2.7.19. Mill Creek

2.7.19.1. About Mill Creek

Figure 2.48 The Mill Creek Tributary (WBID 2460).
Figure 2.48 The Mill Creek Tributary (WBID 2460).
  • East of the St. Johns River feeding into Sixmile Creek
  • Primary Land Use: Wetlands/forest
  • Current TMDL reports: Fecal Coliform, DO/Nutrient, Mercury
  • 2016 Verified Impairment for Iron (2460)
  • WBID Area: 11.6 sq. mi.
  • Beneficial Use: Class III F (Recreational – Freshwater)

2.7.19.2. Data sources

Data were downloaded from the FL STORET and WIN websites (DEP 2010f; DEP 2018c) and filtered based on the stations (DEP 2010g) in Mill Creek WBID 2460 (DEP 2014c) shown above. The filtered dataset reflects water column concentrations and was used to generate Table 2.20.

2.7.19.3. Discussion

Water quality data for Mill Creek are shown in Table 2.20. Historically, the fecal coliform level, averaged over all the stations in Mill Creek, was above the WQC of 400 colony-forming-units (CFU) per 100 mL. Thus, a TMDL for fecal coliform was published in 2009 (Rhew 2009c). (Note: the data analyses in the TMDL are based on different criteria than those used in this report). Limited sampling in 2018 show fecal coliform concentrations below the WQC.

In addition, Mill Creek has been identified as impaired for dissolved oxygen and associated nutrients and, a TMDL addressing this was published in 2010 (Magley 2010). Limited measurements between 2017 and 2019 indicate elevated total phosphorus concentrations, with most samples exceeding the WQC. Mill Creek has been listed as impaired for iron, but this may potentially be a natural condition (common in Florida blackwater streams such as this) (DEP 2016j). FDEP considers Mill Creek a high priority for TMDL development to address iron levels.

Water quality data for Mill Creek are limited in WIN and STORET. No recent measurements were available in WIN or STORET between 2017 and 2019 for the following parameters:

  • Arsenic
  • Iron
  • Lead
  • Zinc
  • Cadmium
  • Nickel
  • Copper
  • Silver

Historical water quality data for these parameters in Mill Creek are available in previous versions of the River Report.

Table 2.20 Water quality data for Mill Creek.

 Water QualityAverage and Number of Samples º
ParameterCriteria (FW)201720182019
Dissolved Oxygen (mg/L)≥34% sat. (≥3.0) FW1.45
(0 of 2 samples)
6.56
(0 of 5 samples)
6.19
(0 of 4 samples)
Total Nitrogen (mg/L)<1.541.51
(2 of 3 samples)
1.37
(1 of 5 samples)
1.23
(0 of 6 samples)
Total Phosphorus (mg/L)<0.120.18
(2 of 2 samples)
0.24
(4 of 5 samples)
0.18
(4 of 5 samples)
Chlorophyll-a (µg/L)<20 FW1.45
(0 of 2 samples)
9.62
(1 of 5 samples)
2.18
(0 of 5 samples)
Fecal Coliform (CFU/100 mL)<400Not available140
(0 of 5 samples)
1600
(2 of 4 samples)
Turbidity (NTU)<294.40
(0 of 2 samples)
3.58
(0 of 5 samples)
4.50
(0 of 6 samples)
Note: Hardness-dependent freshwater criteria for cadmium, copper, lead, nickel, and zinc were generated based on a hardness concentration of 100 mg/L.
° = Number of samples below Water Quality Criteria for Dissolved Oxygen; Number of samples above Water Quality Criteria for all other parameters.
FW = freshwater; SW = saltwater (marine). Values denoted with (*) indicate a proposed criterion, which has not yet been adopted.
Values denoted with (‡) are reference values based on EPA criteria (EPA 2010b), but the water body is not regulated by this standard.