BACTERIOLOGICAL ASSESSMENT OF VADOSE ZONE CONNECTIVITY AT MAMMOTH CAVE NATIONAL PARK, USA, FOLLOWING SEWER LINE BREAK SUMMER 2014

Mammoth Cave National Park, KY, contains the longest known cave system in the world, houses several endangered species, receives over 500,000 tourists a year, and is dedicated to the preservation of a vast karst groundwater system. A sewage leak occurred in May 2014, raising concern for the impact on the cave fauna, tourists, and water resources. Building on occasional water sampling pre-dating the spill, a more systematic collection was initiated starting after the event focused on 4 cave and 7 surface locations, with higher frequency after rain events. Samples were analyzed for E. coli and fecal coliform using the Colilert method. Two of the cave sites (Cataracts and Cascade Hall) had the highest number of samples due to their proximate location under the spill site and perennial vadose flow. The data shows typically low values (<10 col/100 mL) during base flow, punctuated with elevated colony counts reaching 2400 col/100 mL after at least one inch of rainfall. Coliform counts are almost categorically higher at Cataracts, which is in a higher elevation cave passage than Cascade Hall. The lower bacterial counts in the deeper site may be due to downward flow between them but with bacterial die off, or, could be because vadose flow to Cascade Hall is not sourced directly from the stream affected by the sewage break. Spatial-temporal interpretation of the coliform breakthrough curves is supporting the testing of hypotheses of recharge pathways and connectivity. It is recommended that the Park continues sampling during the summer of 2015 to better understand the karst vadose hydrological connections in general. Given that surface runoff samples distant from the sewage leak had elevated coliform counts, the recommended further sampling for summer 2015 will specifically constrain natural background levels of coliforms when no sewage is present.