LAND USE AND GROUNDWATER QUALITY AT SINKING SPRING, ABRAHAM LINCOLN BIRTHPLACE NATIONAL HISTORICAL SITE, KENTUCKY

The site where Thomas Lincoln settled near Hodgenville, Kentucky in 1808, and where his son Abraham would be born, was chosen in large part because of the water supply provided by Sinking Spring. Located on karst terrain, this perennial spring flows from a small cave and provides one of the few reliable water sources in the area. The spring is a now an important interpretive feature and visitor attraction at Abraham Lincoln National Historical Site, which commemorates Lincoln's birthplace.

In 1996, the authors began studying Sinking Spring and water quality/land use interactions to assist park managers of the historic site to better focus their efforts on areas of concern which may effect the spring. In the first phase, they delineated the recharge area and flow system using fluorescent dye tracing, cave survey, and unit base flow discharge analysis. Using Geographic Information Systems (GIS), they also mapped land use within the identified source areas. An aerial photography fly over allowed development of a one-foot contour interval topographic map of the spring area. The GIS constructed from this topographic information was used to study flooding mechanisms within the sinkhole surrounding Sinking Spring. Field measurements showed that the spring's catchment area was primarily within the 45-hectare park, along with adjacent agricultural land. Two unsuccessful die traces indicate that drainage from Highway 31E, which bi-sects the historic site, doesn't flow to the spring. Floodwaters that occasionally fill the large sink appear to result from subsurface hydraulic damming from the South Fork Nolin River.

Storm pulse sampling to quantify spring water quality is underway - a rainfall event during June 2001 was sampled with one-hour resolution. Overall, water quality is considered fair for karst flow draining agricultural land. The most significant impacts were from fecal coliform bacteria (maximum result: 2,000+ colonies/100 mL) and the broadleaf herbicide Trifluralin (maximum concentration result: 25 µg/L). No other chemicals of concern, including 11 other tested pesticides, were identified. Student research training in field and laboratory work, as well as GIS techniques, is a critical feature of this project, and central to the cooperative effort with the National Park Service.