Assessment Comments
Assessment is based on results of (1) IDNR bacterial monitoring near Stone City conducted for the city/county beach monitoring program from 2008-10, (2) 2006 IDNR/UHL stream REMAP biological sampling, (3) IDNR Fisheries Bureau fish sampling in 2003 and (4) U.S. EPA/IDNR fish contaminant monitoring in 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” based on high levels of indicator bacteria from IDNR sampling from 2008 through 2010 near Stone City (STORET station 15530001). The Class B(WW1) aquatic life uses remain assessed (evaluated) as "fully supported" based on the IDNR/UHL stream REMAP biological sampling conducted in 2006 and IDNR Fisheries Bureau sampling in 2003. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of U.S. EPA/IDNR fish contaminant monitoring in 2006.
EXPLANATION: The Class A1 uses are assessed (monitored) as "not supported" based on violations of state criteria for indicator bacteria (E. coli). Results of IDNR bacteria monitoring conducted near Stone City as part of the city/county beach program during recreational seasons of 2008 through 2010 suggest high levels of E. coli in this river segment. The geometric means of indicator bacteria (E. coli) in the 19 samples collected during the recreational seasons of 2008 through 2010 were as follows: the 2008 geometric mean was 430 orgs/100 ml, the 2009 geometric mean was 470 orgs/100 ml and the 2010 geometric mean was 446 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. From 50 to 67% of the exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml during the three recreation seasons. 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 “not supported.”
The Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supported” based on data collected in 2006 as part of the DNR/UHL 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 65 (good) and the BMIBI score was 48 (fair). The IDNR Fisheries Bureau 2003 FIBI score was 50 (fair). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 1994-2004. The non-riffle habitat FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52. This assessment is considered evaluated because the drainage areas (1306 and 1263 mi2) above these sampling sites are greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed both the FIBI BIC and BMIBI BIC (using the UAV of 8 points), 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.
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Central City in 2006. The composite sample of fillets from channel catfish had low levels of contaminants. Levels of primary contaminants were as follows: mercury: 0.263 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 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 levels of contaminants in the sample analyzed for the 2006 RAFT program do not exceed any of the new (2006) advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
