Bailer Groundwater Sampling - When to Use It and How to Do It Right

What a Bailer Is

A bailer is a simple hollow tube - usually PVC, polyethylene, or HDPE - that you lower into a monitoring well on a cord to collect a groundwater sample. A ball check valve at the bottom seals when the bailer is pulled up, trapping the water inside.

Bailers have been used for environmental groundwater sampling since the early days of the industry. They are cheap, portable, require no power source, and work at any depth. They are also the most operator-dependent sampling method, and their limitations are well documented. Low-flow sampling has largely replaced bailers for compliance monitoring and site characterization, but bailers still have legitimate uses.

When Bailers Are Appropriate

Bailers are a reasonable choice in specific situations:

BUSTR closure assessments. Bailer sampling is common at Ohio BUSTR sites, especially when monitoring wells will be abandoned after the final sampling round. BUSTR regulates VOCs, PAHs, and TPH in groundwater - not metals - so the analyte list is manageable for bailer collection. Investing in a bladder pump setup for a one-time closure sampling event may not be cost-effective.

Low-yield wells. Wells that do not produce enough water to sustain a pump can still be sampled with a bailer. You let the well recover and bail what is available.

Grab samples for screening purposes. If you need a quick field screening result to make a real-time decision - not a compliance sample - a bailer is fast and practical.

Remote locations without power. Battery-powered pumps exist, but a bailer works anywhere with no equipment failures. If you are sampling a well on a remote hilltop with no vehicle access, a bailer and a cooler may be your only option.

LNAPL (light non-aqueous phase liquid) recovery. Top-filling bailers are designed specifically for recovering free product floating on the water table. This is one application where bailers outperform pumps.

Very deep wells with shallow water columns. Lowering a pump on hundreds of feet of tubing to sample a short water column may not be practical. A bailer on a cord can reach any depth.

When to Use Something Else

If any of the following apply, low-flow sampling with a pump is the better method:

• The sampling is for long-term compliance monitoring where data comparability matters
• VOCs are a primary contaminant of concern and low detection limits are needed
• The regulatory program specifically requires or prefers low-flow methods
• You need to minimize investigation-derived waste (purge water)
• The wells will continue to be monitored after this sampling event
• Data defensibility is critical (litigation support, NFA requests)

Low-flow sampling produces less variable results, generates less waste, and is increasingly preferred by regulators. If you have the equipment and the wells support it, low-flow is almost always the better choice for compliance-grade data. See our Low-Flow Groundwater Sampling guide for that procedure.

Equipment

Bailer: Use a disposable, pre-cleaned bailer sized to fit the well casing. For a standard 2-inch monitoring well, use a 1.5-inch diameter bailer to allow clearance. Disposable bailers come individually sealed in plastic to prevent contamination.

Bailer cord: Polypropylene or polyethylene cord is standard. Use new cord for each well to prevent cross-contamination. White polypropylene cord is inexpensive enough to discard after each use. Never use cotton rope or nylon cord with dyes that could introduce contaminants.

Bottom-emptying device (recommended): A bottom-drain attachment lets you release water from the bottom of the bailer into sample containers with minimal turbulence. This is significantly better for sample quality than pouring water over the top of the bailer. Double check-valve bottom-draining bailers are recommended by EPA Region 4 and the Ohio EPA TGM.

Water level meter: Measure static water level before any purging or sampling.

Field parameter meter: If you are monitoring purge parameters (pH, conductivity, temperature, turbidity, dissolved oxygen, ORP), you need a calibrated multi-parameter meter.

Sample containers: Provided by your laboratory based on the analytical program. Pre-preserved containers for specific analyses (for example, HCl-preserved VOA vials for VOCs, HNO3-preserved bottles for metals).

Procedure

1. Measure Static Water Level

Before opening the well or inserting any equipment, allow the well cap to vent briefly, then measure and record the static water level and total well depth using a decontaminated water level meter. Record the depth to water below the top of casing (TOC) and the total depth of the well.

