Assessment Comments
Assessment is based on: (1) IDNR/UHL REMAP sampling conducted in 2003, and (2) IDNR/UHL monthly ambient chemical/physical water quality monitoring conducted upstream from Spencer at the County Road M-38 bridge southwest of Spencer from January 2006 through December 2008 (STORET station 10210001 (formerly station 924003))
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 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 2008 and 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 are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of IDNR/UHL REMAP sampling conducted in 2003. The Class B(WW2) assessment is considered evaluated because of equipment failure by staff gathering the fish data. The equipment failure led to the use of only one backpack shocker on the site which averaged 63 feet in width. The partial support applies because the FIBI score failed to meet the FIBI BIC for this ecoregion. However, the results from IDNR/UHL monthly ambient chemical/physical water quality monitoring conducted upstream from Spencer at the County Road M-38 bridge southwest of Spencer from January 2006 through December 2008 (STORET station 10210001 (formerly station 924003)) suggest this segment is "fully supporting" the designated aquatic life use.
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 21 samples collected at the IDNR/UHL ambient monitoring station southwest of Spencer during summer recreational seasons of 2006-2008 (310 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Eleven of the 21 samples (52%) 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(WW2) aquatic life uses remains based primarily on biological data collected in 2003 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 biocriteria 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 2003 FIBI score was 28 (fair) and the BMIBI score was 47 (fair). The aquatic life use support was assessed (evaluated - see above) 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 aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. 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).
Conversely, the chemical/physical monitoring at the IDNR/UHL city station southwest of Spencer showed no violations of Class B(WW2) water quality criteria during the 2006-2008 assessment period for dissolved oxygen (minimum value = 7.0 mg/l), pH (range = 7.8 to 8.5 units), or ammonia-nitrogen (maximum value = 0.96) in the 33 samples analyzed. Levels of toxic metals in the 2 samples analyzed were all below their respective Class B(WW2) chronic criteria. (Note: pesticides were not monitored at this site from 2006 through 2008.) These results suggest "full support" of the Class B(WW2) aquatic life uses.
