Loch Ayr IA 05-GRA-1381

Assessment Comments

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses and the Class B(LW) aquatic life uses remain "not assessed."  The Class C (drinking water) uses remained assessed as "fully supported / threatened."  Fish consumption uses remain "not assessed."  EXPLANATION:  The Class A (primary contact recreation) uses remain "not assessed" due to the lack of information on levels of indicator bacteria at this lake.   The Class B(LW) remain "not assessed" due to the lack of recent information on the status of aquatic life at this lake.   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 January to December 1998 (2.8 ug/l, N=30, maximum=10.5 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 Loch Ayr were assessed as "fully supported / threatened."  Based on results of the "Iowa Volunatary Atrazine Monitoring Program," the levels of atrazine in raw and finished water from Loch Ayr are some of the highest known in Iowa water supply reservoirs.   Thus, this lake is a candidate for inclusion on Iowa's Section 303(d) list of impaired waters.   Fish consumption used remain "not assessed" due to lack of fish contaminant monitoring at this lake.