Geology topics

William C. Brandon

Publications and source records attributed to William C. Brandon.

3 recordsLinked to original sources

USGS2020

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

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.

Remediation Journal↗

USGS2010

Integrated use of surface geophysical methods for site characterization — A case study in North Kingstown, Rhode Island

A suite of complementary, non‐invasive surface geophysical methods was used to assess their utility for site characterization in a pilot investigation at a former defense site in North Kingstown, Rhode Island. The methods included frequency‐domain electromagnetics (FDEM), ground‐penetrating radar (GPR), electrical resistivity tomography (ERT), and multi‐channel analysis of surface‐wave (MASW) seismic. The results of each method were compared to each other and to drive‐point data from the site. FDEM was used as a reconnaissance method to assess buried utilities and anthropogenic structures; to identify near‐surface changes in water chemistry related to conductive leachate from road‐salt storage; and to investigate a resistive signature possibly caused by groundwater discharge. Shallow anomalies observed in the GPR and ERT data were caused by near‐surface infrastructure and were consistent with anomalies observed in the FDEM data. Several parabolic reflectors were observed in the upper part of the GPR profiles, and a fairly continuous reflector that was interpreted as bedrock could be traced across the lower part of the profiles. MASW seismic data showed a sharp break in shear wave velocity at depth, which was interpreted as the overburden/bedrock interface. The MASW profile indicates the presence of a trough in the bedrock surface in the same location where the ERT data indicate lateral variations in resistivity. Depths to bedrock interpreted from the ERT, MASW, and GPR profiles were similar and consistent with the depths of refusal identified in the direct‐push wells. The interpretations of data collected using the individual methods yielded non‐unique solutions with considerable uncertainty. Integrated interpretation of the electrical, electromagnetic, and seismic geophysical profiles produced a more consistent and unique estimation of depth to bedrock that is consistent with ground‐truth data at the site. This test case shows that using complementary techniques that measure different properties can be more effective for site characterization than a single‐method investigation.

Rhode Island↗

USGS1999

Distribution of salinity in ground water from the interpretation of borehole-geophysical logs and salinity data, Calf Pasture Point, Davisville, Rhode Island

The distribution of salinity in ground water at Calf Pasture Point, a small coastal peninsula bounded by Narragansett Bay on the east and Allen Harbor on the west, in Davisville, Rhode Island, was interpreted from borehole-geophysical data and previously collected salinity data to help identify potential flowpaths of contaminated ground water to surface-water bodies. The surficial material at this 40-acre site, which ranges in thickness from about 30 to 85 feet, is composed of an upper sand unit, a silt unit, and a till unit overlying bedrock. Borehole-geophysical data indicate that fresh ground water is present in all surficial units in the northern and northwestern part of the site. In the central and eastern parts of the site, where most of the current land surface is composed of dredged fill placed in a small saltwater embayment, brackish and saline ground water predominate. Fresh ground water moving into this area from upgradient and recharge to this extended land surface from precipitation is diluting the saline groundwater in the upper sand and till units, and to a lesser extent in the silt unit. In this area, the freshwater-flow system is slowly expanding towards Narragansett Bay and the entrance channel to Allen Harbor.

Rhode Island↗