Assessment Comments
Assessment based on 2012 and 2013 IDNR/SHL biological sampling data: CBI = 69 and 55; CW BIC = 60.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) 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) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses remain "not assessed" (IR Category 3a) due to the lack of information upon which to base an assessment. The Class B(CW1) coldwater aquatic life uses are assessed (evaluated) as "partially supported" (IR Category 3b-c) based on results of biological monitoring in 2012 and 2013. Fish consumption uses remain "not assessed" (IR Category 3a) due to the lack of fish contaminant monitoring in this stream segment.
EXPLANATION: The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2012 and 2013 as part of the IDNR/SHL coldwater stream sampling project. A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 CBI score was 69 and the 2013 CBI score was 55. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI score with biological impairment criteria (BIC) established for the 2012 Section 305(b) report. The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011. The CW BIC is 60 and this segment passed the CW BIC 1/2 times in the last five years.
This aquatic life assessment is now considered "monitored" because there were two or more samples collected from this segment in the previous five years. However, this impairment is still considered "tentative" rather than "verified" because there was one passing CBI score and one failing CBI score. There was a 2005 sample collected in this segement but those data are now too old (>5 years) to adequately characterize the resource.
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.
