Middle St. Johns - Florida Department of Environmental Protection

Water Quality Assessment Report: Middle St. Johns 473
RESPONSE: Addressed in comment number 25.
28. As a natural system’s health is determined by many physical and chemical attributes
and their dependence on each other, an impairment for dissolved oxygen (DO)
concentration would manifest itself as an imbalance in other related chemical
parameters as well as in biological conditions. The Draft §303(d) Verified List for
Group 2 Waters in Orange County includes two water bodies that are listed as
impaired solely on the basis of DO concentrations, [Econlockhatchee River (WBID
2991) and Little Econlockhatchee (WBID 3001)]. Data analysis has revealed that
these DO impairments are a natural condition, common for many Florida streams.
The parameters evaluated in support of this conclusion included BOD5 and
chlorophyll-a concentrations, color, and biological conditions. Biological conditions
were measured by the SCI index and results of bio-assessments made on each of the
streams. Results of the data analysis showed that the depressed DO conditions
observed in these WBIDs have not caused a corresponding imbalance in the stream
segments with respect to the other related chemical and biological parameters. The
BOD5 and chlorophyll-a concentrations are low compared to other Florida streams.
The high color data for each of the water bodies also indicate that the stream
segments present conditions that are typical of many natural systems in Florida. In
addition, the review of historical and recent water quality data for these water bodies
shows no evidence that support the conclusion that the low DO concentrations levels
are attributable to pollutant discharges. Results also indicated that, in each case, the
bioassessments and SCI’s have a “good”, “healthy”, or “excellent” rating. It is
recommended that the water bodies listed [above] be removed from the draft Verified
List in consideration of the site-specific alternative criteria, per 62-302.800 FAC.
This recommendation is also supported by 62-303.420.a FAC, based upon the
provision that the water shall not be placed on the verified list when observed
exceedances are not due to pollutant discharges, and reflect either physical alterations
of the water body that cannot be abated, or natural background conditions.
Recommendation: Remove the Dissolved Oxygen impairment listings for the
Econlockhatchee River and the Little Econlockhatchee River from the Verified List
[Orange County TMDL Analysis 5 PBS&J 100504.01 July 2003].
RESPONSE: As of the November 5, 2003 update of the IWR database, the
Econlockhatchee River (WBID 2991) and Little Econlockhatchee River (WBID
3001) is only planning listed for dissolved oxygen, as the cause of the impairment has
not been identified. Nutrients (nitrogen and phosphorus) and biochemical oxygen
demand (BOD) are all within acceptable ranges in this segment and biology (based on
bioassessments) is not impaired. The Department concurs that dissolved oxygen is
naturally low, and bioassessment data indicate that aquatic life use support is being
maintained, therefore these segment have been removed from verified list.
29. Crane Strand Drain (WBID 3014) and Little Wekiva Canal (WBID 3004) are urban
drainage ditches, which function as a conveyance component in Orange County’s
Municipal Separate Storm Sewer System, and are shallow and stagnant waterbodies