Assessment Comments
Assessment is based on results of monitoring for indicator bacteria conducted at Site 25 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is also now presumptively 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 presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The Class B(WW1) aquatic life uses remain “not assessed” due to the lack of water quality information upon which to base an assessment. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this assessment segment. The source of data for this assessment is the results of monitoring for indicator bacteria conducted at Site 25 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 190050002) from April 2008 through October 2010.
The Class A1 (primary contact recreation) uses are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at the IDNR ambient monitoring station UIRW 25 exceeded the Iowa water quality criterion to protect primary contact recreation uses. One of the three recreation season (March-November) geometric means from 2008-10 based on the these 21 samples was above Iowa’s Class A1 water quality criterion of 126 orgs/100 ml: the 2010 geometric mean was 409 orgs/100 ml. The 2008 and 2009 geometric means, however, were below the Class A1 geometric mean criterion: the 2008 geometric mean was 114 orgs/100 ml and the 2009 geometric mean was 100 orgs/100 ml. Nine of the 21 samples (43%) exceeded Iowa’s 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 is greater than the water quality criterion of 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW1) warmwater aquatic life uses and the fish consumption uses remain “not assessed” due to the lack of water quality information upon which to base an assessment.
