Assessment Comments
Assessment is based on: (1) results of IDNR/UHL biological (REMAP) monitoring in 2002, (2) IDNR/UHL biological (Biocriteria) monitoring in 2004, and (3) results of IDNR/UHL ambient monthly water quality monitoring during the 2004-2006 assessment period at STORET station 10910002 (formerly station 426058) at the County Road R27 bridge SE of Norwalk.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(WW) 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 due to the completion of a 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 remain assessed (monitored) as "partially supported” based on results of biological monitoring in 2002 and 2004. Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring in this river segment. The sources of data for this assessment include (1) results of IDNR/UHL biological (REMAP) monitoring in 2002, (2) IDNR/UHL biological (Biocriteria) monitoring in 2004, and (3) results of IDNR/UHL ambient monthly water quality monitoring during the 2004-2006 assessment period at STORET station 10910002 (formerly station 426058) at the County Road R27 bridge SE of Norwalk.
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 (364 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Thirteen of the 24 samples (54%) 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).
The Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supported” based on results of biological monitoring conducted in 2002 and 2004 as part of DNR/UHL biocriteria and REMAP projects. 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 2002 REMAP FIBI score was 29 (fair) and the BMIBI score was 56 (good). The 2004 biocriteria FIBI score was 24 (poor) and the BMIBI score was 65 (good). The FIBI average (n=2) was 26.5 and the BMIBI average (n=2) was 60.5. The aquatic life use support was assessed as Partially Supporting (=PS), 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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This stream segment continues to exhibit movement into, and out of, the range of impairment of aquatic life uses especially the FIBI scores.
Despite the results of biological monitoring that show aquatic life uses to be only "partially supported," results of chemical/physical monitoring in this river segment continue to show relatively good water quality. None of the approximately 100 samples collected during the 2000-2002, 2002-2004, and the 2004-2006 assessment periods at this IDNR monthly ambient station violated Class B(WW1) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen. Also, no violations have occurred in the approximately 20 samples analyzed for toxic metals, pesticides and other toxic organic compounds over the 2000-2006 period.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
