Quality Pipe Services, Inc. (QPS), based in Denver CO, was contracted by Evanco Environmental to rehabilitate badly deteriorated onsite sanitary collection system structures at a major beverage manufacturing plant. Using a mix of technologies including Sprayroq SprayWall lining, QPS managed to rehabilitate and bring the system back online by year’s end.

Problem: The plant’s sanitary sewer line collapsed, causing a huge wastewater backup into the plant. The plant manager realized that the “out of sight, out of mind” syndrome had led to the wastewater collection system never being inspected. The complete system was inspected, revealing that manufacturing process chemicals had severely corroded its concrete structures over 15-20 years.

Affected were two underground vaults, Structure 3-A (approx. 20 feet deep and 20 feet wide), and Structure 3-B, about 15’ x 15’, each with three inlet pipes. Together, they totaled about 10,000 sq. ft. of surface area. These served as collection structures for sanitary wastewater and plant runoff that ran to an on-site treatment plant. They were located beneath the plant’s discharge tanks, between large stairways and next to a railroad line, creating significant accessibility issues.

Also included in the project were the system’s pipelines (rehabilitated by Evanco Environmental, the managing contractor), and 18 manholes downstream of the vaults, totaling roughly 200 vertical feet. Those were also concrete, from 6 to 20 feet deep, and similarly corroded to the point that workers could put their hand all the way through the walls to touch the soil outside.

A creek runs right alongside the plant, so the water table is about nine feet high, creating a significant hydrostatic load that triggered substantial water infiltration into the system’s concrete structures. A very narrow dirt road along the embankment next to the creek had to be widened for QPS to drive their service truck to the work site, but it remained a one-way route, creating logistical access difficulties.

The whole system (2,000-3,000 feet of pipeline and structures) had to be bypassed for nearly three months while preparation and work took place, because the entire rehabilitation had to be completed before the system could be brought back online.

Solution: Two structural lining solutions were considered for the manhole structures; a CIPP liner, and Sprayroq SprayWall®. SprayWall was chosen both because it would work best in conjunction with the rebuilding of the deteriorated structures, and because it provided the best long-term protection for the money.

Evanco Environmental handled the pipeline segment of the system rehabilitation. QPS subcontracted the rehabilitation of the two underground vaults and the 18 manholes.

QPS crews started their rehabilitation at the far end and worked back toward the plant, so the manholes were done first.

Initially, technicians were concerned with the threat of the manholes collapsing because they were in such bad shape. Manhole covers had to stay off until the work was finished, because the crumbling structures couldn’t support them. Road plates and special driving mats had to be put over and around them so that vehicles wouldn’t cause them to collapse. Safety measures such as interior bracing were taken to reinforce the walls to minimize the danger. Where a section of pipeline did collapse, an HDPE manhole was installed and Spraywall applied to both the manhole and that length of pipe.

All manholes required complete removal of corroded material, which was done using a pressure washer. Then QPS technicians applied chemical grout to stop water infiltration. In stubborn spots, they applied one of the high early strength cementitious non-shrink grout to be sure no more water would come through.

After that, two plus inches of one of the high early strength cementitious  rebuilding mortars was used to build back to original surface profile. This process essentially rebuilt the entire structure to industry standard ICRI CSP 4-CSP 6 (International Concrete Repair Institute Concrete Surface Profile), before spraying 500- 827 mils of SprayWall to protect it. Each manhole required about four days of prep work and another three days for the spray lining application, roughly a week each in total. ASTM F1216-09 Appendix X1 protocol was used to calculate the mil thickness to withstand the external loadings, for the Fully Deteriorated manholes lining system.

This work was all performed during very cold weather (10° F and below), and the structures needed to be brought to at least 50° F ambient temperature for effective materials performance. They couldn’t risk the linings being compromised by dampness or freezing. The QPS crew built large huts that were moved over each manhole with a forklift to create a more or less closed atmosphere, and the structures were heated using portable forced-air heaters.

QPS then moved on to the two vaults, whose concrete lids had to be sawed off to create an open pit for their rehabilitation work. Scaffolding was erected inside to apply more than one inch  of cementitious mortar for build-back material to the entire structure, which took two days. Key-in grooves (¼ in. deep and ¼ in. wide and at 60º opposing angles  were spaced at 36 inches along the vertical surfaces, to help the Spraywall liner lock into the concrete substrate and provide additional structural strength. The structural spray of750 mils of Spraywall took another three days to complete.
Note: Sprayroq's proven Flat Wall Design was used to calculate the structural mil thickness that was successfully applied.

Due to the limited access, the spray lining trailer had to be parked 50-75 feet away. The largest vault's first layer of 250 mils was sprayed from the bottom up by multiple shifts of technicians, to make the most of short daylight working hours. The next three days since the re-coat window had closed, each new surface had to be prepped to accept the second and third layers. Following the same process, the smaller vault, which had a design of 500 mils took two days to complete.

The structural design calculations were completed and sent in for review late June 2014. The project was started before Thanksgiving and some crews worked over the Christmas holiday to get it completed by year’s end. There were 6-8 crew members onsite during rehabilitation operations, and most weeks they worked 6 days, though some Sunday work was required.

Result: The plant’s wastewater management system was rehabilitated and placed back in service after three months of being bypassed. Approximately 18,000 lbs. of SprayWall structural liner material was applied over an estimated 200 fifty-pound bags of StrongSeal Profile Plus mix in the vertical structures, to assure long service life of potentially 50 years or more. The entire project was completed ahead of schedule, with costs totaling about $300,000. It was so successful that QPS has been hired through another contractor to come back in September 2016 for further work at the same plant, with future projects being discussed.