Assessment Comments
Assessment is based on the results of (1) monthly chemical/physical monitoring from 2010 through 2012 at the IDNR/SHL ambient city monitoring station located downstream from Spencer at the County Road M50 bridge east of Spencer (STORET station 10210003), (2) 2005, 2012 and 2013 IDNR/SHL stream biological sampling near Spencer, and (3) Iowa DNR/U.S. EPA fish contaminant monitoring at Gillet Grove in 2011.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW1) aquatic life uses, including fish consumption 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) and the results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria. Based on results of ambient water quality monitoring from 2010 through 2012, the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported" (IR 2a). However, results from 2005, 2012 and 2013 IDNR/SHL REMAP and large river biological sampling indicate the Class B(WW1) aquatic life uses should be assessed (evaluated) as "partially supported" (IR 3b-u). Fish consumption uses are assessed as "fully supporting" (IR 2a) based on results of IDNR/U.S. EPA fish contaminant monitoring at Gillet Grove in 2011. The sources of data for this assessment are the results of monthly chemical/physical monitoring from 2010 through 2012 at the IDNR/SHL ambient city monitoring station located downstream from Spencer at the County Road M50 bridge east of Spencer (STORET station 10210003) and 2005, 2012 and 2013 IDNR/SHL REMAP and large river biological sampling near Spencer.
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 Little Sioux River downstream of Spencer were as follows: the 2010 geometric mean was 443 orgs/100 ml, the 2011 geometric mean was 382 orgs/100 ml, and the 2012 geometric mean was 1,181 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Eighteen of the 24 samples (75%) 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.”
Regarding support of the Class B(WW1) aquatic life uses, monitoring at the IDNR/UHL city station downstream from Spencer showed no violations of Class B(WW1) water quality criteria for pH (range = 7.2 to 8.7), dissolved oxygen (minimum value = 5.7 mg/l), temperature (maximum = 26.9C), ammonia nitrogen (maximum value = 0.36 mg/l), chloride, or sulfate in the approximately 36 samples analyzed during the 2010-2012 period. These results suggest "full support" of the Class B(WW1) aquatic life uses.
However, the results from the 2005, 2012 and 2013 IDNR/SHL REMAP and large river biological sampling indicate the Class B(WW1) aquatic life uses should be assessed (evaluated) as "partially supported." This evaluated biological assessment was based on data collected in 2005, 2012 and 2013 as part of the IDNR/SHL REMAP and large river sampling projects. 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 2005 FIBI score was 32 (fair) and the BMIBI score was 48 (fair). The 2012 BMIBI score was 54 (fair) and the 2013 BMIBI score was 44 (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 43 and the BMIBI BIC for this ecoregion is 54. This assessment is considered evaluated because the drainage areas (1104 and 1109 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. In addition to the large drainage area, the conditions at the time of sampling were not conducive to collecting a good fish sample. Sampling staff indicated the fish sample quality was only "fair" with excessive turbidy and width contributing to the poorer sampling conditions. Even though this site failed to meet the FIBI BIC (0/1) and failed the BMIBI BIC (1/3), 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. 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).
Fish consumption uses are assessed as "fully supported" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring at Gillet Grove in 2011. The composite sample of fillets from channel catfish had low levels of contaminants: mercury: 0.115 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 ppm. The average level of mercury in the tissue plugs from five largemouth bass was 0.289 ppm (SD=0.159). 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 levels of contaminants in the tissue samples from fish collected at Gillet Grove do not exceed any of Iowa’s consumption advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody. The average level of mercury in the tissue plug samples from largemouth bass (0.289 ppm), however, approached the one meal per week advisory threshold of 0.3 ppm, and thus additional monitoring will be conducted in this river segment to better define levels of mercury in predator fish.
