Session 25A: Collection & Conveyance
8:00am - 8:45am
Corroded Manhole Assessment, Rehabilitation Design, and Construction
1Jacobs, Boise ID; 2Eagle Sewer District, Eagle ID; ,
Concrete manholes should have more structural strength than peanut butter, but PB-consistency concrete is exactly what Eagle Sewer District found as they conducted their periodic inspection of one section of collection system manholes. The culprit was found to be hydrogen sulfide corrosion from two nearby forcemain discharges. These forcemains, coupled with a very steep sloped pipe (up to 8 percent) down a hillside farther down the main were enough to release H2S that corroded the manholes faster than expected. Compounding the problem was the location of this main, through a high-end neighborhood and adjacent to a golf course. The groundwater up on the hill was not a factor, but the section at the bottom of the hill was in nearly 10-feet of groundwater.
The manholes were assessed first visually and then with a scrape test. From the ground, the 15 to 18-foot deep manholes appeared to be in good to fair condition. The scrape test was performed and the softened concrete sluffed from the wall like tooth paste or soft plaster. The downstream section of the system yielded less than 1-inch of concrete loss. As we worked upstream to the base of the hill and closer to the pump station discharges, up to almost 2-inches was discovered. Next to the pump station discharge, 3 inches of the 5-inch thick manhole wall was missing.
In addition to the condition assessment approach, this presentation will discuss the manhole rehabilitation methods that were considered. These include manhole replacement, liners, inserts, structural coating, and non-structural coatings for corrosion protection. The final design that resulted and the ultimate rehabilitation project will be presented. Lessons learned that will be shared include the how to complete rehabilitation technologies and coordination with neighbors and interested agencies. The manholes were successfully rehabilitated and have performed well for nearly a year and a half.
8:45am - 9:30am
Bringing Spiral Winding Rehabilitation to the Pacific Northwest
1Brown and Caldwell, United States of America; 2City of Portland, Bureau of Environmental Services; ,
Spiral Wound Technology TM (SPR) is a pipeline rehabilitation method using strips of PVC or HDPE. Winding machines unroll strips of material that form to the pipe's shape, creating a new lining. The City of Portland Bureau of Environmental Services (BES) will be using the PVC SPR material on the Carolina Trunk rehabilitation project. Utilities across the globe have installed lining using SPR, including a few in the USA, but this is the first application in the Pacific Northwest. BES often uses pipeline rehabilitation on its aging infrastructure to extend the useful life of its sewer pipes. Upon successful completion of this pilot project, BES plans to add SPR to its toolbox of available rehabilitation techniques for future projects.
A significant advantage of SPR is the ability to install the material without flow diversion. With this method, it is possible to install lining with live flow during low flow periods. Since the Carolina Trunk is a combined sewer, we scheduled the work to take place at night during the summer when there are no rain events expected. Due to the Carolina Trunk's location along a busy arterial, being able to rehabilitate the sewer without diverting flow is critical to project success.
Constructed in 1909, the Carolina Trunk is a 51-inch diameter cast-in-place monolithic concrete circular sewer pipe. Several inspections revealed that the pipe is in fair to poor condition and needs rehabilitation. Defects observed throughout the pipe included longitudinal cracking and pipe deterioration with exposed aggregate and pitting. This project will rehabilitate approximately 800-feet of the trunk using SPR rehabilitation.
9:30am - 10:15am
Implementation of Telemetered Water Quality Sensors in the Sanitary Collection System
Clean Water Services, United States of America;
Collecting continuous, reliable water quality data from the sanitary collection system without an excessive maintenance burden is a serious challenge for utilities, but one that is increasingly necessary for developing enhanced source control programs and protecting treatment plants from potential upsets. For several years, Clean Water Services (CWS) piloted various technologies, implementation methods, installations, and cleaning devices. While none of these pilots were ultimately successful, important lessons were learned in each of them that helped drive CWS towards successful implementation. Over the past two years, CWS has successfully developed and implemented a telemetered, continuous water quality sensing network in its sanitary collection system and has already been successful in tracking down and eliminating a consistent source of problems for one its treatment plants. CWS has developed a unique sensor holder that minimizes ragging and made use of robust sensors that are less sensitive to fats, oil, and grease buildup. To test this technology in addition to future technologies, CWS developed a test flume at its Forest Grove treatment plant that uses post-grit screen influent. This flume can be adjusted to simulate various velocities, depths, and sewer sizes and allows for the study and testing of different sensors, cleaning devices, and containment devices with close observations in a controlled environment that wouldn’t be possible in the sanitary collection system. CWS has conducted various experiments using this flume to study the factors that affect longevity, film buildup, and maintenance frequency for various probes. The lessons learned through CWS’s first few years of unsuccessful pilot studies were presented at PNCWA in 2019. In this talk, CWS will discuss how it finally became successful at developing and implementing a network of water quality sensors in the sanitary collection system, and where it is going from here.