Middle St. Johns - Florida Department of Environmental Protection

480 Water Quality Assessment Report: Middle St. Johns
the verified period, therefore Lake Picket (WBID 3003) is considered unimpaired for
nutrients and was removed from the draft verified list.
41. Salt Creek (WBID 2990) is shown as being impaired for nutrients (chlorophyll-a).
During a technical review of this data, it was determined that several data
measurements were considered highly suspect outliers. Samples taken at the same
station (21 FLSJWMT-2) on the same date showed values of chlorophyll ranging by
more than a 50% discrepancy, in most cases, and in many cases more than three
standard deviations away from the mean of all chlorophyll-a samples for the water
body. Without these highly suspect sample data points, the average annual
chlorophyll-a for this WBID is well below 20 ug/L and therefore does not support the
conclusion that this WBID is impaired for chlorophyll-a. Recommendation: Remove
the Nutrients – Chl-a Impairment from the Verified List [Seminole County TMDL
Analysis 4 PBS&J #100339.02 July 2003].
RESPONSE: There was no evidence, such as field notes, photographs, or data
sheets, that these data points in questions were not representative of the water
segment at that particular point in time, therefore this water segment was retained on
the verified list.
42. Soldier Creek Reach (WBID 2986) has been classified as impaired for historical
chlorophyll-a. However, the FDEP data do not appear to support this determination.
The FDEP data set does not extend prior to 1989, with the first valid yearly Chl-a in
1992 and none of the annual chlorophyll-a values over the period of record for either
the absolute criteria or the 50% over background criteria. Based upon the data in the
FDEP data set, there is a lack of substantiating data to indicate impairment for
historical chlorophyll-a in this water body. Recommendation: Remove historical
chlorophyll 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, Soldier
Creek Reach (WBID 2986) was assessed for nutrient impairment based upon analysis
of current and historic chlorophyll levels. There were no exceedances of the 20 ug/L
chlorophyll threshold in the planning or verified periods. There were adequate data to
calculate two historic five-year means; from 1990 through 1994 and from 1995
through 1999. The lowest of these five-year means was 2.2 ug/L, in the 1990 – 1994
period, thus this value is considered the historic chlorophyll level for the purpose of
comparison to current levels. There were three exceedances in the verified period of
greater than 50% above 2.2 ug/L; in 1996 (3.5 ug/L), 1998 (4.7 ug/L) and in 2000
(3.6 ug/L). Section 62-303.351(2) of the IWR states however that, to consider a
water verified impaired for nutrients based upon analysis of current versus historic
chlorophyll levels, exceedances of greater than 50% over historical levels must occur
for at least two consecutive years. The Department therefore concurs with Seminole
County’s conclusions and has removed this listing from the draft verified list.