Assessment Comments
Assessment based on results of monthly monitoring from 2010 through 2012 at the IDNR/SHL ambient city monitoring station located upstream from Spencer at the Highway 18 bridge northwest of Spencer (STORET station 10210002) and on 2012 IDNR/SHL 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" (IR 5a) 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" (IR 3b-u)based on results of IDNR/SHL biological sampling conducted in 2012. Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river segment The sources of data for this assessment is the results of monthly monitoring from 2010 through 2012 at the IDNR/SHL ambient city monitoring station located upstream from Spencer at the Highway 18 bridge northwest of Spencer (STORET station 10210002) and 2012 IDNR/SHL 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 24 samples collected during the recreational seasons of 2010 through 2012 at the Little Sioux River upstream of Spencer were as follows: the 2010 geometric mean was 233 orgs/100 ml, the 2011 geometric mean was 168 orgs/100 ml and the 2012 geometric mean was 112 orgs/100 ml. All three geometric means very slightly exceed the Class A1 criterion of 126 orgs/100 ml. Fourteen of the 24 samples (58%) 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.”
Based exclusively on the results of ambient water quality monitoring, Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported" . Monitoring at the IDNR/SHL city station upstream from Spencer showed no violations of Class B(WW1) water quality criteria for pH (range = 7.6 - 8.9), dissolved oxygen (minimum = 5.9 mg/L), temparature (maximum - 28.7C), ammonia-nitrogen (maximum = 0.58 mg/L), chloride, or sulfate in the approximately 36 samples collected from 2010 through 2012. These results suggest the Class B(WW1) aquatic life uses should be assessed as “fully supported.”
In contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the aquatic life uses are "partially supporting". This evaluated biological assessment was based on data collected in 2012 as part of the IDNR/SHL large river sampling project. A series of biological metrics that 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 collected in the stream sampling reach. The biological metrics were combined a benthic macroinvertebrate index (BMIBI). The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 BMIBI score was 31 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 54. This assessment is considered evaluated because the drainage area (536 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 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. 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).
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring data for this river segment.
