Waste Water Treatment Plant Expansion

Context

The City of Fernley’s Water Treatment Facility was completed on October 21, 2009. The facility was designed and constructed to bring the City of Fernley into compliance with the United States Environmental Protection Agency’s (EPA) Clean Water Act. The area has naturally high levels of arsenic, which must be processed and removed from the water. To do so, raw water enters the plant and is injected with an iron-based liquid (coagulation) which acts as a “magnet for arsenic.” The coagulated water will then be mixed up (flocculation) in one area, and then allowed to settle (sedimentation) in another area. Any remaining arsenic will be removed when the water is put through filters with very tiny pores (microfiltration). Any material that will be removed in the process will be sent to ponds, dried, and then shipped to the Lockwood Landfill.

Installation of pond #2 improvements began on May 25, 2018 and were completed on July 17, 2018.

Opportunities

To safely handle the material, each pond must be lined with a specialized geomembrane to ensure containment and prevent reintroduction to the surrounding environment. Pond #2 of the treatment facility was scheduled for improvements and it was deemed necessary to line the pond with new geomembrane. Additionally, a decision was made to incorporate floor ballast trenches, which created significant challenges during project construction.

Solution

The core product for the project consisted of 450,000 square feet of AGRU 60 mil HDPE geomembrane and 39,900 square feet of cushion geotextile. In addition, installation included 13,000 square feet of 2′ wide geocomposite venting strips beneath the liner, 48-inch perimeter Air/Gas vents, four safety ladders, 369-inch 6′ long sand filled ballast tubes, and over 2,000 square feet of sand filled ballast trenches located across the floor of the lagoon.

In order to accommodate the earthwork contractor’s task of backfilling the floor ballast trenches, the installation sequence of the HDPE panels was modified to provide access for the prime contractor’s equipment. In addition, the mid-day temperatures necessitated performing trench cap welding in the cool morning hours to eliminate challenges created by the thermal expansion of the geomembrane.

Outcome

The project was completed in a timely manner despite initial challenges. In addition to product familiarity, AGRU geomembrane was chosen due to its close proximity to the project site. Close access to AGRU facilitated logistics and improved quality control. To date, the AGRU geomembrane has been performing well.