Rural pipeline installation on the canadian prairies

Prepared by David Pochylko and Wade Morrison
Presented at the Small Drinking Water and Wastewater Systems Conference, January 12 -15, 2000, Phoenix, AZ

ABSTRACT

Many people living in the rural areas of the Canadian Prairies have individual water supplies of poor quality and/or insufficient quantity to meet their requirements on a secure basis. In areas where individual water supplies are not considered the optimal source, rural water pipelines have been developed to supply a secure source of improved-quality water for household use (domestic), livestock watering, commercial and industrial applications. The development of Polyvinyl Chloride (PVC) and High Density Polyethylene (HDPE) pipe materials; the adaptation of methods developed in the drainage, natural gas and cable installation industries (directional boring, plowed-in pipe/cable) by private sector construction firms; and the recognition by pipe manufacturers that pipe bedding requirements can be relaxed in situations where the soil conditions are favorable, have combined to make rural pipelines more economical and environmentally acceptable.

1.0 INTRODUCTION

People living in the rural areas of Saskatchewan often have individual local sources of surface water and/or ground water. These sources can contain poor quality water, have limited quantity of water available, be unreliable or any combination of the three. Water supplies that address these constraints are sometimes available on a regional basis. In cases like this a rural pipeline may be the preferred option to alleviate water supply concerns (Pochylko et al.,1999).

The number of rural water pipelines in Saskatchewan has grown to the point where over 2000 service connections in the rural community receive water through over 3000 km (2000 miles) of pipe. The diameter of the delivery pipe ranges from 40 to 200 mm with the predominant size range being 40 to 50 mm. There are several key factors that have contributed to the growth of rural water pipelines in Saskatchewan. Government assistance through the Prairie Farm Rehabilitation Administration (PFRA) of Agriculture and Agri-Food Canada has helped to reduce the initial capital cost of the installation of a pipeline. The evolution of a design philosophy that is unique to rural water pipelines has also helped to make rural lines feasible. The design philosophy employs the following approaches which are not typically used in municipal systems:

• The system layout is based on a series of branches with no loops;
• Fire flows are not considered as a system demand;
• Each client receives intermittent delivery over a 24 hour period to satisfy average daily needs;
• Each client on the pipeline installs a storage cistern complete with a pressure system to satisfy their short term peak demands and to ensure a supply of water during periods when the pipeline is not operating; and
• The pressure at each client connection is not guaranteed.

This paper will describe how the following factors have combined to make rural pipelines more economical and environmentally acceptable:

• The use of polyvinyl chloride (PVC) and high density polyethylene (HDPE) plastic pipe material;
• The recognition by pipe manufacturers that bedding requirements can be relaxed in situations where the soil conditions are favorable; and
• The adaptation of pipe installation techniques developed in the drainage, natural gas and cable industries.

2.0 CLIMATE INFLUENCE ON INSTALLATION

On the Canadian Prairies climatic conditions affect when pipe can be installed and how deep it must be buried. Winter conditions that are experienced on the Canadian Prairies result in natural ground freezing to a depth of 1.5 m to 3.5 m (Wheaton,1998a). Frozen ground is difficult to excavate or plow making pipe installation very expensive in the winter time. Cold temperatures (as low as -40 degrees Celsius) and snow cover also make it difficult to install pipe in the winter. Plastic pipe materials become very inflexible and brittle when winter temperatures are experienced. Freezing temperatures may be encountered between August and May (Wheaton,1998b). In the spring , pipe installation is complicated and delayed by the following factors: the ground may remain frozen until May; once the frost is out of the ground the soil is generally saturated and soft which reduces effective vehicle traction; and most depressions and ponds are full of spring meltwater requiring numerous detours. Rural pipelines are generally installed in the summer and fall; however, most have been installed in the fall for the following reasons:

• The permanent surface water bodies are generally at their lowest water levels;
• The low spots that were wet in the spring are now dry;
• There is less potential for crop damages as harvest starts in July and is usually complete by the end of September; and
• Other utilities (gas, electric, and fiber optic) contract for spring /summer installation.

