North Raccoon River IA 04-RAC-1139

[Note: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by DNR 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 2010 cycle and remains there for this cycle.]

The presumptive Class A1 uses are assessed as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at DNR station 10810002 upstream from Sac City were as follows: the 2012 geometric mean was 70 orgs/100 ml, the 2013 geometric mean was 148 orgs/100 ml, and the 2014 geometric mean was 274 orgs/100 ml. The 2013 and 2014 geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. Nine of the 22 samples (41%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired"(see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.” Note: results of ambient monitoring at DNR Station 10810002 have shown low levels of indicator bacteria (E. coli) over the last five Integrated Reporting cycles indicating a consistent pattern of relatively low levels of indicator in this river segment.

The assessment of the Class B(WW1) aquatic life uses (evaluated; partially supported) was based on data collected in 2004, 2012 and 2015 as part of the DNR/SHL stream biocriteria project. The 2004 FIBI score was 56 (good) and the BMIBI score was 44 (fair). The 2012 FIBI score was 24 (poor) and the BMIBI score was 57 (good).The 2015 FIBI score was 62 (good) and the BMIBI score was 62 (good).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 1994-2008. 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 2/3 times and passed the BMIBI BIC 1/3 times in the past 13 years.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years over a recent five-year period to be considered “monitored”. This segment had multiple samples collected in the previous five years (2012-2016); however, the 2004 sample results were needed to complete the assessment. According to DNR’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). DNR 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 was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).

Results of DNR/SHL ambient chemical/physical water quality monitoring at the Sac City station during the 2012-2014 assessment period, however, suggest relatively good water quality in this river segment. Results of this monitoring show no violations of Class B(WW1) (aquatic life) water quality criteria in the 33 samples analyzed for ammonia, pH, temperature, chloride, and sulfate. These results do not suggest impairment of the Class B(WW1) aquatic life uses.