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 2008 through December 2010 (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" (IR Category 5p) 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" (IR Category 3b) 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 2008 through December 2010 (STORET station 10210001 (formerly station 924003)) suggest this segment is "fully supporting" the designated aquatic life use.
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 21 samples collected during the recreational seasons of 2008 through 2010 at Ocheyedan River upstream of Spencer were as follows: the 2008 geometric mean was 259 orgs/100 ml, the 2009 geometric mean was 184 orgs/100 ml and the 2010 geometric mean was 323 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Thirteen of the 21 samples (62%) 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 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 49 (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 segment failed the FIBI BIC and passed the BMIBI BIC (using the 8 point BMIBI uncertainty adjustment value applied to single sample assessments) in 2003.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years in a five year period. 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 2008-2010 assessment period for dissolved oxygen (minimum value = 7.2 mg/l), pH (range = 7.5 to 8.4 units), or ammonia-nitrogen (maximum value = 0.27) in the 32 samples analyzed. (Note: pesticides and toxic metals were not monitored at this site from 2008 through 2010.) These results suggest "full support" of the Class B(WW2) aquatic life uses.
