Assessment Comments
Assessment remains based on (1) results of IDNR/UHL biological (biocriteria) sampling in 1996, 2002 and 2004, (2) results of IDNR/UHL ambient monthly water quality monitoring conducted from March to November 2001 and from April to September 2005 in support of TMDL development, (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2004 and (4) results of IDNR Fisheries Bureau fish sampling in 2005.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW) 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), 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), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life uses remain assessed (monitored) as "partially supported" based on results of IDNR/UHL biological (biocriteria) sampling in 2002 and 2004 and IDNR Fisheries Bureau sampling in 2005. This assessment is also based on results of IDNR/UHL ambient monthly water quality monitoring conducted from April to September 2005 in support of TMDL development. Note: no additional monitoring has been conducted at these stations since 2005. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2004.
Note: A TMDL for indicator the bacteria impairments in the adjacent downstream segment of Black Hawk Creek (IA 02-CED-0370_1) was approved by EPA in 2006. This TMDL, however, did not include the current segment (IA 02-CED-0370_2); thus, this impairment is considered appropriate for Category 5a of Iowa's 2010 Integrated Report.
EXPLANATION: The presumptive Class A1 uses remain assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean of the combined 16 samples from 2001 and 2005 (538 orgs/100 ml) far exceeds the Class A1 criterion of 126 orgs/100 ml, and fourteen of the 16 samples (88%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
The assessment of the Class B(WW1) aquatic life uses was based on data collected in 1996, 2002 and 2004 as part of the IDNR/UHL stream biocriteria project. The 1996 FIBI score was 51 (good) and the BMIBI score was 50 (fair). The 2002 FIBI score was 61 (good) and the BMIBI score was 63 (good). The 2004 FIBI score was 44 (fair) and the BMIBI score was 36 (fair). The 2005 IDNR Fisheries Bureau FIBI was 62 (good). The aquatic life use support was assessed as partially supporting (=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 1994-2004. The non-riffle FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52. This segment passed the FIBI BIC 4/4 times and passed the BMIBI BIC 1/3 times in the past 13 years. This aquatic life use assessment is considered "monitored" because there were two or more samples (FIBI) collected in multiple years from 2004-2008.
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Hudson in 2004. The composite samples of fillets from channel catfish and smallmouth bass had very low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.072 ppm; total PCBs: 0.092 ppm; and technical chlordane: 0.044 ppm. Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.098 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 do not exceed any of the Iowa advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory.
