Drought Watch

Wells for Rural Water Supplies in Saskatchewan

Introduction

Groundwater is an important source of water for Canadians. In Saskatchewan, over 50% of the rural population relies on groundwater for its domestic supply. There are about 60,000 water wells in the province, providing water for agriculture and industrial uses as well as for human needs.

Ground water can generally provide a safe, reliable water supply if appropriate steps are taken to develop a source. The natural purification processes that occur as water moves down through the earth generally results in a safer source of supply than surface water. There are, however, areas in which groundwater is either not available or contains quantities of substances such as iron and other dissolved solids that make it undesirable.

To ensure that the quality and quantity of well water is adequate for present and future needs several factors must be considered when planning and designing a well.

1. Groundwater Source

For information on aquifers in your area, consult your local Sask Water or district PFRA office. Additional information may be gained through discussions with other well owners and certified water well drillers. The final step is having a contractor drill small diameter exploration holes. This work often involves using an electric well logging device (E-log), which increases the information available to the driller in locating water bearing formations.

2. Aquifer Type (Confined and Unconfined)

Groundwater occupies the spaces between soil particles or cracks and fractures in bedrock. Groundwater starts out as surface water, entering the ground through areas generally referred to as recharge areas.

Underground areas or formations which are capable of yielding water in usable quantities are called aquifers. Although water moves through an aquifer, it is not an underground river. Water generally moves slowly through the ground, travelling from metres per day to centimetres per century. Aquifers also vary in size. A small aquifer may only be able to supply a single household, while a large aquifer may be able to supply the water needs of a town, city or region.

Groundwater aquifers are considered to be unconfined or confined.

An unconfined aquifer (also known as a water table aquifer) is not under pressure. This means the aquifer is exposed to the atmosphere. These aquifers are usually shallow, are seldom deeper than 30 m (100 ft.) and are generally low producers. The volume of water stored in unconfined aquifers is predominantly dependent upon seasonal cycles of precipitation.
A confined aquifer is overlain by materials which do not transmit water rapidly. The aquifer is completely saturated with water which is under pressure. When a well penetrates a confined aquifer, the level to which the water will rise in the well is dependent on the amount of pressure on the aquifer. A well in which the water level rises above the upper surface of the aquifer is generally called an artesian well. A flowing artesian well is one in which the water level rises to above the ground surface. Confined aquifers include sandstones, fractured shales and deeper deposits of sands and gravel. They may reach depths of 300 m (1000 ft.), and may yield from one to several hundred gallons per minute.

3. Well Site

Location can affect the safety and performance of a well. The well owner should ensure all possible site considerations have been identified and all utilities located prior to requesting drilling. Site considerations must include the possibility of contamination or hazard. Wells must be:

at least 3 m (10 ft.) from any building;
at least 8 m (25 ft.) from a septic holding tank
at least 30 m (100 ft.) from any barns, corrals or septic disposal field;
at least 2 m (6 ft.) from an insulated low voltage power line;
at least 15 m (50 ft.) from any high tension power line;
at least 2 m (6 ft.) or more from any property line;
at least 90 m (300 ft.) from the property line along a highway unless authority has been granted in written form;
accessible for cleaning, inspecting, test-pumping, repairing, and treating;
located away from underground utilities and easements.

Check provincial and municipal guidelines and legislation before locating your well.
This information may be obtained by contacting Sask Water, Saskatchewan Environment and Resource Management, Saskatchewan Health, Rural Municipality, etc .

Low lying areas are not recommended for wells. If a well must be constructed in such a location, the casing should extend above ground and impervious fill hauled in to raise the surrounding surface to prevent runoff from entering the well.

A well must not be located in the basement of any building or in a pit.

4. Well Type and Construction Method

The four common well types in Saskatchewan are rotary drilled, bored, sand point, and excavated.

Rotary drilled wells
Rotary drilled wells or small diameter wells are constructed using a drill bit on the end of a rotary drill stem. Drilling fluid is circulated down through the drill stem into the hole and back to the surface to remove cuttings. Rotary drilling rigs are relatively fast and can reach depths to 300 m (1000 ft.). A typical small diameter well is shown in Figure 1.

Casing
Casings are made from three common materials: steel, fibreglass, and plastic (PVC). A steel casing is the strongest, but is susceptible to corrosion. Fibreglass or plastic casings will last indefinitely, and are generally less costly than steel. Casing diameters vary from 11 to 46 cm (4.5 in. to 18 in.) inside diameter. The casing must be large enough to house the pump, and allow sufficient clearance for the pump's installation and efficient operation.

Screens
A proper well screen is recommended in nearly all well construction. A screen selected to match the characteristics of the aquifer will maximize the yield of sediment free water from the aquifer. They are available in various slot sizes and materials. The most common materials used are stainless steel and PVC. Generally, a slotted well casing is not recommended for use as a well screen.

Figure 1: Typical Small Diameter Well Installation

Developing the Well
Well development is the process of repairing the damage done to the formation caused by the drilling procedures. Fine sediment from the area immediately surrounding the well screen is removed to increase the porosity and permeability of the materials surrounding the intake or well screen, thus improving the well's ability to produce water.

Well development is done by jetting, surging, backwashing or over-pumping of the well. Fine materials that are in the immediate formation are pumped or bailed out of the well. This procedure is continued until no fine particles are remaining and the water is clear. The removal of the fine particles results in coarser material surrounding the screen. If the aquifer does not naturally have any or enough coarse material to form a filter, then an artificial sand filter pack will be added. The sand pack is placed around the screen so the well can be developed, with care given to match the material size in the sand pack with the screen slot size.

