Assessment Comments
Assessment is based on (1) IDNR/SHL REMAP biological sampling conducted in 2003, (2) IDNR/SHL biological sampling conducted in 2012 and (3) IDNR/SHL monthly ambient chemical/physical water quality monitoring conducted upstream from Spencer at the County Road M-38 bridge southwest of Spencer from January 2010 through December 2012 (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 current 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" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed (evaluated) as "partially supported" (IR 3b-c) based on results of IDNR/SHL conducted in 2003 and 2012. However, the results from IDNR/SHL monthly ambient chemical/physical water quality monitoring conducted upstream from Spencer at the County Road M-38 bridge southwest of Spencer from January 2010 through December 2012 (STORET station 10210001 (formerly station 924003)) suggest that the aquatic life uses of this segment should be assessed as "fully supporting".
EXPLANATION: The presumptive Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at Ocheyedan River upstream of Spencer were as follows: the 2010 geometric mean was 323 orgs/100 ml, the 2011 geometric mean was 143 orgs/100 ml and the 2012 geometric mean was 149 orgs/100 ml. All three geometric means very slightly exceed the Class A1 criterion of 126 orgs/100 ml. Ten of the 24 samples (42%) 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 IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (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.”
The assessment of the Class B(WW2) aquatic life uses remains based primarily on biological data collected in 2003 and 2012 as part of the IDNR/SHL REMAP and large river sampling 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 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 49 (fair). The 2012 BMIBI score was 61 (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 1994-2008. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This segment failed the FIBI BIC in 2003 and passed the BMIBI BIC 1/2 times in the last 10 years.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years in a recent 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).
Conversely, the chemical/physical monitoring at the IDNR/SHL city station southwest of Spencer showed no violations of Class B(WW2) water quality criteria during the 2010-2012 assessment period for dissolved oxygen (minimum value = 7.3 mg/l), pH (range = 7.5 to 8.6 units), temperature (maximum = 27.9C), or ammonia-nitrogen (maximum value = 0.27) in the approximately 36 samples analyzed. None of the 36 samples analyzed for chloride or sulfate violated the respective Class B(WW2) criteria. These results suggest "full support" of the Class B(WW2) aquatic life uses.
