
San Antonio cuts SSOs by improving its approach to cleaning and maintenance.
As part of one of the oldest cities west of the Mississippi River, the San Antonio Water System’s wastewater collections operation has seen a lot of changes over the years.
It started with the water system — a series of irrigation canals dating back to 1720. Those same canals wound up being the first, unofficial sewer system, carrying waste downstream.
A century later in 1836, the aquifer was restricted to supplying drinking water and cooking water, and penalties were imposed for using it for bathing or sewage disposal. Then, an 1866 cholera epidemic prompted the city to reform its water supply and sewer disposal practices.
Construction of the city’s first modern wastewater collections system began in 1895 and was completed in 1900. Today, “we are one of the largest systems in the country,” says Jeff Haby, SAWS vice president of production and treatment.
A century later, San Antonio is once again rebuilding how it collects its wastewater, with new technology to help do the job better.
In 2013, SAWS and the federal Environmental Protection Agency signed a consent decree committing SAWS to eliminate sanitary sewer overflows in the system.
The leading cause of overflows — about 75% of the problem — is debris such as wipes along with fats, oils and grease. So regular cleaning is a major part of the remedy.
In addition, the decree prescribes more frequent inspections; checking pipes to determine whether they’re large enough for the volume of sewage they carry, replacing undersized lines with larger-capacity mains; and repairing or replacing damaged pipes, and repairing or eliminating damaged lift stations.
“Prior to the consent decree, there were efforts to maintain clean pipes,” says Annette Duron, interim director of operations support for SAWS. That included CCTV inspections as well as cleaning.
But the federal action spurred the system to rethink its approach and methods.
“The consent decree gave us more of a focus on ‘trigger’ pipe that was more vulnerable and an older part of the system,” Duron says. “That laid out the plan for us and our approach. We really revamped how we were collecting data, and both cleaning and televising.”
SAWS developed a routine for moving through the system. Varied cleaning cycles were set — from monthly to every 60 months — based on how quickly different sections became vulnerable to damage and overflows.
The shorter cleaning cycles, however, quickly started wearing on the utility’s budget and monopolized the focus of the cleaning program.
“We were spending too much time on the frequent-cleaning pipes and not getting to the rest of our pipes that we needed to continue to clean,” Haby says.
The 204 sites assigned to monthly cleaning cycles alone accounted for 2,448 cleanings a year. At $500 per cleaning, those pipes ended up costing over $1.2 million a year.
SAWS had already been experimenting with SmartCover Systems — manhole covers equipped with ultrasonic detection systems. The device monitors the level of flows both upstream and downstream of where the sensor is located. A rising level, indicating obstructions, triggers an alarm, which then leads to a work order for the site.
An early test was promising. SmartCover Systems were installed at sites where there had been repeat SSO events. “We’d monitor it, and if it started to back up, we’d send a cleaning crew out there to respond to it,” Haby explains.
The devices enabled San Antonio to reduce the cleaning frequency at many of the sites where they were installed.
After the consent decree was signed, Duron suggested that the utility ramp up its use of the SmartCover Systems. “We started with a pilot of 10 and put them on the frequent-cleaning pipes,” Haby says. When the volume of flow in the area started to rise, usually from debris or grease, crews would go clean the line. “Instead of going once a month and cleaning it whether it needs it or not, we only clean it when it starts showing that it’s backing up.”
Following a competitive bidding process, the utility has acquired over time a total of more than 500 units and moves them around to vulnerable sections of the system until more permanent repairs can be made, such as putting in new, larger pipes where more capacity is needed, or until FOG and debris problems stop recurring. It also uses 125 flowmeters to monitor other potentially vulnerable stretches of pipe.
The utility has also supplemented its sewer evaluation technologies, historically CCTV, with new sonar and laser inspection equipment.
More recently, San Antonio has contracted with a third-party service to maintain the SmartCover Systems units, including replacing batteries and undertaking repairs as needed. That has also helped save money, according to Duron and Haby, and allowed the utility to deploy its staff more effectively for cleaning and repairs.
Grease, roots, debris and similar problems continue to be the largest contributors to SSOs, Haby says. “SAWS does experience inflow and infiltration during rain events, which does result in SSOs, but the number of I&I-related SSOs is much less.”
A robust public education effort focused on FOG as well as so-called flushable wipes is also underway, with public messages on the SAWS website and other programs.
In the meantime, the utility continues to proceed with repair and replacement under the remedial measures plan required by the consent decree.
“Historically, sewer mains were predominantly constructed of clay and concrete. We are finding that a large majority of our concrete mains are needing repair and replacement along with a portion of our clay mains,” Haby says. PVC and fiberglass-reinforced plastic are the pipe material of choice today.
“SAWS has an ongoing capacity, management, operations and maintenance program, which is used to provide the guidance for repair and replacement of sewer mains due to condition and capacity.”
Many of the projects require replacement because of the need for more capacity. Where that is not necessary, the utility has been employing various trenchless approaches to repair existing sewers, Haby says.
For the current construction season, a total of 51 sewer-related repair and replacement projects are underway. The projects are part of SAWS’ comprehensive capital improvement program to upgrade the city’s aging wastewater infrastructure, as well as to expand the system to accommodate growth in both the residential population and business.
SAWS doesn’t just rely on age to determine when lines need to be replaced. Instead, it examines the conditions of pipes. “This allows us to extend the useful life span of pipes that have aged well while more aggressively pursuing replacement of those with the highest likelihood of failure,” as the utility notes in a public message on its website.
Today, SAWS officials look back at the original consent decree as an opportunity to refocus how they do their work while meeting the requirements it laid out.
“Focusing on providing needed work for the EPA consent decree has brought an organized approach to assessment of system needs to respond to the decree; planning for the needed work; and now implementation of new processes in assessing the condition and capacity of pipes, and replacing sections of the system that are undersized or need condition improvements,” Haby says.
And while the decree set forth a timeline to meet its requirements, the impact will last far beyond the deadline date on the calendar, he adds. “We believe that we have implemented best practices, which now have become part of our everyday work.”
Breaking ground in recycling
When it comes to the problem of what to do with treated effluent from the municipal sewer system, the San Antonio Water System is something of an unsung leader.
Through its sewer division, SAWS is making recycling purified sewer products a top priority.
“Our goal is to approach 100% recycling at our treatment plants,” says Anne Hayden, communications manager for the agency.
SAWS recycles the purified water after it’s treated, reducing strain on the Edwards Aquifer that serves the water distribution side of the system. It recycles the solids, and it collects the natural gas produced by the sewage digesters and pipes it to a contractor that then distributes the fuel on the open market, says Jeff Haby, vice president of production and treatment.
“Most people don’t realize we have the largest direct use recycling system in the country,” he says.
This is purified water, not graywater, Haby points out. “It’s been chlorinated and dechlorinated. It has gone through tertiary treatment.”
Even so, the recycled water is not used in the residential market.
Instead, recycled water from the system’s three treatment plants is purified and then distributed to industrial users, including several major manufacturers and area universities, where it is used for industrial and irrigation purposes, he explains.
It is also used by local golf courses for irrigation. And it has yet another use.
San Antonio’s famed Riverwalk is one of the city’s prime amenities for local residents as well as a distinctive tourist attraction. But during the dry season, the springs that feed the river for which the feature is named dry up.
“It receives recycled water to keep it flowing,” Haby says.
Source: Municipal Sewer & Water Magazine