Case Studies Case Studies: Treated Wastewater Pipeline Restoration

Thursday, November 11th, 2021 by Brooke Donnelly

Challenge

The Orange County Sanitation District is a public agency that provides wastewater treatment for approximately 2.6 million people in central and northwest Orange County, California. The sanitation district has two reclamation plants; Plant No. 1 located in Fountain Valley and Plant No. 2 located in Huntington Beach. The treatment plants include aboveground and underground pipelines and flow control structures for wastewater inlet and treated water outlet. An outflow system is used to discharge treated wastewater not needed for further treatment at the water treatment plant. At plant No. 2, the outflow system includes a main outflow pipeline and a backup outflow pipeline, which is used for overflow or if the main pipeline needs to be shutdown for repairs. An interior inspection of the backup outflow pipeline at Plant No. 2 showed that two, 60-inch diameter, reinforced concrete outlet pipelines had experienced vertical and horizontal movement along an approximate 27-foot long section. The movement had resulted in separation of the rubber seals between some of the pipe sections, which allowed soil to enter and collect at the bottom of pipe. Ground penetrating radar (GPR) was used to identify voids in the soil surrounding the pipelines. The results of the GPR survey showed approximately 100 cubic feet of voids around the pipelines. Based on the results of the pipe inspections and GPR survey, an option to fill the voids surrounding the pipelines and repairing the pipe connections was needed. The void filling and repairs would be performed from inside the pipelines, which would require a confined space permit and installers certified to work in confined spaces. Another complication for the project was that the backup outflow pipelines discharged into the Santa Ana River and during periods of high tide, river water could enter the pipelines. To prevent water from entering the pipelines during repair operations, temporary dams would need to be constructed within the pipelines at the discharge end.

Solution

The optimal remedial repair method for the void filling was determined to be injection of high-strength, rigid polyurethane foam. PolyLevel® PL400 was the chosen foam for the application, given its high strength, fast reaction time, low weight, and hydrophobic properties. PolyLevel PL400 is a two-part liquid urethane that is mixed and injected through small 3/8-inch drilled holes in the slab to expand into a rigid foam with a compressive strength of 70 to 80 psi and an in-place density of 4 to 6 pcf. The line of PolyLevel expanding foam products is ideal for filling voids and stabilizing concrete, or with strategic and continued injection, lift settled concrete back toward its original elevation. Given the confined space requirements, the installation crew used Self-Contained Breathing Apparatus (SCBA) units for the foam injection operations. Access to the pipelines was through the flow control structures. The temporary dams were constructed at the outlet of each pipeline and approximately 400 pounds of PolyLevel® PL400 were injected into the base of the pipelines to fill any voids and stabilize the pipeline support. Then another 400 pounds of foam were injected at void areas detected by the GPR survey and at 2, 4, 8 and 10 o’clock positions around the pipeline circumference. Injection points were spaced at 3 feet in these positions along the length of the pipeline. At areas that required pipeline section seal replacement, the foam was applied between the pipeline joints. The joint seal replacement was performed by the general contractor after the void filling operations. Saber completed the polyurethane foam injection work in two days.

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