Rural Water Resources Planner: Well Monitoring

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Why Monitor Your Water Well?

Regular well monitoring is essential for assessing the operation and condition of your well. A monitoring checklist should be developed to assist in identifying potential problems before they become serious and to prevent or reduce the rate of well deterioration. As monitoring data is collected over time, informed decisions can be made on scheduling preventative maintenance and repairing or replacing any deficiencies.

The following three key areas should be monitored:

Water Level Monitoring

One of the key elements of well monitoring is the recording of water level measurements on a regular basis (see Procedures for Water Level Measurement ) Both non-pumping and pumping water levels should be taken at least a monthly basis. Changes in the non-pumping level or "static" water level may signal possible aquifer depletion, while changes in the pumping level may indicate a possible decline in well performance as a result of screen plugging.

Selection of an appropriate measuring method will usually depend on the well's accessibility, the depth to water and the measurement frequency. To ensure consistency and comparability of water level measurements, a measuring point (e.g. top of well casing) must be established and marked on the well and all future measurements must be taken from this point.

Most wells are not easily accessible for water level monitoring, therefore, "user-friendly" well designs are recommended that include an access tube for water level monitoring.

Water level measurements

When recording water level measurements the following information should be included:

  • 1. Date and time of measurement
  • 2.
    Time of day- the measurement should be taken approximately the same time every day
  • 3. Record the depth of water below a consistent measuring point
  • 4. Identify measuring point and its elevation (i.e. distance from ground level)
  • 5. Identify any nearby influences (e.g. nearby pumping wells, cascading water in well)

Measurement methods

The electric sounder. is commonly used to measure water levels in a well. Other methods include sonic water level meters and electronic pressure transducers linked to a data logger.

Electric sounder

The electric sounder is one of the simplest devices for measuring water levels in a well. An electrical sounder consists of two parallel insulated wires with a weight attached to the end. When the wires contact the water the current travels through the water completing the circuit. This contact causes an ammeter, buzzer or light to signal that the circuit has been completed. The current is supplied by batteries usually housed in the tape reel assembly of the sounder. Commercial units are usually marked with regular intervals so that the depth of water from the top of the casing can be easily determined.

Electric sounder measurements can sometimes be affected by leaks in the pump column. As the sounder is lowered into the well the water leaking from the pump column may cause a premature signal. Installing an access tube will keep leaking water from coming in contact with the sounder tape and it will help to ensure that the tape does not become entangled down hole.

Sonar water level meters

A sonar water level meter uses sound waves to measure water levels and doesn't require the installation of a down-hole probe. Generally, the only requirement is an access port of at least 15 mm in diameter, in the well cap. This type of meter is easy to use and provides a direct readout on the display unit of the device. Simply insert the measuring duct through the well cap, push the power-on switch and the measurement is completed in a few seconds.

Electronic pressure transducers

Electronic pressure transducers with data logging capabilities (see Figure below) can be installed in a well to record and store water level data. This data can then be periodically downloaded and displayed on a computer to observe the data and potential water level trends. These devices measure water levels as pressure readings (i.e. the height of water about above the device). Therefore, at the time of installation, the depth of the device relative to ground level or top of well casing needs to measured. However, these devices may not compensate for barometric changes, and therefore, the recorded water levels must be corrected by obtaining local barometric data from a local weather station or by installing a pressure transducer that measures and records changes in atmospheric pressure.

The "Well Minder" is a new type of electronic pressure transducer that is currently being evaluated and tested by the the Agri-Environment Services Branch of Agriculture and Agrifood Canada. This device was developed by a Canadian company and is intended for the rural well owner. This device has a downhole probe that is permanently installed in the well and connected to a display unit that provides a direct read-out of the water level. The probe can be located up to 600 metres from the display unit which can be mounted in the well owner's home or any nearby heated building with an AC power outlet. This device compensates for barometric changes, and therefore the recorded water levels do not have to be corrected. The new Well Minder DL model also has data logging capabilities and a USB port from which the data can be downloaded to a standard USB memory device.