In order to deliver water year round the pipe must be buried below the average depth of frost penetration. In Saskatchewan the pipe is generally buried below 2.4 m. Where the pipeline crosses roads or other areas where the snow cover may be removed the pipe is installed as deep as 4.0 m.

3.0 SURFICIAL GEOLOGY

Some knowledge of the local geology is required to determine the pipeline routing. Southern Saskatchewan has been glaciated extensively and has relatively minor exposures of bedrock sediments. Most of the bedrock exposures are located in sparsely populated areas where pipelines are not a viable option. As Figure 1 (348Kb Adobe pdf) illustrates virtually all pipeline projects have been constructed in glacial clay or glacial lacustrine deposits. A significant portion of the glacial deposits have been modified and resorted by water action shortly after deposition; these modifications usually are positive with respect to foundation characteristics for installation; however, there are exceptions.

The primary installation restriction is the number and size of stones within the till deposits. Some equipment is unable to work in soils where the rock diameters exceed 150-200 mm. Other pieces of equipment can be used in rockier soils if the rocks are infrequent in the lower third of the installation depth, and if the upper soil matrix is sufficiently soft to allow the rocks encountered to be lifted clear or pressed back into the soil matrix. Hydraulic excavators are available to remove almost any rock size but the expense of rock burial and trench restoration can increase costs to the point where other water sources are more viable.

Completing testholes at spacings as close as 200 m has not provided sufficient information for design or contract purposes. The testhole results mean little to the contractors who are interested in installing the pipe, particularly those interested in plowing the pipe in. A detailed explanation of the plowed-in method of pipe installation is given in Section 6.0. The geological review now consists of reviewing topography, geology and land resource maps, a field inspection of the proposed pipeline route and determining testpit locations that reflect both general and extreme soil conditions. The testpits are available for viewing in the precontract period and contractors are given the option of requesting additional testpits. This approach to addressing the uncertainty of foundation conditions has been endorsed by the contractors and has lowered installation prices in most instances.

4.0 PIPE TECHNOLOGY

The development and application of plastic pipe technology has had a dramatic impact on the cost of installation of rural pipelines. Experience in Saskatchewan indicates that plastic pipes in diameters less than 200 mm have cost and life cycle advantages over traditional pipe materials (steel and concrete). Polyvinyl Chloride (PVC) has been used extensively in municipal watermains and pipelines. In 1967 the first group rural water pipeline in Saskatchewan was installed in the Lanigan area using PVC pipe.

In the early 1980's Saskatchewan undertook a major program to provide natural gas to rural residents through a network of High Density Polyethylene (HDPE) pipes. This initiative helped to develop the HDPE pipe installation industry in Saskatchewan. The HDPE pipe, because of its flexibility and manufacturing process, is able to be shipped as rolled reels. The rolls vary in length of from 1600 m for 38 mm diameter pipe to 100 m for 125 mm diameter pipe. Thermal fusion of the pipe ends results in a continuous pipe of any required length. In 1986 fused HDPE pipe was first used for a rural pipeline in the Tuxford area of Saskatchewan. In Saskatchewan HDPE pipe is now used almost exclusively while in Alberta and Manitoba, PVC is the pipe of choice (Pochylko et al., 1999). The use of HDPE pipe rolls and fusing of joints has allowed for innovations in installation technology as indicated in the Section 6.0.

5.0 PIPE BEDDING REQUIREMENTS

Traditionally municipal watermain design has required sand bedding for burial depths of 2.4 m. Experience gained in the gas and drainage industry made it apparent that for burial depths of less than 1.2 m small diameter HDPE (< 150 mm) did not require sand bedding for most soil conditions. The HDPE pipe manufacturers examined their bedding requirements for burial depths of 2.4 m and determined that they could relax the requirements for rural water pipelines. This allowed the pipe to be bedded directly on the sub-grade provided that the sub-grade is not rocky or otherwise unsuitable. The PVC manufacturers have also relaxed their bedding requirements for rural water pipelines to allow the pipe to be bedded directly on the sub-grade provided that conditions are suitable. Initial backfill characteristics for PVC pipe must still be assessed and inspected during construction. The relaxation of bedding requirements for plastic pipe has allowed the use of innovative installation technologies (plowed-in pipe, directional boring) and has reduced the cost of open trench methods.

