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How To Implement Passive Sampling into Your Existing Groundwater Monitoring Program

Many active groundwater monitoring programs could benefit from implementing passive sampling methods on their site. But what is the best way to implement passive sampling into your existing program?

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.

Frequently Asked Questions

Q1: How can project managers effectively communicate the advantages of passive sampling to stakeholders who are accustomed to traditional methods?

To effectively communicate the benefits of passive groundwater sampling to stakeholders familiar with traditional methods, project managers can focus on tangible benefits and real-world examples. Begin by highlighting the cost-effectiveness of passive sampling, emphasizing savings in labor, equipment, and operational expenses. Demonstrate how these savings can be redirected to other project aspects such as remediation, enhancing overall efficiency and scope.

Next, showcase the accuracy and reliability of data obtained through passive sampling. Explain how the minimal disturbance to the water column allows samples to be acquired without disturbing the stagnant water, which eliminates labor-intensive and time-consuming purging. Clients with remote or high-traffic areas will benefit from the quick, “in-and-out” sampling enabled by passive methods. Case studies or comparisons from similar projects can show where passive sampling was proposed, tested, and used for similar applications.

Address environmental concerns by discussing the reduced environmental footprint of passive sampling. This includes less water withdrawal, lower energy consumption, and less waste, which are increasingly important in a world focused on sustainable practices.

Finally, ensure clear communication through visuals, such as graphs or charts, to compare the efficiency, cost, and accuracy of passive sampling against traditional methods. Personalize the message to the specific concerns and interests of the stakeholders, showing a direct link between passive sampling benefits and the project’s goals.

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Passive Groundwater Sampling vs. Traditional Methods

Environmental consulting often involves the crucial work of managing groundwater monitoring programs at impacted sites. Assessing groundwater quality and implementing a sampling plan have traditionally involved labor-intensive sampling methods, such as purging monitoring wells, before a sample can be acquired.

Passive groundwater sampling methods, with their distinct equipment, methodology, and staffing requirements are rapidly rising as efficient alternatives.

This article will contrast passive sampling with other groundwater sampling methods, providing environmental consultants with a clear understanding of its unique attributes and benefits.

Understanding the Fundamentals of Groundwater Sampling Methods

Before diving into the specifics of passive sampling, it’s important to review the traditional groundwater sampling methods. Typically, these involve purging three to five well volumes of water or purging at a low flow rate until water quality parameters are stable. These purge techniques are in place to ensure that the sample taken is representative of the aquifer water and not biased by stagnant water pulled into the well.

Equipment Differences: The Passive Advantage

Passive sampling equipment is characterized by its simplicity and specificity.

Passive Samplers are typically small, simple, and lightweight devices that are attached to a suspension tether and lowered into monitoring wells at the desired interval of sampling.

Unlike other methods, passive sampling doesn’t require pumps or power sources, thus reducing equipment needs and potential sources of additional environmental impact.

Methodology Differences: Efficiency in Practice

The methodology of passive sampling sets it apart through its non-intrusive nature.

• No Purging: Passive samplers bypass the stagnant zone and capture their sample directly within the well screen. Groundwater flow naturally refreshes the sample interval through the well screen, creating representative sample conditions without the need to purge the well. The samplers collect the representative water in the screen without creating water movement that could pull in stagnant water.
• Reduced Time on Site: Since there’s no need for equipment setup or purging, the time spent on site is significantly reduced with passive sampling.

ProcessDifferences: Efficient Operations

With passive sampling, your team can spend less time monitoring each site and more time on remediation, compliance, and managing more projects.

• Less Labor-Intensive: No setup time or purging means each sample can be collected in ten minutes or less with as little as one person on site.
• Specialized Skills: It is easy to train staff members on the simple process of deploying and retrieving passive samplers, and they don’t need to manage complex pumping equipment.

Comparison with Low-Flow Sampling

Low-flow sampling is currently the most prevalent sampling method. It involves slowly pumping water from the well while measuring water quality parameters.  Only when the parameters stabilize can a representative sample be taken. In contrast, passive sampling:

• Eliminates Flow Rate Concerns: There’s no need to spend time and resources to pump and monitor the flow rate and water quality with passive samplers.  This eliminates a critical, and time-consuming component of low-flow sampling.
• Reduces Equipment Impact: Because passive sampling captures a representative sample without inducing flow, there is a lower probability that equipment will increase turbidity above site background levels when compared to active sampling methods. Artificially high turbidity can bias sample results for many contaminants, including metals and PFAS.

