Assessment Comments
Assessment is based on: (1) results monthly monitoring from January 2004 through December 2006 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 (monitored) 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 2006 through December 2008 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 (2010) Integrated Report.
EXPLANATION: The Class A1 (primary contact recreation) uses were assessed as "not supported" due to levels of indicator bacteria (E. coli) that violated Iowa’s Class A water quality criteria during recreational seasons of 2006, 2007 and 2008. The geometric mean of E. coli bacteria in the 22 samples collected at the IDNR/UHL ambient monitoring station (10700004) from 2006-2008 was 413 orgs/100 ml; this geometric mean exceeds Iowa’s Class A1 criterion of 126 orgs/100 ml. Thirteen of the 22 samples (59%) 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 are "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Results at IDNR/UHL TMDL station 11070005 are similar and also suggest nonsupport of the Class A1 uses. The geometric mean of E. coli in the seven samples collected from April to September 2005 (461 orgs/100 ml) also exceeds the Class A1 criterion of 126 orgs/100 ml; six of the seven samples (86%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. Note: Monitoring for indicator bacteria (E. coli) has not been conducted at TMDL station 11070005 since 2005.
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 2006 through 2008. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for ammonia-nitrogen in the 33 samples analyzed during the 2006-2008 assessment period. None of the approximately 30 samples analyzed for dissolved oxygen and pH violated the respective water quality criteria during the 2006-08 period. In addition, no violations of state criteria for toxic metals occurred in the two samples analyzed during the assessment period from this monitoring station. 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 (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.
