Assessment Comments

Assessment is based on results of (1) IDNR/UHL ambient monthly monitoring SW of Waterloo from 2002-04, (2) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2004, and (3) IDNR/UHL ambient monitoring at three sites in 2001 as part of TMDL development.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed (monitored) as "not supported" due to continued high levels of indicator bacteria that violate state water quality standards.   The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of ambient water quality monitoring.   Fish consumption uses are 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 2002 through December 2004 at the IDNR ambient station at Ridgeway Avenue SW of Waterloo (station 10070004) and (2) 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 2006 assessment/listing cycle (indicator bacteria) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).

EXPLANATION:  The Class A (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 2002, 2003 and 2004.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.   The geometric mean of E.  coli bacteria in the 57 samples was 457 orgs/100 ml.   Also, 32 samples (56%) exceeded Iowa’s single-sample maximum value 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).  

The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of monitoring from the IDNR ambient station SW of Waterloo (STORET Station 10070004) from 2002 through 2004.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for pH or ammonia-nitrogen in the approximately 40 samples analyzed during the 2002-2004 assessment period.   One of the 45 samples analyzed for dissolved oxygen did exceed the Iowa Water Quality criterion to protect Class B uses.   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen suggest "full support" of aquatic life uses.   Thus, the percentages of violations of the dissolved oxygen criterion at this station (2%) does not suggest an impairment of aquatic life uses in this stream segment.   In addition, no violations of state criteria for toxic metals and toxic organic compounds (e.g., pesticides) occurred in the ten samples analyzed during the assessment period from this monitoring station..  

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Hudson in 2004 (see the assessment for the 2000 reporting cycle for information on previous RAFT monitoring in this stream segment).   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.   Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.   In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol.   This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol).   Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.   This scenario, however, does not apply to the fish contaminant data generated from the 2004 RAFT sampling conducted in this assessment segment:  the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory.