Wekiva Nitrate Sourcing
In the 2006-07 General Appropriations Act, line item 1798, the Florida
Legislature established the following requirement for the department:
"From the funds in Specific Appropriation 1798, $250,000 from the
General Revenue Fund is provided to conduct a Wekiva River and Florida
Aquifer study to determine nitrate impacts to the system."
The Divisions of Water Resource Management and Environmental Assessment &
Restoration have undertaken the required
study in conjunction with the St. Johns River Water Management District. It
was divided into two phases.
Phase I of the study involved an assessment of available data
on nitrate impacts to the Wekiva River and Floridan aquifer system,
preliminary identification of relative nitrate contributions to water
resources in the area and an identification of data gaps to be filled. The
work was performed under contract by MACTEC, Inc., a large consulting
company that specializes in a wide variety of scientific and engineering
disciplines. MACTEC's findings on the preliminary issues it was contracted
to investigate are available in the
Phase I Report, Wekiva River Basin Nitrate Sourcing Study, prepared for
the department and the St. Johns River Water Management District. (The
document is large, with 183 pages of text, graphs, charts and maps, and it
will take time to download.)
As noted, the MACTEC report represents a preliminary investigation
based on existing data. It is not a final accounting of nitrate impacts in
the Wekiva area nor does it reflect final conclusions or recommendations
associated with the study the department was charged with conducting.
Phase I estimates of nitrate loadings to the Wekiva Basin, partitioned by
source, are shown in the figure to the right.
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Phase II of the department's study will test and supplement the
work MACTEC has done in order to provide an effective assessment of nutrient
impacts on water quality in the Wekiva area and inform future public policy
decisions at the state, regional and local levels.
Phase II will re-visit MACTEC’s nitrate loading estimates for residential
fertilizer by conducting field studies of nitrate concentrations in shallow
ground water from fertilizer application along with documenting lawn
management activities in the Wekiva Study Area. The study will also evaluate
the effectiveness of best management practices in reducing nitrate leaching
to ground water from lawn and turf fertilization. Details are available from
the Phase II
study design.
This second phase will be limited to evaluating the impacts of fertilization
practices on residential land uses because they are the least understood
source of nitrate in the Wekiva Basin. Other potential nitrate sources
identified during Phase I (including septic tanks, domestic wastewater,
livestock and agriculture) are not included in Phase II because the body of
scientific evidence describing nitrate loading from these sources is more
extensive and conclusive. Consider the following:
- Nitrate loading from septic tanks has been documented in several
parts of Florida, including the Wekiva Study Area. The findings of DEP's
Phase I study are generally consistent with the Department of Health
Final Project Report,
Nitrogen Impact of Onsite Sewage Treatment and Disposal Systems in the
Wekiva Study Area, dated June 30, 2007.
- Domestic wastewater, a DEP-regulated source, is routinely monitored
against specific pollutant limits and therefore has a well known and
documentable source contribution.
- Agricultural fertilizers have been well studied and reliable data describing nitrate
loadings from various agricultural activities is readily available.
If the Phase I estimate for residential fertilizer (20%--see chart above)
changes as a result of the Phase II study, the relative impact of other
source contributions will be adjusted.
If you have questions about the Phase II study, please contact Bonnie
Hall at bonnie.hall@dep.state.fl.us.
Domestic Wastewater Treatment in the Wekiva Study Area
DEP's original 2004 study,
A Strategy for Water Quality Protection:
Wastewater Treatment in the Wekiva Study Area, is also available. This led to
development of DEP's
specific Wekiva wastewater rules,
62-600.550, Florida Administrative Code.
