Assessment Comments

Assessment is based on results of IDNR quarterly ambient water quality monitoring near the mouth of the Rock River from 1995-1997 and on DNR stream use assessments conducted in Sioux county.

Basis for Assessment

Used assessment of support of the Class B(WW) aquatic life uses developed for the 1994 report, in combination with results of DNR quarterly WQ monitoring from Oct 95 to Jul 97 near the mouth of the Rock River, to assess support of the Class B(WW) uses as FST.   Results from the DNR WQ monitoring station show no violations of Class B(WW) WQ criteria for either toxic or conventional contaminants in the 8 samples collected over the Oct 95 to Jul 97 period.   In addition, this station was monitored for common agricultural pesticides.   Levels of pesticides were relatively low, and none of the samples contained levels of pesticides that exceeded respective MCLs.   The following are ranges of pesticide levels in the eight samples collected:  atrazine (MCL=3.0 ug/l):  0.10- 0.33 ug/l; alachlor (MCL=2.0 ug/l): all samples < 0.1 ug/l; cyanzine (MCLG=1.0 ug/l):  0.1-0.11 ug/l.   The atrazine metabolites deethylatrazine and deisopropylatrazine were analyzed for but were not detected (detection level=0.1 ug/l).  This river reach is not designated for Class C drinking water uses.