Assessment Comments
Assessment is based on: (1) results of IDNR/UHL monthly ambient monitoring conducted from 2004 through 2006 on Indian Creek at a bridge 4.8 miles north of Colfax and 1.8 miles east of Green Castle in Jasper County (station 10500001) and (2) IDNR/UHL biological (REMAP) monitoring near Mingo in 2003.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring and on results of biological monitoring results from a 2003 REMAP site. The sources of data for this assessment are (1) results of IDNR/UHL monthly ambient monitoring conducted from 2004 through 2006 on Indian Creek at a bridge 4.8 miles north of Colfax and 1.8 miles east of Green Castle in Jasper County (station 10500001) and (2) IDNR/UHL biological (REMAP) monitoring near Mingo in 2003.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the 24 samples collected (407 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Thirteen of the 24 samples (54%) exceed Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical, physical, and biological water quality monitoring. Results of chemical/physical monitoring at the IDNR/UHL station show no violations of Class B(WW2) criteria for dissolved oxygen, pH, or ammonia nitrogen (maximum value = 0.50 mg/l) in the 36 samples analyzed during the 2004-2006 assessment period, no violations of Class B(WW2) chronic criteria for pesticides in the seven samples analyzed or for toxic metals in the 10 samples analyzed. This assessment is consistent with the assessment developed for previous (2004 and 2006) Section 305(b) reporting cycles.
Additionally, the assessment remains based on biological data collected in 2003 as part of the DNR/UHL stream REMAP project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2003 FIBI score was 30 (fair) and the BMIBI score was 57 (good). The aquatic life use support was assessed (evaluated) as Fully Supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. The assessment is considered FS-evaluated because both the FIBI and BMIBI scores met the respective BICs with the use of the UAVs (used on single samples): FIBI = 7 points and BMIBI = 8 points.
