Determining the Geologic Controls on Coastal Ground-Water Resources and the Location and Isolation of Hazardous Waste

Monitoring Coastal Environments near Assateague Island National Seashore: Groundwater Discharge to Delmarva Coastal Bays

Pictured above: The USGS Hover Probe.

Assateague Island National Seashore is a barrier island along the outer margin of Chincoteague Bay, Maryland. In early June, the USGS cooperative groundwater project in the Delmarva Peninsula deployed a Hover Probe in Chincoteague Bay, to test its ability to core, pump and log sub-bay strata to test for submarine discharge of fresh water. Fresh water was found to be within the sediment a few meters below the bay floor from 120 to ~400 m from shore, indicating groundwater flow and discharge in this region. A marsh core was also obtained from Assateague Island, Maryland.

The Hover Probe is not only able to move on land and water, but also incorporates a highly effective vibra-drilling tool that can recover nearly undisturbed sediments to a depth of more than 15 meters. The Hover Probe also accommodates a screened well-point pumping system able to recover large amounts of fluids within the sediment.

Sourcing Tar Residues on Santa Rosa Island, Channel Islands National Park, California

Pictured above: A map of Santa Rosa Island showing sample sites.

The USGS is assessing tar residues on all accessible coastlines of Santa Rosa Island in the Channel Islands NP. These samples are tested for trace minerals and ratios of chemical components to fingerprint, or determine the genealogy of, collected samples, and determine the tar’s sources. Sixty-eight samples of tar residues were collected during the six-day field trip pictured in the map below-right.

Pictured above: This blowhole is lined with tar and thus protected from rapid erosion by incoming tidal waters.

Although tar was expected and was found on the north-facing shorelines due to prevailing currents and suspected sources, residues were also common on the south-facing shorelines adjacent to the Santa Barbara channel where natural oil seeps and oil-production platforms are plentiful. A most interesting tar occurrence was found at Carrington Point, the northernmost site on the island, where a blowhole concentrates floating tar that forms a massive mat on the marine terrace. Preliminary geochemical analyses indicate several sources for the tar residues, most of which appear to be from natural oil seeps.