Assessment Comments

Assessment is based on results of IDNR ambient monthly monitoring SW of Waterloo, fish tissue (RAFT) monitoring near Hudson in 1998.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "not supported" and the Class B(WW) aquatic life uses were assessed as "fully supported."  Fish consumption uses remain "fully supported."  Sources of data for this assessment include (1) results monthly monitoring from October 1999 through September 2001 at the IDNR ambient station at Ridgeway Avenue SW of Waterloo, (2) results from monthly monitoring conducted at three additional locations in this stream segment from March to November 2001 as part of monitoring in support of TMDL development and (3) U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 1998 near Hudson.   EXPLANATION:  The Class A (primary contact recreation) uses were assessed as "not supported."  The geometric mean of indicator bacteria (fecal coliforms) in the 14 samples not materially affected by surface runoff during the recreational seasons of 2000 and 2001 at the IDNR ambient monitoring station exceeded the Iowa water quality criterion to protect primary contact recreation uses.   For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  The geometric mean of fecal coliform bacteria in the 14 non-runoff-affected samples was 247 orgs/100 ml, with five samples (36%) exceeding the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if the geometric mean is greater than 200 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Results of monitoring at the three TMDL stations during the recreational season of 2001 are consistent with this assessment:  geometric means in six non-runoff affected samples at these stations ranged from 563 to 880 organisms/100 ml (N=6) with from 67 to 83% of the samples exceeding the single-sample maximum value of 400 organisms/100 ml.   The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station SW of Waterloo in 2000 and 2001 and from the three stations monitored in 2001 in support of TMDL development for this stream reach.   Monitoring at these four stations show no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen.   In addition, no violations of state criteria for toxic metals and toxic organic compounds occurred in the four samples analyzed during the biennial period from the ambient monitoring station SW of Waterloo.   Fish consumption uses remain assessed as "fully supported" based on the results of EPA/DNR fish tissue (RAFT) sampling in 1998 near Hudson (see assessment for the 2000 report above).