Idaho Wastewater Facility Expands

Story by Stephanie Worrell | September 28, 2010

It's a given that growth can be glamorous, producing eye-pleasers such as beautifully designed buildings and state-of-the-art roadways. Yet, as most everyone in the commercial construction business knows, the backend of growth — what's underneath — is usually the most crucial.

That is, of course, the case when it comes to building or expanding a wastewater treatment facility in response to rapid growth. In Meridian, Idaho — one of state's fastest growing communities — the current wastewater treatment plant is in the middle of a two-year Biosolids Improvement Project carrying an approximate $10.3-million price tag.

The job, scheduled for completion in September 2008, is being built by the Ewing Co. Ewing is well known in the region for its wastewater treatment facility work, including major wastewater projects in Eagle, Caldwell, West Boise, Horseshoe Bend, and Ontario, Ore.

"The city of Meridian completed a Wastewater Treatment Plant Facility Plan Update in 2004 that identified a series of upgrades that would be needed over the next several years," said Clint Dolsby, assistant engineer for the city. "Following the completion of the Facility Plan Update, we selected Carollo Engineers to design the project that consisted of upgrades to the liquid and solids stream at the wastewater treatment plant."

According the city's website, Meridian has grown by over 400 percent since 1990, and the Wastewater Division's treatment capacity has kept pace with growth. Proactive planning and construction of needed treatment processes have kept Meridian on the high end of projected growth curves.

JC Constructors (Meridian, Idaho) was awarded the initial bid for the liquids phase improvements in September 2005 for $8.4 million. Then in September 2006, the Ewing Co. was awarded the bid for the Biosolids Improvement Project.

Additional Capacity

The Biosolids Improvement Project consists of construction of cast-in-place concrete structures, including two 750,000-gallon anaerobic digesters with fixed steel covers, digester gas-conditioning equipment, progressing cavity sludge transfer pumps, dewatering centrifuge, and hot water boilers, including miscellaneous process equipment, piping, electrical and controls, coatings, and appurtenances.

"Upon completion, the facility will provide solids stream capacity for the next several years," said Dan Crawford, Ewing Co. superintendent and a 31-year industry veteran. "It should keep up with the growth in the area and provide solids stream capacity for the next several years."

The city of Meridian Wastewater Division of the Public Works Department operates and maintains a 5.5- million-gallon-per-day wastewater treatment plant and more than 200 miles of sewer lines, which will be elevated to 9 mgd when the current project is complete. Construction on the wastewater plant adds 4 million gallons of capacity along with the capability to remove nutrients that cause water quality issues in the environment.

Sommer Construction of Nampa prepared the site for the current phase and installed the exterior piping, which included a wide range in diameter of ductile iron and Schedule 80 PVC piping. The new interceptor pipelines vary in size up to 42 inches in diameter. The new pipe is larger in diameter and will increase the carrying capacity necessary for the growing population.

Because there were no extraordinary environmental issues related to the site prep, a good Storm Water Pollution Protection Plan (SWPPP) prepared prior to construction was the foremost environmental concern.

The SWPPP has been carefully administered to ensure that there has been no potential to cause water pollution. Implementation of the SWPPP began when construction began, even before the initial clearing, grubbing and grading operations, since these activities can usually increase erosion potential on the site. During construction, the SWPPP plan has been referred to frequently and amended as changes have occurred in construction operations, which could have significant effects on the potential for discharge of pollutants.

Crawford noted that this project has included SWPPP efforts such as dust control and ensuring that the fuel oil does not contaminate the soil or atmosphere, along with protecting the nearby canal bank.

Lots of Stainless Steel

Lacey Mechanical of Boise installed all of the interior piping related to the project, including ductile iron and galvanized stainless steel piping. Again, corrosion is a foremost concern, which is why stainless steel piping is utilized. Hot and cold water lines will heat the digesters and keep the matter inside the digesters at the proper temperature.

"The use of this much stainless steel on a project is rare, but necessary due to corrosion issues," said Crawford. "Only in hospital and restaurant construction is it as prevalent and necessary."

All of the structures in this current phase of construction are complete. Crews are fitting the structures together with piping and are about two-thirds finished. Crawford noted that the entire project should be completed prior to the September 2008 deadline barring any extraordinary circumstances.

Massive amounts of concrete and rebar were used to build the two digesters — the walls are 16 inches thick and the floors 31 inches, while each measures 70 feet in diameter and 28 feet in height. A 1,300-square-foot, split-block, state-of-the-art control building is included in the digester facility construction.

"Over 1,000 cubic yards of concrete was utilized in forming the floors and walls, totaling approximately 1.4 million pounds," said Crawford. "The weight provided by the concrete is important to create buoyancy."

The steel dome covers, which will be placed on top of each digester, weigh about 70,000 pounds and are currently undergoing multiple applications of polyurea protective coating to defend against corrosion — 64 millimeters thick.

"You can't apply the coats all at once because they need to dry in between to achieve maximum thickness," said Crawford. "And, the weather can play a big role because of temperature issues."

Once the protective coating process is complete, the massive domes with be set with a large commercial crane, then they will be vacuum-tested to ensuring proper sealing.

Final Phase

Setting the domes and tying the facility together with piping will prompt the final phase of construction — ensuring everything is operational and ready to serve the citizens of Meridian, Idaho.

The project also employs glass-lined ductile iron pipe, adds a redundant scroll-type centrifuge for dewatering digested sludge and two 60-horsepower boiler units that supply hot water to jacketed draft tube mixers used to heat digester sludge. Scrubber and booster equipment is being used to condition digester gas for use in the hot water boilers, which saves the City money over using natural gas.

Additional key construction subcontractors for this phase include Quality Title of Boise (roofing), Color Craft of Boise (painting), Custom Electric (electrical) of Emmett, Specialty Painting of Twin Falls, and Specialty Coating (dome coating) of New Jersey.

"During this project, we have utilized proven technologies combined with the experience we have at the wastewater plant from operating similar systems to give the best product for the city," said Dolsby. "Additionally, we have been keeping an eye on the project budgets to avoid unnecessary costs."