The Beaches Environmental Assessment and Coastal Health Act of 2000 (BEACH Act) requires states to monitor bacteria levels in recreational coastal waters. High levels of bacteria increase the potential for many illnesses to beach goers, so coastal towns are forced to post advisories or close beaches after many rainfall events, which potentially decrease tourism profits. Stormwater outfalls, common in many coastal towns, empty stormwater from roads, parking lots, etc., contaminated with bacteria and other pollutants, into the ocean or sounds.
The NC Department of Transportation and the Town of Kure Beach wanted to reduce the amount of stormwater from nearby US 421 and other residential and commercial sites from entering ocean recreational areas. Two stormwater Dune Infiltration Systems were designed to divert a portion of the flow into the beach dunes. Sand filters have historically been successful in bacterial removal. The infiltration systems were constructed using commercially available open-bottomed infiltration chambers. Due to limited land area, the systems were designed to infiltrate 0.5 in storms, which comprise approximately 80% of the rainfall events at the site. The watersheds of both sites were small (4.5 ac and 8.1 ac) and of mixed urban and residential land use. Water table measurements indicated a tidal influence, but approximately 7 ft of sand was available for infiltration in the vertical direction.
Overall, the two Dune Infiltration Systems (DIS) captured 96.6% of runoff produced from 25 storm events during March - October 2006. Inflowing stormwater runoff had concentrations of fecal coliform concentrations ranging from 181 CFU/100 ml to 28300 CFU/100 ml with a median of 7600 CFU/100 ml, and enterococcus concentrations from <10 CFU/100 ml to >2005 CFU/100 ml with a median of 1298 CFU/100 ml. The groundwater concentrations were significantly less (p< 0.001) than the inflow with fecal coliform concentrations ranging from <1 CFU/100 ml to 214 CFU/100 ml with a median of 1.5 CFU/100 ml. For enterococcus concentrations the range was from <10 CFU/100 ml to 2005 CFU/100 ml with a median of 10 CFU/100 ml. The groundwater enterococcus concentrations at both sites were also significantly (p<0.01) less than the stormwater runoff inflow concentration. North Carolina¿s indicator bacteria standards were exceeded only in Site M¿s groundwater. Groundwater samples surpassed the limit on 2 of the 25 events for fecal coliform and 6 of the 22 for enterococcus. Based on these results, the DIS has potential as an effective BMP at the remaining ocean outfalls in Kure Beach and elsewhere.
