Deployment and Retrieval of Mineral Samplers

We've developed tools to monitor biogeochemical processes directly in situ, which enables accurate real-world observations that overcome the limitations of traditional benchtop studies. Conventional methods really rely on costly, disruptive soil coring. This protocol uses Min-Trap samplers for repeated in-situ testing that reduces expense while preserving site integrity.

To begin, select the matrix to be used inside the mineral traps. If using the site soil, collect 250 to 300 grams of material using drilling, coring, or other collection methods. Ship the collected material to the vendor for incorporation into the sampler.

To begin field deployment, obtain the mineral trap unit from the vendor. Purge the well as if collecting a groundwater sample. Then tie a nylon rope to the eye bolt on the top of the mineral trap housing and connect the rope to the well cap using a length that reaches the desired endpoint within the well screen.

Deploy the mineral trap directly within the screened interval of the monitoring well. Attach a weight to the bottom eye bolt if needed to help the mineral trap reach deeper depths within the screen. Incubate the mineral trap sampler in the monitoring well for the desired deployment interval, typically one to two months.

Assemble the materials needed for retrieval, including a vacuum sealer and vacuum sealer bags or anaerobic gen bags. Fill the coolers with ice and label the sample bag with the site name, well name, sampling date, destination laboratory, desired analysis, and sampler initials. If using a vacuum sealer rather than an anaerobic gen bag, seal three sides of the bag and leave one side open to allow insertion of the mineral trap samples.

Start a timer to ensure that less than 15 minutes elapse from removal of the unit from the well to vacuum sealing of the pillows. Now, carefully pull the nylon line to remove the mineral trap from the monitoring well. Denote any precipitate such as gray, black, or brown material on the mineral trap housing or any odors from the housing.

Photograph the appearance of the mineral trap housing. Unscrew the top of the mineral trap to expose the inner mesh insert containing the material-filled pillows. Using scissors, cut the loop or zip tie that secures the mesh insert to the top of the housing unit.

Denote and photograph any precipitate present on the mesh insert and place the mesh insert into the gen bag or vacuum seal bag and close it immediately. Next, put a large one gallon zippered polyethylene bag on the sampler and photograph the sample. Place the sample in the cooler on ice immediately.

Stop the timer and record the elapsed time in the field logbook. Repeat the retrieval procedure for each well as needed, ensuring the samples remain on ice at all times. Finally, complete the chain of custody documentation.

Securely package the cooler and ship it to the laboratories for overnight delivery. Elemental mapping from the scanning electron microscopy energy dispersive X-ray spectroscopy image showed co-location of iron and sulfur in the mineral trap sample, confirming in-situ precipitation of iron sulfides. Similarly, in another sample, co-location of nickel and sulfur was noted.

QuantARRAY MIC and CENSUS qPCR results from a four-month mineral trap incubation indicated high abundances of several bacteria, including fermentors, iron-reducing and sulfate-reducing bacteria. In groundwater samples from the same well, molar fraction analysis over time showed a marked shift from chlorinated ethenes to ethene and ethane following treatment, along with a sustained decrease in chlorine number. The highest absorption of polyfluoroalkyl substances was observed in mineral traps containing the activated carbon matrix at monitoring wells MW-1, MW-7, and MW-8.

This protocol enables direct, passive collection of mineralogical data in situ, supporting precise assessment and optimization of diverse environmental remediation strategies. Using the Min-Trap, we can easily study contaminant distributions between the groundwater and the representative site soil that's within the trap.