6.0 INSTALLATION TECHNOLOGY AND INNOVATION

Rural pipelines have been installed using excavators (backhoes), chain trenchers, bucket wheels, trenchless plows. Utility crossings are completed by identifying/daylighting the utility alignment and tunneling by directional boring machines, hydraulic jacks or air hogs. Each of these machines has its advantages and disadvantages and each has been used in particular circumstances.

The use of an excavator (backhoe) results in significant ground disturbance; a concern for both roads and cropland. In granular soils it is difficult to maintain trench stability resulting in a very wide excavation. In clay soils the trench is usually stable but requires wide construction areas and extensive site restoration in farmland. Excavating through wet areas can result in undesirable environmental impacts and extensive site remediation. In general, areas with standing water are technically difficult to cross while areas of flowing water are both technically difficult and have significant restrictions due to environmental concerns. The use of excavators is the only method that can effectively deal with rocky conditions. Excavators are often used to install individual user service connections and are required wherever isolation valves or tees are installed. At road and railway crossings other methods are used (directional bore, hydraulic jacks and air hogs), but excavators permit access on each side of the crossing at the desired depth below ground. Care must be used when backfilling the pipe so that falling soil or rocks do not damage the pipe. Under most conditions approximately 500 m of pipe can be installed in a day by one excavator.

Chain trenchers are commonly used to install pipe in Saskatchewan. This piece of construction equipment has a long boom with a moving chain complete with teeth. The boom is placed into the ground as the chain is moving. The teeth dig the soil and deposit it on the surface on either side of the trench causing some ground disturbance. Sandy soils can result in difficulties in maintaining an open trench and are abrasive to the chain and its bearings. Excavating through wet areas and areas where rocks larger than 200 mm are common, is difficult and can result in undesirable environmental impacts. The trench created by a chain trencher is generally narrower than that made by a excavator; however, care must still be exercised when backfilling so that falling soil or rocks do not damage or distort the pipe. The chain trenchers used in Saskatchewan can install up to 1500 m of pipe in a day.

Bucket wheels are generally not used to install rural water pipelines in Saskatchewan because of the wheel size required (>3.0 m in diameter).

The trenchless plow method has been adapted for rural water pipeline installation by private sector construction firms which originally specialized in drainage, natural gas and cable installations. In these industries HDPE pipe, phone cable, fiber optic lines and power lines have been plowed into depths of 1.2 m. Contractors who had plowed in small diameter (> 100mm) HDPE for the natural gas industry proposed to plow in HDPE pipe to a depth below frost penetration (2.4 m).

The contractors modified their equipment and began to plow in pipe to depths as great as 2.7 m. Each contractor has incorporated unique design aspects in their plows based solely on the experience they have gained through operation. The plows are made from large rectangular shaped steel sections that can be inserted into the ground to a depth of 2.7 m. The plows are mounted on the back of a Caterpillar D 9 crawler tractor or equivalent. The plow shaft is inserted into the ground using hydraulic rams on the crawler tractor. The plow shaft can also be moved like a ships rudder by hydraulic rams on the crawler tractor to facilitate changing direction. The plow shaft has an attached shoe and pipe sleeve to guide the pipe into the slit left by the plow. The pipe that is being installed is either mounted on spools on the front of the crawler tractor or is prefused and laid out in front in the direction the plow is moving. The pipe is guided over the canopy of the crawler tractor and fed down the back of the plow shaft into the shoe and placing sleeve. The plow crawler tractor is generally pulled by at least two other crawler tractors. This combination of plow and crawler tractors is referred to as the plow train. In some cases where the ground is hard, crawler tractors work ahead of the plow train pre-ripping the ground to a depth of 1.2 m. This makes it easier for the plow train to install the pipe to the desired depth of 2.4 m.

