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.

Process Differences: 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. Or check out The Ultimate Guide to Passive Groundwater Sampling.