Lessons Learned During Sewer Rehabilitation On Public And Private Property
By Bob Kelly, Scott Belz, and Jim Smolik
The City of Westlake, OH, is located in the northeastern part of the state. The city is mostly residential with light industrial and a population of 34,000 people.
In 1992, the city implemented an inflow/infiltration (I/I) program based on flooding problems. Since 1992, four areas have been investigated. Each area used similar rehabilitation techniques; however, certain lessons were learned from the testing to the construction phase.
The four areas are: King James Subdivision, Salem-Radcliffe Subdivision, Berkeley Estates, and Canterbury. All of the areas were built between the 1950s and 1970s, with separate storm and sanitary sewers.
Methodology
Prior to any sewer rehabilitation or repairs, a sewer investigation must be conducted to identify the types and location of defects in the sewer system. These investigations utilize different testing techniques that focus on both public and private property. Both of these areas have different sewer components that are susceptible to deterioration and malfunction.
For all of the projects undertaken by the city, either contractors or consultants conducted the testing as part of the sewer investigation. Testing for all of the project areas included some or all of the following testing methods:
• Flow monitoring
• Mainline dye testing
• Residential dye testing
• Manhole inspection
• CCTV
Once the testing was complete, a detailed report was submitted to the city with recommendations for rehabilitation to the system based on the best engineering judgment at the time of the report. These reports included recommendations for mainline sewer lining, lateral lining, manhole sealing, and grouting.
Results
King James Subdivision
The King James Subdivision was the first area to be investigated and rehabilitated by the city. The investigation for this area was conducted by a contractor and data was provided to the city as data with no engineering recommendations. While engineering was completed internally, the contractor data report lacked the backup and details of the testing commonly provided by a consultant.
Testing in this area was focused on public property only. No flow monitoring was conducted for either post- or pre-rehabilitation monitoring. Testing consisted of mainline dye testing which included adding dyed water to the storm sewer system and looking for leaks in the sanitary sewer, then using a CCTV camera to identify the leak and its location. From the testing results, a rehabilitation plan was developed and included the sealing of manholes and lining the sanitary sewer with a cured-in-place (CIP) sewer liner.
The city revisited investigating the area since the flooding problems were not solved. The city felt that the problems may lie on private property as well as public property, and all 50 houses in the area were dye tested by adding dye to each downspout. Wherever dye transferred from the downspout of a house to the sanitary sewer, rehabilitation was performed.
The city was faced with the issue of who should pay for the new repairs which included work on private property. City council agreed that residents should pay for structural repairs outside the right-of-way (ROW) and the city would pay for all work in the ROW and lateral grouting outside the ROW. The result was that only $5,000 of the total of $338,000 for rehabilitation costs fell under the homeowner’s responsibility (approximately 1.5 percent of the contract).
Lessons learned from the King James Subdivision showed that both public and private sides need to be addressed when completing sewer system rehabilitation. The city also decided that all of the future rehabilitation work for these types of projects shall be 100 percent funded by the city.
Salem-Radcliffe Subdivision
The next area to be investigated was the Salem-Radcliffe Subdivision. The sewer investigation for this area was also conducted by a contractor and data was provided to the city as data with no engineering recommendations. For this area, CIP sanitary lateral lining was utilized from the mainline sewer to the house. The CIP method used consisted of a felt liner with a polyester resin and steam curing. A pit was used to expose both storm and sanitary laterals for cleaning and televising, sanitary lateral lining, and installation of new cleanouts. Manhole sealing was conducted using a spray applied polyurethane liner.
Lessons learned from the Salem-Radcliffe Subdivision showed that the liner was installed short of the mainline with the work not addressing the mainline sewer/lateral interface. This allowed groundwater to migrate down the lateral to the path of least resistance at the mainline/lateral connection. In manholes that had the spray liner applied, the grade ring area was not sealed with a flexible product. This allowed groundwater to enter and led to the product cracking at the grade interface.
Berkeley Estates
Berkeley Estates was the first area to be tested by a consultant. Both mainline and residential dye testing was completed in this area showing that both public and private property sewers were contributing to I/I in the system.
The same type of lateral lining CIP process from the mainline sewer to the house was used for this area. The CIP method used consisted of a felt liner with a polyester resin and ambient curing instead of hot water. A pressure launching vessel was used for the inversion and the lateral/main interface was grouted with a lateral packer.
Manhole sealing was conducted using a cementitious product with a flexible urethane product at the grade ring. This was an improvement from the last project which did not use a flexible material. Prefabricated rubber membranes with expansive straps were also used in several manholes.
