Assessment Comments

Assessment is based on results of USGS ambient water quality monitoring conducted on the Little Sioux near Turin from February 2008 to December 2010.

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 violations of Iowa’s water quality criteria for indicator bacteria.   This is a new impairment for this assessment segment.   The Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported” based on results of chemical water quality monitoring by USGS.   Fish consumption uses are “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 USGS ambient water quality monitoring conducted on the Little Sioux near Turin from February 2008 to December 2010.

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 15 samples collected during the recreational seasons of 2009 through 2010 at the Little Sioux River near Turin were as follows: the 2009 geometric mean was 2159 orgs/100 ml and the 2010 geometric mean was 924 orgs/100 ml.   Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Ten of the 15 samples (67%) 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.”  

The Class B(WW1) aquatic life uses were assessed (monitored) as "fully supported" based on results of water quality monitoring by the U.S.  Geological Survey near Turin from 2008-2010.   No violations of state water quality criteria occurred in the approximately 30 samples analyzed for dissolved oxygen (minimum = 5.2), pH (range = 7.2-8.5), and ammonia (maximum = 0.87 mg/L).   No violations for DDE occurred in the approximately 30 samples collected from 2008 through 2010.   There was however one violation of the Class B(WW1) criterion for dieldrin (3%) and one violation of the Class B(WW1) chronic criterion for chlorpyrifos (3%).   According to IDNR's assessment methodology these results are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(WW1) uses.   These results suggest that the Class B(WW1) aquatic life uses should be assessed as “full supporting.”

Note:  IDNR conducted monitoring in this assessment segment at station 10670003 from October to December in 2010.   Too few data were produced from this monitoring during the 2008-2010 assessment period (three samples) to be of use for assessment for purposes of either Section 305(b) reporting or Section 303(d) listing.

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river reach.