Reinforced Polypropylene Geomembrane Lining Material Offers Solution to Challenging Irrigation Reservoir Project
Extreme weather conditions combined with an aggressive project schedule posed many challenges for an irrigation reservoir project located on the newly developed Little Creek Casino and Resort property in Washington State’s Kamilche Valley. Though monumental at times, the challenges did not hinder the successful and timely completion of the job.
The irrigation reservoir is part of a multifaceted wastewater reclamation and reuse project initiated by the Squaxin Island Tribe, which owns the land in Kamilche Valley.
The property development plan included the construction of the region’s first small membrane bioreactor wastewater reclamation plant, which treats 150,000 gallons of water per day. The plant receives wastewater from the tribal government campus, the resort and casino, and a residential area on a neighboring hillside. The wastewater plant then treats the effluent and transports it as Class A reuse water into a 7.3-acre irrigation reservoir with a capacity of 23.25 million gallons. Water from the reservoir is available for many uses including irrigating the resort’s Salish Cliffs Golf Course, regional fire suppression, and as reuse water on the resort property.
Part of something bigger
According to Dan Neelands, construction manager for the Squaxin Island Tribe, the irrigation reservoir not only serves the immediate property area, but the entire region. In addition to treated wastewater, the reservoir serves as a harvest point for rainwater coming from an area of about 1,000 acres.
“In 2004, as part of a major upgrade to Olympic Highway — which runs right through Kamilche Valley — the Squaxin Island Tribe and Indian Health Service allocated funds to install reuse lines throughout the region,” said Neelands. “Instead of just laying new sewer and water lines, we added the reuse lines so that rainwater from the entire area can be fed into the water reclamation plant and ultimately into our reservoir. Water can then be pumped back out to the region, as necessary, for fire suppression or irrigation. Essentially, what we’ve done is to take control of water management in our valley.”
Although Washington has very stringent rainwater management regulations, the tribe is a sovereign nation and, as such, was not required to meet state regulations. They did, however, choose to meet them voluntarily. Additionally, the tribe was required to comply with EPA operational standards, as well as those set forth by the National Pollutant Discharge Elimination System (NPDES). As a result, the water reclamation system is in full compliance with all governing bodies.
In addition to governmental compliance, collection of runoff water was crucial to the Squaxin Island Tribe. “This is a fishing tribe that has treaty fishing rights in this area, so we are extremely sensitive regarding what water runs off this property and into the fish-bearing streams. We don’t want anything to harm the aquatic life of our waterways,” said Neelands.
Reservoir site and design
According to Craig Peck, project engineer for Craig A. Peck and Associates, Tacoma, Wash., several factors were taken into consideration when selecting the location for the irrigation reservoir including soil permeability, equipment access and availability for disposal of excavated material. Several locations, both on site and off site were reviewed.
“Irrigation volume requirements for initial grow-in and annual maintenance of the golf course also were analyzed and compared with treatment plant discharge and available runoff from resort and industrial drainage basins,” said Peck.
The construction team ultimately selected a hilltop site in the southeast corner of the casino property. “In addition to these many factors, this particular site was selected so that we could take full advantage of gravity,” said Neelands. “Everything about this system took gravity into consideration. The wastewater plant is at the lowest point of the entire valley, and the reservoir is at one of the highest.”
Once the site was determined, drilling equipment was brought in to conduct subsurface soil exploration and geotechnical analyses to locate suspected rock layers. “As rock was located, we adjusted the reservoir design to retain maximum volume while avoiding areas that could require blasting,” said Peck. “We made several adjustments throughout this process, but the resulting size and shape met our volume goal.”
The reservoir’s sustainable design also met the Squaxin Island Tribe’s cultural requirements. “Many irrigation reservoirs of this kind simply take up valuable real estate and are an eyesore. That would not be acceptable here. We found a way to offer function without sacrificing aesthetics,” said Neelands.
Site challenges
Excavation of the irrigation reservoir began in October 2006. According to Jeff Boys, vice president and project manager for ACF West, Portland, Ore., soil composition, high water tables, rain and extreme cold temperatures provided significant challenges to the project. “The water tables in this area are very high to begin with, and excessive rains only made the excavation more difficult,” he said.
Ideally, the reservoir project would have been delayed to allow for winter to pass and the ground to dry out a bit; however, an aggressive construction timetable was needed to allow the casino and resort to open on schedule in mid-April 2007. “The owners needed to get the reservoir in line with the wastewater reclamation plant in order to service the property’s facilities, so the project had to proceed in spite of the weather conditions,” Boys said.
Although the water tables were high, the soil was too permeable to retain the water volume required in the reservoir. This presented an interesting “Catch 22” situation.
“We realized that we would have to install a lining system to ensure a somewhat consistent volume,” Peck stated. Neelands investigated several materials and suppliers, and Peck concurred with his recommendation.
The construction team initially specified an EPDM lining material due to its many desirable characteristics, but they ultimately changed the specification to fPP-R Geomembrane, a reinforced polypropylene membrane. The heat-welded seams of the product made it ideal given the wet and cold winter conditions. Other product characteristics that made fPP-R Geomembrane the right choice for the application were puncture resistance and minimal elongation.
“Elongation of reinforced polypropylene is minimal compared to competitive products, so deploying the panels on the long, sloping sides of the pond was easier because we didn’t have to worry about the membrane moving around as much,” said Boys. “A non-reinforced product would have been much more difficult to work with on this project.”
As with the excavation, high groundwater levels created the biggest challenge for the membrane installation. To overcome the problem, ACF West recommended the installation of underlayment materials over the mud floor of the reservoir. “The engineer wanted to make sure that the membrane didn’t float. To prevent this from happening, we put down a non-woven cushion fabric and a geocomposite drainage material as an underlayment system not only to provide a good base for the membrane, but also to allow water to be drained from underneath it,” Boys said.
To prevent water from accumulating under the lining system, a well was dug next to the reservoir and pipes were installed on the pond floor to draw water up from underneath the membrane and into the well. “This takes ground water pressure off the lining system, and then the water can be reclaimed by pumping it back into the reservoir,” said Boys. During the membrane installation, water was continually being pumped out into the well.
A total of 12 pipes serve to pump ground water into the well, and can also be used for irrigation purposes. Additional pipes were installed at various levels around the perimeter of the reservoir, which serve to pump water into the reservoir from the wastewater reclamation plant. Custom pipe boots were fabricated from the fPP-R Geomembrane and sealed around each pipe.
During the membrane system installation, there were several inches of standing water in the reservoir at all times. To account for this, numerous custom-sized fPP-R Geomembrane panels were prefabricated from 60’ x 250’ rolls to fit the site and reduce waste. The remaining 14 seams were field-welded using a custom-built floating support system. “We used a large foam block and wrapped it in membrane. Then, we put that block under our wedge welder and pulled it across the seams on this floating device so that we could weld out of the water,” said Boys.
Successful outcome
Installation of the membrane began in mid-February 2007 and was completed on schedule 10 days later by a crew of 12 men. Water was first pumped into the reservoir from the wastewater reclamation plant in April 2007, and the reservoir already has been used to irrigate the golf course, which is scheduled for phased completion in 2009.
Article provided by Firestone Specialty Products, an Indianapolis-based leader in the lining and geomembrane; modular roofing; thru-wall flashing and sustainable products industries. For more information, visit www.firestonesp.com.
