Assessment Comments
Assessment is based on results of monthly monitoring from 2008 through 2010 at the IDNR/UHL ambient city monitoring station located upstream from Spencer at the Highway 18 bridge northwest of Spencer (STORET station 10210002).
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. The Class B(WW1) aquatic life uses remain assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2008 through 2010. 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 monitoring from 2008 through 2010 at the IDNR/UHL ambient city monitoring station located upstream from Spencer at the Highway 18 bridge northwest of Spencer (STORET station 10210002).
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 upstream of Spencer were as follows: the 2008 geometric mean was 283 orgs/100 ml, the 2009 geometric mean was 464 orgs/100 ml and the 2010 geometric mean was 233 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.”
The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring. Monitoring at the IDNR/UHL city station upstream from Spencer showed no violations of Class B(WW1) water quality criteria for pH (range = 7.6 - 8.6), dissolved oxygen (minimum = 6.3 mg/L) or ammonia-nitrogen (maximum = 0.12 mg/L) in the 32 samples collected from 2008 through 2010. (Note: samples were not collected for pesticides or toxic metals at this site from 2008 to 2010.) These results suggest the Class B(WW1) aquatic life uses should be assessed as “fully supported.”
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring data for this river segment.
