Assessment Comments
Assessment remains based on results of (1) biological monitoring conducted by IDNR Fisheries in 2000 and (2) IDNR/UHL ambient water quality monitoring conducted in 2002 and 2003 in support of TMDL development.
Basis for Assessment
[Note Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.pdf) and due to the completion of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW2) uses).]
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (evaluated) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses remain assessed as “fully supported.” The sources of data for these assessments are (1) results of biological monitoring for fish conducted in 2002 by the IDNR Fisheries Bureau and (2) results of IDNR/UHL ambient water quality monitoring conducted during the 2002-2004 assessment period as part of TMDL monitoring (TMDL station 6; STORET station 11600005). Because the data upon which these assessments are based are now more than five years old, and because as data age beyond five years they are less able to represent current water quality conditions, the assessment type is changed from “monitored” (a higher confidence assessment) to “evaluated” (lower confidence assessment.)
EXPLANATION: The Class A1 uses remain assessed (evaluated) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the 18 samples collected at the IDNR/UHL TMDL monitoring station near Doon during summer recreational seasons of 2002-2003 (311 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Ten of the 18 samples (56%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supporting” based on data collected in 2000 as part of an IDNR Fisheries stream sampling project: Manchester research station. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2000 FIBI score was 62 (good). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 43 and this segment passed the FIBI BIC 1/1 times in 2000.
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 single sample collected in 2000. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Similarly, results of chemical/physical water quality monitoring conducted by IDNR/UHL from March 2002 through December 2003 in support of TMDL development suggest relatively good water quality in this stream and "full support" of aquatic life uses. None of the 21 samples collected had levels of dissolved oxygen, pH, or ammonia-nitrogen that violated state water quality standards (these samples were not analyzed for toxic metals or pesticides). These results, although somewhat limited in terms of parameter coverage, suggest "full support" of the Class B(WW2) aquatic life uses.
