East Nodaway River IA 05-NOD-1391

The Class A1 (primary contact recreation) uses are assessed (monitored) 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 2014 through 2016 at the East Nodaway River near Clarinda (STORET station 10730002) were as follows: the 2014 geometric mean was 467 orgs/100 ml, the 2015 geometric mean was 789 orgs/100 ml, and the 2016 geometric mean was 544 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Sixteen of the combined 24 samples (67%) 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."

Results of chemical/physical water quality monitoring at the East Nodaway River near Clarinda (STORET station 10730002) suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 0.8 mg/L), 36 Dissolved Oxygen samples (minimum = 7.1 mg/L), 36 pH samples (range = 7.3 to 8.6), 36 Temperature samples (maximum = 26.2 °C), 36 Chloride samples (maximum = 27 mg/L), or 36 Sulfate samples (maximum = 82 mg/L) occurred during monitoring from January 2014 to December 2016. 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(WW1) aquatic life uses.

Results of biological sampling, however, suggest that the Class B(WW1) uses should be assessed (evaluated) as "partially supported" based on DNR/SHL biocriteria sampling in 2004 and 2012. The 2004 FIBI score was 23 (poor) and the BMIBI score was 46 (fair). The 2012 FIBI score was 39 (fair) and the BMIBI score was 43 (fair). This suggests the aquatic life use support be assessed as partially supported (=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 31 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI BIC 1/2 times and passed the BMIBI BIC 0/2 times in the last 13 years.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years in a recent five year period to be considered “monitored”. This segment had multiple samples collected in the previous 13 years; however, the multiple samples were not collected during 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).

Fish consumption (Class HH) uses remain "not assessed" due to the lack of recent fish tissue monitoring in this river reach.