Assessment Comments

Assessment is based on: (1) results monthly monitoring from January 2008 through December 2010 at the IDNR ambient station at Ridgeway Avenue SW of Waterloo (station 10070004), (2) results of IDNR/UHL TMDL-related monitoring conducted in 2005 at Waterloo (station 11700005), and (3) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2004 near Hudson.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to continued high levels of indicator bacteria that violate state water quality standards.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring.   Fish consumption uses remain assessed (evaluated) as "fully supported" based on results of fish contaminant monitoring in 2004.   Sources of data for this assessment include (1) results monthly monitoring from January 2008 through December 2010 at the IDNR ambient station at Ridgeway Avenue SW of Waterloo (station 10070004), (2) results of IDNR/UHL TMDL-related monitoring conducted in 2005 at Waterloo (station 11070005), and (3) U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 2004 near Hudson.  

Note:  A TMDL for indicator bacteria in this segment of Black Hawk Creek was prepared by IDNR and approved by EPA in 2006.   Because all Section 303(d) impairments identified for the 2008 assessment/listing cycle (indicator bacteria) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved) of the current Integrated Report.  

EXPLANATION:  The Class A1 (primary contact recreation) uses are assessed as "not supported" due to levels of indicator bacteria (E.  coli) that violated Iowa’s Class A1 water quality criteria during recreational seasons of 2008, 2009 and 2010.   The geometric means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at station 10070004 at Waterloo were as follows:  the 2008 geometric mean was 584 orgs/100 ml, the 2009 geometric mean was 276 orgs/100 ml and the 2010 geometric mean was 183 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Thirteen of the 22 samples (59%) 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.”

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of monitoring from the IDNR/UHL ambient station SW of Waterloo (STORET Station 10070004) from 2008 through 2010.   Monitoring at this station showed no violations of Class B(WW1) water quality criteria for ammonia-nitrogen in the 30 samples analyzed during the 2008-2010 assessment period.   None of the approximately 33 samples analyzed for dissolved oxygen and pH violated the respective water quality criteria during the 2008-10 period.   Similarly, none of the seven sample collected as part of IDNR/UHL TMDL monitoring in 2005 at station 11700005 contained violations of Class B(WW1) criteria for dissolved oxygen, pH, or ammonia.  

Fish consumption uses remain assessed (evaluated) 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.