Assessment Comments
Assessment remains based on 1997 IDNR/UHL biological monitoring data: FIBI = 44, 35 (fair); BMIBI = 64, 70 (good). FIBI BIC = 43, BMIBI BIC = 54.
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(WW-2) aquatic life uses are assessed (evaluated) as partially supported based on results of IDNR/UHL biological (biocriteria) sampling in 1997. The 1997 sampling data are now greater than five years old; therefore, this assessment is now considered "evaluated" instead of "monitored".
EXPLANATION: The assessment was based on results of IDNR/UHL biological sampling in 1997. Sampling was conducted at two sites on this river segment. The FIBI scores were 44 and 35 (both fair); the BMIBI scores were 64 and 70 (both good). The aquatic life use support was assessed (evaluated) 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 FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI BIC 1/2 times and passed the BMIBI BIC 2/2 times in 1997.
The IDNR placed this segment in Category 4c instead of 3b or 5b for the following reasons:
1) the data are now more then five years old and are now unreliable for determining the current biological condition;
2) the benthic macroinvertebrate data indicate good water quality and score 13 points higher than the ecoregion BMIBI BIC and;
3) even though the fish data score marginally lower than the ecoregion FIBI BIC, after evaluating the habitat data, it was concluded that habitat alterations/hydromodification most likely led to the decreased FIBI scores.
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 1997; however, the multiple samples were not collected during 2004-2008 and were not collected in multiple years. 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). 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 4c based on previous Section 305(b) IR assessments.
