Assessment is based on: (1) IDNR monthly ambient monitoring conducted during the 2004-2006 assessment period at the County Road C-70 bridge north of Sioux City (STORET station 10750001 (formerly station 950110)) and (2) DNR/UHL biological monitoring in 2000 and 2001.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this river segment was designated only for Class B(WW1) aquatic life uses, including fish consumption 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) and the results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The 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(WW1) aquatic life uses are assessed (evaluated) as "partially supported" based on results of biological monitoring in 2000 and 2001 that suggest potential impairments of the Class B(WW1) aquatic life uses. The previous aquatic life impairments due to elevated levels of lead and copper are removed for the 2008 cycle due to more recent data showing low levels of these metals. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. This assessment is based on results of (1) IDNR monthly ambient monitoring conducted during the 2004-2006 assessment period at the County Road C-70 bridge north of Sioux City (STORET station 10750001 (formerly station 950110)) and (2) DNR/UHL biological monitoring in 2000 and 2001.
EXPLANATION: The 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 at the IDNR/UHL ambient monitoring station north of Sioux City during summer recreational seasons of 2004-2006 (1,001 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Nineteen of the 24 samples (79%) exceed Iowa’s single-sample maximum criterion 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).
Regarding support of the Class B(WW1) aquatic life uses, monitoring at the IDNR/UHL monthly ambient monitoring station north of Sioux City showed no violations of Class B(WW1) water quality criteria for ammonia, dissolved oxygen, or pH in the 36 samples analyzed, for pesticides in the 13 samples analyzed, or for toxic metals in the 10 samples analyzed during the 2004-2006 assessment period. Although violations of Class B(WW1) criteria for ammonia have occasionally occurred during past assessment cycles (most recently in July 2002), the absence of violations during the past four years of monthly monitoring suggests that levels of ammonia do not represent a water quality concern in this segment of the Floyd River.
Regarding toxic metals, previous assessment cycles have suggested impairment of the Class B(WW1) aquatic life uses of this river segment due to violations of criteria for both lead and copper. During the current (2004-2006) assessment period, however, no violations occurred in the 10 samples analyzed (maximum values: 10 ppb for copper; 20 ppb for lead). This lack of violations over the last three years suggests an improving water quality trend and the absence of a metals impairment of the aquatic life uses of this assessment segment. Thus, the metals (lead and copper) impairments identified for previous listing cycles is removed for the 2008 cycle.
Biological sampling results suggest that the aquatic life uses should be assessed (evaluated) as partially supporting based on IDNR/UHL data collected in 2000 and 2001. This evaluated biological assessment was based on data collected in 2000 and 2001 as part of the DNR/UHL stream monthly ambient sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria 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 2000 FIBI score was 45 (fair) and the BMIBI score was 28 (poor). The 2001 BMIBI score was 56 (good). The BMIBI average was 42. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54. This assessment is considered evaluated because the drainage area (882 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC and failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river reach.