Assessment Comments
Assessment is based on results of (1) the 1999-2001 "Iowa Voluntary Atrazine Monitoring Program, (2) ISU report on lake phytoplankton communities, and (3) surveys of the DNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses remain assessed as "fully supported / threatened." The Class C (drinking water) uses remain assessed as "fully supported / threatened." Fish consumption uses remain "not assessed." EXPLANATION: The previous (1998) assessment of support of the Class B(LW) uses was reviewed and approved by the DNR Fisheries Bureau in 2000. The assessment of support of the Class C (drinking water) uses was based on (1) the UHL survey of water supply reservoirs in 1995 (Miller and Kennedy 1995) (see assessment developed for the 1996 report above) and (2) 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 from the Montezuma raw water source from January to December 1998 (1.6 ug/l, N=31, maximum=4.2 ug/l) was below the MCL of 3.0 ug/l. Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, but a level in one or more samples is above the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported / threatened." Thus, the Class C uses of Diamond Lake were assessed as "fully supported / threatened." Fish consumption uses were "not assessed due to the lack of fish contaminant monitoring at this lake.
