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Borehole‐scale testing of matrix diffusion for contaminated‐rock aquifers

February 28, 2020

A new method was developed to assess the effect of matrix diffusion on contaminant transport and remediation of groundwater in fractured rock. This method utilizes monitoring wells constructed of open boreholes in fractured rock to conduct backward diffusion experiments on chlorinated volatile organic compounds (CVOCs) in groundwater. The experiments are performed on relatively unfractured zones (called test zones) of the open boreholes over short intervals (approximately 1 meter) by physical isolation using straddle packers. The test zones were identified with a combination of borehole geophysical logging and chemical profiling of CVOCs with passive samplers in the open boreholes. To confirm the test zones are within inactive flow zones, they are subjected to a series of hydraulic tests. Afterwards, the test zones are air sparged with argon to volatilize the CVOCs from aqueous to air phase. Backward diffusion is then measured by periodic passive-sampling of water in the test zone to identify rebound. The passive (non-hydraulically stressed) sampling negates the need to extract water and potentially dewater the test zone. We also monitor active flowing zones of the borehole to assess trends in concentrations in other parts of the fractured rock by purge and passive sampling methods.

Publication Year 2020
Title Borehole‐scale testing of matrix diffusion for contaminated‐rock aquifers
DOI 10.1002/rem.21637
Authors Philip Harte, William C. Brandon
Publication Type Article
Publication Subtype Journal Article
Series Title Remediation Journal
Index ID 70208777
Record Source USGS Publications Warehouse
USGS Organization New England Water Science Center