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Microbial Source Tracking in Murrells Inlet, Horry County Volunteer Monitoring Luncheon April 30, 2013 Inlet Affairs Tiered Approach Weight of Evidence Microbial Source Tracking Cost Intensive sampling using standard FIB measurements; Infrared thermography Sanitary Survey Identification of impaired areas based on long-term monitoring Effort Weight of Evidence Source Tracking Strategies • Space and Time – Targeted wet and dry weather sampling • Tracers – Fecal bacteria concentrations • Enterococcus • E. coli – Chemical concentrations • Water mass indicators • Optical brighteners • Caffeine – Host animals • Multiple antibiotic resistance of fecal bacteria • Genetic markers of fecal bacteria Sample Sites Fecal Indicator Bacteria (FIB) Summary • All sites have at least one contravention of WQS’s for FIBs • Sites 1 & 6 have the highest FIB concentrations • Some sites are relatively clean, i.e. some of the samples <WQS • No consistent pattern with rainfall Genetic Marker Overview • Warm-blooded signal generally shows the same pattern of concentrations as FIB concentrations • Canine signal concentrations appear high at many sites. Detections are most common and concentrations highest after rain. • Only 2 of 27 samples were positive for human signal (sites #1 and 5). • The bird assay is not ready but samples are archived for future analysis. Canine sources • High concentrations of canine-sourced fecal bacteria suggest that dogs are an important contributor to FIB loading at sites 2, 3, 4, 5, 7, & 8 – These sites are all in residential areas where residents likely walk pets – Sites 3, 4, & 8 are downstream of a pond – Sites 2, 5, & 7 are adjacent to grassy areas on the inlet. Human Sources • Site 1 (Woodland Dr. Pond) has high E. coli concentrations in volunteer monitoring data – High FIB levels may reflect human sources concurrent detections of OB, caffeine and BacHum • Site 5 is a SC DHEC shellfish monitoring site (04-01) that has exhibited high and continual contraventions of the shellfish FC WQS. – Site 5 exhibits signs of human influences elevated FIB, OB, and a low level detection for BacHum Human Sources (cont) • Site 6 drains a medium density modular and multi-family home community – Results suggest strong human influence – high levels of FIB, caffeine, and OB – However, no BacHum signal was detected Sample Sites Moving Forward • One dry and wet event still to be sampled – May confirm preliminary conclusions – May detect tracers that went undetected due to dilution from flushing (compared to Withers) • Bird assay to be measured on all samples • Iterative process? May warrant further testing • Georgetown County intends to undertake similar approach in next fiscal year (budget pending)