Lessons learned from the Berkeley Estates project showed that liner failures, possibly due to ambient curing or the resin introduction process, impacted the ability to grout the mainline/lateral connection. This area was previously serviced with septic systems and records were not available on how they were tied into the mainline when they were converted. This resulted in the contractor sometimes needing to excavate two pits to expose both the storm and sanitary laterals which was not in the bid document. Storm laterals were difficult to locate due to lacking data from not televising the storm sewer prior to the repair work.
The city found that testing requirements need to be established to verify that the liner met the performance strength requirements that were specified in the contract documents. Vacuum testing for manhole products also needs to be implemented on future projects. This project also showed that more research needs to be conducted during the design stage of the project, especially in identifying the pipe layout in septic tank conversions.
Canterbury Area
The Canterbury Area was the most recent area investigated with a rehabilitation of the mainline sewers and laterals based on the recommendations of the investigation. Like Berkeley Estates, a consultant conducted the exact type of testing and provided an engineering report.
Again, sanitary lateral lining utilized a CIP process from the mainline to the house. The original CIP installation utilized a felt liner with a polyester resin and ambient curing. However, the resin was changed to epoxy because it was available domestically. The method of curing the CIP was also changed to recirculating hot water to meet the performance specification of the product. Similarly, a pit was used to expose both storm and sanitary laterals, lateral lining, and install cleanouts during the lining procedure.
Mainline grouting was completed in areas identified from the mainline dye testing results. Grouting of interface was also completed between the sanitary lateral and the mainline sewer.
Manhole sealing utilized a cementitious product with a flexible urethane product at the frame/wall interface. This product seemed to work the best in comparison to previous products used.
Testing that was implemented on this project included pre- and post flow monitoring, pre- and post dye testing, vacuum testing of the manholes, air testing from the cleanout to the mainline sewer, and physical testing of the CIP liner to verify strength parameters (flexural modulus and flexural strength).
Lessons learned during the Canterbury Area focused on complications due to the houses being septic tank conversions. Many had branch connections and could not be lined, and some liners had to stop short of the house due to a 4” diameter reducer at the interface of the lateral and the house. Some laterals failed due to workmanship. For example, resin was not cured properly, not measured correctly due to faulty equipment, calibration bladders were pulled prior to curing, or installed too short. In some instances, the liner was installed too short from the pit to the main.
Conclusions
Throughout all four of the rehabilitation projects, lessons were learned in each one and at different phases of the project, from testing during the investigation, to bid and specification items, to product specification and testing, to construction methods and installation. Key items for each segment of the project are discussed below.
Testing techniques
During the residential testing, locating the exact source or potential location of the leak will assist the engineering judgment of recommending lateral lining or spot repair at a specific house. Altering the testing procedures to spend more time searching for the leak on private property rather than discerning if it was positive or negative may possibly eliminate the lining and associated costs.
Bid and specification items
By conducting rehabilitation on several projects, the overall bid and specification document improved at each project. Important items that protected both the city and the contractor were eventually included in the package. Specifically, number of cleanout pits, length of the lateral liners, how to deal with lateral branches, type of product, and quality assurance testing requirements were all things that made important decision making points at various times of construction during the project and provided insight for future improvements. It is important to include the proper testing procedures and requirements and hold the contractors and manufacturers to those requirements.
Product recommedations
While several products were used on these projects, overall success was based on the cumulative effort of the product, installation, and workmanship. Products that were successful were CIP liners, which were felt liners with an epoxy resin with hot-water curing. Chemical grouting was also successful on the mainline sewer joints; however, long-term exposure of the product has not been endured, as this was only installed within the last five years. Manhole liners worked much better with a flexible urethane grade ring than the rubber liners with straps.
Construction methods
One of the key lessons learned during these projects was the ability to find a contractor that has extensive experience in installing, testing, and overall knowledge of the product limitations. Throughout these projects, different contractors were used and each with varying degrees of knowledge and competence which wasn’t identified until the project was ongoing or had ended. With the advances in technology and new products being introduced to the market every year, it is important to find a contractor that has experience with a specific product.
Bob Kelly is Director of Engineering for the City of Westlake since 1992. He is responsible for 300 miles of sewers systems and has over 30 years in municipal sewer maintenance and design.
Scott Belz is Manager of Field Operations for URS in Cleveland, OH, and has over 35 years of experience in sewer collection systems.
Jim Smolik is an engineer and inspector for the City of Westlake since 2000. He is responsible for inspections and project management.