Near shore beach volume modeling approach for setting beach bacteria TMDLs: A case study, Hickory Grove Lake, Iowa

A novel approach to set bacteria Total Maximum Daily Load (TMDL) using a Near-Shore Beach Volume (NSBV) model was described along with recommendations for design of a monitoring network to support this method. Sources of fecal bacteria in the Hickory Grove Lake watershed include unpermitted septic systems, manure applications in the watershed, livestock access to streams, waterfowl, and wildlife. The Lake Inlet, Lake Outlet, and Lake Beach were monitored for E. coli concentrations from 2010-2012, this monitoring data was used to assess relationships between watershed bacteria loads and the beach bacteria levels. Fecal bacteria from waterfowl were identified as the major source to the Lake Beach causing the water quality impairment. The bacteria TMDL for the Hickory Grove Lake beach was set at 1.87E+11 orgs/day for the single sample maximum target and 1.01E+11 orgs/day for the geometric mean target, which correlates to the presence of fewer than five resident geese. Monitoring recommendations to support this approach include weekly beach water quality monitoring and post-event sampling; periodic spatial sampling of the lake; weekly and post-event grab sampling of the water quality at the lake inlet mixing zones; and weekly and post-event grab sampling of the water quality at the lake outlet