Analyzing Bailers: A Traditional Staple

Bailers have been a staple in groundwater sampling for their simplicity and portability. However, passive sampling offers several advantages.

• Sample Integrity: Bailers can agitate the water column, increasing turbidity and potentially moving stagnant water from the casing through the screen, into the aquifer, affecting sample integrity. Passive samplers maintain the integrity of the groundwater while still capturing a representative sample because the only movement is natural groundwater flow through the saturated screen.
• No Investigative Derived Waste: Passive samplers require no purging so you can eliminate the manual labor and gallons of IDW created from purging the monitoring wells.

Conclusion

Passive groundwater sampling presents a significant shift from traditional methods, offering a more efficient, cost-effective, and environmentally sensitive approach.

For environmental consultants exploring the potential of passive sampling, understanding these differences is crucial in adopting this innovative method.

Passive sampling redefines groundwater monitoring by offering a sustainable alternative that aligns with evolving needs. Are you ready to transition to a more efficient monitoring method that promises precision, ease of use, and cost-efficiency?

Book a free consultation to learn more.

Frequently Asked Questions

Q1: What site-specific factors should I consider when choosing between passive sampling and traditional methods?

When choosing between passive and traditional sampling methods, consider:

• How long are your monitoring well screens, and at what point are they saturated with water?
• What are the contaminants of concern that you are sampling for, and what is the minimum required volume the lab will need to test the samples.
• The objectives of the monitoring program (e.g., compliance monitoring, site assessment).
• Site accessibility, equipment needs, and safety concerns that may affect sampling logistics and frequency.

Q2: How can the data from passive sampling be integrated with historical data collected through other methods?

Passive sampling data can be integrated with historical data by:

• Using side-by-side sampling to establish a correlation between passive and active methods.
• Adjusting historical data for comparability if prior methodologies introduce biases.
• Presenting both data sets in context that aligns with the goals of your monitoring program.

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Elevating Efficiency: The Compelling Advantages of Passive Groundwater Sampling

As groundwater sampling requirements have expanded, the use of efficient, cost-effective, and environmentally friendly sampling techniques have become a more common solution. Passive sampling offers numerous advantages over traditional active sampling techniques that rely on pumping and/or purging.

This article explores the many benefits of passive sampling for those familiar with conventional groundwater sampling but new to this simpler approach.

Cost Efficiency of Passive Groundwater Sampling: Maximizing Budgets

One of the most immediate benefits of passive sampling is its impact on project budgets.

By eliminating the need for expensive pumps and the associated maintenance, consultants can see a decrease in equipment purchase and maintenance costs. More significantly, the reduction of time on-site decreases the labor cost within a groundwater monitoring program.

Industry studies corroborate these findings, with reports indicating that passive sampling can reduce sampling costs by 50-70% compared to traditional methods (source: Former McClellan AFB Study)

Smart Spending with Long-term Gains

Once passive sampling is implemented, the labor reduction can be applied again and again across multiple monitoring events, offering long-term savings. This reduction in labor cost, coupled with the minimal initial setup cost and reduced equipment needs, makes passive sampling a financially savvy choice.

Time Savings: Accelerating Project Timelines

Traditional sampling methods involve purging 3-5 well volumes or pumping until the water quality parameters stabilize.  These processes can take hours or even days on large project sites.

Passive sampling eliminates these time-consuming steps, allowing for immediate sample collection upon retrieval of the samplers. This reduction in sample time can free up consultants to spend their time on other areas, such as remediation or compliance.

Reducing Waste: A Sustainable Approach

Environmental sustainability is an added benefit of passive sampling. Passive methods do not generate purge-water waste, a common byproduct of traditional sampling methods. In the case of hazardous contaminants like PFAS, the logistics, expense, and environmental impact of waste storage and disposal are eliminated. Less hazardous waste means a cleaner and safer work environment.

Alignment with Environmental Stewardship

Passive sampling reflects the industry’s move towards more sustainable practices, aligning with the values of clients and stakeholders who prioritize environmental responsibility. Less equipment, no gasoline, batteries, or air compressors with their life-cycle impacts.

