Lake Lashane IA 05-GRA-1374

Assessment Comments

Assessment remains based on results of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000 by Syngenta Crop Protection, Inc.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses, Class B(LW) aquatic life uses, and the fish consumption uses remain "not assessed" due to the lack of information upon which to base an assessment.     The Class C (drinking water) uses remain assessed (evaluated) as "fully supported."  The source of data for this assessment is the results of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000 by Syngenta Crop Protection, Inc.    This is the same assessment as that developed for previous assessment/listing cycles.    

EXPLANATION:  The Class A1 and Class B(LW) uses remain not assessed due to the lack of water quality information needed to assess these uses.      

The Class C (drinking water) uses remain assessed (evaluated) as "fully supported" based on the results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" from March to October 2000 (Lake Leshane has not been part of the Voluntary Atrazine Monitoring Program since 2000).    This monitoring showed that the time-weighted mean level of atrazine in samples collected from this lake in 2000 was far below the MCL of 3.0 ug/l.     The time-weighted mean of atrazine in 2000 (N=20) was 0.87 ug/l; no sample values exceeded the MCL (maximum atrazine level = 0.3 ug/l).     Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, and no sample values exceed the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported."  Because this data is now greater than 5 years old the assessment is considered "evaluated" (of lower confidence) rather than "monitored" (of higher confidence).      

Fish consumption uses were "not assessed due to the lack of fish contaminant monitoring at this lake.