Middle St. Johns - Florida Department of Environmental Protection

Water Quality Assessment Report: Middle St. Johns 481
43. 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 Seminole County includes seven water bodies that are listed as
impaired solely on the basis of DO concentrations; [Econlockhatchee River (WBID
2991 and 2991A), Little Econlockhatchee River (WBID 3001), Soldier Creek (WBID
2986), Sweetwater Creek (WBID 2992), Wekiva River (WBID 2956A) and Wekiva
River Lower (WBID 2956B)]. Data analysis has revealed that the alleged DO
impairment is a natural condition, which is common for 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 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, with exception of Sweetwater Creek in 1997,
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 request is also supported by 62-303.420.a FAC, by which if the
exceedances are not due to pollutant discharges and reflect either physical alterations
of the water body that cannot be abated or natural background conditions, the water
shall not be placed on the verified list. Recommendation: Remove the Dissolved
Oxygen from the Verified List [Seminole County TMDL Analysis 4 PBS&J
#100339.02 July 2003].
RESPONSE: As of the November 5, 2003 update of the IWR database, the
Econlockhatchee River (WBID 2991), the Wekiva River Lower (WBID 2956B), the
Econlockhatchee River (WBID 3001), the Little the Econlockhatchee River (WBID
2991A), the Wekiva River (WBID 2956A), and Soldier Creek Reach (WBID 2986)
are only planning listed for dissolved oxygen, as the cause of the impairment has not
been identified for these segments. Nutrients (nitrogen and phosphorus) and
biochemical oxygen demand (BOD) are all within acceptable ranges in these
segments and biology (based on bioassessments) is not impaired. The Department
believes that the dissolved oxygen is naturally low, and bioassessment data indicate
that aquatic life use support is being maintained, therefore these water segments are
not listed.