Calculate the water column height (total depth minus depth to water) and the well volume:

Well volume (gallons) = 0.0408 x D^2 x H

Where D is the inside casing diameter in inches and H is the water column height in feet.

For a 2-inch well with 10 feet of water: 0.0408 x 4 x 10 = 1.63 gallons. One well volume is about 1.6 gallons.

Bailer volume by diameter: The volume a bailer holds per trip depends on its diameter. Common sizes:

• 1.5-inch diameter bailer (for 2-inch wells): approximately 0.25 gallons per trip
• 2-inch diameter bailer (for 4-inch wells): approximately 0.5 gallons per trip

Use these volumes to calculate how many trips you need per well volume. For the example above (1.6 gallons per well volume with a 1.5-inch bailer holding 0.25 gallons), you need roughly 7 trips per well volume, or 21-35 trips for 3-5 well volumes. Knowing this number before you start prevents guesswork in the field.

2. Purge the Well

Traditional bailer purging requires removing 3 to 5 well volumes before sampling. The purpose is to remove stagnant water from the casing so the sample represents formation water, not water that has been sitting in the pipe.

Purging procedure:

1. Slowly lower the bailer into the well. Do not drop it - a fast-falling bailer churns the water column and mobilizes sediment from the bottom of the well.
2. Allow the bailer to fill. You can feel it when the bailer hits the water and when it is full (the cord tension changes).
3. Pull the bailer up slowly and steadily. Minimize agitation.
4. Empty the bailer into a purge water container (bucket or drum, depending on volume and disposal requirements).
5. Track the volume purged. Use the bailer volume for your bailer diameter (see well volume calculation above) to count how many trips you need per well volume.
6. Continue until you have removed the target number of well volumes.

If the well purges dry (bails dry): Stop purging, allow the well to recover, and sample the first water that comes back. Record the time the well went dry and the time you began sampling. This is acceptable and common for low-yield wells.

Monitoring field parameters during purging: Some firms and regulatory programs require field parameter readings during bailer purging, typically by collecting a reading from each bailer-full near the end of purging (pH, conductivity, temperature, turbidity, dissolved oxygen, ORP). The readings will generally be less stable than low-flow stabilization readings due to the agitation involved, but they still provide useful data. Follow your work plan and program requirements for whether parameter monitoring is required during purging.

3. Collect Samples

After purging, collect your samples from the next bailer-full of water. Use a bottom-emptying device to transfer water into sample containers. If no bottom-emptying device is available, pour slowly from the top of the bailer.

Sample collection order (collect in this order to minimize cross-contamination and volatile loss):

1. VOCs (if applicable) - fill first, directly and slowly with no air bubbles, zero headspace
2. Other volatile or gas-sensitive parameters (dissolved gases, alkalinity)
3. SVOCs, PAHs
4. TPH
5. Metals (total and/or dissolved)
6. General chemistry parameters (anions, nutrients, etc.)
7. Field-filtered samples last (dissolved metals)

Note that for BUSTR sites, you will typically only be collecting for VOCs, PAHs, and TPH. Metals are not regulated under BUSTR, so the analyte list is shorter and the sampling is more straightforward.

For VOC samples specifically:

• Fill the VOA vials slowly, allowing water to flow gently down the inside wall of the vial
• Fill until a meniscus forms above the rim, then cap with the septum side down so no air is trapped
• Check for air bubbles by inverting the vial. If you see a bubble, discard and refill. Any headspace invalidates the sample.
• Do not rinse or pre-condition the VOA vials - they come pre-preserved from the lab

For dissolved metals (when required):

• Filter in the field using a 0.45-micron in-line filter or syringe filter
• Filter directly into the preserved sample container (typically HNO3-preserved)
• The distinction between field-filtered and lab-filtered matters for data interpretation. Field filtering is the standard practice for dissolved metals - it captures what is actually dissolved in the groundwater at the time of collection, before sample handling and transport can change the chemistry.