Reliable Results: Trust in Data Integrity

The integrity of sampling data is paramount, and passive sampling provides results that consultants can trust. By sampling the natural flow of groundwater as it refreshes the screened interval, accurate samples representing the aquifer can be collected without disturbing the stagnant or aerated water at other levels in the well. Over a million deployments and numerous third-party studies over the years have validated passive sampling as a reliable sampling method.

Consistency Across Sampling Events

Passive sampling methods offer consistent results over multiple sampling events. This consistency is critical for monitoring and assessing long-term trends in groundwater quality.

Industry Endorsement: The Professional Perspective

The environmental consulting industry is increasingly recognizing the benefits of passive sampling. Professional bodies and regulatory agencies endorse and use passive methods as best practices where appropriate. This professional validation is a testament to the method’s reliability and effectiveness.

Leveraging Industry Studies for Credibility

Citing industry studies and professional endorsements within environmental reports reinforces the credibility of passive sampling methodologies. For instance, studies by the Interstate Technology & Regulatory Council (ITRC) have provided guidance on the use of passive samplers, emphasizing their advantages in various monitoring scenarios.

Final Thoughts: Embracing Passive Sampling

Passive groundwater sampling offers cost efficiency, time savings, waste reduction, and reliable results that can significantly enhance the environmental monitoring and consulting landscape. For consultants ready to embrace these advantages, passive sampling is not just an option—it’s the next step towards smarter, sustainable, and scientifically robust groundwater monitoring.

Passive sampling is changing the landscape of groundwater monitoring. Are you ready to be part of this change and lead your projects with efficiency and environmental integrity?

Book a free consultation to learn more.

Frequently Asked Questions

Q1: How can the introduction of passive sampling impact the competitive positioning of an environmental consultancy?

The introduction of passive sampling can:

• Position a consultancy as a leader in innovative, cost-effective monitoring solutions.
• Attract clients interested in sustainable and less invasive monitoring methods.
• Enhance the consultancy’s ability to operate in sensitive environments where traditional methods are less feasible.
• Reduce costs and improve profit margins for groundwater monitoring projects

Q2: What are the challenges in adopting passive sampling in regions with stringent regulatory frameworks, and how can they be addressed?

Challenges include:

• Gaining acceptance for passive methods as compliant with regulatory standards.
• Demonstrating that passive sampling provides data of equal or superior quality to traditional methods.

Addressing these challenges can involve:

• Engaging with regulators early in the transition process.
• Running side-by-side tests to demonstrate the effectiveness of passive sampling
• Contributing to or citing peer-reviewed studies that validate passive sampling methods.
• Providing clear, transparent data and reports highlighting the reliability and relevance of passive sampling data.

• Blog

What is 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 monitoring well, allowing for an accurate representation of conditions.

Advantages of Passive Groundwater Sampling Over Active Sampling

Passive groundwater sampling offers several advantages over other methods:

• Time Efficiency: Without extensive purging or waiting for stabilization, time on site is reduced.
• Cost-Effectiveness: It saves equipment, labor, and sample disposal costs.
• Reduced Turbidity Bias: Passive sampling will pick up any background turbidity within the well without adding any artificial, method-induced turbidity into the sample.
• Representative Sampling: It provides samples representative of the actual groundwater conditions, free from agitation caused by pumping or bailing.
• Environmental Considerations: Because there are few materials, no batteries, gasoline, compressed air, or electricity required, there are fewer impacts to the environment, making passive sampling a greener and more sustainable sampling solution.

Understanding the Science Behind Passive Samplers

Passive groundwater sampling uses the established principle that groundwater flowing naturally through a saturated section of well screen has the same chemical properties as the surrounding aquifer.  Passive samplers are devices that can acquire a sample of this water from the screen interval without artificially moving water from other intervals or pulling stagnant, chemically different, water in from the casing. Bypassing the stagnant water means purging and stabilization are not needed to obtain a representative sample of the aquifer.

There are two main types of passive groundwater samplers that function differently but have the same general benefits of cost reduction, ease of use, and they do not produce purge water.

• Passive Grab Samplers, capture a whole-water sample at an interval in the saturated screen. The water and everything in the water are recovered without inducing flow in the well that could cause mixing with stagnant well water. The HydraSleeve is the most-used passive grab sampler. See Video Here.
• Passive Diffusion Samplers collect a water sample containing contaminant molecules that have diffused through the pores of a semipermeable membrane filled with deionized water. The contaminant concentration in the sampler reaches and maintains the same concentration as the surrounding water.

