USGS Extensometer Drilling in Virginia

Along the Atlantic Coast, a 2000+ ft deep hole has been drilled by the USGS to assess the issues of groundwater pumping, relative sea-level rise, and land subsidence. This video shows the drilling of the first extensometer to measure land subsidence in the North Atlantic Coastal Plain in 30+ years.

Land subsidence has been observed at various locations in the southern Chesapeake Bay region at rates of 1.1 to 4.8 millimeters per year (Eggleston and Pope, 2013; Holdahl and Morrison, 1974). A major cause of land subsidence is extensive groundwater pumping that causes regional aquifer-system compaction (Pope and Burbey, 2004). Although aquifer-system compaction was measured from the late 1970s to the mid 1990’s at two stations in Virginia, at Suffolk and Franklin, it has not been measured anywhere in Virginia since 1995.

The Hampton Roads Sanitation District’s (HRSD) Sustainable Water Initiative for Tomorrow (SWIFT) is a program to inject treated wastewater into the subsurface. Injection of water into the subsurface is expected to raise groundwater pressures, thereby potentially expanding the aquifer system, raising the land surface, and counteracting land subsidence occurring in the Virginia Coastal Plain. Working together, the HRSD and USGS are constructing an extensometer monitoring station that will provide the ability to accurately measure land-surface elevations, bedrock-surface elevations, and changes in aquifer-system thickness.

References Eggleston, Jack, and Pope, Jason, 2013, Land subsidence and relative sea-level rise in the southern Chesapeake Bay region: U.S. Geological Survey Circular 1392, 30 p., http://dx.doi.org/10.3133/cir1392. Holdahl, S.R., and Morrison, N.L., 1974. Regional investigations of vertical crustal movements in the U.S., using precise relevelings and mareograph data. In: R. Green (Editor), Recent Crustal Movements and Associated Seismic and Volcanic Activity. Tectonophysics, 23 (4): 373- 390. Pope, J.P., and Burbey, T.J., 2004, Multiple-aquifer characterization from single borehole extensometer records: Ground Water, v. 42, no. 1, p. 45–58.