THE IMPACTS OF THE EARTHQUAKE THAT STRUCK NEAR MINERAL VIRGINIA ON GROUNDWATER RESOURCES IN NORTHERN VIRGINIA

A recent earthquake that struck on August 23, 2011 near Mineral, Virginia was one of the largest on record for the eastern United States. The earthquake was followed by no less than six aftershocks ranging from 2.2 to 4.5 on the Richter scale. During this very active seismic period, groundwater levels were being continuously monitored by Emery & Garrett Groundwater, Inc. in a series of bedrock observation wells in both the Limestone Conglomerates underlying Loudoun County, Virginia, as well as in the sedimentary and igneous rocks of the Triassic Culpeper Basin in Fauquier County, Virginia. Turbidity was also being continuously monitored in the Limestone Conglomerates during the earthquake period. This discussion will focus on the groundwater data that was collected from these wells, which showed dramatic changes in both water quality and groundwater levels. In some wells, groundwater levels rose by as much as 20 feet as a direct result of the seismic disturbances. In one well, new water-bearing fracture zones were created as evidenced by changes in production water quality, which was later confirmed by a borehole video log. This discussion will summarize all of the hydrogeologic data collected and the lessons learned from this unique geologic event.