Earthquake Impacts Groundwater Supplies in Northern Virginia

Emery & Garrett Groundwater, Inc. recently presented a landmark groundwater discovery at the Southeastern Section meeting of the Geological Society of America held in Asheville, North Carolina on April 1, 2012.  The presentation entitled, “The Impacts of the Earthquake that Struck Near Mineral, Virginia on Groundwater Resources in Northern Virginia” focused on the observed sudden rise of groundwater levels within a well established “cone of depression” surrounding a public water supply Production Well in northern Virginia.  The groundwater level within the cone of depression rose more than 20 feet.  This rapid rise in groundwater levels happened as a direct result of the August 23, 2011 earthquake in Mineral, Virginia at a time when no other groundwater recharge events to the bedrock aquifer were occurring.

Additionally, as a direct result of the earthquake, one of the primary Production Wells at the site sustained adverse changes to the quality of water it produced.  Since the earthquake, this community’s Primary Production Well has been contaminated with Coliform and E.coli bacteria.  As a result, the Virginia Department of Health (VDH) has determined that the well has changed from its status as a groundwater source and has now classified it as being “Groundwater Under the Direct Influence of Surface Water” (GUDI), even though the well had produced bacteria-free water for more than 15 years.

A borehole video log of the contaminated Production Well has determined that new shallow water-bearing fractures were formed (or opened up) during the earthquake event.  It has also been suspected that the sanitary cement grout seal of the production well sustained damage during the earthquake.  The Community has since had to use a “back-up” emergency well.  Although this emergency back-up well had been drilled and built within the same bedrock aquifer and in accordance to the same well construction standards, it continues to pump bacteria-free water.  The community is now considering its mitigation options.

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