Bored Wells
Bored wells or large diameter wells are usually constructed with a bucket auger rig. This unit consists of a cylindrical bucket with auger like teeth on the bottom. The soil is cut by the blades and is collected inside the bucket. When the bucket is full, it is raised out of the bore hole and the soil is dumped to the side. Well depths rarely exceed 30 m (100 ft.). The diameters of the wells in Saskatchewan are usually 762 mm (30 in.). A typical large diameter well is shown in Figure 2.

Figure 2: Typical Large Diameter Well Installation

Cribbing
The most common cribbing materials are: galvanized corrugated steel, plastic and fibre glass. Bored wells are commonly completed by perforating the cribbing that will be located in the water bearing zone. Manufactured, large diameter, stainless steel or galvanized sand screens are available. Although they are relatively expensive, it may be money well spent. An end cap should be placed on the cribbing if the well terminates in porous material.

Developing
Over-pumping or bailing the well is the simplest and most common method used for removing fine particles from water bearing formations. The wells are usually bailed, surged or pumped until the water is sediment free.

Sand Point
Shallow small diameter wells can usually be installed by jetting or driving a pointed screen into place. Although driving a well requires the screen and casing to be made of steel, the more economical plastic can be used when jetting a well into place. A jetting point has a one-way valve that allows water to be jetted outward, allowing the screen and casing to be pushed into sandy soil aquifers. The diameter of the sand point is usually 50 mm (2 in.). Jetted wells are rarely deeper than 10 m (30 ft.)

Excavated Well
Normally, this type of well is excavated by hand or by a backhoe, to a level just below the water table. Well depths vary but are normally not deeper than 10 m (30 ft.). It is difficult to protect the aquifer from contamination during the excavation process.

5. Yield Test

A yield test is important because the information obtained assists the driller in determining the rate at which to pump the well and the depth at which to place the pump.

All wells should be pump tested to determine the yield (the continuous rate of pumping that a well can sustain without excessive lowering of the water level in the well) and the draw down rate (the rate at which the water level drops in the well during pumping). At a sustainable pumping rate, the water level in the well should remain steady. Water levels that do not completely recover in an acceptable time after a pump test is stopped, indicate the well is drilled into a small, isolated aquifer. These wells generally go dry in a short period of time.

Water levels should be monitored periodically as a means of preventive maintenance. Falling water levels could indicate conditions such as screen incrustation, aquifer depletion or over-pumping.

6. Well Disinfection, Water Analysis and Water Treatment

Disinfection
When the pump test is completed, the well should be disinfected with a strong chlorine solution. A chlorine solution of 250 parts per million should be attained when mixed with the total volume of water retained within the well. The chlorinated solution is left in the well for at least 12 hours to ensure any bacteria present are destroyed. Chlorination is also done after the pumping equipment is installed and after any maintenance work on the well.

Analysis
Water testing should include both a bacteriological and general chemical analysis. A bacteriological analysis should be done if the water is to be used for human consumption. Contact your local health district office for a container for collecting water samples. A routine chemical analysis should be performed to measure the presence of substances such as iron, sodium, sulphates, chlorides, nitrates, and nitrites. The water well driller can generally complete a conductivity test during drilling which will provide a qualitative assessment of the quality; however it is the owner's responsibility to test the potability of the water. Contact the local PFRA or Sask Water Office for more information.

Treatment
The consistency of groundwater quality and temperature can simplify the treatment required compared to surface water. Groundwater usually contains less suspended material than surface water and is usually free from disease-causing micro-organisms. Dissolved solids such as calcium, magnesium, iron and manganese can normally be removed, however, higher than acceptable levels of dissolved salts can prove costly to treat.

7. Contamination

Proper construction of a new well and proper abandonment of an unused well or test hole is critical if the aquifer is to be protected from contamination through the entrance of surface water or other material. Several important practices are highlighted below.

Surface water should be drained away from wells in addition to ensuring proper sealing of the casing.
The upper 5 m (16 feet) of the casing must be completely water tight and there should be no joints except for factory joints that are water tight and permanent. The spacing between the hole and the casing should be filled with a grout seal such as cement, bentonite or tamped clay.
The well cap must be weatherproof and securely fastened.
Abandoned water wells and test holes should be filled with impermeable clay or cement grout.

All aquifers must be protected. Their recharge areas should be identified and kept free of contamination from agricultural chemicals, sewage disposal or intensive livestock operations. This is especially important for shallow aquifers.

The use of a pitless adapter is strongly recommended in well construction. It provides a watertight subsurface connection for buried pipe installation below the frost line, thereby eliminating the need for a pit. Where a submersible pump is installed in the well, the use of a pitless adapter allows the pump to be installed or removed without disturbing the underground discharge pipe. A typical pitless adapter installation is shown in Figure 3.

Figure 3: Typical Pitless adapter installation

Note: Pitless adapters are used on both large diameter and small diameter wells.

8. Choosing a Contractor

Well drilling is costly for both the customer and the driller. Therefore, a written agreement should be drawn up before a well is drilled. The following points should be kept in mind:

ensure that the driller is trade certified and a reputable contractor;
agree on the costs for each item listed in the agreement;
agree on the acceptable yield of the well. If the yield is lower than the required demand, storage facilities, (i.e. cisterns) may be required;
determine what warranties are provided;
determine if the drilling contractor carries insurance against personal injury or property damage.

Members of the Saskatchewan Ground Water Association are generally knowledgeable of, and are informed about, the latest methods of well construction.

Additional information on groundwater and wells can be obtained from a workbook and video series entitled Water Wells That Last for Generations produced in Alberta. Contact your local PFRA office for this and/or other information.