Applications of source-tracking and site-specific models for water quality assessment of tidal waters: Upper inlet creek, mount pleasant, South Carolina

In South Carolina, there are 504 water bodies identified as impaired for recreation or shellfishing activities and 78% of those impairments are due to pathogen levels above regulatory limits. Upper Inlet Creek, located in a tidal basin along the Atlantic Intracoastal Waterway in Mount Pleasant, SC, is an important habitat for a variety of estuarine life and supports local molluscan shellfish operations. According to the South Carolina 303(d) list for impaired waterways, Upper Inlet Creek is impaired for shellfishing activities due to high levels of fecal coliform, a type of bacteria indicator. However, it is unknown whether this impairment is due to human fecal contamination (i.e. sewage or septic) or due to non-point sources such as stormwater runoff, pets and/or wildlife. The goal of this study was to determine possible causes and sources of fecal coliform contamination by using various inexpensive source-tracking methods. Methods included the use of targeted sampling for fecal indicator bacteria fecal coliform and enterococci, optical brightener measurements, and water quality monitoring and analysis for pH, temperature, turbidity and conductivity. Objectives of this study were to (1) provide monthly water quality and bacteria monitoring for the impaired waterway for a 12 month period, and (2) identify potential bacterial sources and (3) provide data for best management practices (BMPs) that could be implemented to reduce bacteria loading in coastal streams similar to Upper Inlet Creek. Results show that optical brighteners were adequate screening tools in determining whether human waste from impaired sewer or septic systems was present, and combined with microbiological data and site-specific models, ruled out human waste streams as the primary source of fecal coliform pollution in Upper Inlet Creek. Results from site-specific models for stormwater runoff, and potential fecal coliform loading, identified pets and wildlife as the largest potential contributors of fecal coliform bacteria loading to Upper Inlet Creek. The impact of development on stormwater runoff and bacteria loading in the watershed was found to be significant, and recommendations for future remediation include on-site BMPs and the use of predictive modeling to understand how land use change will affect fecal coliform loading in a tidal basin.