Assessment Comments
Assessment is based on (1) 2005 and 2011 IDNR/SHL biological sampling and (2) results of monitoring at Site 12 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(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 are assessed (monitored) as “not supported.” This is a new impairment for this assessment segment. The presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported.” The Class B(CW1) coldwater aquatic life uses remain assessed (evaluated) as "partially supported" based on results of biological monitoring. The sources of data for this assessment include (1) results of IDNR/SHL biological monitoring from 2005 and (2) the results of monitoring for indicator bacteria conducted at Site 12 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910006) from April 2008 through October 2010. Fish consumption uses remain “not assessed” due to lack of fish contaminant monitoring in this stream segment.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as not supported based on levels of indicator bacteria that exceeded state water quality criteria while the presumptive Class A2 (secondary contact recreation) uses are assessed as "fully supported". The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at UIRW Site 12 were as follows: the 2008 geometric mean was 133 orgs/100 ml, the 2009 geometric mean was 69 orgs/100 ml and the 2010 geometric mean was 239 orgs/100 ml. Two of the three geometric means (2008 and 2010) slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2009 geometric mean is far below the Class A1 criterion of 126 orgs/100 ml. All three geometric means are well below the Class A2 geometric mean criterion of 630 orgs/100 ml. Six of the 21 samples (29%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; only one of the 21 samples (5%) 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); thus, the presumptive Class A1 (primary contact recreation) uses are assessed as “not supported.
The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2005 and 2011 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 61 and the 2011 CBI score was 50. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI scores 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 a seven-year period (2005-2011).
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 five-year period to be considered “monitored”. This segment had a mulitple samples collected in a seven-year period (2005-2011). 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). Despite this change in assessment methodology and type, this waterbody remains in IR Category 5b and remains on Iowa’s 2012 Section 303(d) list of impaired waters.
