Whether you are assessing a site to understand potential contamination, watching for long-term changes, or evaluating the effectiveness of remediation efforts at known contaminated sites, groundwater monitoring is a critical aspect of environmental management.
Bailing and pumping are active sampling methods that have been the de-facto methods for acquiring groundwater samples. Innovations over the past 25 years, particularly the use of Passive Grab Samplers, have transformed the way environmental consultants can approach sampling tasks. This article delves into the mechanics of Passive Grab Samplers where they can be used and highlights the benefits they offer over active groundwater sampling methods.
Understanding Passive Grab Samplers
How They Work:
Passive Grab Samplers are simple and efficient. The process relies on natural groundwater flow to bring aquifer-quality water through the screen, where the passive sampler “grabs” the water from an interval without changing the velocity or direction of natural flow. The water and everything in it is sealed inside the device, isolating it from overlying water layers as the sampler is removed from the well.
Unlike active methods, passive sampling collects a groundwater sample without pulling stagnant or aerated water in from the casing or other intervals. The stagnant and other non-representative water is by-passed and therefore no purging and time-consuming monitoring of stabilization parameters is needed to obtain a representative sample.
HydraSleeves – A Leading Example:
The HydraSleeve is a passive grab sampler that makes groundwater sampling a simple, three-step operation that is more efficient than traditional purge methods involving pumps or bailers.
The HydraSleeve is a collapsible, flexible tube of low- or high-density polyethylene (LDPE or HDPE) that is sealed at the bottom end and has a self-sealing reed valve at the open top end. The HydraSleeve sampler is installed into the water column within the screen interval of the well, causing very little displacement or disturbance. Hydrostatic pressure keeps the device closed until it is pulled upward through the water during retrieval. As the sampler is pulled upward, to collect the sample, the tube opens and sleeves around the stationary water to collect a “core” of the water in the interval. When the sampler is full the valve closes and seals, ensuring that only the specific target interval is sampled.
HydraSleeve works using a 3-step process:
- Lower the empty HydraSleeve into the target interval of the well screen on a simple, reusable suspension tether. You may stack multiple sleeves on the suspension tether for vertical profiling or additional volume.
- Once the well has re-stabilized from the slight disturbance of adding the sampler to the well, pull the HydraSleeve upward through the sample interval. This allows the check valve to open and the sample to be collected. When the sampler has passed through the sample zone and is full, the check valve will automatically close.
- Retrieve the full HydraSleeve from the well, discharge into the appropriate lab bottles, and send to the lab per standard procedures.
Suitability for Different Sites
Optimal Site Conditions:
Passive Grab Samplers excel in most groundwater environments but are particularly advantageous at long term monitoring sites with multiple sampling events because they can acquire samples at a fraction of the cost of pumping or bailing. Passive Grab Samplers are also a good solution for sites with slow recharge, diverse contaminant profiles, unknown contaminants, contaminants of emerging concern (PFAS, 1,4 Dioxane) or those requiring depth-specific sampling. They are ideal for monitoring contaminated sites, solid waste disposal areas, and mining sites, where accurate and comprehensive water quality data is crucial.
Benefits Over Traditional Methods
Time and Cost Efficiency:
One of the most significant advantages of Passive Grab Samplers is their time and cost efficiency. Traditional methods, often labor-intensive and time-consuming, can escalate project costs. Passive Grab Samplers can collect samples in less than 10 minutes and cut total field time by more than half.
Sample Integrity and Reliability:
Passive Grab Samplers offer enhanced sample integrity. They reduce the risk of cross-contamination and disturbance to the water’s chemistry, ensuring an accurate representation of in-situ conditions.
Ease of Use and Safety:
Passive Grab Samplers like HydraSleeves require minimal training and no special tools. They are also small, easy to transport, and require no set up time prior to sample collection. This means less exposure for field personnel at high-traffic areas and less gear to lug to remote sites.
Environmental Impact:
From an environmental standpoint, Passive Grab Samplers are less intrusive. They minimize disturbance to the aquifer and require no power source to function. Because no purge-water is generated, storage, transportation, and disposal of hazardous or contaminated IDW is eliminated. The small materials footprint aligns with the increasing emphasis on sustainable and eco-friendly practices in environmental monitoring.
Conclusion
The shift towards Passive Grab Samplers like HydraSleeve represents a significant advancement in groundwater monitoring. Their ease of use, cost-effectiveness, and ability to provide reliable and accurate data make them an excellent choice for environmental consultants. As the field of environmental monitoring continues to evolve, embracing these innovative tools will be key to efficient, effective, and responsible groundwater management.