The Role of Epikarst in Controlling Water Quality

In the United States, karst aquifers supply approximately 40% of the groundwater used for drinking. Urban development and agriculture have increased contamination of karst aquifers, while also increasing the demands for water from such aquifers. With increased demands, it is important to characterize karst's ability to transmit and purify water. Recharge of karst aquifers can occur via allogenic streams draining from non-karst areas or via autogenic infiltration through the epikarst, which is the region of vegetation, soil, and weathered bedrock lying between the land surface and shallow karstic aquifers.

This study will examine the role of epikarst in controlling water quality by comparing chemical characteristics of precipitation, internal stormwater runoff, and cave drip water (representing autogenic recharge). One surface station and three drip stations in James Cave (Pulaski County, Virginia) have been instrumented and are currently measuring and data-logging precipitation rate, cave drip rate, and basic geochemical parameters (pH, temp, specific conductance, dissolved oxygen, oxidation-reduction potential). To evaluate how epikarst controls water quality in James Cave, the following will be performed: 1) conduct an electrical resistivity tomography survey to map high conductivity pathways in the epikarst; 2) survey the relative orientation and elevation of drip stations; and 3) analyze precipitation, cave drip water, and cave stream water for major ions, dissolved organic carbon, water and carbon isotopes, and the presence/absence of agricultural pollutants (e.g., fecal coliform, nitrate) in each cave zone. Results from such analyses will help to answer how the characteristics of epikarst (e.g., thickness, presence of hydraulically connected pathways) affect water quality.