Chapter Description

Identifying the appropriate location for test holes or dewatering wells will dictate the success or failure of a project [e.g., verifying a conceptual site model (CSM), lowering water table to the desired elevation, or optimizing the performance of a pump and treat system]. Before the drill, auger or excavator goes in the ground, a comprehensive planning process would help identify the right location for the test hole or dewatering well. This chapter discusses siting and planning processes for test holes and dewatering wells.

This chapter does not cover holes used in geotechnical investigations that are not wells.

Regulatory Requirements - Siting Considerations & Initial Planning

Relevant Sections - The Wells Regulation

  • Location of Wells – Subsections 12(1) to (6)
  • Surface Drainage – Section 12.3
  • Records – Well Clusters – Section 16.4

The Requirements - Plainly Stated

The Wells Regulation requires or exempts the following regarding the well’s location:

Exemption - Setback Distance

A person constructing a test hole or dewatering well is exempt from all setback distance requirements found in the Location of Wells section of the Wells Regulation.

Exemption - Well Site

Test holes and dewatering wells are exempt from the requirements to be:

  • made accessible for cleaning, treatment, repair, testing, inspection and visual examination at all times, and
  • sited higher than the immediately surrounding area.

Surface Drainage

The person constructing the test hole or dewatering well must ensure that surface drainage is such that water will not collect or pond near or at the well. Proper surface drainage can be ensured by proper mounding of earth around the well and outward from the well to direct surface drainage away from the well.

Planning Well Clusters

If the person constructing the test hole or dewatering well is considering installing a number of wells on one or more properties, and completing a single well record for a group of test holes or dewatering wells, there are several well location and timing (construction phase) requirements that must be met. See Chapter 15: Well Records, Documentation, Reporting & Tagging.

Reminder - Even though a test hole or dewatering well can be constructed on land that is an agricultural operation with a nutrient management plan, section 46 of the General regulation (O. Reg. 267/03) as amended made under the Nutrient Management Act prohibits a person from applying certain materials within specified distances from wells including test holes and dewatering wells. For further information see the “Initial Project Considerations” section in this chapter for these requirements.

Reminder - Requirements for the Records of Site Condition regulation are provided in the “Initial Project Considerations” section and the “Considerations for Test Holes and Monitoring Wells Constructed as Part of an Environmental Site Assessment for a Record of Site Condition” section of this chapter.

Key Concepts

Study areas can be chemically and geologically complex and heterogeneous. This may contribute to a number of uncertainties with respect to the site. Inexact or incomplete characterization of the geology or hydrogeology, poor definition of the contaminant distribution on contaminated sites or waste disposal sites, or inadequate collection of data can result in:

  • improper placement of monitoring wells,
  • inadequate number of monitoring wells
  • improper chemical analyses,
  • ineffective remediation methods, and
  • improper dewatering system design (e.g., ineffective dewatering system, overburden collapse or unanticipated interference problems).

It is important to assess the physical conditions of the overburden and bedrock geology and hydrogeology to define contaminant sources, pathways and receptors. This determines the proper site monitoring for long-term exposure and site remediation. Wells play an important part in all aspects of initial site characterization, long-term monitoring and remediation.

Determination of the physical conditions of the overburden and bedrock geology and hydrogeology will also help a project team to design a dewatering system to lower and control groundwater levels around a construction excavation or to collect contaminants.

Improperly constructed and located wells create a high potential for cross-contamination by mobilizing the contaminant plume or by creating a path for contaminants to move. It is important that the well location and the construction be such that there is a reduced risk of surface water or contaminants entering the well or moving between water bearing zones.

Test holes and dewatering wells are used in projects such as:

  • assessing groundwater conditions for property transfers,
  • assessing groundwater conditions for proposed waste disposal applications,
  • assessing groundwater conditions for large and small drinking water systems,
  • delineating wellhead protection areas,
  • assessing the presence or absence of contamination and its extent,
  • creating, refining and verifying a three-dimensional, conceptual site model,
  • lowering and controlling groundwater levels, and
  • remediating contaminated sites using techniques such as vapour extraction, and pump and treat systems.

