Little Sioux River IA 06-LSR-1565

[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).]

The Class A1 (primary contact recreation) are assessed as "partially 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 2012 through 2014 at the Little Sioux River near Smithland were as follows: the 2012 geometric mean was 148 orgs/100 ml, the 2013 geometric mean was 120 orgs/100 ml, and the 2014 geometric mean was 159 orgs/100 ml.  Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Ten of the combined 24 samples (42%) exceeded Iowa’s 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 the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (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 "partially supported".

Regarding support of the Class B(WW1) aquatic life uses, monitoring at the IDNR/SHL ambient station northeast of Smithland showed no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 1.2 mg/L), 36 Dissolved Oxygen samples (minimum = 6.7 mg/L), 36 pH samples (range = 7.4 to 8.6), 36 Temperature samples (maximum = 28.9° c), 36 Chloride samples (maximum = 33 mg/L), or 36 Sulfate samples (maximum = 150 mg/L) occurred during monitoring from January 2012 to December 2014.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

However, the results of the 2006 and 2011-2014 IDNR/SHL REMAP and large river biological sampling near Rodney and Smithland suggest only "partial support" of the Class B(WW1) aquatic life uses.   This evaluated biological assessment was based on data collected in 2006 and 2011-2014 as part of the IDNR/SHL REMAP and large river projects.   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 2006 FIBI score was 12 (poor) and the BMIBI score was 69 (good).   The 2011-2014 BMIBI scores were 34, 54, 55 (all fair) and 68 (good).   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 1994-2008.   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 areas (2713 and 2687 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site failed to meet the FIBI BIC (0/1) and passed the BMIBI BIC (4/5), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don’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 a lack of recent fish contaminant monitoring in this river segment.