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Reference Guide

Groundwater Monitoring Protocol

Complete protocol for monitoring well installation, purging and sampling procedures, parameter selection, QA/QC requirements and data interpretation for groundwater investigations

Well Installation Purging & Sampling Parameter Selection QA/QC Monitoring Frequency Well Development Data Interpretation

Well Installation Standards

Monitoring well installation follows ASTM D5092 (Standard Practice for Design and Installation of Groundwater Monitoring Wells). Proper construction ensures representative groundwater samples and prevents cross-contamination between aquifer zones. Wells must be designed for the specific hydrogeological conditions and target contaminants at each site.

Well Materials

  • PVC (Schedule 40): Most common for routine monitoring. Low cost, chemically resistant to most inorganics. Not suitable for chlorinated solvent sites (sorption) or NAPL investigations.
  • Stainless Steel (304/316): Required for VOC/SVOC investigations. Inert to organic solvents. Higher cost but eliminates sorption bias.
  • PTFE (Teflon): Highest inertness. Used for trace-level organic investigations. Very expensive, rarely standard.
  • Standard diameter: 50 mm (2 in.) for sampling-only wells; 100 mm (4 in.) for wells requiring pump installation.

Screen Selection

  • Slot size: Typically 0.010 in. (0.254 mm) or 0.020 in. (0.508 mm). Selected based on formation grain size analysis.
  • Screen length: 1.5 m (5 ft) standard for point-of-compliance wells; up to 3 m (10 ft) for water table wells in unconfined aquifers.
  • Screen placement: Straddle the water table for unconfined aquifers; place within the target zone for confined aquifers.
  • Material: Must match casing material. Factory-cut machine slots preferred over hand-cut.

Filter Pack & Grouting

  • Filter pack: Clean silica sand (e.g., #2 or #3 Monterey sand) placed around the screen, extending 0.6 m (2 ft) above the screen top.
  • Transition seal: Fine sand or bentonite pellets (minimum 0.3 m / 1 ft) above filter pack to prevent grout migration into screen zone.
  • Annular seal: Bentonite grout (20-30% solids) or cement-bentonite mix from transition seal to surface. Tremie-grouted from bottom up.
  • Hydration: Bentonite pellets require minimum 30-minute hydration before grouting above. Do not rush.

Surface Completion

  • Flush-mount: Traffic-rated vaults set in concrete pad for areas with vehicle traffic. J-plug or locking cap inside.
  • Stick-up: Protective steel casing (stickup guard) with locking cap, set in concrete pad. 0.6-1 m above grade. Bollard protection if in traffic areas.
  • Concrete pad: Minimum 0.6 m x 0.6 m, sloped away from well to prevent surface water infiltration.
  • Survey: All wells surveyed for top-of-casing elevation (to 0.01 ft / 0.003 m) and horizontal coordinates (sub-meter GPS minimum).

The goal of purging is to remove stagnant water from the well casing so that samples represent actual formation water. Low-flow sampling is the preferred method for most regulatory programs as it minimizes disturbance and produces more representative results.

Low-Flow (Micropurge) Sampling

  • Equipment: Peristaltic pump, bladder pump, or adjustable-rate submersible pump. Bladder pump preferred for VOCs (no aeration).
  • Pump placement: Intake positioned within or just above the screened interval. Avoid placing at the bottom (sediment disturbance).
  • Pumping rate: <500 mL/min, ideally 100-300 mL/min. Adjust to maintain minimal drawdown (<0.1 m / 0.3 ft).
  • Drawdown monitoring: Use electronic water level indicator. Record water level every 3-5 minutes during purging.

Stabilization Criteria

  • pH: +/- 0.1 standard units over 3 consecutive readings
  • Temperature: +/- 0.2 degrees C over 3 consecutive readings
  • Specific conductance: +/- 3% over 3 consecutive readings
  • Dissolved oxygen (DO): +/- 10% or +/- 0.2 mg/L over 3 consecutive readings
  • ORP: +/- 10 mV over 3 consecutive readings
  • Turbidity: <10 NTU preferred; +/- 10% over 3 consecutive readings for higher values

Conventional (Volume) Purging

  • Volume: Remove 3-5 well volumes before sampling. Well volume = pi x r^2 x water column height.
  • Method: Bailer, submersible pump, or inertia pump. Higher flow rates acceptable during purge.
  • When acceptable: Low-permeability formations where low-flow stabilization is impractical, or when required by a site-specific sampling plan.
  • Limitations: Can mobilize sediment, increase turbidity and bias dissolved metals results high. Less representative than low-flow for most parameters.
  • Purge water: Must be containerized and disposed of per applicable regulations. Do not discharge on the ground near wells.

No-Purge Samplers

  • Passive diffusion bags (PDBs): Low-density polyethylene bags filled with deionized water. Deployed in well for 2+ weeks. VOCs equilibrate through membrane. Only for VOCs/some SVOCs.
  • HydraSleeve: Single-use, no-purge grab sampler. Self-sealing sleeve deployed in the screened interval and retrieved after equilibration. Suitable for a wide range of analytes.
  • Snap Sampler: Sealed bottles triggered to open and close at depth. Collects discrete samples at specific intervals.
  • Advantages: No purge water to manage, reduced labor and equipment costs, eliminates pump-induced turbidity.
  • Limitations: Must be pre-approved by regulatory authority. Not suitable for all analytes or well configurations.

Analytical parameter suites should be tailored to the known or suspected contaminants at the site. Every groundwater sampling event should include field parameters measured during purging plus laboratory analysis for site-specific contaminants of concern.

Site Type Primary Parameters Supporting Parameters Field Parameters
Petroleum Hydrocarbon (PHC) Sites
Gas stations, fuel storage, refineries BTEX (benzene, toluene, ethylbenzene, xylenes), PHC fractions F1-F4 (CCME), PAHs Dissolved metals (lead, MTBE where applicable), dissolved oxygen, nitrate, sulfate, iron, manganese pH, temperature, conductivity, DO, ORP, turbidity
Chlorinated Solvent Sites
Dry cleaners, metal degreasing, manufacturing VOCs (TCE, PCE, 1,1-DCE, cis-1,2-DCE, vinyl chloride, 1,1,1-TCA) Dissolved gases (methane, ethane, ethene), dissolved iron, sulfate, chloride, alkalinity, TOC pH, temperature, conductivity, DO, ORP, turbidity
Metals Contamination Sites
Mining, smelting, industrial, landfills Dissolved and total metals (full scan or site-specific: As, Cd, Cr, Cu, Pb, Ni, Zn, Hg) Alkalinity, hardness, major ions (Ca, Mg, Na, K, Cl, SO4), pH, TDS pH, temperature, conductivity, DO, ORP, turbidity
General / Baseline Monitoring
Pre-development, compliance, landfill perimeter Major ions (Ca, Mg, Na, K, Cl, SO4, HCO3), nutrients (nitrate, nitrite, ammonia, phosphate) Dissolved metals, TDS, alkalinity, hardness, COD/BOD (if applicable) pH, temperature, conductivity, DO, ORP, turbidity
Field Parameters - Always Measured

Field parameters are measured in a flow-through cell during purging using a calibrated multi-parameter meter. They serve dual purpose: confirming stabilization for sampling and providing geochemical context for data interpretation. Calibrate the meter daily using certified standards before the first well and verify at the end of each day.

QA/QC samples verify that field and laboratory procedures are not introducing errors or contamination. They are recorded on the chain of custody alongside regular samples using blind identifiers so the laboratory cannot distinguish them from project samples.

QA/QC Type Minimum Frequency Purpose Acceptance Criteria
Field Duplicates 1 per 10 samples (10%) Assess sampling precision and natural variability at collection point RPD <30% (water), <50% (soil). Assign blind ID (e.g., "QC-01").
Trip Blanks 1 per cooler (VOC samples only) Detect contamination during transport and handling All target analytes non-detect. Lab-prepared, never opened in field.
Equipment Blanks 1 per day or per decontamination event Verify decontamination of non-dedicated equipment is effective All target analytes non-detect. Rinse DI water through cleaned equipment.
Field Blanks 1 per sampling event (if applicable) Assess ambient contamination at the sampling location All target analytes non-detect. Exposed to field conditions during sampling.

Data Validation Levels

  • Stage 1: Data completeness check. Verify all requested analyses are reported, correct sample IDs, holding times met.
  • Stage 2: QA/QC assessment. Review lab QC (method blanks, lab duplicates, surrogate recoveries, MS/MSD). Flag exceedances.
  • Stage 3: Full data validation per EPA CLP or equivalent. Applied qualifiers (U, J, R) to individual results. Performed by independent validator.
  • Stage 4: Usability assessment. Evaluate qualified data against project data quality objectives. Determine if data are fit for intended use.

Common QA/QC Failures

  • Trip blank detections: Indicates cross-contamination during transport. All VOC results from that cooler are suspect.
  • Equipment blank detections: Decontamination procedure is inadequate. Results from all wells sampled with that equipment may be biased.
  • High RPD on duplicates: May indicate poor sampling technique, heterogeneous conditions, or matrix interference.
  • Holding time exceedances: Results qualified with "HT" flag. Volatile and microbiological parameters most affected.

Monitoring frequency depends on site conditions, regulatory requirements and plume status. Higher frequency is typical during active remediation or when contaminant concentrations are changing. Frequency may be reduced once plume stability is demonstrated.