Persons constructing test holes and dewatering wells are exempt from setback distance requirements in the Wells Regulation to allow for groundwater testing, monitoring and rehabilitation projects near sources of contamination.

Initial Project Considerations

When designing a project to collect field data, which will include the installation of test holes or the removal of groundwater using dewatering wells, the following should be considered before the wells are installed on the site:

  • results from previous investigations,
  • regional and local geological and hydrogeological reports and maps to establish aquifer characteristics for a conceptual site model,
  • current and historical topographical maps, aerial photographs and satellite photographs to establish topography, drainage patterns, regional geology and structures,
  • soil surveys to identify soil and overburden deposits,
  • location of previous or existing wells on the site and their status (e.g., in use, abandoned, buried),
  • location of wells on adjacent properties,
  • well records and Permit to Take Water approvals in the vicinity of the site to help establish groundwater characteristics and possible natural gas issues,
  • site plan maps, as built drawings and engineering drawings for the site,
  • accessibility of various types of well construction equipment to enter the site (e.g., drill rigs),
  • location or planned location of underground and above ground storage tanks and their status,
  • historical property ownership,
  • records of waste generated and disposed of on the property,
  • known or suspected contaminants and their Material Safety Data Sheets,
  • reports of spills, orders and charges by regulators,
  • insurance records,
  • location of hydro lines or underground services (utilities) from the owner, municipality or other sources,
  • climate data to help establish loadings to the groundwater, and
  • findings from any site reconnaissance performed to verify data collected, and to make observations of overburden and bedrock, and any possible contamination sources, pathways and receptors.

The preliminary information will allow a project team to create a conceptual site model (CSM) for the site. The CSM will, in turn enable the:

  • definition of the study area,
  • delineation of aquifer types, groundwater levels and groundwater gradients,
  • identification of the strength and compressibility of cohesive overburden,
  • identification of overburden and bedrock stratigraphy
  • identification of wells, wetlands and other surface water resources that could be impacted by the project,
  • identification of the likely source(s) and location of contaminants on contaminated sites or waste disposal sites, and
  • delineation of pathways through the overburden and bedrock including the groundwater on contaminated sites or waste disposal sites.

The CSM can be used to design a data collection system, which is an approach to refining or confirming the conceptual site model. The data collection system for the site should include the location, equipment and well construction methods for initial test holes. These initial test holes can be used to assess aquifer and other stratigraphic unit characteristics for various projects (e.g., investigation of new municipal water systems, dewatering control for proposed excavations and contaminated sites or waste disposal sites). These initial test holes can also be used to assess the nature and extent of a contaminant, a contaminant’s pathways and receptors on and around contaminated sites. In addition, initial test holes may also be used to determine the likelihood for interference from dewatering control systems.

Best Management Practice – “Cradle to Grave” Approach for Test Holes and Dewatering Wells

Test holes or dewatering wells are commonly found on sites where there are problematic and sometimes hazardous environmental conditions. The Ministry of the Environment and Climate Change frequently encounters sites where the person constructing the well, project manager and owner of the land have failed to meet their responsibilities and the well degrades and become pathways for contaminants. Therefore, it is important for a person involved in well design or construction to take a “cradle to grave” approach with every well installed for an environmental investigation, groundwater research project, remediation project or dewatering project. This means that, in addition to considering the existing conditions and the goals and objectives of the project that will affect how a well is designed and constructed, a clear plan should be in place to:

  • address the ongoing requirements for well maintenance and, ultimately, proper abandonment of every well involved in a particular project to meet the Wells Regulation and minimize the risk of any well becoming a pathway for contamination,
  • identify triggers regarding when a well would need to be repaired or properly abandoned, and
  • identify the person or persons responsible for the implementation of the construction, maintenance and abandonment portions of the plan.

The “cradle to grave” plan should be retained at the site or with the persons responsible for the site and made available to all persons that may be involved in the construction, maintenance and abandonment of any test hole or dewatering well that is part of the project.

