Ocheyedan River IA 06-LSR-1638

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at Ocheyedan River upstream of Spencer were as follows: the 2012 geometric mean was 149 orgs/100 ml, the 2013 geometric mean was 264 orgs/100 ml, and the 2014 geometric mean was 209 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Ten of the combined 22 samples (45%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (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 "partially supported".

The assessment of the Class B(WW2) aquatic life uses was based primarily on biological data collected in 2003, 2012 and 2013 as part of the DNR/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) and the 2013 BMIBI score was 45 (fair). 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 1/3 times in the last 14 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 DNR’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). DNR 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 DNR/SHL city station southwest of Spencer showed no violations of Class B(WW2) water quality criteria for 32 Ammonia samples (maximum = 1.7 mg/L), 33 Dissolved Oxygen samples (minimum = 5.4 mg/L), 32 pH samples (range = 7.5 to 8.6), 33 Temperature samples (maximum = 27.9° c), 33 Chloride samples (maximum = 38 mg/L), or 33 Sulfate samples (maximum = 300 mg/L) occurred during monitoring from January 2012 to September 2014. According to U.S.EPA guidelines for Section 305(b) water quality assessments (U.S.EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW2) aquatic life uses.