Freshwater or Salt with That?
When the bolide, plummeted into the water and down into the Earth’s surface, the massive impact disrupted subsurface rock units that serve as very important aquifers (underground beds or layers yielding groundwater for wells and springs). By disrupting the aquifers, the crater left present-day freshwater aquifers resting right above deep, salty brine, making the entire lower Chesapeake Bay area susceptible to groundwater contamination. Before we can understand the importance of the disrupted aquifers, we must understand Virginia’s coastal plain and the geology below it.
For millions of years, Virginia’s coastal plain has consisted of sloping layers of sedimentary beds made up of sand, silt, clay, and limestone. After studying the sediment beds for more than 200 years, geologists have found nine aquifers existing within the layers. After the aquifers were identified, they were tapped for freshwater. The intention was to quench the thirst of many Virginians and to provide water for local industries. Information regarding groundwater in Virginia’s coastal plain was first recorded and reported 95 years ago by Samuel Sanford. In 1913, Sanford charted well-known wells on a map and then drew lines connecting the wells that contained equal amounts of salty water. Sanford’s connected lines resulted in what has since been referred to as an inland bulge around the lower Chesapeake Bay area, centered around Cape Charles. Years passed, and during the 1940s, the demand for water was increasing because of needs generated by World War II; preexisting wells were no longer sufficient. At the time, there was an incredible demand for water in the region, so the USGS sent John Cederstrom out to find supplies of freshwater. While drilling for water, Cederstom ran across an extremely unusual group of sediments all mangled and mixed together, which he named the Mattaponi Formation. During that time, technology for obtaining core samples was primitive, so wells were made by chipping fragments of dirt or rock that could be flushed out. Cederstrom took samples from 52 test wells, and still the search for freshwater was unsuccessful. Instead of finding freshwater, Cederstrom and his crew were coming up with samples of salty, briny water. Cederstrom had encountered what Powars would many years later define as the “inland saltwater wedge.” Cederstrom was scorned by his colleagues and other fellow scientists at the time, as they did not accept his hypothesis that the jumbled formation, which he had named Mattaponi, had been formed by natural processes. Cederstrom was accused of contaminating samples and mixing up fossil specimens, which ultimately led to the loss of his job. Even though he was re-hired years later, Cederstrom retracted his published work in the 1950s, saying, under pressure, that he must have been wrong about his earlier findings.
Currently, more than two million people count on groundwater that comes from the Chesapeake Bay area, causing scientists along with the State Water Control Board to worry about continuous saltwater findings and disrupted aquifers. These concerns arose because of growth in the Hampton Roads area, (the cities of Chesapeake, Hampton, Newport News, Norfolk, Portsmouth, Suffolk, Yorktown and Virginia Beach, along with the Eastern Shore communities that were already scrambling for water), combined with developers plans to build more housing, schools and businesses in a place where water is needed the most. Research indicates that six of the 13 cities and counties that provide public water locally depend solely on groundwater; four cities blend groundwater and surface water. Plus there are another 327 private water systems and 320 noncommunity wells that also draw groundwater. Scientists realize that it is extremely important to understand the effects and significance of the Chesapeake Bay impact crater in order to figure out how to maintain and manage the Chesapeake Bay areas’ groundwater supply for future generations.