As part of the “cradle to grave” approach, a person constructing a test hole or dewatering well and any professional engineer or professional geoscientist managing these projects should take steps to ensure the owner of the land fully understands and agrees with:

  • the cradle to grave approach for every well on the property, and
  • the well owner’s ongoing legal obligations under the Wells Regulation to properly maintain or abandon every well on the property.

Note that, the well purchaser is one of the well owners with responsibilities for well maintenance and abandonment.

Best Management Practice – Setback Distance of a Test Hole or a Dewatering Well to Water Supply Wells

During the planning phase of a project, an assessment of all nearby wells should be identified and assessed to determine the impact that the planned well construction could have on the well. If it is determined there is a likelihood that the planned well construction operation may impair the water in a nearby well, drilling should not proceed or proper contingency plans should be put in place to protect the nearby well water supply.

When planning a project and as a preventative measure, the separation distance between:

  • the test hole and any existing water supply wells should be at least 15 m (50 feet). This will reduce the risk of contamination of the existing water supply well if the test hole inadvertently becomes a pathway for contamination.
  • the dewatering well and any existing water supply wells should be at least 15 m (50 feet) or a distance that is outside of a predicted radius of influence, whichever is greater. The location should reduce the risk of a quantity interference problem with an existing water supply well due to the pumping of the dewatering well and the risk of contamination of the existing water supply well if the dewatering well inadvertently becomes a pathway for contamination.

Best Management Practice – Avoiding Low-Lying Areas

Placing a well in any low-lying ground surface area of a site should be avoided. Care should be taken to ensure that test holes or dewatering wells are not installed in locations that are subject to periodic flooding.

When planning all test holes and dewatering wells, a project team should be aware of the following requirements in the Wells Regulation, the Records of Site Condition regulation and the General regulation in the Nutrient Management Act.

The Wells Regulation - Surface drainage must be such that water will not collect or pond near a well. As such, a test hole or dewatering well must not be located within or below a surface water body.

Records of Site Condition regulation - Significant amendments to O. Reg. 153/04 (Records of Site Condition) came into force on July 1, 2011. When conducting a phase one environmental site assessment to be used to submit a record of site condition for filing, the qualified person must comply with a large number of detailed requirements, including the requirement to create a CSM. The requirements are found in Schedule D of O. Reg. 153/04 made under the EPA: O. Reg. 511/09: Records of Site Condition - Part XV.1 of the Act. All records of site condition submitted after July 1, 2011 must comply with these requirements, so qualified persons are well advised to take account of them now whenever it is possible that work underway may lead to a record of site condition being submitted after this date.

Even though a test hole or dewatering well can be constructed on land that is an agricultural operation with a nutrient management plan, starting on January 1, 2011, the General regulation (Regulation 267/03 as amended made under the Nutrient Management Act) requires that a person cannot apply:

  • An agriculture or non-agriculture source material* to land within 15 metres of a test hole or dewatering well if the well has a depth of at least 15 metres and a watertight casing from the ground surface to at least 6 metres below the ground surface
  • A non-agriculture source material that is both CM1* and CP1* or an agriculture source material to land within 30 metres of the test hole or dewatering well that does not meet the casing and depth requirements of the first bullet
  • A non-agriculture source material that is CM2* or CP2* to land within 90 metres of the test hole or dewatering well that does not meet the casing and depth requirements of the first bullet
  • A commercial fertilizer or compost that meets the Compost Guidelines to land within 3 metres of the test hole or dewatering well

Reminder - See the Definitions section and section 46 of Regulation 267/03 (General) as amended made under the Nutrient Management Act, 2002, S.O. 2002, c. 4 for further information.

