Assessment Comments
Assessment is based on results of (1) IDNR/SHL monthly ambient monitoring conducted during the 2010-2012 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)), (2) USGS monitoring from July to September of 2012, (3) IDNR/SHL stream REMAP biological sampling in 2006, and (4) fish tissue (RAFT) monitoring in 2007.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river segment was designated for Class B(WW) aquatic life uses, including fish consumption uses and for Class C (drinking water) 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 also now presumptively designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), for fish consumption uses (now termed Class HH (human health/fish consumption uses), and for Class C (drinking water) uses.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 5p) due to high levels of indicator bacteria (E. coli). The results of the water quality sampling indicate that the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported"; however, the 2006 biological sampling data indicate the Class B(WW1) aquatic life uses should be assessed (evaluated) as "partially supporting" (IR 3b-u). The Class C (drinking water) uses are assessed (monitored) as "fully supported” (IR 2a). Fish consumption uses are assessed (monitored) as “fully supported” (IR 2a) based on fish contaminant monitoring in 2007. This assessment is based on (1) results IDNR/SHL monthly ambient monitoring conducted during the 2010-2012 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)), (2) results of monitoring for nitrate by USGS at station 06817000 near Shambaugh from June-September of 2012, (3) IDNR/SHL stream REMAP biological sampling in 2006, and (4) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2007 south of Shambaugh.
EXPLANATION: The 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 the West Nodaway River near Shambaugh were as follows: the 2010 geometric mean was 1,007 orgs/100 ml, the 2011 geometric mean was 646 orgs/100 ml, and the 2012 geometric mean was 1,920 orgs/100 ml. All three geometric means far exceed the Class A1 criterion of 126 orgs/100 ml. Twenty-one of the 24 samples (88%) 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.” Note: The February 2010 version of the Iowa surface water classification shows at least portions of this river segment designated for Class A2 (secondary contact recreation) uses. This state-level designation, however, has not yet been approved by U.S. EPA. Even if this segment was reclassified as Class A2, the impairment would remains as the geometric means in 2010 and 2012 far exceed the Class A2 criterion of 630 orgs/100 ml.
Regarding support of the Class B(WW1) aquatic life uses, results of ambient monitoring at the IDNR/SHL station near Shambaugh showed no violations of Class B(WW1) water quality criteria during the 2010-2012 assessment period for dissolved oxygen (minimum value = 6.0 mg/l), pH (range: 7.4-8.9 units), or ammonia-nitrogen (maximum value = 0.36 mg/l) in the approximately 34 samples collected. These results suggest "full support" of the Class B(WW1) aquatic life uses.
However, the 2006 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 31 (fair) and the BMIBI score was 25 (poor). 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 36 and the BMIBI BIC for this ecoregion is 54. This assessment is considered evaluated because the drainage area (779 mi2) above this sampling site 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 (using the uncertainty adjustment value of 7 points applied to single samples) and failed to meet the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’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 seven samples (14%) analyzed during the 2010-12 assessment period (maximum value = 4.6 ppb). The mean (0.76 ppb) and median (0.1 ppb) values of atrazine during the 2010-2012 period, however, were well-below the Class C criterion. The level of nitrate was below the Class C criterion of 10 mg/l (=EPA’s MCL) in all of the 36 samples collected by IDNR/SHL during the 2010-2012 assessment period (maximum value = 5.7 mg/l). The mean (4.0 ppm) and median (4.0 ppm) values of nitrate during the 2010-2012 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 (monitored) 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.
