Rathbun Reservoir - Main Basin IA 05-CHA-1309

Assessment Comments

Assessment is based on results of water quality monitoring conducted by the U.S. Army Corps of Engineers.

Basis for Assessment

Used results of WQ monitoring conducted by the U.S.  Army Corps of Engineers at the Rathbun Lake outlet (RA-28), at intake area (RA-3), 10 miles uplake from dam (RA-7), and 10.4 miles uplake from dam (RA-8) to develop assessments of support of the Class B(WW) aquatic life uses and the Class C drinking water uses.   Based on the approximately 20 samples collected between April and September 1997 at the intake area (RA-3), assessed support of the Class B(WW) aquatic life uses as FST due to lack of Class B(WW) WQ criteria for either conventional or toxic contaminants.   In addition, the March/April 1998 Iowa Conservationist identifies Rathbun Lake as providing good to excellent angling opportunities for white bass, crappie, channel catfish, and walleye.   Used assessment of support of the Class A primary contact recreation uses (=FST) developed for the 1996 report.   Class C drinking water uses were assessed as FST: 1 of 20 samples in 1997 at intake area exceeded the MCL for atrazine (mean=2.31; median=2.34; max=3.2 ug/l).  Higher levels were detected approx 10 miles uplake from dam, with from 38-57% of the 21 samples exceeding the MCL for atrazine at stations RA-7 & RA-8).   Thus, as noted in summary of ACOE monitoring in 1997, "pesticide levels pose a continuing threat to the drinking water supplies.  .  ." Fish consumption uses assessed as FS based on results of fish contaminant monitoring conducted by ACOE in 1990.