THE USE OF DYE TRACING TO DEVELOP A MITIGATION AND RESPONSE PLAN FOR TWO KARST-BASED PUBLIC WATER SUPPLIES IN AUGUSTA COUNTY, VIRGINIA

Construction of buried infrastructure presents potential impacts to karst aquifers upon which local communities depend for drinking water. Therefore, it is important to identify any features that could be insurgences for contaminated water generated by land-disturbing activities. Two public water supplies were identified that could be potentially impacted by the construction of the Atlantic Coast Pipeline: Gardner Spring, which supplies half the drinking water for the City of Staunton (pop. 24,528); and the well and springs of the Town of Deerfield (pop. 132).

At Deerfield, dye placed just upstream from a sink point in the Hamilton Branch was detected less than 24 hours later. A hydrologic connection was also established between Gardner Spring and a sinkhole located approximately 4.1 miles to the south. The dye arrived at Gardner spring in less than 12 days, suggesting conduit flow. In contrast, dye placed in a sinkhole closer to the spring was traced to several other locations, but no connection to Gardner spring was verified. Interestingly, both injection points were within a previously delineated recharge zone for the spring based on fracture trace analysis and topography. However, the current study suggests the recharge zone and karst aquifer network in this region is complex and contains several discreet hydrogeological compartments.

Based on the findings of these dye trace studies a site-specific plan to preclude potential impact to the karst aquifer has been developed, in conjunction with a specific response and notification plan to coordinate with the municipalities dependent on the aquifer for potable water.