4. Decontamination

If you are using disposable bailers (recommended), decon is simple:

• Discard the bailer and cord after each well
• Decontaminate your water level meter between wells (Alconox wash, tap water rinse, DI rinse)
• Change gloves between wells

If using a reusable bailer (not recommended for most environmental work):

• Full Alconox wash, tap water rinse, DI water rinse between each well
• Check your work plan for additional requirements such as solvent rinses

Investigation-Derived Waste

Bailer purging generates more investigation-derived waste (IDW) than low-flow sampling. Three to five well volumes of purge water from a dozen wells adds up quickly.

Managing purge water:

• Contain all purge water in labeled drums or tanks pending analytical results
• If results show the water is not contaminated above applicable standards, it can typically be discharged on site (check your project requirements and state regulations)
• If contaminated, the purge water must be characterized and disposed of at an appropriate facility
• This is one of the practical reasons low-flow sampling has gained favor - it generates a fraction of the waste volume

Common Mistakes

1. Dropping the bailer. Lowering the bailer too fast or letting it freefall creates a piston effect that pushes water ahead of it, stirs up sediment, and produces turbid samples. Lower slowly and steadily.

2. Using the same cord for multiple wells. Cord is cheap. Cross-contamination defense is expensive. Use new cord for each well.

3. Overfilling sample containers. Overfilling or rough handling during transfer splashes preservative out of the container. For metals bottles with HNO3 preservative, losing the acid means the sample is not properly preserved and may produce biased results.

4. Pouring over the top of the bailer for VOCs. The cascading action aerates the water and strips volatiles. A bottom-emptying device is not optional for VOC sampling with a bailer - it is necessary for defensible data.

5. Not recording the number of well volumes purged. This is a basic QA element. If you cannot document that the well was adequately purged, the data is vulnerable to challenge.

6. Sampling a turbid well without noting it. If the sample is turbid despite proper technique, record the turbidity and note it in your field records. Turbidity affects metals results significantly - high turbidity means elevated total metals due to suspended sediment, which may not represent actual dissolved-phase contamination.

7. Forgetting to measure depth to water before purging. The static water level measurement must be taken before any equipment enters the well. Once you start bailing, you have altered the water level and cannot recover the static measurement.

8. Not allowing the well to equilibrate before measuring water level. If the well was recently developed, sampled, or otherwise disturbed, let it sit for a reasonable period before taking your static measurement. Check your work plan for the required equilibration period.

Bailer Types

Single check-valve (top-filling): Water enters through the top as the bailer sinks. The ball valve at the bottom seals when the bailer is pulled up. Most common type. Used for groundwater sampling and LNAPL recovery.

Double check-valve (bottom-draining): Has valves at both top and bottom, allowing controlled release from the bottom. Significantly reduces sample agitation during transfer. Preferred for environmental sampling.

Weighted bailer: Heavier construction for use in deeper wells or wells with small-diameter tubing. Useful when the standard bailer does not sink fast enough or drifts in the water column.

Teflon (PTFE) bailer: Required at some sites where PVC may interact with specific contaminants. More expensive. Check your work plan for material requirements.

Stainless steel bailer: Reusable, durable, inert. Requires decontamination between wells. Rarely used now that disposable options are available and accepted.

Bailers vs. Low-Flow - Choosing the Right Method

Factor	Bailer	Low-Flow
Cost per well	Lower (equipment)	Higher (pump, tubing, flow cell)
Labor per well	Higher (many trips to purge)	Comparable (setup time vs. purge time)
Sample quality	Adequate for many purposes	Superior, especially for VOCs and metals
IDW generated	3-5 well volumes	Minimal (typically less than 1 gallon)
Data variability	Higher between events	Lower, more reproducible
Regulatory preference	Accepted, not preferred	Increasingly required or preferred
Equipment needed	Bailer, cord, containers	Pump, tubing, flow cell, power
Depth limitations	None (cord reaches any depth)	Depends on pump type and tubing length
Best use case	BUSTR closures, grab samples, remote sites	Long-term monitoring, compliance data

The decision often comes down to what the project and the regulatory program require. When in doubt, ask your project manager or the regulatory agency reviewer before committing to a method.