Assessment Comments
Assessment is based on 2000, 2005 and 2010 IDNR/UHL biological monitoring data: FIBI = 29, 30, 39 (fair) and 57 (good); BMIBI = 32, 45 (fair) and 74 (good) (non-riffle habitat FIBI BIC = 32; BMIBI BIC = 62) and on results of bacteria monitoring conducted as part of a Section 319 project from June 2009 to October 2010.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream 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, and due to the completion of a Use Attainability Analysis in 2007, this segment is now designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this assessment segment. The source of data for this assessment is the results of monitoring at one site (EBIR8) conducted as part of a Clean Water Act Section 319 water quality project from June 2009 through October 2010. The Class B(WW-2) aquatic life uses are assessed (evaluated) as "partially supported" based on results of IDNR/UHL biological (biocriteria) sampling in 2000 and 2005.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as “not supported" (IR Category 5p) due to levels of indicator bacteria (E. coli) that exceed the Class A1 geometric mean criterion. The geometric means of indicator bacteria (E. coli) in the 19 samples collected during the recreational seasons of 2009 and 2010 at the Section 319 monitoring station EBIR8 were 436 and 432 orgs/100 ml, respectively. Both of these recreation season geometric means exceed Iowa’s Class A1 geometric mean criterion of 126 E. coli orgs/100 ml, thus indicating nonsupport of the Class A1 primary contact recreation uses. Eleven of the 19 samples (58%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 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 is greater than the respective criterion (126 orgs/100 ml for Class A1, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW2) aquatic life uses were assessed (evaluated) as “partially supported” based on biological data collected at two sites in 2000 and one site in 2005 and 2010 as part of the IDNR/UHL stream biocriteria projects. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and 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) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2000 FIBI scores were 29 and 39 (fair) and the 2000 BMIBI scores were 32 and 45 (fair). The 2005 FIBI score was 30 (fair). The 2010 FIBI score was 57 (good) and the BMIBI score was 74 (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 1994-2004. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC 2/4 times and passed the BMIBI BIC 1/3 times in the last 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 over a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 11 years (2000-2010); however, the multiple samples were not collected during a five-year period. 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 Section 303(d) list of impaired waters as biologically impaired.
