Construction of a new zero-discharge wastewater treatment plantconsisting of three separate 12-acre geosynthetic lined evaporation ponds and gas venting system to replace Hugo’s existing wastewater treatment facilities.
Good communication between installer, general contractor, engineer, and material suppliers was critical to be able to complete this project when the raw materials supply chain was stressed by the pandemic. When the approved manufacturer was not able to acquire resin fast enough to manufacture the specified geomembrane and with construction of the ponds already underway, the project management team went back to the drawing board. Meeting all required properties, Raven’s N45B, a scrim reinforced Linear Low-Density Polyethylene (LLDPE-R) geomembrane was selected as an alternate to the specified 45 mil Reinforced Polypropylene (fPP-R) geomembrane. Once approved, the installer coordinated with the fabricator to prioritize which panels were needed to begin the installation. And only 14 days after material approval, the first set of trucks carrying the fabricated panels arrived on site. These trucks were quickly followed with just-in-time delivery of the other factory fabricated panels needed through completion of the other two containment ponds during the project.
One important design feature is the sand ballasting used across the floor of each pond. The native soil excavated during construction of the ponds was stockpiled and once final inspection and sign off of each pond was complete, the excavated sand was placed directly on top of the 45 mil LLDPE-R geomembrane as ballast and protective cover. This ballast/soil cover operation required extreme care to protect the integrity of the geomembrane because only six inches of soil cover was specified. Three-foot thick haul roads were constructed on the geomembrane to transport material inside the ponds. The soil cover sand was placed using GPS equipped Low Ground Pressure (LGP) equipment to precisely place the sand ballast and obtain the needed thickness. Constant monitoring of the soil cover operation and wrinkle management precautions were implemented to minimize damage and stress to the geomembrane and other geosynthetics. During installation of the 36 acres of geosynthetics the installer performed 53 liner repairs. After backfilling and ballast/ cover soil operations were complete an additional 88 repairs were needed and performed by the installer over two return visits.
Follow-up visit to the site revealed how post-installation weather can also have an effect or pose challenges. In this case it was observed that the sand cover across the pond floor was displaced by heavy winds. Leaving the liner uncovered in one area, and drifted sand in other. Further displacement of the cover material was mitigated by adding fluid to the dry cells to keep the ballast in place.
Using fabricated panels was the only way this project could have been completed in the allotted timeframe. Nearly 800 individual roll widths of geomembrane were factory welded to make 127 panels that were shipped to the site. The panels were fabricated in Texas and shipped to Hugo, Colorado. Factory fabrication allowed 81% of the geomembrane seams to be welded and tested in the factory under clean and controlled conditions, which reduced the amount of field seaming and testing by 5-fold. It also resulted in far fewer destructive seam samples and patches and installation of the geosynthetics completed five (5) days earlier than expected.