Assessment Comments
Assessment is based on: (1) results of IDNR/UHL biological (biocriteria) monitoring in 1998 & 2004 and (2) results of IDNR/UHL ambient chemical/physical monitoring upstream from Sac City from 2006-2008 at STORET station 10810002.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is also now presumptively designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) 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" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported” based on results of IDNR/UHL biological (biocriteria) sampling in 1998 and 2004. Results of IDNR/UHL ambient monitoring 2006 through 2008, however, suggest good chemical/physical water quality. 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 include (1) results of IDNR/UHL biological (biocriteria) monitoring in 1998 and 2004 and (2) results of IDNR/UHL ambient chemical/physical monitoring upstream from Sac City from 2006-2008 at STORET station 10810002.
Note: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by IDNR and approved by EPA in June 2008. Because this TMDL covers bacterial impairments, this impairment was moved from IR Category 5a from the 2008 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the current (2010) cycle.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) 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 22 samples collected (152 orgs/100ml) slightly exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Eight of the 22 samples (36%) 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 assessment of the Class B(WW1) aquatic life uses (evaluated; partially supported) was based on data collected in 1998 and 2004 as part of the IDNR/UHL stream biocriteria project. The 1998 FIBI score was 55 (good) and the BMIBI score was 61 (good). The 2004 FIBI score was 56 (good) and the BMIBI score was 45 (fair). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores 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 riffle habitat FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 0/2 times in the past 11 years.
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 between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous 11 years (1998-2008); however, the multiple samples were not collected during 2004-2008 and/or were not collected in multiple years. 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). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b and remains on Iowa’s 2010 Section 303(d) list of impaired waters.
In contrast, results of IDNR/UHL ambient chemical/physical water quality monitoring from 2006 through 2008 suggest relatively good water quality in this river segment. Results from this monitoring show no violations of Class B(WW1) criteria for dissolved oxygen, pH, or ammonia in the 34 samples collected, for toxic metals in the five samples collected, or in the three samples analyzed for pesticides. These results suggest relatively good water quality and do not suggest impairment of the Class B(WW1) aquatic life uses.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
