The Erie County Water Authority (ECWA) required an expansion of its transmission main system to improve water supply capability in the northern region of the county. The primary objective of the project was to extend an existing 36-inch main over two miles. At a critical point, the pipeline route crossed the North Diversion Channel of Ellicott Creek. This section contained a wetland, recreational bike path, and extremely poor soil conditions. Several options for crossing the channel were considered, including Horizontal Directional Drilling (HDD) of a flexible-joint pipeline without a casing pipe. Through the bidding process, the HDD system was deemed to be the most economical and efficient.
The design team and the ECWA worked extensively with the contractor to establish expectations and design construction parameters for the HDD crossing of the channel. The extent of the directional drill was over 800 feet, with a maximum vertical deflection of over 25 feet. Over 800 feet of the Ductile Iron Pipe (DIP) sections for the crossing were connected, wrapped in polyethylene, and strung out on a lubricated polyethylene bedding upstream of the drill hole. Following several passes to enlarge the drill hole, the pipe was successfully pulled through the hole, utilizing only a fraction of the maximum pulling strength of the drilling rig. The HDD for this project is believed to be a record in size and length for this type of operation.
In addition, the project designers had to contend with:
- extremely poor geotechnical conditions;
- groundwater elevations approximately five feet below ground surface;
- installation of casing pipe under the two overpasses and adjacent to every structure;
- soil conditions that would have corroded the DIP, which necessitated wrapping it with polyethylene;
- construction of the entire project within an archaeologically sensitive area;
- extensive permitting because of the sensitive environmental conditions.
The entire project was completed more than two months ahead of the original schedule, due in part to the speed of the directional drill procedure for the creek crossing. In addition, the final project cost was lower than the original budget. The completed transmission main will fulfill its role of increasing the stability of the water system in northern Erie County for years to come.