Black Hawk Creek IA 02-CED-546

[Note: A TMDL for indicator the bacteria impairments in the adjacent downstream segment of Black Hawk Creek (IA 02-CED-545) was approved by EPA in 2006. This TMDL, however, did not include the current segment (IA 02-CED-546); thus, this impairment is considered appropriate for Category 5p of Iowa's Integrated Report.]

The presumptive Class A1 uses remain assessed as "not supported" based on results of Section 319 monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2009 and 2010 at Section 319 monitoring station BHC 13 were as follows: the 2009 geometric mean was 1,195 orgs/100 ml and the 2010 geometric mean was 765 orgs/100 ml. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Eighteen of the 21 samples (86%) 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 DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the 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 “impaired.”

The Class B(WW1) aquatic life uses are assessed as “fully supporting” based on data collected in 2002, 2004 and 2012 as part of the DNR/SHL stream biocriteria project. The 2002 FIBI score was 61 (good) and the BMIBI score was 64 (good). The 2004 FIBI score was 44 (fair) and the BMIBI score was 41 (fair). The 2012 FIBI score was 60 (good) and the BMIBI score was 65 (good). The 2005 DNR Fisheries Bureau FIBI was 62 (good). The aquatic life use support was assessed as fully supporting (=FS), 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 1994-2008. 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 2/3 times in the past 15 years. This aquatic life use assessment would be considered "monitored" because there were two or more samples (FIBI) collected in multiple years in a five year period however, the data used for the assessment are now more than five years old. Old data can't accurately characterize current water quality conditions; therefore, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). This current assessment indicates that the aquatic life uses in this segment are fully supporting; however, because the assessment is evaluated, this waterbody remains in IR Category 5b-t.

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/DNR fish contaminant 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.