Schedule Typical Application Rationale
Monthly Active remediation systems (pump-and-treat, in-situ injection), initial plume delineation, emergency response Track rapid concentration changes and remediation system performance in real time
Quarterly Active contaminated sites under regulatory order, operating remediation systems, compliance monitoring Captures seasonal variation (high/low water table) while providing sufficient data frequency for trend analysis
Semi-Annual Stable plumes with consistent concentration trends, sites transitioning from active to passive monitoring Adequate for sites where concentrations are predictable. Captures wet/dry season variation.
Annual Long-term monitoring, post-closure landfills, sites approaching regulatory closure, institutional control verification Sufficient for stable or declining plumes where data history is well established
Event-Triggered Spill response, construction dewatering, sudden water level changes, new contamination discovered nearby Responsive sampling outside regular schedule when conditions change unexpectedly
Frequency Reduction Criteria

Most regulatory programs allow frequency reduction after demonstrating 4-8 consecutive rounds of stable or declining concentrations. Statistical support (e.g., Mann-Kendall trend test) strengthens the request. Always obtain written regulatory approval before reducing monitoring frequency.

Well development removes drilling fluids, fine sediment and filter pack fines from the well and surrounding formation. A properly developed well produces low-turbidity water that is representative of the aquifer. Development should occur within 48 hours of installation and at least 48 hours before the first sampling event.

Development Procedures

  • Surging: Rapidly move a surge block or bailer up and down within the screen interval to pull fines into the well bore for removal.
  • Pumping: Overpump the well at a rate 2-3x the expected sampling rate. Alternate between surging and pumping.
  • Bailing: Acceptable for shallow, low-yield wells. Labor-intensive but effective for removing settled sediment.
  • Air lifting: Use compressed air to lift water. Effective for deep or high-yield wells. Avoid if VOCs are target analytes (aeration bias).
  • Jetting: High-pressure water directed through screen slots. Used in conjunction with pumping. Effective for low-permeability formations.

Completion Criteria

  • Turbidity: <10 NTU, ideally <5 NTU. This is the primary indicator of adequate development.
  • pH and conductivity: Stabilized within field parameter criteria (same as sampling stabilization).
  • Volume removed: Minimum 5-10 well volumes, or until turbidity criteria are met (whichever takes longer).
  • Sediment: No visible sediment settling out of purge water within 30 seconds of collection in a clear container.
  • Specific capacity: Stable yield during pumping, consistent with expected formation permeability.
Development Log Template

A development log should record: well ID, date, start/end time, development method(s) used, pump rate, water level before/during/after development, volumes removed per interval, turbidity readings at regular intervals, final turbidity reading, pH, conductivity, water appearance (color, odor, sediment), and developer name. Attach the log to the well completion record.

Groundwater data interpretation combines hydrogeological analysis with contaminant chemistry to understand plume behavior, migration pathways and attenuation trends. Effective interpretation requires consistent datasets collected over multiple monitoring events.

Groundwater Flow Direction

Method: Measure static water levels in 3+ wells to construct a potentiometric surface map. Flow direction is perpendicular to equipotential lines, from high to low head.

Key data: Surveyed top-of-casing elevations, depth-to-water measurements (same day, same tide cycle), well construction details.

Output: Groundwater elevation contour maps with flow arrows. Calculate hydraulic gradient (i = dh/dl) for transport modeling.

Contaminant Plume Delineation

Method: Interpolate contaminant concentrations across the monitoring well network using kriging or inverse distance weighting (IDW). Define plume boundaries at applicable screening criteria.

Key data: Concentration values from all wells per event, well locations (coordinates), applicable standards/guidelines (CCME, provincial, site-specific).

Output: Isoconcentration maps showing plume extent, core, and leading edge. Compare events to assess migration or contraction.

Trend Analysis & Statistics

Mann-Kendall test: Non-parametric statistical method for detecting monotonic trends (increasing, decreasing, or stable) in time-series data. Does not require normally distributed data.

Sen's slope estimator: Paired with Mann-Kendall to estimate the rate of concentration change over time. Used for plume stability assessments.

Minimum data: 8+ data points over 4+ events recommended for reliable trend detection. Include non-detects as half the reporting limit.

Plume Classification

  • Expanding: Plume boundaries increasing, concentrations rising at sentinel wells. Requires more aggressive monitoring and/or remediation.
  • Stable: Plume extent and concentrations not changing significantly. Natural attenuation may be balancing source loading.
  • Shrinking: Plume contracting, concentrations declining at all wells. Supports monitored natural attenuation (MNA) approach.
  • Detached: Plume migrating downgradient with no connection to source zone. Source may be removed or depleted.

Data Management Best Practices

  • Database: Maintain a structured database (not spreadsheets) for all groundwater data. Include lab electronic data deliverables (EDDs) for automated import.
  • Non-detects: Handle consistently - typically use half the method detection limit for statistical analysis. Document the approach.
  • Outlier evaluation: Investigate outliers before excluding. May indicate a real event (e.g., remobilization, seasonal effect).
  • Reporting: Include time-concentration plots for all key wells, potentiometric maps, plume maps and statistical trend summaries in monitoring reports.

This guide is for general educational purposes. Specific well installation, sampling and QA/QC requirements vary by regulatory program, jurisdiction, site conditions and analytical methods. Always confirm requirements with your regulatory authority, qualified hydrogeologist and analytical laboratory before implementing a monitoring program.

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