Middle St. Johns - Florida Department of Environmental Protection

Water Quality Assessment Report: Middle St. Johns 227
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Through ad valorem and local government sources, the SJRWMD is
coordinating 1-foot contour mapping for the Howell Creek watershed.
• Wetlands restoration: A project encompassing approximately 1,300 acres is
currently under way.
• Dredging and removal of sedimentation: A FWC project is scheduled to begin
in fiscal year 2002–03.
• Nutrient load reductions from Lake Nina: Lake Nina, a 12-acre lake with a
surface runoff area of approximately 79 acres, is a contributing surface water in the Lake
Jesup Planning Unit. The Lake Nina project will reduce the nutrients discharged into
Lake Jesup. The existing Trophic State Index (TSI) for the lake indicates eutrophic
conditions; the future TSI goal for the lake is mesotrophic. A 15 percent reduction in
phosphorus loading is required to reach that goal. Most of the watershed contains a fourlane
divided roadway that discharges all of its stormwater runoff into the lake,
contributing approximately 25 pounds of phosphorus per year to the lake. Instead of
excavating a single portion of the adjacent park for a wet detention system, the entire
park will be regraded to serve as a treatment area during rain events. During dry weather
the park will be open to the public. The project was funded as part of the 2001/2002
special legislative appropriation.
• Lake Waunatta Remediation Project: Lake Waunatta is one of many Orange
County lakes that has experienced extensive urbanization and altered drainage patterns in
recent years. These alterations have inevitably increased stormwater flow and degraded
water quality in the lake. In the mid-1990s, Lake Waunatta experienced high water levels
during an unusual wet weather period. A basinwide stormwater assessment by Orange
County in 1996 documented the need for stormwater flood controls and recommended
further water quality studies. Pollutants of concern are dissolved nitrogen and
phosphorus, which enter the lake from atmospheric deposition, untreated and partially
treated stormwater runoff, and baseflow of surficial groundwater that may include
contributions from treated septic tank effluent.
A simplified pollutant loading model was developed for Lake Waunatta, based on
yearly estimated mass loadings, to predict the pollutant loadings that could enter the lake.
In addition, potential loadings from on-site sewage treatment and disposal systems
(OSTDSs) were evaluated for the lake’s immediate shoreline. Together, the latter two
sources could be controlled through engineered solutions. Based on the findings of the
loading analysis, about 2,100 pounds of nitrogen and 290 pounds of phosphorus are
generated annually from runoff in the watershed. About 60 to 80 percent of this loading
reaches Lake Waunatta. Pollutants from OSTDSs in the watershed potentially account
for only about 15 pounds of nitrogen and 3 pounds of phosphorus. According to model
predictions, a 20 percent reduction in annual loadings may improve trophic status by
about 5 percent. Improvements to Lake Waunatta include stormwater storage
improvements and long-term water quality improvements. Improved maintenance in the
Kmart and Unigold Shopping Plaza ponds would provide an immediate, cost-effective