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 2010 through October 2012.
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 are assessed (monitored) as “partially supported” due to levels of indicator bacteria that exceed state water quality criteria (IR 5p). 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 2010 through October 2012.
The Class A1 (primary contact recreation) uses are assessed as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the 19 samples collected during the recreational seasons of 2010 through 2012 at the IDNR ambient monitoring station UIRW 25 exceeded the Iowa water quality criterion to protect primary contact recreation uses. Two of the three recreation season (March-November) geometric means from 2010-12 slightly exceeded Iowa’s Class A1 water quality criterion of 126 orgs/100 ml: the 2010 geometric mean was 409 orgs/100 ml, and the 2012 geometric mean was 131 orgs/100 ml. The 2011 geometric mean (75 orgs/100 ml), however, was well below the Class A1 geometric mean criterion. Six of the 19 samples (42%) 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 should be assessed as "impaired" (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. Monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 25 included analysis for ammonia. None of the 20 samples collected violated the ph/temperature-dependent aquatic life criteria for ammonia with ammonia levels all 20 samples being reported as less than the analytical level of detection (0.05 mg/l).
