Introduction
Drilling and sampling are the core investigative activities of a Phase II Environmental Site Assessment (ESA). While a Phase I ESA identifies potential environmental concerns through historical research and site reconnaissance, it is Phase II that confirms whether contamination is actually present—and if so, to what extent.
At the heart of this process is the collection of physical samples from the subsurface. Soil, groundwater, and sometimes soil vapour are carefully extracted, analyzed, and interpreted to provide a scientifically defensible understanding of site conditions.
This work is highly technical, regulated, and methodical. Every step—from drilling a borehole to sealing a monitoring well—must be executed with precision to ensure the data is accurate, reliable, and legally defensible.
In this article, we take a comprehensive look at drilling and sampling in a Phase II ESA, including the equipment, procedures, quality control measures, and best practices that define a successful investigation.
The Purpose of Drilling and Sampling
The primary objective of drilling and sampling is to:
- Confirm the presence or absence of contaminants
- Determine concentration levels
- Define the vertical and horizontal extent of contamination
- Support risk assessment and remediation decisions
Unlike Phase I, which is largely qualitative, Phase II is quantitative and evidence-based.
Key Equipment and Personnel
A successful drilling program depends on both the right equipment and the right expertise.
Drilling Rig
Drilling rigs are mobile units used to advance boreholes into the subsurface.
Common types include:
- Track-mounted rigs – ideal for uneven terrain and restricted access
- Truck-mounted rigs – suited for accessible, open sites
These rigs provide the power and stability needed to penetrate soils and, in some cases, bedrock.
Drilling Technologies
Different subsurface conditions require different drilling methods.
Hollow-Stem Auger (HSA)
- Best suited for unconsolidated soils above the water table
- Allows for continuous sampling without borehole collapse
- Commonly used in geotechnical and environmental investigations
Direct Push Technology (DPT) / Geoprobe
- Ideal for soft soils and shallow investigations
- Provides continuous soil cores
- Enables rapid sampling and temporary well installation
Rotary Sonic or Core Drilling
- Used for bedrock or dense formations
- Provides high-quality core samples
- Suitable for deeper or more complex investigations
Sampling Equipment
Sampling tools are selected based on drilling method and sample type.
- Split-spoon samplers – used with HSA for discrete soil samples
- Core barrels – used with DPT or sonic drilling for continuous cores
- Bailers and pumps – for groundwater sampling
- HydraSleeves – passive groundwater sampling devices
Each tool is designed to preserve sample integrity during retrieval.
Qualified Person (QP)
A Qualified Person (QP) oversees all field activities.
Typically a:
- Geologist
- Environmental engineer
- Environmental scientist
The QP is responsible for:
- Logging subsurface conditions
- Identifying signs of contamination
- Ensuring adherence to protocols
- Maintaining data quality and defensibility
The Drilling Process
The drilling and sampling process follows a structured sequence to ensure consistency and reliability.
1. Site Preparation
Before drilling begins:
- Utility clearance must be completed
- Borehole locations are marked based on the Sampling and Analysis Plan (SAP)
- Equipment is mobilized to site
Proper planning minimizes risk and ensures efficient field operations.
2. Borehole Advancement
The drilling rig advances the borehole using the selected method.
During this process, the QP:
- Logs soil stratigraphy (soil type, colour, moisture, texture)
- Notes any evidence of contamination, such as:
- Odours
- Staining
- Presence of non-aqueous phase liquids (NAPL)
This logging process is critical for interpreting subsurface conditions.
3. Sample Collection
Soil samples are collected at regular intervals, typically:
- Every 0.75 m (2.5 ft)
- Or at changes in soil conditions
Each sample is:
- Retrieved using appropriate equipment
- Immediately assessed for visual and olfactory indicators
- Prepared for laboratory analysis
4. Monitoring Well Installation
If groundwater investigation is required, monitoring wells are installed.
A typical well consists of:
- Screened section – allows groundwater to enter
- Riser pipe – extends to surface
- Protective casing – prevents damage
Installation Steps
- Filter sand is placed around the screened interval
- Bentonite seal is installed above the sand
- Remaining borehole is backfilled to surface
This design prevents cross-contamination between soil layers.