Plows can work in rockier soils if the rocks are infrequent in the lower third of the installation depth and the upper soil matrix is sufficiently soft to allow the rocks encountered to be lifted clear or pressed back into the soil matrix. If the rocks are too frequent and the soil matrix is not soft enough a plow cannot be used to install the pipe.

The plow train can install pipe in areas where it would be difficult for excavators, chain trenchers and bucket wheels because the pipe is installed and backfilled as the plow train moves along, requiring only minimal clean up. Shallow wet areas can be plowed through by winching the plow crawler tractor across. This creates only minor disturbances. Crop damage is limited to the width of the plow train. Spools can be added at road allowances or areas where there is less sensitivity. Contractors have successfully installed up to, and including, 150 mm diameter HDPE pipe by using the trenchless plow method. Installation rates depend on pipe size. Average rates are between 3,000 to 6000 m per day.

Directional bore machines are commonly used where access is limited, where no ground disturbance can be tolerated (at river/stream crossings, at large deep ponds ) or in sensitive areas (easements with numerous utility crossings, tree plantations). A boring head is driven through the ground at a depth below frost penetration or deeper if required to not impact on the sensitive area. The boring head exits the ground in a less sensitive area and the pipe is then pulled back through the hole by the boring machine. Drilling mud is generally used to keep the hole open and to act as a lubricant to reduce the drag on the pipe as it is pulled back through the hole.

Jacking and air hogs are used to install pipes under roads, paved areas and railways where no surface disturbance can be tolerated. In most cases the width to be crossed is less than 30 m. In general a casing pipe is forced through at the desired depth and the water pipe is installed inside the casing. These methods require access at both ends at the desire depth below ground. In areas where pipe is installed under pavement the pipe is generally buried in excess of 3.0 m.

Surficial geological conditions, and the experience and preferences of the local contracting community determine the installation techniques used in any given area. In Alberta and Manitoba, trench-installed PVC pipe is most common, whereas plowed-in polyethylene pipe is the preferred option in Saskatchewan. Experience in Saskatchewan indicates that designs and tenders which give the contractor options in the use of materials and installation methods generally result in the lowest-cost development (Pochylko et al., 1999).

7.0 PIPELINE ROUTE SELECTION

The final decision on the pipeline route is the responsibility of the rural water pipeline group. The group's decision is based on the advice and recommendations they receive from PFRA and their professional engineering consultant. Route selection is based on minimizing capital cost while considering potential future development, land control and sensitive areas. Points to consider for minimizing capital cost when selecting a pipeline route are:

• Generally speaking the shortest route between two clients is the cheapest;
• The cost of railway, road or utility crossings may be reduced by prudent route selection;
• Detours around major elevation shifts may eliminate the need for additional booster pump stations and pressure reducing vaults; and
• Identify and avoid areas where land control is difficult to obtain or routes where environmentally sensitive areas are encountered.

Future development, though difficult to quantify, should be considered when selecting a rural water pipeline route. At the preliminary design phase the route selection is further complicated by the fact that the clients have not signed agreements with the group. In some cases the pipeline is developed in phases in which the group has a more accurate idea of the developments that are expected. In most cases the group must make some subjective decisions regarding route selection that, if accurate, can result in higher initial cost but may result in a lower cost in the long term.

Once the basic route selection is determined the group must decide if it is going to install the pipeline in easements obtained from land owners, or in the road allowances which are either controlled by the Rural Municipalities (RM) or by the provincial highways authority. In many cases the group uses a combination of easements and road allowances. To install the pipe in a RM road allowance the pipeline group obtains a resolution from the RM council stating it approves the installation along with any conditions or restrictions that may apply.