Figure: Measuring water levels with pressure transducers

Well Performance Monitoring

Well performance monitoring is performed to evaluate the well efficiency and assist in identifying any potential problems. The well, pump and aquifer systems are interrelated, and therefore, it is often difficult to determine the source of the problem when well yield starts to decline. Deterioration in well yield could be the result of an inefficient pump, plugging of the well intake area, or reduced production from the aquifer. To assist in identifying the onset or cause of yield problems, well performance tests can be conducted periodically to determine if there are any changes in well yield, drawdown or overall production of the well over the long-term. The results from these tests are then compared to the baseline data recorded when the well was first installed. If this baseline data is not available, periodic testing should commence immediately to accumulate data for future comparison.

Well performance tests

The main well performance tests are the step-drawdown test and specific capacity test. The length of a pump test will generally depend on the type of test performed, the type of aquifer, the resources available and any site limitations. However, pump tests will only provide reliable data if carried out systematically, accurately recording time, discharge rate and drawdown measurements.

Prior to conducting a pumping test the following should be carried out or determined:

  1. Maximum drawdown available
  2. The discharge rate(s) and best way to measure
  3. Best method to accurately measure water levels and time intervals
  4. Suitable length of pump test
  5. Disconnect pump from pressure storage tank and treatment systems
  6. Ensure water is discharged a safe distance to prevent re-circulation
  7. Potential interference effects, such as near by surface water bodies, aquifer boundaries, and other pumping wells

Step drawdown test

A step drawdown test is often used to assess the performance of a well. In this test, the well is pumped at successively higher pumping rates, and the total drawdown at each rate is recorded. Usually, three to five pumping steps are performed. The time interval for each step is the same and the discharge rate at each step must remain constant. A valve set-up is necessary to vary the discharge rate and an appropriate method to measure the discharge would be required (i.e. flow meter or calibrated pail). From these test results, the well efficiency, drawdown and specific capacity can be determined at a given pumping rate. Since this test involves pumping the well at various discharge rates it may not always be possible for an individual well owner to perform, therefore, the specific capacity test would generally be more practical.

Specific capacity test

The specific capacity test is performed to evaluate the productivity of the well. Specific capacity is defined as the well yield divided by the drawdown, at a designated time interval. The duration of this test can vary from 30 minutes to several hours depending on the pumping characteristics of the aquifer. The specific capacity of a well usually varies with the pumping duration; as the pumping time increases the specific capacity decreases. Therefore, reliable specific capacity calculations depend on accurate data collection. If specific capacity tests are conducted regularly, any changes in well performance will be noticed and appropriate actions can then be taken before the performance of the well deteriorates significantly.

When should a specific capacity test be conducted?

The specific capacity test should be conducted at least twice a year to determine if there are any changes in the well performance. When these tests are conducted in the spring and fall, they may also indicate if there are any seasonal fluctuations in the specific capacity of the well. Pumping tests to measure the specific capacity and overall well performance should also be conducted prior to any anticipated groundwater development or any change in overall water use. This could include new commercial/developments, irrigation well development, drilling activity by the petroleum industry, or expansion of farming operation. The purpose of conducting these short-term pumping tests is to establish well performance parameters prior to any of this activity and compare the results to pump test data collected after these activities have been completed. For comparison purposes, the pre and post pump tests must be performed using identical procedures.

In addition to collecting background data on a well, there is some basic information that must be collected for a specific capacity test and other well performance tests. This information is described on the Specific Capacity web page.

Water Quality Monitoring

Regular and systematic monitoring should be conducted to ensure a safe and healthy water well supply. Groundwater contains natural chemical constituents that are derived from the soil and rock materials that the water passes through. Although not generally harmful to human health, these chemical constituents can consist of potentially harmful parameters like arsenic, selenium, boron or radon that may present health problems depending on the concentration present.

Besides natural chemical constituents, groundwater can become contaminated from nearby agricultural or human activities such as improper storage of wastes or agricultural chemicals, animal manure storage, poorly maintained septic systems, leaking underground storage tanks and accidental spills.

Understanding and identifying any potential problems early is essential to safe-guarding a groundwater supply. A well owner should have a water quality analysis performed when the well is initially constructed and then test the water at least once a year for any microbiological contamination and any water quality parameters of concern identified in the initial analysis (see Monitoring Checklist ). An explanation of the general water quality parameters is provided in the Groundwater Quality section.

Additional water quality monitoring should be considered if there is a change in nearby land use activity or flooding of the well. The occurrence of an accidental spill in the vicinity of the well can also trigger a higher order of monitoring. Also, a change in colour, taste and odour of the water may also indicate a change in water chemistry or bacteriological quality.