Considerations for Test Holes Constructed as Part of Preliminary Data Collection Systems

It is important that data collection systems include the construction of preliminary test holes to obtain groundwater information (e.g., groundwater levels, hydraulic conductivity, transmissivity, water samples). In addition, the test holes may be used to collect overburden, bedrock, gas, and/or free product samples. Many different considerations should be taken into account before choosing the well construction equipment and location of the well including the following:

  • objectives of the study, which will determine the quality of data required and the scope of the investigation,
  • physical characteristics of the site (e.g., rapid sampling tools such as direct push units can be used in overburden deposits but conventional rotary drilling equipment may be required for bedrock environments),
  • well depth requirements and limitations,
  • anticipated contaminants and their concentrations,
  • equipment characteristics [e.g., equipment durability and limitations, cost of equipment, and whether the site is accessible with the equipment (e.g., off road and indoor locations)]
  • production of drill cuttings and groundwater during development to limit waste costs,
  • static water level, and if necessary, taking steps to prevent any uncontrolled flow at the well site,
  • the need for a Permit to Take Water for any taking from the well (including discharges during well construction, well yield tests, aquifer pumping tests and flowing wells) that is greater than 50,000 litres in any one day (see following section),
  • the discharge water, drilling mud or drill cuttings from a well must not cause an adverse effect to the natural environment,
  • proper storage and disposal of any overburden and bedrock core sample to prevent an adverse effect to the natural environment
  • the need for a sewage works Certificate of Approval if groundwater, drill cuttings or other material is anticipated to discharge from the well (see following section),
  • potential for disturbance on-site and off-site,
  • quality assurance for the project,
  • health and safety plans for the site,
  • site security and proper authorization to access the site,
  • contingency plans for reporting and rectifying potential problems (e.g., during well construction, the well begins to flow or well encounters an explosive gas) and
  • proper abandonment (decommissioning) of preliminary test holes to prevent vertical pathways of contamination.

Depending on the above considerations, a project team will have to decide whether one or more of the following well construction methods are used to construct test holes:

  • direct push,
  • sonic drilling,
  • air rotary,
  • conventional rotary,
  • hollow stem augers,
  • bucket auger and/or
  • excavating equipment.

Further details on well construction methods are found in Chapter 6: Constructing the Hole, Casing & Covering the Test Hole or Dewatering Well.

A project team will also have to determine the type of equipment to install into the test holes to conduct field and sample analyses. For example, the diameter of the well will determine which sampling equipment will fit in the well.

Further details on sampling equipment are found in Chapter 12: Equipment Installation.

Permit to Take Water, Discharge Approval and Waste Generation Consideration

Permit to Take Water

Reminder - If groundwater is anticipated to be taken (e.g., pumped) or is anticipated to be discharging from a well or a number of wells during construction at a volume of more than 50,000 litres (11,000 Imp gal) on any one day, a Permit to Take Water under the Ontario Water Resources Act may be required.

If it is anticipated that during well construction a Permit To Take Water will be required, an application for a Permit To Take Water should be submitted well in advance of the undertaking. Presently, an application may require scientific reports to support the application. The application, once submitted with sufficient supporting documentation, may take up to 90 days for the Ministry to process and make a decision on whether or not to issue a permit.

A person constructing the well, the well owner or a retained Professional Engineer or Professional Geoscientist should pre-consult with Ministry of the Environment and Climate Change’s Regional Technical Support Section; Water Resources Unit staff about any application prior to submission (see the Additional Resources portion at the end of the manual for Ministry of the Environment and Climate Change office locations). Regional permit coordinators, hydrogeologists and surface water specialists have the local expertise and knowledge to assist applicants. Pre-consultation will reduce the risk of incomplete applications and allow for the Ministry to promptly process the application.

Coordinating all of the equipment and persons needed to conduct a short term pumping test progressively and seamlessly is difficult and expensive. As a result, the Ministry can fast track Permits To Take Water for short term pumping tests to test the yield of the well or an aquifer; however, applications should be submitted in advance to allow a permit to be in place for the scheduled test and prevent unnecessary delays and expense.

If an unanticipated flow of groundwater occurs at more than 50,000 litres on any one day, contingencies should be in place to deal with this issue including immediately reporting the situation to the nearest Ministry of the Environment and Climate Change office and taking measures to control or stop the flow of water.

More information on Permit to Take Water approvals can be found on Ontario.ca.