Installing the pipeline in the road allowance allows the group to deal with the Rural Municipality(s) and Saskatchewan Highways and Transportation instead of every land owner along the route. If the group decides to install the pipeline on private property an easement agreement must be written for each parcel of land the pipeline route crosses. Usually a significant number of the landowners on the pipeline route are members of the rural pipeline group and are quite accommodating regarding the easements.

Easements can be delineated by a legal survey, described by a metes and bounds statement or a caveat/easement. A legal survey is very expensive and time consuming and is only used when the pipeline route across private property intersects other registered surveys and cannot be accurately described by the following methods. Metes and bounds uses a written description to accurately and unambiguously describe the required easement from a start point to an end point within a parcel. A caveat/easement uses the pipeline route plans to describe the parcels of land to be crossed.

Construction in the road allowance is typically more difficult than on private property. The unused portion of the road allowance is generally narrow making it difficult to deal with excavated material if chain trenchers or excavators are used. For plowed-in pipe, traction may be reduced in the road allowance due to sideslopes and moister surface soils. Remaining within the road allowance is difficult when deep water bodies are encountered forcing the group to obtain easements from private land owners. Future alterations to roadway alignment or grade may necessitate moving the pipeline which usually occurs at the pipeline groups cost. An advantage of installation within the road allowance is that the snow cover imparts additional protection against freezing of the pipe.

Installing the pipe on private property requires that the group obtain easements from all land owners whose property is affected by the installation and operation of the pipeline. This generally requires more work by the group but can reduce the overall cost. Instead of following road allowances, which are on a grid system, the pipeline route can take the shortest route between two points. Easements are negotiated to provide more space for pipeline installation than is normally available within a 30 m road allowance and generally the ground surface provides better traction for the plow train. Pipeline groups generally use a combination of road allowances and private property to install the pipeline because, in certain situations, each has its advantages.

8.0 LINE COMMISSIONING

The commissioning process insures that the pipeline is ready to deliver water to its clients. Once the pipeline is in the ground the Contractor is responsible to ensure that the interior of the pipe is clean and free from air pockets and debris. This is critical in maximizing delivery capacity and ensuring the pipe does not have any material in it that may be a health concern. Cleaning is accomplished by pigging and flushing the pipe to remove air and debris. The pipeline is also pressure tested after cleaning to ensure that it is leak free when operational.

When the cleaning and pressure testing is completed the pipe is disinfected. Disinfection is accomplished by hyperchlorinating the interior of the pipeline as specified in AWWA C651-92. Hyperchlorination occurs when the pipe is filled with water that has a chlorine concentration of at least 25 mg/l. The chlorine solution is held in the pipeline for a period of 24 hrs after which time the concentration of chlorine must not have dropped below 10 mg/l. After hyperchlorination is complete, the pipeline is flushed with water that is chemically and biologically equal to the water the pipeline is expected to carry. When flushing is complete the pipeline is ready to deliver water to the clients.

9.0 CLOSING REMARKS

Rural water pipelines are an option to address existing water supply constraints in rural Saskatchewan. The installation infrastructure has been developed by a partnering of the private sector and government agencies. The public response to rural pipelines has been very favorable and interest continues to grow for new pipeline construction and additional connections to existing pipelines.

10.0 REFERENCES

PFRA Northern and Southern Saskatchewan Regions, Rural Pipeline Handbook For Saskatchewan - Draft Copy, Saskatoon, Saskatchewan, July 25,1997.

Pochylko, D., Powley, R. and Brandt, G. Rural Pipelines - Addressing the Needs of the Prairies Proceedings, Canadian Society for Civil Engineers, Regina, Saskatchewan, June 2-5, 1999.

Wheaton, E. But It's a Dry Cold, Fifth House Ltd., Calgary, Alberta, Canada, pg 63, 1998a.

Wheaton, E. But It's a Dry Cold, Fifth House Ltd., Calgary, Alberta, Canada, pg 42, 63 & 75, 1998b.