Nodaway River (aka West Nodaway R.) IA 05-NOD-1389

The presumptive 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 2012 through 2014 at the West Nodaway River near Shambaugh were as follows: the 2012 geometric mean was 1920 orgs/100 ml, the 2013 geometric mean was 1040 orgs/100 ml, and the 2014 geometric mean was 1505 orgs/100 ml.  All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Nineteen of the combined 24 samples (79%) 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 IDNR’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 "not supported."

Results of chemical/physical water quality monitoring at the West Nodaway River near Shambaugh suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 0.8 mg/L), 36 Dissolved Oxygen samples (minimum = 6 mg/L), 35 pH samples (range = 7.2 to 8.9), 36 Temperature samples (maximum = 28.1° c), 36 Chloride samples (maximum = 22 mg/L), or 36 Sulfate samples (maximum = 37 mg/L) occurred during monitoring from January 2012 to December 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(WW1) aquatic life uses.

However, the 2006 and 2013 biological sampling suggest that the Class B(WW1) aquatic life uses should be assessed (evaluated) as “partially supported.” This evaluated biological assessment was based on data collected in 2006 as part of the IDNR/SHL stream REMAP project. A series of biological metrics that 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 2006 FIBI score was 34 (fair) and the BMIBI score was 25 (poor). The 2013 BMIBI score was 31 (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 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 assessment is considered evaluated because the drainage area (777 and 779 mi2) above the sampling sites was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC and failed to meet the BMIBI BIC (0/2), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don’t fall in the calibrated watershed size.  Also, 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).

The Class C (drinking water) uses are also assessed (monitored) as "fully supported." Levels of atrazine exceeded the Class C criterion of 3 ppb (=EPA’s MCL) in one of the 26 samples (4%) analyzed during the 2012-14 assessment period (maximum value = 4.6 ppb).The mean (0.39 ppb) and median (0.1 ppb) values of atrazine during the 2012-2014 period, however, were well-below the Class C criterion. The level of nitrate exceeded the Class C criterion of 10 mg/l (=EPA’s MCL) in 2 of the 36 samples collected by IDNR/SHL during the 2012-2014 assessment period (maximum value = 12 mg/l). The mean (3.6 ppm) and median (3.1 ppm) values of nitrate during the 2012-2014 period are also well-below the Class C criterion. Levels of nitrate were also below the Class C criterion in eight samples collected by USGS from July to September of 2012 (maximum value = 5.9 mg/l). According to IDNR guidelines for Section 305(b) assessments, these results suggest "full support" of drinking water uses for this assessment segment.

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at the Nodaway River south of Shambaugh in 2007. The composite samples of fillets from channel catfish had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.087 ppm; total PCBs: <0.09 ppm; and technical chlordane: 0.068 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2007 RAFT sampling conducted at this river segment show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.