Assessment Comments
Assessment is based on the results of monthly chemical/physical monitoring from 2008 through 2010 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 2008 through 2010, 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 2008 through 2010 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 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at the Little Sioux River downstream of Spencer were as follows: the 2008 geometric mean was 262 orgs/100 ml, the 2009 geometric mean was 502 orgs/100 ml and the 2010 geometric mean was 443 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Fifteen of the 21 samples (71%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
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 = 7.2 to 8.6), dissolved oxygen (minimum value = 6.7 mg/l) or ammonia nitrogen (maximum value = 0.13 mg/l) in the 32 samples analyzed during the 2006-2008 period. (Note: pesticides and toxic metals were not monitored at this site during the 2008-2010 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 48 (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.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years to be considered “monitored”. This segment had multiple a single sample collected in 2005. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5a based on the bacteria impairment.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring data for this river segment.
