Assessment Comments
Assessment based on: (1) the results of monitoring for indicator bacteria conducted at Site 20 of the Upper Iowa River Watershed (UIRW) project from April 2010 through October 2012 and (2) results of IDNR/SHL biological sampling in 2003 & 2011.
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 assessed (evaluated) as “fully supported” (IR 2a) based on results of biological sampling in 2003 & 2011. Fish consumption uses remain “not assessed” (IR 3a) due to the lack of fish contaminant monitoring in this assessment segment. The sources of data for this assessment include (1) the results of monitoring for indicator bacteria conducted at Site 20 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910013) from April 2010 through October 2012 and (2) results of IDNR/SHL biological sampling in 2003 & 2011.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 19 samples collected during the recreational seasons of 2008 through 2010 at UIRW Site 20 were as follows: the 2010 geometric mean was 262 orgs/100 ml, the 2011 geometric mean was 36 orgs/100 ml and the 2012 geometric mean was 346 orgs/100 ml. Two of the three geometric means (2010 and 2012) slightly exceeded the Class A1 geometric mean criterion. Seven of the 19 samples (37%) 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) aquatic life uses remain assessed (evaluated) as “fully supported” based on biological data collected in 2003 and 2011 as part of the IDNR/SHL stream biocriteria project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2003 FIBI score was 77 (excellent) and the BMIBI score was 81 (excellent). The 2011 FIBI score was 77 (excellent) and the BMIBI score was 79 (excellent). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI and BMIBI BICs 2/2 times in the last 10 years.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a recent five-year period to be considered “monitored”. This segment had multiple samples collected in a 10 year period (2003-2012). The assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 20 included analysis for ammonia. Of the 20 samples collected, 19 samples contained less than the limit of detection (0.05 mg/l); the one detected sample contained 0.06 mg/l of ammonia. This level is well below any Class B(CW1) aquatic life criterion for ammonia. These results do not suggest impairment of the Class B(CW1) aquatic life uses.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this assessment segment.
