ROCK RUN: JOLIET'S LARGE DIAMETER RURAL INTERCEPTOR REHABILITATION

Interceptor Details The Rock Run Interceptor is a large-diameter reinforced concrete sanitary interceptor tributary to the City of Joliet's Westside WWTP, carrying average daily flows (ADF) of 10 MGD and peak daily flows of 15 MGD without accounting for inflow and infiltration (I/I). Its diameter ranges from 42 inches to 60 inches. Much of the interceptor is in remote locations in forest preserves along Rock Run Creek. The interceptor was inspected with multi-sensor technology which found signs of significant deterioration due to the effects of hydrogen sulfide attack. Almost all inspected segments had visible aggregate, the beginning stages of corrosion, and/or exposed reinforcement. To avoid cherry-picking segments, the City determined to address the areas with the most badly deteriorated pipes and rehabilitate two sections along the creek comprising about 6,500 linear feet of 42-inch pipe and 2,650 linear feet of 48-inch pipe The Project Alignment The route started north of a fire station, which had to maintain 24/7 ingress/egress. It then crossed the approach path for the Joliet Regional Airport and continued along the creek, crossing rural roads on its way and picking up pumped flows from neighboring districts. At the southern end, the sewer crossed under the Illinois and Michigan Canal (I&M) which is under the control of the Army Corps of Engineers (USACE). Engaging and managing the needs of all the stakeholders was a major undertaking. Bypass Pumping The bypass pumping required an extraordinary amount of planning, as its path encompassed a canal, creek, airport and trail. The bypass system was comprised of three 12-inch pumps and an 18-inch suction discharge, capable of pumping over 30 MGD. The work was broken out into two sections, the upper and lower bypasses - the upper bypass encompassing approximately 9,000 feet, and the lower bypass equaling 2,600 linear feet. The upper bypass had to work around the fire station, airport and numerous small creeks. For the portion near the airport, none of the bypass segments could encroach on the airport property, so large concrete blocks were used to contour the bypass pipe around the perimeter of the airport grounds and behind the fire station. I&M Canal Crossing The bypass lines crossed numerous small creeks, as well as the I&M canal. The USACE determined that the canal was non-navigable, so a large, elevated structure was not required. Consequently, a floated bypass was approved for the crossing. The work had to be completed by January, so as open the canal trail to snow mobile users. Access and Protection For the CIPP lining massive machinery was used to facilitate construction. The largest truck was a 90,000 pounds tractor-trailer, which even required special permits to drive on public roadways to the site. In consultation with the Forest Preserve, a minimum of trees was removed for work to proceed. For the remaining trees in the immediate area, trunk padding was applied to protect them. Forest floor protection was comprised of swamp mats, which made it especially tricky to navigate the 45 ton truck on such a small footprint. Further complicating matters, two 30-inch high-pressure gas transmission pipelines also crossed the area. The gas company required that anywhere equipment or bypass piping crossed these pipelines also had to be protected due to the heavy loads. This expanded the area of swamp mats needed significantly. CIPP Lining For the most part, the lining went as planned, however, a few snags were encountered along the way. The entire project was designed to be completed during the winter months when trail usage was minimized, however this posed challenges for pipe curing. To ensure the proper temperature was achieved for complete curing, temperature sensing wire was run throughout the alignment. Obtaining enough water to cure large diameter pipelines in the middle of a forest preserve added a degree of difficulty. Water was pumped from approximately 2,000 feet away, which required a booster pump to help get the flow to its destination. Rehabilitating the Manholes Concurrently manholes along the alignment were rehabilitated using epoxy liner. The challenge was to reconcile the difference in material thickness between the CIPP and the epoxy coating. To do this, engineers worked with the epoxy manufacturer to specify a sand bulking agent to provide a thicker epoxy coating that would seamlessly blend the manhole lining with the thickness of the new CIPP to create a rigid, water-tight structure. The winter weather also created challenges for manhole rehabilitation efforts. For the epoxy to cure, temperatures had to be above freezing. This was achieved by placing tents over the manholes and heating the tents while the work was performed. This raised the ambient temperatures of the structure and enabled proper curing to occur. Community Outreach Work began early on to generate buy-in from stakeholders. Condition images were shared with relevant parties to impress upon them the necessity of repairing the Interceptor before a failure occurred. The trail was kept open throughout the duration of the project, save for temporary closures to allow for work to be undertaken in the immediate vicinity. Press releases were distributed to inform the public about trail detours and temporary closures, and temporary structures were built to ensure the public was able to safely cross over the large bypass pipelines. Project Impacts Beside restoring the structural integrity of the Interceptor, the project had a few other lasting impacts for the area. While the tree cutting crews were on site, as part of forest preserve negotiations, an additional swath of invasive trees was removed from between two prairies. This helped the preserve achieve their goal of creating a single unified prairie. None of the trees that were removed were chipped on-site. This ensured the aesthetics of the areas were preserved and maintained a clean, natural appearance for forest preserve visitors. Even though swamp mats were used, the nature trail bore signs of heavy construction equipment. So remediation efforts were made to restore the trail, which ultimately saw its condition improved to a greater degree than before the project was started. Conclusions The project was highly successful thanks to the high level of pre-planning and coordination. While heavy storms and negotiations with the forest preserve caused some scope creep - cutting down an entire swath of trees that divide two huge prairies will do that -- the overall project was completed on budget and within the adjusted time frame.