Assessment Comments
Assessment remains based on: (1) the results of monitoring for indicator bacteria conducted at Site 16 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010 and (2) results of IDNR/SHL biological monitoring in 2005. EPA approval of Class A3 UAA recommendation moves the bacterial impairment to Category 5a of Iowa's Integrated Report.
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, and due to the completion of a Use Attainability Analysis, this segment is also now designated for Class A3 (children’s contact recreation) and for 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: Both the Class A3 (children’s contact recreation) uses and the Class A2 (secondary contact recreation) uses are assessed as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The impairment of the Class A2 (secondary contact recreation) uses is a new impairment for this assessment segment. The Class B(CW1) coldwater aquatic life uses are assessed (evaluated) as “partially supported" based on results of biological monitoring conducted in 2005. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment. The sources of data for this assessment are (1) the results of monitoring for indicator bacteria conducted at Site 16 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910009) from April 2008 through October 2010 and (2) results of biological monitoring conducted in 2005 as part of the IDNR/UHL stream biocriteria project.
EXPLANATION: The Class A3 (children’s contact recreation) uses and the Class A2 (secondary contact recreation) uses are assessed (monitored) as “not supported” (impaired) due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at UIRW Site 16 were as follows: the 2008 geometric mean was 774 orgs/100 ml, the 2009 geometric mean was 227 orgs/100 ml and the 2010 geometric mean was 2183 orgs/100 ml. All three geometric means exceed the Class A3 criterion of 126 orgs/100 ml; the 2008 and 2010 geometric means exceed the Class A2 geometric mean criterion of 630 orgs/100 ml. Sixteen of the 21 samples (76%) exceeded the Class A3 single-sample maximum criterion of 235 orgs/100 ml; five of the 21 samples (24%) exceeded the Class A2 single-sample maximum criterion of 2,880 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).
The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2005 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 2005 CBI score was 51. 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 0/1 times in 2005.
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 in a five-year period to be considered “monitored”. This segment had a single sample collected in 2005. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
In contrast to the benthic macroinvertebrate sampling, the updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2011, suggests the Class B(CW1) uses be assessed as "fully supported". According to the updated summary, Trout Creek (aka Trout Run) is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of brown trout without any stocking.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
