West Lake (Osceola) IA 04-LDM-1082

Assessment Comments

Basis for Assessment

Used assessments of support for the Class B(LW) aquatic life uses developed for the 1994 report (=FST).   Used previous information on levels of pesticides in lake water in combination with results of sampling conducted in February 1995 as part of a survey of 19 water supply reservoirs (Miller and Kennedy 1995) to continue to assess support of the Class C (drinking water) uses as PS due to (1) levels of atrazine near the dam (2.2 to 2.4 ug/l) higher than the average reportable concentration for the 19 WS reservoirs, (2) levels of cyanazine (4.3 to 4.7 ug/l) approx four times the average reportable concentration (1.03 ug/l), and (3) the highest sediment concentrations of atrazine (21 ug/kg) and cyanazine (33 ug/kg) in the study.   Previous studies (especially Kalkhoff 1993, in combination with Miller and Kennedy 1993 and 1995) suggest that spring/summer levels of atrazine may exceed the MCL of 3.0 ug/l.