Assessment is based on results of monthly monitoring from January 2008 through December 2010 at the IDNR ambient monthly monitoring station located near Janesville in Bremer Co. (STORET station 10090001).
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW) 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, and due to the completion of a 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" based on results of ambient monitoring for indicator bacteria during recreational seasons of 2008 through 2010. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient 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 January 2008 through December 2010 at the IDNR ambient monthly monitoring station located near Janesville in Bremer Co. (STORET station 10090001). Note: USGS conducted monitoring at station 05458500 near Janesville in October 2010. Too few data were produced from this monitoring during the 2008-2010 assessment period (one sample) to be of use for assessment for purposes of either Section 305(b) reporting or Section 303(d) listing.
The Class A1 uses are assessed (monitored) as "not supported.” The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10090001 near Janesville were as follows: the 2008 geometric mean was 133 orgs/100 ml, the 2009 geometric mean was 32 orgs/100 ml and the 2010 geometric mean was 70 orgs/100 ml. Only the 2010 geometric mean exceeds the Class A1 criterion of 126 orgs/100 ml, and the geometric mean (133 orgs/100 ml) is probably not statistically different from the Class A1 criterion of 126 orgs/100 ml. The geometric means for the recreation seasons of 2008 and 2009 are well below the Class A1 criterion. Four of the 22 samples (18%) 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.” Despite the 2010 and 2012 assessments of the Class A1 uses as impaired, this river segment has a history of low E. coli levels, and the monitoring results from the 2008-2010 assessment period are consistent with that history.
The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of monitoring from the IDNR ambient station near Janesville from 2008 through 2010. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 33 samples collected during this assessment period.
Fish consumption uses remain not assessed due to the lack of recent fish tissue monitoring in this river segment.