Assessment Comments
Assessment remains based on 2005 IDNR/UHL biological monitoring data: FIBI = 18 (poor), BMIBI = 58 (good). FIBI BIC = 33; BMIBI BIC = 41.
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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively 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 (2010) 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 remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of biological (REMAP) monitoring in 2005. Sources of data for this assessment include (1) IDNR/UHL biological monitoring conducted in 2005 as part of the REMAP project and (2) ambient water quality monitoring conducted by the U.S. Geological Survey in 1998 and 1999. Note: monitoring was again conducted by USGS in this assessment segment beginning in 2009. These data, along with any subsequent data collected in 2010, will be used to develop the 2012 Section 305(b) assessment.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information for the assessment period (2006-2008) upon which to base an assessment. Historically, the monitoring conducted in this assessment segment has not included analysis for indicator bacteria.
The assessment of the Class B(WW2) aquatic life uses remains based on data collected in 2005 as part of the DNR/UHL stream REMAP project. A series of biological metrics which reflect 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 and fish species 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 2005 FIBI score was 18 (poor) and the BMIBI score was 58 (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 FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. 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.
Despite results of biological monitoring that suggest impairment, results of chemical/physical monitoring conducted in 1998 and 1999 suggest "full support" of the Class B(WW2) aquatic life uses. This assessment is based on chemical water quality monitoring conducted in 1998 and 1999 by the U.S. Geological Survey at two stations (Milton and Mount Sterling) (see May et al. 1999 and Nalley et al. 2000). USGS monitoring in 1998 and 1999 showed no violations of Class B(WW2) water quality criteria for dissolved oxygen, pH, and ammonia-nitrogen in the approximately 12 samples collected at the Milton and Mt. Sterling stations. Of the 12 samples analyzed for toxic metals, one sample at each station exceeded a state water quality criterion. The samples collected on June 10, 1999 at Milton (60 ug/l) and June 11, 1999 at Mt. Sterling (100 ug/) both exceeded the Class B(WW2) chronic water quality criterion for copper (55 ug/l). These samples were collected during a high flow event on the Fox River; the June 10 stream flow at the Milton station was 259 cfs; the June 11 stream flow at the Mt. Sterling station was 1010 cfs. According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), this one violation of a toxic contaminant does not suggest an impairment of the aquatic life uses. Although not designated for Class C (drinking water) uses, from 40 to 50 percent of the 10 samples from each station analyzed for pesticides exceeded the U.S. EPA MCL for atrazine of 3.0 ug/l. None of the approximately 12 samples at each station exceeded the nitrate MCL of 10.0 mg/l.