Implementation of Passive Sampling in the Field

The process of implementing a passive sampling routine involves a few key steps:

• Understand your Monitoring Well Configuration: Be sure the passive is located within the saturated screen. In wells with saturated screens longer than ten feet, consider which interval best represents the project sampling objectives, or whether multiple intervals should be sampled.  
• Sampler Selection: Choose the correct type of passive sampler based on the contaminants of concern and the project’s objectives.
• Deployment: Construct or purchase a simple suspension tether, attach the passive sampler(s) and lower the samplers to the intended depth.
• Retrieval and Analysis: Retrieve the samplers any time after the minimum designated period, discharge the contents into standard laboratory bottles, and send the samples to your laboratory the same way as pumped samples. Then, simply place a new sampler on the tether and lower into the well for the next event.

Best Practices for Passive Groundwater Sampler Deployment

To ensure the accuracy and reliability of the data collected, follow standard groundwater sampling best practices, including,

• Avoid cross-contamination: Use clean equipment and gloves during deployment, retrieval, and discharge.
• Proper Documentation: Recording each sampler’s depth, date, and deployment and recovery time. Note and unusual occurrences and water level changes from previous events.
• Quality Control: Acquire field equipment rinsate, and deionized water  blanks and duplicates in accordance with project requirements as quality checks on the sampling process.

EON provides several Passive Sampler SOPs to help companies help ensure they get consistent, reliable results from passive samplers.

Case Studies: Success Stories of Passive Sampling

For over 25 years, numerous case studies have demonstrated the benefits that passive groundwater sampling can bring while also providing consistent, reliable data.

For instance, at a Superfund site in California, passive sampling was shown to cost 70-80% less than per well than pumped samples. Another study at landfills in Kansas demonstrates extremely reliable data with a significantly lower cost of operation.

Passive groundwater samplers are in use across all types of groundwater monitoring sites including those managed by the USEPA, USACE, USGS, and DoD, as well as many state and private sites in the US and other countries.

Read the case studies.

Concluding Thoughts

Passive groundwater sampling represents a leap forward for groundwater monitoring. For environmental consultants looking to enhance their groundwater monitoring practices, passive sampling offers a compelling, cost-effective, and environmentally conscious choice.

By integrating these insights into your practice, passive groundwater sampling can be a game-changer in environmental monitoring. Have you considered the benefits it might bring to your projects?

Frequently Asked Questions

Q1: How can passive groundwater sampling be integrated into existing monitoring networks?

Passive groundwater sampling can be integrated into existing networks by:

• Identifying sites where; pumping or waiting for parameters to stabilize adds to labor cost, large numbers of wells mean days at a site, high-traffic, remote locations, or equipment needs cause logistical problems, contaminated purge waste (IDW) disposal is difficult or expensive.
• Selecting appropriate sites where sampling laboratory sample volume requirements align with passive sampler specifications.
• Evaluating passive samplers along with traditional methods on a few representative wells at your site to compare and validate data sets.
• Gradually transitioning monitoring wells to passive samplers, starting with those used for long-term monitoring where minimal disturbance is preferred.

Q2: What are the limitations of passive groundwater sampling and how can they be mitigated?

The limitations of passive sampling include:

• High sampling volume requirements – if more volume is needed than is present within the saturated well screen, passive sampling may not work for your site.
• Always reach out to your lab prior to your first passive sampling event to let them know you are transitioning methods and ask them the minimum volume required for each test. Some labs may eliminate duplicates and decrease your sampling volume required to align with your passive method.

Q3: Can passive groundwater sampling methods be used for all types of contaminants, or are there specific scenarios where they are most effective?

While passive sampling can be used to sample any contaminant found within the monitoring well, it is important to select the correct sampler for your project:

• Passive Grab Samplers like the HydraSleeve can sample for any compound
• If sampling for PFAS, EON recommends using an HDPE sampler
• Passive Diffusion Samplers can be made from different membranes to sample different compounds
• The original, Equilibrator PDB samples for VOCs only
  • The Dual Membrane PDB can sample for all dissolved compounds, including PFAS