An effluent pond in Southeast Texas was suffering from years of erosion. Recently, an escalation of subsurface water seepage through the pond’s embankment threatened the community’s main water source.
Quail Valley is a residential community located in Missouri City, Texas. The small community is filled with ponds and flowing creeks. An effluent pond in Quail Valley was suffering from soil erosion at its east bank. Erosion control at the pond had been an ongoing struggle and concern for the Missouri City officials and the Public Works Department. The pond is part of the Quail Valley Waste Water Treatment Plant, and through wastewater reclamation, the pond is used to water nearby fairways at the city-owned Quail Valley Golf Course.
Over time, the pond bank’s minor erosion issues escalated to the extent that water was traveling through the bank’s subsurface soil, entering Stafford Run Creek more than 10 feet east of the pond. Standing atop the bank, an individual could see where water was flowing from the pond to the creek. The pond was slowly draining into the creek through the east bank, while, simultaneously eroding and weakening the bank soils. If the problem continued unaddressed the city could lose its watering source for golf course fairways and the weak bank could potentially collapse, damming Stafford Run Creek.
In 2010, a portion of the troublesome pond bank was mudjacked with cementitious slurry in an attempt to stabilize bank soils and cut-off water migration. Unfortunately, the solution was only temporary. Bank soils continued to erode and water continued migrating into Stafford Run Creek. As needed, rip-rap was brought in to fill-out and improve structural integrity at the degrading bank. The effluent pond lies within sight of golfers at Quail Valley Golf Course, as a result, in 2013, while golfing, Missouri City mayor, Allen Owen, noticed that the pond was extremely low. He immediately notified Public Works Department employees. Soon afterwards, the east bank had a major blowout due to heavy rains. It was decided that a permanent solution was needed to stop erosion and water migration.
Working off a 2012 geotechnical study of the pond bank, companies began submitting solutions. One engineering company presented a solution that was expected to cost upwards of $1 million. In the end, the city awarded the contract to URETEK ICR Gulf Coast, a specialized groundwork contractor that uses geopolymer injection methods. URETEK proposed an economical solution that would stop water migration and stabilize bank soils with minimal site work. They intended to create an underground curtain inside the bank by utilizing a polymeric compaction grouting method. The underground curtain would travel along a large portion of the east and south bank. It is designed to stop migrating water, cut-off potential migration routes and provide much needed structural support to the pond bank.
The project was proposed and designed by URETEK’s Blake Grappe, project and sales manager. Grappe planned on using a method similar to mudjacking, but instead of using cementitious slurry, they would be using their patented geopolymer and they’d be injecting it deeper into the bank. URETEK’s geopolymer, also known as polyurethane foam, is a two-part poly that, when mixed, expands into a high-density, structural grade foam capable of lifting and supporting multi-tonnage. Another important characteristic to stopping water migration is its closed-cell makeup and hydro-insensitivity. The geopolymer’s closed-cell makeup will allow it to expand and cure in the presence of water and its hydro-insensitivity will allow it to repel water and maintain structure in heavily saturated conditions.
Soon after Missouri City accepted the proposal, URETEK technicians mobilized to make bank repairs. To create the underground curtain, a series of linear holes were drilled every five feet along the east and south pond bank.
The holes are injection sites for the geopolymer. Starting at -20 feet, URETEK technicians began injecting geopolymer to depth, where it expands. As the geopolymer expands, it compresses loose soils, fills subsurface voids, fissures and bonds with surrounding soils. Technicians watch for visual cues like outcropping or soil movement. These signs demonstrate positive results.
After injecting at -20 feet, technicians inject at -15 feet, then -10 feet and finally -5 feet. Technicians then move to an adjacent hole and repeat the injection process, creating a water-tight underground curtain one section at a time. At an especially weak section of the east bank where migrating water had heavily eroded the bank, three rows of underground curtains were created for extra reinforcement.
By the end, URETEK injected geopolymer at more than 100 injection sites,successfully creating a 500 foot underground curtain along the east and south pond bank. All water migration ceased and the effluent pond was contained. Pond bank repairs allowed the city to continue using its reservoir to water golf course fairways. “I’ve used geopolymer in similar ways for past projects and had great success,” said Grappe. “I had no concerns whether or not it would work. Our geopolymer is a versitile tool that can be applied in many applications.”
Project of the Year
URETEK ICR Gulf Coast’s efforts were recognized by the American Public Works Association’s Texas Chapter for Project of the Year Award– (less than $2 Million) at the TPWA’s 2014 Annual Conference’s Reception and Awards Banquet in Galveston, TX on June 19, 2014.