5. Borehole Abandonment / Backfill
Boreholes not converted into monitoring wells must be properly sealed.
Common materials include:
- Bentonite chips
- Cement grout
Proper abandonment:
- Restores site conditions
- Prevents vertical migration of contaminants
Sampling Procedures and Quality Control
Accurate data depends on strict adherence to sampling protocols.
Industry Standards
Sampling must comply with recognized guidelines, such as those from the
Canadian Standards Association (CSA Group).
These standards ensure:
- Consistency
- Reliability
- Legal defensibility
Soil Sampling Procedures
Sample Handling
Immediately after collection:
- Samples are transferred to laboratory-provided containers
- Containers are sealed and labeled
For volatile contaminants:
- Specialized containers with preservatives (e.g., methanol) are used
- This minimizes loss of volatile compounds
Headspace Analysis
Field screening is often performed using a:
- Photoionization Detector (PID)
This measures volatile organic compounds (VOCs) in soil samples.
Purpose
- Identify areas of highest contamination
- Select samples for laboratory analysis
Groundwater Sampling Procedures
Groundwater sampling requires additional steps to ensure representativeness.
Well Purging
Before sampling:
- 3 to 5 well volumes of water are removed
This eliminates stagnant water in the casing.
Parameter Monitoring
During purging, field parameters are measured:
- pH
- Temperature
- Conductivity
- Turbidity
- Dissolved oxygen
- Redox potential
Sampling occurs only when these parameters stabilize.
Sample Collection
Groundwater samples are:
- Collected in laboratory bottles
- Preserved as required (e.g., acidification)
- Stored on ice for transport
Maintaining temperature and preservation is critical.
Investigation-Derived Waste (IDW) Management
Drilling activities generate waste materials, including:
- Soil cuttings
- Purge water
- Disposable equipment
Proper Handling
All IDW must be:
- Collected and contained
- Characterized if necessary
- Disposed of at licensed facilities
This ensures compliance with environmental regulations.
Data Compilation and Reporting
The final step is translating field data into actionable information.
Phase II ESA Report Includes:
- Borehole logs
- Soil and groundwater data
- Laboratory analytical results
- Site interpretation
- Conclusions and recommendations
Decision-Making
The report determines:
- Whether contamination exceeds regulatory standards
- If remediation is required
- Next steps for the site
Common Challenges in Drilling and Sampling
Despite careful planning, challenges often arise.
Subsurface Variability
- Unexpected soil conditions
- Variable groundwater levels
Equipment Limitations
- Access constraints
- Mechanical issues
Contamination Complexity
- Mixed contaminants
- Irregular plume distribution
Weather and Site Conditions
- Rain, freezing temperatures
- Difficult terrain
Best Practices for Successful Investigations
1. Thorough Planning
- Develop a detailed SAP
- Anticipate site conditions
2. Use Appropriate Methods
- Match drilling technique to geology
3. Maintain Sample Integrity
- Follow strict handling protocols
4. Ensure Qualified Oversight
- Experienced QP is essential
5. Document Everything
- Accurate logs and records
6. Follow Regulatory Guidelines
- Adhere to CSA and local standards
The Role of Technology in Modern ESAs
Modern tools are enhancing drilling and sampling workflows:
- Digital borehole logging
- Real-time data capture
- Integrated data platforms
These innovations improve:
- Accuracy
- Efficiency
- Data accessibility
Conclusion
Drilling and sampling are the foundation of a Phase II ESA.
They transform uncertainty into measurable data—providing the evidence needed to assess environmental risk and guide remediation decisions.
From selecting the right drilling method to ensuring proper sample handling and waste management, every step must be executed with precision and care.
When done correctly, drilling and sampling provide:
- Reliable data
- Clear insights
- Confidence in decision-making
As environmental regulations tighten and projects become more complex, the importance of high-quality Phase II investigations will only continue to grow.
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