Every town or city has a complex network of wastewater pipes running through it, which transport residential and commercial waste away from our homes and businesses, where they can be safely treated and clean water discharged back to the environment. Although most of these pipes are of a smaller diameter and are located beneath city streets and roadways connected through a series of manholes and pumping stations, almost all sanitary sewer collection systems have components that are larger, more complex and remotely located.
Oftentimes, these pipes can be the most critical and have the highest consequence of failure if they were to fail due to structural defect or hydraulic capacity deficiency. Further complicating routine maintenance activities such as cleaning and inspection, these pipes can be among the oldest in the system and at times, so remotely located or inaccessible, that traditional maintenance equipment alone cannot service them adequately.
In spring 2014, one New England community called on Ted Berry Co. of Livermore, Maine, to provide a hydraulic assessment and cleaning approach that would reduce or eliminate the potential for backup of the combined sewer system during wet weather events. The pipe segment consisted of approximately 1,500 lf of 58-in. x 36-in. brick sewer, which ran from a city street remotely under a local minor league baseball stadium and adjacent football field, city park and, eventually, to the wastewater treatment facility. Matt Timberlake and Dave Beauchamp of the Ted Berry Co. met with city personnel and groundskeepers for each of the sports facilities to develop an approach that would yield the best results, at the lowest cost, while minimizing any disruption to the ongoing sports seasons.
The 1,500 lf consisted of eight line segments of varied lengths from 51 to 300 lf. Of the eight manholes, only three could be accessed with the flushing and vacuum equipment required. Two of the inaccessible manholes were actually located below the surface of the baseball field, one being under first base and one being directly under right field. Three of the inaccessible manholes were located beneath the football field, which was constructed of artificial turf. The manholes were primarily constructed as brick chimney manholes, which limited access into the sewer line, as they were only approximately 24 in. in diameter.
Having a Cleaning Plan
A cleaning plan was developed that would clean the pipe from the three accessible manholes using high-velocity flushing and vacuuming equipment. A preliminary CCTV inspection would be performed to evaluate the general structural condition of the pipe, as well as the type and quantity of debris present so the proper configuration of nozzle, flow and pressure could be applied, which would efficiently move the debris to a manhole for removal. Oval brick pipe can present challenges during cleaning, as it is common for it to fail at the invert. Therefore, the cleaning system should be configured to maximize the ability to transport debris through the pipe with maximum flows and minimum pressures required. Additionally, the large diameter pipe was laid on a minimum slope and debris was prone to settle if the cleaning operation wasn’t kept continuous and speed of nozzle movement and debris removal not maintained. The cleaning system would be fed from a 3-in. supply line adapted through a hydrant connection that would be metered and supplied through a back flow preventer and air gap fill.
As cleaning commenced, grit, debris and other solids were removed, dewatered and transported to a local municipal solid waste landfill. Following removal of approximately 100 tons of debris, a final CCTV inspection was performed during low flow conditions using NASSCO PACP certified operators and coding system to provide a full, structural and O&M condition assessment. Surprisingly enough, this sewer system, constructed more than 100 years ago, was still in good structural condition. The cleaning and inspections were scheduled during the minor league baseball team’s away travel schedule and needed to be completed prior to its return back to its home stadium.
Although it may have been easier to access and excavate the manholes beneath the baseball stadium, this would have caused a significant amount of work and destruction that the grounds crews would have then had to deal with for the rest of the playing season.
During the inspection, the three manholes located below the football playing surface, were determined to be unnecessary and with upcoming construction of a new playing surface, it was desired for them to be abandoned, thus reducing the future threat of any backup through the playing surface. The Ted Berry team proposed abandoning the brick chimney manholes in place, using an internal forming system, reinforced steel, anchored into the existing manhole structure and a controlled density grout, which would be of high-compressive strength and low weight. As previously stated, this was further complicated to the access being through very small holes cut in the artificial turf surface and all equipment needing to be located off the playing surface during the work.
As with most communities, these remote and large diameter pipelines are given the least amount of attention and consideration through preventative maintenance activities because of the difficulty of access and assumption that these pipes have adequate capacity even though they are often constrained with debris from years of operation, and often times upstream flushing programs which simply transport those materials downstream into the larger pipes. However, these are most often the most critical sewers in our communities and have the highest consequence of failure, therefore from a risk management standpoint, these critical sewers should be amongst the first to be cleaned and routinely inspected. Even the simplest of preventative maintenance programs that consist of basic visual inspections can significantly reduce risk as the collections system operator can detect minor problems in the system before they become major.
Madeline Timberlake is a fourth generation of the Ted Berry team. Matt Timberlake is vice president and principal of the Ted Berry Co., which was founded in 1972 by his grandfather Ted Berry.