How To Implement Passive Sampling in Your Existing Groundwater Monitoring Program

Many active groundwater monitoring programs could benefit from implementing passive sampling methods on their site. For many, this raises the question of how to implement passive sampling into their existing programs?

While the idea of changing sampling methods mid-project may initially seem like a burden, the effort pays off quickly for the consultants and stakeholders who make this transition. In many cases, the transition pays for itself in the first year, providing benefits for the remaining project life-cycle.

Adding or changing to passive samplers will make the sampling events much easier, will reduce the amount of time it takes to sample, and will eliminate storage and compliance costs of handling IDW. These benefits can result in recurring cost reductions to your sampling programs of 50-70%.

This blog post will explore how you can effectively integrate passive sampling into your active groundwater monitoring programs for optimal results.

Understanding Passive Groundwater Sampling

Before diving into integration strategies, it’s important to understand passive groundwater sampling. Passive groundwater sampling is a technique that collects groundwater samples without the need for purging prior to sampling.

A passive sampler captures a representative sample within a specific interval of the monitoring well screen, avoiding the aerated or stagnant water at the top of the screen or in the casing. This method utilizes the natural flow of groundwater from the surrounding aquifer to refresh the water in the screen, allowing for an accurate representation of conditions.

Integrating Passive Sampling into Your Monitoring Program

The integration of passive sampling into an existing program requires careful planning. Begin by assessing the objectives of your monitoring program. Consider factors like the contaminants of concern, the size of the well and location of saturated screen intervals, and sample volume requirements. Identify sites where passive sampling can yield the most benefit, especially long-term monitoring projects, sites with sampling events that take the most amount of time, or sites with contaminants like PFAS that require special field sampling efforts.

Once you have identified the sites where passive sampling can provide the most benefit, it is time to get your local regulatory agency involved. Many regulators are familiar passive sampling and may not require much additional information to approve the changes to your monitoring plan.

In some circumstances, regulators may request side-by-side evaluations between passive samplers and the legacy method of sampling at that site. These evaluations are straightforward and generally low cost, with a few representative wells used to compare results from passive samplers to historical or real-time results from the method being replaced.

EON Products has helped many customers plan and implement successful side-by-side evaluations prior to adding passive sampling to their monitoring programs.

Can Passive and Traditional Sampling Coexist in a Single Project?

Yes, many sites can use more than one sampling method across their monitoring well network, depending on the hydrogeological conditions and goals of the project.

For example, a site may adopt passive sampling on most of their wells as a strategy to reduce time on site and decrease cost. However, there may be a few wells that are sampled for more contaminants of concern that may require more volume than a passive sampler can provide. In this scenario, a combination of passive samplers at some wells and pumps at others could be the most effective and efficient way to manage the project. This is a common setup in landfills with wells in various stages of regulatory compliance.

Transition and Training

Transitioning to an approach that includes passive sampling involves training and adaptation. Ensure your team is well-versed in both passive and traditional sampling techniques. This dual expertise allows for flexibility and adaptability in various project scenarios.

The good news is that passive sampling methods require little training or special equipment and are much easier to install and use than low-flow pumps.

EON Products provides field-practical, Standard Operating Procedures and training videos for each passive sampling technique and side-by-side evaluation. Our staff are always ready to assist in setting up your program, using experience gained from hundreds of successful passive sampling installations. 

Meeting Site Objectives

Before introducing a new sampling method, it is helpful to list the project objectives and decision criteria. That helps ensure that you compare results from the old and new methods through a lens that aligns with your monitoring program’s goals.

• Is this a site assessment that requires sampling for a large list of contaminants at low lab reporting limits?
• Is it a long-term monitoring project with the focus on whether Maximum Reporting Limits (MCLs) are exceeded?
• Is this an active remediation site looking at the remediation efficiency? 
• Perhaps a site working toward eventual closure and contaminant concentration trends?
• Are there contaminants requiring special sampling efforts?

Highlighting the project sampling objectives up-front helps determine what is important when comparing results from different sampling methods, so that practical sampling method decisions can be made.

Best Practices for Implementing Passive Sampling

Site Selection: Use site-specific information to decide where passive sampling can be most effective.

Consult with your Regulator: Work with your Regulator to understand what requirements are needed, if any, for approval of passive sampling on your site.

Evaluation Study Planning: If a side-by-side method evaluation is required, work with EON to ensure the SOP for the evaluation meets all requirements. Determine the right correlation method that aligns with your project’s monitoring plan.

What to Keep in Mind When Using Both Methods

Cost-Benefit Analysis: Evaluate the cost savings from reduced labor and equipment needs against the initial investment required to make changes to your monitoring plan, then compare the project life-cycle costs.

Regulatory Compliance: Ensure that passive sampling meets all regulatory requirements and is acceptable for reporting purposes. If regulators are unfamiliar with Passive Sampling, EON Products can assist in technical discussions.

Environmental Impact: Consider the reduced environmental footprint of passive sampling, as it requires less contaminated water withdrawal and disposal, no gasoline, batteries, air compressors or generators, and significantly less material waste for disposal.

Conclusion

Integrating passive groundwater sampling into your monitoring program can offer significant cost, efficiency, and environmental benefits. By understanding the strengths of both passive and traditional sampling methods, and adding passive sampling to your tool kit, you can develop a flexible, robust, and comprehensive groundwater monitoring strategy with added benefits for you and your clients.

Learn more in The Ultimate Guide to Passive Groundwater Sampling.