Illinois Village Solves Its I/I Problem Through Trenchless Methods
November 22, 2011The Village of Villa Park, Ill., located about 20 miles west of downtown Chicago, took on a comprehensive review of its Sanitary Sewer Master Plan in order to update it according to present and future needs.
The goals of the update were to ensure adequate future capacity from possible annexation of unincorporated areas and to prepare a 10-year capital plan to reduce inflow and infiltration (I/I) to the system and to provide long-term service.
RJN Group Inc. (RJN) initially entered into an agreement with the Village to develop a detailed sanitary collection system Facility Plan with system rehabilitation options. The RJN team of engineers, design specialists and field technicians undertook a comprehensive sewer system evaluation survey.
The evaluation incorporated results of field investigations, flow monitoring and existing historical data. Hydraulic modeling was performed using XPSWMM software to pinpoint capacity limitations within the existing system. The revisions to the Sanitary Sewer Master Plan included recommendations for system rehabilitation.
Upon approval of the Facility Plan by the Illinois Environmental Protection Agency (IEPA), RJN began design services for extensive rehabilitation of a major portion of the system, including CIPP lining of more than 50,000 lf of sanitary sewer with pipe diameters ranging in size from 8 to 18 in.
Many of the sanitary sewers located within streets were built either in the 1920s with vitrified clay pipe (VCP) or in the 1950s with unreinforced concrete pipe. More than 7,000 ft of pipes in residential backyards were built post-World War II using vitrified clay pipe and many of these sewers were inaccessible for point repairs because of retaining walls, garages, sheds, large and mature trees and overhead utilities. The VCP sanitary sewers were in poor structural condition, while the unreinforced concrete pipes were showing signs of major deterioration from hydrogen sulfide (H2S) corrosion, with exposed aggregate, holes and missing pipe.
In the backyard locations, lining was used wherever possible, even with severely deformed pipe. The use of trenchless techniques was essential in order to perform the rehabilitation without disturbing or destroying residential property; however there were some defects — specifically collapsed sewers — that could not be lined and required point repairs.
The defective break-in lateral connections were identified through pre- and post-lining television inspections. Grouting was used to repair the lateral connections in most cases, and T-lining was performed on others. The injection grouting program used Avanti AV 100 and extended into the lateral beyond the first joint. T-Liner, a lateral connection sealing system, used a cured-in-place liner with a minimum 3-ft extension into the lateral. In total, more than 100 lateral connections were repaired as a part of this program.
Directional Drilling Solves Construction Obstacles
As part of the recommendations from the Sanitary Sewer Master Plan update, RJN continued its work with the Village, preparing the design documents and providing bidding and construction phase engineering for a relief sewer on South Myrtle Avenue.
The Village’s South Myrtle Sanitary Relief Sewer Project consisted of the design and installation of a sanitary relief sewer from Harrison Street and Myrtle Avenue to the South Villa lift station, located at Sugar Creek Golf Course. Relief sewer design was necessary in order to provide alternative means of wastewater flow and in-line storage capacity to attenuate peak flow conditions.
The project entailed the design of a 3,000-lf gravity sewer that ranged in size from 8 to 21 in. A survey of approximately 2,700 lf along Harrison Street, Myrtle Avenue, Julia Drive and Villa Avenue was conducted.
A 225-lf section of the proposed sewer line (14-in. OD) crossed the newly reconstructed South Villa Avenue. Additional project complexities were encountered because the sewer route also traveled under Sugar Creek.
The existing pipe under the creek had deteriorated at the joints and was allowing significant inflow and infiltration (I/I) into the sewer system.
Several no-dig construction alternatives were evaluated for construction of the roadway and creek crossing sections including directional boring, pipe bursting and pipe ramming. Directional drilling techniques provided the most cost-effective solution for preserving the roadway pavement and replacing the existing pipe section under the creek.
Replacement of the 225 lf of pipe that crossed under South Villa Avenue required no excavation in the new roadway and had minimal impact on traffic flow. The existing 175 lf of sewer pipe running under Sugar Creek was upsized with new high-density polyethylene (HDPE) plastic pipe with fused joints to eliminate any potential inflow and infiltration from entering the system from the creek.
After installation of the sanitary relief sewer and the rehabilitation of sewer lines, the wet-weather flow situation has improved in three ways:
1. Reduction in base infiltration levels
2. Shaving of the inflow “peaks”
3. Faster recovery time to normal flow levels at the downstream pump station
RJN and the Village could not easily estimate the level of I/I reduction that would be achieved through the mainline rehabilitation program. The smoke testing showed that the laterals, as well as their connections to the main line sewers were in poor condition, and often in such cases, “flow migration” up the defective laterals can offset some of the I/I reduction anticipated by lining the sewers.
However, given the severity of the condition of backyard VCP sewers and the deteriorated concrete pipes, it was thought that a measurable flow reduction might be evident following rehabilitation. The southern basin discharges to a pump station, so in the absence of flow meter data, RJN and the Village analyzed the pump station data in the years prior to the comprehensive rehabilitation and then compared it to the data from the last 15 months.
Analysis was complicated by the unusually high rainfall total this spring and summer, which prevented the groundwater table from receding to typical summer levels, making it difficult to determine whether there had been a reduction in base infiltration. However, data taken from post-rehabilitation fall 2010 pump station records indicates at least a 5 percent reduction in base infiltration.
Overall, the data shows that the station now returns to normal pump run times much faster after a rainfall, and a detailed analysis of the pump station data indicates a 15 percent reduction in the total inflow generated by a one-year storm and a 30 percent reduction in total inflow from a five-year storm, as compared to the pre-rehabilitation conditions.
Anecdotal evidence from Village staff indicates that the rise in the lift station wet well levels is not as severe during rain storms. As an example during a large storm in July 2011, (greater than a 25-year event), the pump station did not experience an overflow.
Catherine Morley, P.E., is project manager for RJN, Vincent Bergl, P.E., is an engineer with RJN and Vydas Juskelis, P.E., is public works director for the Village of Villa Park, Ill.