Assessment Comments
Assessment is based on results of IDNR/SHL monthly ambient monitoring conducted during the 2010-2012 assessment period NE of Smithland (STORET station 10970001 (formerly station 911078)) and 2006, 2011 and 2012 IDNR/SHL stream biological sampling near Rodney and Smithland.
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 2006, 2011 and 2012 IDNR/SHL stream biological sampling. Results of ambient water quality monitoring from 2010 through 2012, however, suggest "full support" (IR 2a) of the Class B(WW1) aquatic life uses. Fish consumption uses remain "not assessed" (IR 3a) due to the lack of recent fish contaminant monitoring in this river segment. This assessment is based on results of (1) IDNR/SHL monthly ambient monitoring conducted during the 2010-2012 assessment period NE of Smithland (STORET station 10970001 (formerly station 911078)) and (2) 2006, 2011 and 2012 IDNR/SHL stream biological sampling near Rodney and Smithland.
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 near Smithland were as follows: the 2010 geometric mean was 232 orgs/100 ml, the 2011 geometric mean was 69 orgs/100 ml, and the 2012 geometric mean was 148 orgs/100 ml. The 2010 and 2012 geometric means very slightly exceed the Class A1 criterion of 126 orgs/100 ml. Eight of the 24 samples (33%) 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/SHL ambient station northeast of Smithland showed no violations of Class B(WW1) water quality criteria for pH (range = 7.9 to 8.6), dissolved oxygen (minimum value = 7.2 mg/l) or ammonia nitrogen (maximum value = 0.39 mg/l) in the 36 monthly samples analyzed during the 2010-2012 period. Similar to the previous assessment periods, these results suggest "full support" of the Class B(WW1) aquatic life uses.
However, the results of the 2006, 2011 and 2012 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, 2011 and 2012 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 BMIBI score was 34 (fair) and the 2012 BMIBI score was 55 (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 1994-2008. 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 (2/3), 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 a lack of recent fish contaminant monitoring in this river segment.
