- ENGINEERING INFO
- CASE STUDIES
Floods, poor water quality, limited water capacity, and an oil and gas driven economic boom in western North Dakota make fresh water a prized commodity in this part of the country. As a result, over $110 million has recently been allocated to improve the area's potable water infrastructure over a multi-year period. Hundreds of miles of new transmission and distribution pipelines are slated to be installed by 2014 to meet the growing demand.
Advanced Engineering and Environmental Services (AE2S) has been tasked with design and construction management of this massive pipeline project. Having successfully used Fusible PVC® pipe on multiple projects, AE2S once again included it in the project specifications for both the direct-bury and trenchless sections. The first phase of the project bid in 2011 and was awarded to Molstad Excavating, Inc. of Grand Forks.
|Pipeline Details and Project Summary|
|Project:||Western Area Water Supply Project Phase 1|
|Engineer:||AE2S - Bismarck, ND|
|General Contractor:||Molstad Excavating, Inc. - Grand Forks, ND|
|Directional Drill Contractor:||King Contracting - Lincoln, NE|
|Direct-Bury:||19,500 LF 20" DR18 and 700 LF 20" DR21 Fusible C-905®|
|Horizontal Directional Drill:||5,550 LF of 20" DR21, and 5,000 LF 20" DR18 Fusible C-905®|
The first phase of the project required over 50,000 LF of 20-inch pipe to be installed. The alignment ran along Highway 85 between Williston and Watford City. The ebb and flow of the Missouri River dictated the design of the initial project. While fused pipe was required to cross a nearly 3,000 LF section of the river, the rest of the project also needed a better long-term solution. Much of the alignment passed through a flood zone which had experienced flooding during the several previous years, resulting in portions of the alignment where pipe would be below the groundwater level for some portion of each year. Accordingly, AE2S required fused pipe (either HDPE or Fusible PVC® pipe) for nearly half the project alignment.
There was also a significant length of pipe to be restrained in areas where the pipe alignment made steep vertical bends out of the river basin. Chris Saxton, AE2S Project Manager, provided the following insight: "The use of fused pipe on the lowland area was to reduce maintenance, since this area tends to flood in the spring. The steep hillsides coming out of the river basin were a good opportunity to use Fusible PVC® pipe because restrained joints were required to keep the pipe from pulling apart."
Direct Bury Sections For the majority of the flood prone area, bidding contractors could select either a 24-inch DR7 HDPE pipe or a 20-inch DR18 Fusible PVC® pipe, specified at similar pressure and hydraulic capacities. The majority of the connections were to be made to a 20-inch gasketed PVC pipeline. Fusible PVC® pipe was selected by Molstad due to the lower overall installed cost of the pipe and ease of making reconnections without reducers and fused-on flange adaptors. In the restrained (hilly) areas, contractors could also use restrained 20-inch ductile iron pipe or Fusible PVC® pipe. Molstad also chose to use Fusible PVC® pipe in these areas due to lower overall cost. The Project Superintendent from Molstad stated, "The pipe was a good fit for the project and we would definitely use it again."
Horizontal Directional Drilling With nearly two miles of horizontal directional drilling required (crossing the Missouri River, multiple roads, and extremely wet areas), HDD contractors could select either 24-inch HDPE or 20-inch Fusible PVC® pipe. King Contracting - with a track record of multiple 3,000 LF crossings in the Dakotas utilizing Fusible PVC® pipe - determined that Fusible PVC® pipe was the lower cost and lower risk alternative due to a smaller required borehole, higher tensile capacity (2x versus HDPE), and lighter pipe weight. The longest bore on the first phase involved 2,500 LF of 20-inch Fusible PVC® pipe drilled under the Missouri River.
2012 and Beyond An additional 50,000 LF of 20-inch and 24-inch Fusible PVC® pipe was installed in 2012 by other contractors using direct-bury and HDD methods. The primary difference between the first phase and future project phases is that most of the pipe will be installed outside of the wetlands area. As the project progresses toward its expected 2014 completion, additional updates will be provided.