Discharge Approval

Reminder - During well construction, it is important that the location of any groundwater, drill cuttings and other material discharging from the well does not cause environmental impacts such as erosion, impairment of surface water bodies or off-site flooding. This may require the use of settling ponds on the property. A sewage works environmental compliance approval under the Ontario Water Resources Act may be required if the person constructing the well discharges the water, drill cuttings and other material off the well owner’s property or if the discharge capacity exceeds 10,000 litres per day on the property. It is important for the person to determine if an environmental compliance approval is required before discharging the water, drill cuttings and other material from the well. A guide to explain the sewage works process can be found on Ontario.ca.

Requirements Related to the Generation of Waste During Well Construction

During well construction, it is important to consider any approvals or legislation related to the generation of any groundwater, drill cuttings, drilling fluid and other material that may be contaminated and deemed hazardous waste. Ontario has a comprehensive legislative and regulatory framework to help manage hazardous wastes in an environmentally safe manner. Through the Environmental Protection Act (EPA) and accompanying regulations, the Ministry of the Environment and Climate Change (MOECC) has established a cradle to grave management system, which includes the systematic control of collection, storage, transportation, treatment, recovery and disposal of this waste.

More information on hazardous waste identification, generation, storage and disposal, can be found on Ontario.ca.

Consideration for Test Holes and Monitoring Wells Constructed as Part of an Environmental Site Assessment for a Record of Site Condition

One of the objectives of the planning of the site investigation component of a phase two environmental site assessment is to develop a sampling and analysis plan that will adequately assess all areas of the phase two property where contaminants may be present in land or water on, in or under a property. Anyone working on a phase two property should consult O. Reg. 153/04 prior to beginning any work.

Requirements Starting on July 1, 2011

This section provides an overview of the requirements related to initial planning of test holes and monitoring wells for a phase two environmental site assessment (ESA) under the Records of Site Condition (RSC) regulation starting on July 1, 2011. Requirements that are not related to test holes and monitoring wells are not included.

Starting on July 1, 2011, amendments to O. Reg. 153/04 came into force and apply to phase two environmental site assessments (ESAs) conducted in support of records of site conditions (RSCs). For any such RSC submitted on or after this date, a qualified person must:

  • ensure that the sampling and analysis plan includes a quality assurance and quality control program, data quality objectives, standard operating procedures and a description of any physical impediments that interfere with or limit the ability to conduct sampling and analysis

  • develop standard operating procedures for the field investigation methods including:

    • hole drilling,
    • excavating,
    • monitoring well installation,
    • monitoring well development,
    • field measurement of water quality indicators, including calibration procedures,
    • soil sampling, and
    • groundwater sampling

  • ensure the sampling and analysis plan includes identification of, and rationale and procedures for:

    • the choice of sampling system, such as a judgmental, random or grid sampling system,
    • sampling depth intervals, including the screened intervals of the monitoring wells, and
    • other field information to be obtained, including water levels, field measurements, and elevation surveying

  • ensure the groundwater sampling method to be used to characterize contamination or determine if the concentration of a contaminant is above, at or below an applicable site condition standard or standard specified in a risk assessment for the contaminant, meet the following:

    • sampling depth intervals, including the screened intervals of monitoring wells must be positioned, within the geologic formation in which a contaminant may be present so as to:

      • isolate the zones where contaminants may be present, and
      • delineate both dissolved and separate phase contaminants
  • ensure that where petroleum hydrocarbons or light non-aqueous phase liquids may be present on, in or under the phase two property, sampling depth intervals, including screened intervals of monitoring wells, are positioned to intersect the water table
  • ensure that where a monitoring well is being used, monitoring well screens do not exceed 3.1 m (10 feet) in length, based on the saturated length of the screen

  • determine the groundwater flow direction during the site investigation. This includes:

    • determining a reference elevation for each monitoring well reported to the nearest centimetre relative to a geodetic or permanent and recoverable benchmark, and
    • installing a minimum of three monitoring wells, not placed in a straight line, in each aquifer to be investigated, at locations and in a manner appropriate to interpret horizontal flow directions

Records of Site Condition regulation - There are additional obligations for plans and procedures. For further details please refer to O. Reg. 153/04 for RSC requirements.

