Assessment Comments

Assessment is based on results from IDNR ambient monthly monitoring.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are considered "not assessed," and the Class C drinking water uses were assessed as "fully supported."  The fish consumption uses remain assessed as "fully supported."  EXPLANATION:  The previous assessments of support of the Class B(WW) uses and Class C uses were based on results from the DNR quarterly monitoring station near Shambaugh (station 787044).   This station was last monitored from October 1993 through September 1995, and data from this monitoring period are considered too old (greater than five years) for characterizing current water quality conditions.   As part of DNR's expanded water quality monitoring program, monthly monitoring at the Shambaugh station began in October 1999.   Results from this monitoring will allow development of an updated assessment of support of beneficial uses for the 2002 report.   The Class C (drinking water) uses were assessed as "fully supported" based on the 1998 results of the Novartis "Iowa Voluntary Atrazine Monitoring Program."  This monitoring showed that the time-weighted mean level of atrazine in samples collected Clarinda's raw water source from January to December 1998 (0.3 ug/l, N=30, maximum=2.0 ug/l) was well below the MCL of 3.0 ug/l.   Based on DNR's Section 305(b) assessment methodology, these results, combined with the historical low levels of nitrate (see assessment for the 1998 report above), suggest "full support" of the Class C (drinking water) uses.    Fish consumption uses remain assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring in early fall 1994 (see assessment for the 1998 report above).   Station 787044 is now being monitored on a monthly basis as part of DNR's expanded water quality monitoring program.