Assessment Comments
Assessment based on: (1) the results of monitoring for indicator bacteria conducted at Site 19 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010 and (2) an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012.
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 are both assessed (monitored) as “not supported” (IR 5p) due to levels of indicator bacteria that exceed state water quality criteria. The Class B(CW1) coldwater aquatic life uses remain assessed (evaluated) as “fully supporting” (IR 2a) based on a summary of trout stream reproduction prepared by the IDNR Fisheries Bureau. Fish consumption uses remain “not assessed” (IR 3a) due to the lack of fish contaminant monitoring in this stream segment. The sources of data for this assessment include (1) the results of monitoring for indicator bacteria conducted at Site 19 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910012) from April 2010 through October 2012 and (2) an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012.
EXPLANATION: The Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses are both assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2010 through 2012 at UIRW Site 19 were as follows: the 2010 geometric mean was 1,683 orgs/100 ml, the 2011 geometric mean was 259 orgs/100 ml and the 2012 geometric mean was 932 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml; the 2010 and 2012 geometric means exceed the Class A2 geometric mean criterion of 630 orgs/100 ml. Seventeen of the 20 samples (85%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; three of the 20 samples (15%) 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 Class B(CW1) coldwater aquatic life uses are now considered “not assessed” due to the age of the biological data (greater than 10 years) upon which previous assessments (“fully supporting”) were based. In past IR cycles, the assessment of the Class B(CW1) aquatic life uses was based on data collected in 1999 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 1999 CBI score was 54. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 1/1 times in 1999. This segment passed the CBI using the eight CW UAV (uncertainty adjustment value) applied to single sample assessments. Additional biological monitoring is needed to update the aquatic life assessment for this stream segment.
An updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2012 suggests that the Class B(CW1) uses should be assessed as "fully supported". According to the updated summary, Coon Creek 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 recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for brown trout at this time (Category II stream). This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
Monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 19 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 0.12 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 lack of fish tissue monitoring in this stream segment.
