Enviro liner30 mil - Snow Storage Facility
LOCATION: Edmonton, AB TIMEFRAME: Summer 1999 SCOPE OF WORK: To line snow storage settling ponds with geomembrane for collection of heavy metals and road salts PROJEECT PARTNERS: Owner: City of Edmonton
The collection and storage of snow from the streets in The City of Edmonton has been a task very similar to many major centers in Canada. Currently there are 8 different snow storage facilities in Edmonton. Of these, only two of the facilities are lined with a geomembrane. In the case of the Poundmaker Snow Storage Facility, a geomembrane liner was used in a settling pond for the collection of heavy metals and road salts. Once the metals and salts have settled, the water is moved from the site to the North Saskatchewan River via the underground utility system.
The City had used the land this project had taken place on for the past ten years. Normal practice was to collect, dump and store the snow on the site. In other major centers, snow storage facilities have been constructed in order to reduce the infiltration of large amounts of salts, metals and suspended solids into rivers or other bodies of water.
The problem had come to light that as the snow was melting and running off, a large amount of road salt was also accumulating and being deposited into the river. The City of Edmonton, in conjunction with Alberta Environment, adopted a new policy of storage in order to collect the road salts and reduce the possible contamination into a body of water.
The design of the settling pond for this project required a geomembrane for the purposes of erosion protection on the slopes of the pond. The Engineer’s design incorporated a 30 mil Enviro Liner Geomembrane as supplied by Layfield. The Enviro Liner has a wide range of pH levels (2-13) and can be prefabricated in the Layfield manufacturing facility in Edmonton, Ab.
On the base of the pond a rolled compacted concrete (RCC) was placed. The RCC terminated at the toe of the pond, just below the anchor trench (see figure 1) for the geomembrane liner. The RCC was used on the base due to the fact that the salts and heavy metals need to be removed from the settling ponds as they accumulated. A geomembrane liner could have been place under the RCC, but was not necessary due to the fact that this was not critical containment, and a small amount of seepage was acceptable through the RCC.
At the top of the pond on the north and west side (see figure 2) a synthetic fiber erosion control blanket was used in an overflow swale. The swale was design to intercept any melting snow from the dumping area and properly direct it into the far end of the pond. This would ensure that the melting snow would enter the settling pond at the proper location in order for the salts and heavy metals to properly settle. The design required a Bon Terra SFB rolled erosion control blanket. At the main inlet of the pond, a rip-rap channel was constructed (see figure 3) to help protected against high flows of water as snow melted. The channel was designed to withstand flow rates of over 7.9 meter per second of flow velocity. Under the rip rap channel a non-woven geotextile was incorporated in to the design. Layfield supplied an LP 8 non-woven geotextile. The LP 8 is a 247 g/m2 geotextile fabric, which is used to separate the rip-rap armor and the sub-soils, thus reducing any displacement of the armoring stone during high flow events.
The Poundmaker Snow Storage Facilities Development Project was put out for tender to over fifteen different General Contractors in the Edmonton area. Layfield was awarded the work as the sub-contractor to Deford Contracting Ltd. of Edmonton, Ab. The project was awarded to Layfield in June 1999 with the condition that the geomembrane liner would be supplied and installed by the Layfield Environmental Systems Division, which provides the services for the installation of the geomembrane liner.
The incorporation of a geomembrane liner on the slopes of the settlement pond enabled the design engineer to look at a viable containment and erosion material that was much more economical that roller compacted concrete. The total amount of Enviro Liner 30 mil installed at the project site was 2000 m2.
The Enviro Liner 30 mil was prefabricated into five custom panels. Each panels was 5.5 m meters wide x 75 meters long. The panels each weighed 136 kilograms and were shipped to the project site on wooded pallets. The prefabrication of the Enviro Liner allows for the easy shipment to the project site.
The ability to prefabricate geomembrane liners allows any installation to take place in much quicker time periods. Layfield is one the few manufactures in Canada that has the ability of prefabricating a wide variety of synthetic membranes. Both scrim supported and unsupported geomembrane liners can be prefabricated in Layfield’s state of the art manufacturing facility located in Edmonton, Ab.
The Enviro Liner 30 mil was prefabricated in the Edmonton manufacturing plant. All five panels were fabricated in late August 1999, placed on shipping pallets, packaged, labeled, and put into storage. The General Contractor, Deford, was delayed due to extra work and poor weather. Based on the time of year, Layfield’s installation crews are busy installing geomembrane lining systems seven days a week during the months of June and October throughout Canada and the Pacific Northwest. The timing for any installation can become difficult due to time restrictions. The prefabrication of a geomembrane liner reduces the amount of material that is required to be seamed on the project site, thus reducing the overall installation costs.
In the case of the Poundmaker Snow Storage Facility, the design consideration took into account the useful aspect of what a geosynthetic can offer into a difficult construction project. In some cases traditional materials may not be economical and feasible due to cost restrictions or design requirements. The design Engineer considered the durability of a geomembrane to replace roller compacted concrete or other hard armoring solutions that can have costs between $ 50.00 to $ 80.00 m2. The Enviro Liner 30 mil geomembrane liner was installed for less than $ 15.00 m2. Although costs cannot be considered as the main design requirement, it can be shown that geosynthetic materials can be seen as a viable option for many applications.
The Poundmaker Snow Storage Facility (see figure 4) used three different types of geosynthetic materials in the construction of this project: a Enviro Liner 30 mil on the slopes of the settling pond, an Erosion Control Blanket (Layfield’s SFB) in the interior drainage swale, and a non-woven geotextile (LP 8) under the rock rip rap located at the pond inlet. Layfields’ Environmental Systems Division supplied and installed the geomembrane liner while the General Contractor own forces installed the erosion control blanket and the non-woven geotextile.
After one complete season (November 1999 to February 2000) the Poundmaker Snow Storage Facility is working very well and no problems have been reported.