Determined through a multi-step hydraulic condition assessment to be badly leaking, a rehabilitation project to greatly reduce infiltration-and-inflow (I/I) was needed for two New Castle County, Del., neighborhoods.
Multiple technologies were employed on this 7,200-lf project. These included CCTV, pipe joint testing and grouting, mainline cured-in-place pipe lining (CIPPL), lateral T-lining, lateral lining to manholes, new cleanout installation, CIP point repairs, manhole replacement, fiber-reinforced cement lining of manholes and injection grouting of leaking manholes.
The New Castle County Department of Special Services (NCC) owns and operates a sewer system that contains 1,800 miles of gravity sewer and interceptors, 38,000 manholes and more than 150 pump stations. Included in this system is the Brandywine Hundred Sewer System, which accounts for 420 miles of the system and is located in the County’s most densely populated area, containing the oldest and most problematic sewers in NCC’s inventory.
To safeguard the aging, yet valuable infrastructure investment represented by the Brandywine Hundred Sewer System and to address the changing operational and maintenance requirements represented by both the current aged condition of the system, NCC is implementing a 25-year, comprehensive program to identify and prioritize operational and capital improvements to its wastewater infrastructure.
This program, called the Brandywine Hundred Sewer Rehabilitation and Capacity Assurance Program, has a goal of preventing sufficient amounts of groundwater and rainwater entry (i.e. I/I) into the collection system to achieve a significant reduction in basement sewage backups, the occurrence of wet weather-related sanitary sewer overflows (SSOs) and interceptor surcharging.
This comprehensive program includes significant planning, budgeting, scheduling and public involvement components, in addition to the engineering and construction aspects of the work. The program includes sewer flow monitoring, inspections, internal testing and engineering evaluations to identify and prioritize those sections of the Brandywine sewersheds that need to be repaired or replaced (R&R) and to provide a benchmark for determining the effectiveness of implemented solutions.
A complete baseline condition assessment of the existing system, which included development of monitoring programs intended to identify the nature, extent and sources of I/I, cross connections and structural failures, was accomplished through a multi-part process. First, a multi-step Hydraulic Condition Assessment (HCA) was used to identify the sections of the system that leak the most. For the HCA, extended flow metering, nighttime weiring, above-grade storm inflow observations, door-to-door basement inspections, smoke testing, data mining through asset management software and the transfer of knowledge through interviews with operations staff were used.
For segments found to be leaking badly, a follow-up physical condition assessment was conducted to identify the best method of rehabilitation to use, based on the pipe, lateral and manhole’s structural condition. In-pipeline inspections, digital state-of-the-art CCTV cameras were used.
The Northcrest-Afton area sewer system was one area identified as having major I/I problems. The primary objective of the project was to rehabilitate the sewers, laterals and manholes of these two adjacent neighborhoods high in the system, so as to significantly reduce the amount of I/I entering them. Removal of I/I from areas high in the system was given higher priority because the I/I would not need to be carried through the entire system.
The HCA confirmed reports from NCC’s operations department that the sewers of these two neighborhoods leaked badly. Flow meter data suggested these sewers suffered extended rainfall-induced infiltration and illegal sump pump or punctured floor drain impacts during and after storms. Nighttime weiring showed baseline infiltration during normal springtime generally exceeded 10 gpm/lf of sewer main, and in some cases many times that rate.
Smoke testing confirmed that there were no roof drains or cross-connected sewers, but door-to-door basement inspections confirmed the presence of illegal sump pumps and punctured floor drains. Most of these were found to be from the original construction of the homes. In a neighborhood with shallow bedrock under clay, many natural springs and basements with underlying sewer laterals meant high flows during wet and dry flow conditions.
Once determined to be a leaker, the sewers of NCA were inspected to determine the most appropriate rehab methods to use to reduce the I/I. This involved NASSCO PACP-coded CCTV inspection. As expected, the predominantly terracotta clay sewer showed numerous cracks and fractures and several instances of broken, distorted or collapsed pipe. Unexpectedly, many of the segments of terracotta pipe were in perfect structural condition, suffering only from leaking joints.
Based on these various conditions of the pipe, economic factors and site constraints, four primary rehabilitation technologies were selected for the pipes. B. Frank Joy of Maryland served as general contractor for this project and was assisted by a host of subcontractors.
Packer injection grouting, or test and seal, was selected for those pipe segments that had no structural defects. Video Pipe Services of New Jersey used Avanti International AV-100 chemical grout, which mixed with dichlobenil for root retardation and Avanti IcoSet for strength retention, proved sufficient to seal the leaking joints. This was so much the case that lateral taps that had not been leaking prior to mainline grouting began leaking afterward. Approximately 3,900 lf of mainline pipe had its joints tested and sealed.
For laterals connected to segments receiving test and seal, lateral taps were grouted to their second joint and 53 tap connections were tested. With a failure rate of 33 percent, 17 taps were grouted. Four laterals connected to manholes upstream of segments receiving test and seal were grouted to the property line with a push packer to minimize transferring the I/I further upstream.
CIPPL was selected for rehabilitation of the sewer mains with structural defects. Approximately 3,800 lf of mainline pipe was lined. Polyester resins combined with non-woven tube and cured with steam by Am-Liner East Inc. provided strong, smooth plastic pipes to function as pipe replacements or pipe liners inside cracked, fractured and broken terracotta pipe. To prevent the leakage in the annular space between the host pipe and the liner from coming out at the manholes, Hydrotite end seals were employed at every manhole and drop connection.
To prove the installed product would provide the minimum design life of 50 years, restrained pipe samples of the installed product were tested for thickness, using ASTM D2990 long-term creep modulus and ASTM D790 short-term flex modulus.
To prevent the leakage in the annular space between the host pipe and the liner from coming out at the tap connection cuts, for laterals connected to segments receiving CIPPL, each lateral tap received a cured-in-place lateral liner (CIPLL) using LMK T-Liners.
The T-liners were installed to at least the edge of the property line and, where agreeable to the property owner, as close to the building foundation as was convenient.
Once cleanouts were installed, the lateral was cleaned and televised to confirm there were no obstructions and measurements were taken of each lateral. These measurements were sent to the factory where each liner was specifically manufactured for each lateral, including coning of the liner for the 4- to 6-in. transitions and preparation of specific mixtures of the two-part polyester resin for each lateral.
B. Frank Joy conducted the lateral lining installation, which involved bypass pumping in the mains, wetting out the liner onsite, transporting to the mainline tap connection, inverting the liner through a special packer assembly and steam curing of the liner for about 15 minutes. Fifty-three CIPLLs for laterals connected to the mainline sewer were installed. An additional seven laterals were lined in a similar fashion, less the mainline wrap connection, from manholes.
It took two months of submittal preparation and review time and six months of field time to complete the work. The contractor’s initial bid of $1.26 million was modified via post-award value engineering proposals to $1.14 million. All construction work is complete.
James W. Shelton, P.E., is a program manager with Malcolm Pirnie, based in Wilmington, Del. Michael T. Harmer is a civil engineer II with the New Castle County Department of Special Services Operations, New Castle, Del.