Reminder - For clarification on the term “monitoring well” in the Records of Site Condition regulation see Chapter 2: Definitions & Clarifications, Table 2-2.

Reminder - As part of a standard operating procedure for the well construction, a plan for decontamination of equipment between wells should be created.

Considerations for Long-Term Monitoring Wells and Remediation Wells

Based on the preliminary data collection, management and interpretation, the three-dimensional conceptual site model can be validated or if necessary revised. The validated or revised CSM can be used to develop long term monitoring and remediation plans, which include the following considerations for test holes and dewatering wells:

  • Well locations for contaminated sites or waste disposal sites:

    • near to the source(s) of contaminants,
    • along the contaminant pathways,
    • near the leading edge of the plume to achieve containment using dewatering wells (e.g., pump and treat), and
    • near supply wells, surface water bodies and other receptors,
  • Points of compliance (e.g., property boundary)

  • Well locations to monitor quantity interference:

    • near a groundwater taking such as a quarry or municipal well, and
    • between the receptors (e.g., private supply well, creek, other groundwater users) and the groundwater taking to monitor the lowering of the area’s groundwater levels,
  • Depths of the wells including the length of the screened interval
  • Well construction methods
  • Sampling, monitoring, testing and/or pumping equipment to be installed in or onto the test hole or dewatering well
  • Type of materials used to construct the wells
  • Potential for chemical and bacterial fouling
  • Health and safety considerations for construction and sampling
  • Proper handling, storing and discharging of drill cuttings or groundwater during well construction and development
  • Obtaining necessary water taking and discharge approval instruments
  • Contingency plans for reporting and rectifying potential problems (e.g., during well construction, the well begins to flow or encounters an explosive gas)

Considerations for Dewatering Wells Used to Lower or Control the Groundwater Level

Based on the preliminary data collection, management and interpretation, the three-dimensional conceptual site model can be validated or if necessary revised. The validated or revised CSM can be used to develop a dewatering plan to lower or control the area’s groundwater level to the needed elevation which includes the following considerations:

  • Well locations:

    • location of possible contamination sources nearby that may be mobilized laterally or vertically between aquifers,
    • sufficient distance from supply wells and other receptors to prevent quantity interference problems,
  • Depths of the wells including the length of the screened interval
  • Well construction methods
  • Pumping, sampling, monitoring and/or testing equipment to be installed in or onto the well
  • Location of discharge line/piping/header systems
  • Type of materials used to construct the monitoring wells
  • Health and safety considerations for construction and sampling
  • Proper handling, storing and discharging of cuttings during well construction and groundwater during construction, development and dewatering
  • Prevention of soil collapses, sink holes, soil liquefaction, building damage and erosion at surface
  • Potential for chemical and bacterial fouling
  • Rehabilitation and maintenance
  • Obtaining necessary water taking and discharge approval instruments. (see the “Considerations for Test Holes Constructed as Part of Preliminary Data Collection Systems section of this chapter)
  • Contingency plans for reporting and rectifying potential problems (e.g., during well construction, the well begins to flow or well encounters an explosive gas)

Reminder - Further detailed information on environmental site characterization and initial planning for test holes and dewatering wells can be found in the Practical Handbook of Environmental Site Characterization and Groundwater Monitoring, 2nd Edition, Edited by D. Nielson, 2006.

Reminder - Further detailed information on groundwater lowering or control can be found in Construction, Dewatering and Groundwater Control New Methods and Applications 3rd Edition, Powers, J. Patrick et al. 2007.

Where to Record the Well Location

It is important to accurately record and report the location of each well constructed as part of a project. Inaccurate location information on the well record, not reporting a well on a well record or not delivering the well record to the well owner or the Ministry could lead to problems locating a well in the field and inaccurate interpretation of: spatial data, plume location and groundwater flow direction.

Reminder - For details on requirements and best management practices related to completing a well record, see Chapter 15: Well Records, Documentation, Reporting & Tagging.