Assessment Comments
Assessment is based on: (1) results of monitoring for indicator bacteria conducted at Site 26 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010, (2) results of IDNR/SHL biological monitoring in 2003 and 2011 and (3) an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011.
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)).] This stream segment is identified as an Outstanding Iowa Water under the antidegradation policy in the Iowa Water Quality Standards.
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The presumptive Class A2 (secondary contact recreation) uses are also assessed (monitored) as “not supported”; this is a new impairment for this assessment segment. The Class B(CW1) coldwater aquatic life uses are assessed (evaluated) as "fully supported" based on results of biological monitoring in 2003 and 2011. Fish consumption uses remain “not assessed” due to lack of fish contaminant monitoring in this stream segment. Sources of data for this assessment include (1) results of monitoring for indicator bacteria conducted at Site 26 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 190050003) from April 2008 through October 2010, (2) results of DNR/SHL biological monitoring in 2003 and 2011, and (3) results of a 2011 trout reproduction survey.
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 mean of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at UIRW Site 26 were as follows: the 2008 geometric mean was 159 orgs/100 ml, the 2009 geometric mean was 139 orgs/100 ml and the 2010 geometric mean was 669 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Although the 2008 and 2009 geometric means meet the Class A2 geometric mean criterion of 630 orgs/100 ml, the 2010 geometric mean (669 orgs/100 ml) slightly exceeds this criterion. Ten of the 21 samples (48%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; 2 of the 21 samples (10%) 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 2003 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 2003 CBI scores were 75 and 82. The 2011 CBI score was 48. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 2/3 times in a nine-year period.
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 multiple samples collected in a nine-year period (2003-2011). Despite this change in assessment methodology and type, this waterbody was placed in IR Category 2a.
In addition, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011, also suggests the Class B(CW1) uses are "fully supported". According to the updated summary, Waterloo 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 fairly consistent natural reproduction and maintain a viable population of brown trout without any stocking. This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this assessment segment.
