Assessment Comments
Assessment is based on the results of monthly chemical/physical monitoring from 2006 through 2008 at the IDNR/UHL ambient city monitoring station located downstream from Spencer at the County Road M50 bridge east of Spencer (STORET station 10210003) and 2005 IDNR/UHL stream REMAP biological sampling near Spencer.
Basis for Assessment
[Note: Prior to the 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. Based on results of ambient water quality monitoring from 2006 through 2008, the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported." However, results from the 2005 IDNR/UHL stream REMAP biological sampling indicate the Class B(WW1) aquatic life uses should be assessed (evaluated) as "partially supported." Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. The source of data for this assessment is the results of monthly chemical/physical monitoring from 2006 through 2008 at the IDNR/UHL ambient city monitoring station located downstream from Spencer at the County Road M50 bridge east of Spencer (STORET station 10210003) and 2005 IDNR/UHL stream REMAP biological sampling near Spencer.
EXPLANATION: The Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the 21 samples collected at the IDNR/UHL ambient monitoring station downstream from Spencer during summer recreational seasons of 2004-2006 (496 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Fifteen of the 21 samples (71%) 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 city station downstream from Spencer showed no violations of Class B(WW1) water quality criteria for pH (range = 7.8 to 8.5), dissolved oxygen (minimum value = 6.2 mg/l) or ammonia nitrogen (maximum value = 1.3 mg/l) in the 32 samples analyzed during the 2006-2008 period. In addition, levels of toxic metals in the two samples analyzed, were all below their respective Class B(WW1) criteria. (Note: pesticides were not monitored at this site during the 2006-2008 period.) These results suggest "full support" of the Class B(WW1) aquatic life uses.
However, the results from the 2005 IDNR/UHL stream REMAP biological sampling indicate the Class B(WW1) aquatic life uses should be assessed (evaluated) as "partially supported." This evaluated biological assessment was based on data collected in 2005 as part of the IDNR/UHL stream REMAP 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 2005 FIBI score was 32 (fair) and the BMIBI score was 49 (fair). 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 43 and the BMIBI BIC for this ecoregion is 54. This assessment is considered evaluated because the drainage area (1109 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. In addition to the large drainage area, the conditions at the time of sampling were not conducive to collecting a good fish sample. Sampling staff indicated the fish sample quality was only "fair" with excessive turbidy and width contributing to the poorer sampling conditions. Even though this site failed to meet the FIBI BIC and met the BMIBI BIC (with the aid of the BMIBI UAV of 8 points), 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 data for this river segment.
