Home Lake IA 05-GRA-1373

Assessment Comments

Assessment is based on results of Syngenta's Iowa Voluntary Atrazine Monitoring Program from 2000-04.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses and the Class B(LW) aquatic life uses are "not assessed" due to the lack of water quality information upon which to base an assessment.   The Class C (drinking water) uses remain assessed (monitored) as "not supported " due to average levels of atrazine above state water quality criteria and the U.S.  EPA MCL.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.   The source of data for this assessment is the results of the Iowa Voluntary Atrazine Monitoring Program conducted from 2000 through 2004 by Syngenta Crop Protection, Inc.  

EXPLANATION:  The Class A and Class B(WW) uses remain "not assessed" due to the lack of water quality information for this lake.  

The Class C (drinking water) uses remain assessed (monitored) as "not supported " based on results of sampling conducted as part of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000, 2001, and 2002 by Syngenta Crop Protection, Inc.   Results of more recent (2003-2004), monitoring, however, suggest a decline in atrazine levels at this lake.   Results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" from 2000 through 2002 showed that the time-weighted mean level of atrazine in samples collected from Home Pond in 2002 (4.4 ug/l) was above the MCL of 3.0 ug/l.   In addition, 10 of the 46 moving annual averages calculated for the 2000-02 period were above the MCL of 3 ug/l (range:  1.0 to 4.9 ug/l).   According to IDNR's Section 305(b) assessment methodology, if the average contaminant level in source water (either a time-weighted annual average or a moving annual average) is greater than the MCL, the Class C (drinking water) uses of the source water should be assessed as "not supported."  Thus, the Class C uses of this lake were assessed as impaired for the 2004 Section 305(b) reporting cycle.

Similarly, nine of the 63 moving annual averages for atrazine for the years 2002 through 2004 at Home Pond exceeded the MCL (maximum moving annual average = 3.9 ug/l).   Based on DNR's Section 305(b) assessment methodology, if the average (time-weighted annual average or moving annual average) contaminant levels in source water are greater than the MCL, the Class C (drinking water) uses of the source water should be assessed as "not supported."  This impairment continues to be based on the prolonged high levels of atrazine that occurred at Home Pond in late spring and summer of 2002:  sample levels were greater than 4 ug/l from May 20 to September 9, 2002.  

More recent results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program", however, suggest declines in atrazine levels at Home Pond.   The time-weighted mean levels of atrazine in samples collected in calendar years 2003 and 2004 were both below the MCL of 3.0 ug/l, thus suggesting a decline (improvement) in atrazine levels at this lake.   The time-weighted mean of atrazine in 2003 (N=27) was 1.0 ug/l, and in 2004 (N=32) was 1.8 ug/l.   The overall mean (2.1 ug/l) and median (1.6 ug/l) atrazine levels over the 2002-2004 period (N=73) were both less than the MCL of 3 ug/l.   While the maximum sample value for the 2002-2004 period was 14.6 ug/l on May 20, 2002, the maximum value during 2003 and 2004 was 3.1 ug/l on July 30, 2003.   [Note:  rounding is required when comparing levels of atrazine to its MCL.   Because the MCL, as published by U.S.  EPA, is 0.003 mg/l, any values compared to the MCL must be in the proper MCL units and compared at the same number of significant figures.   Thus, the maximum sample value of 0.0031 mg/l rounds down to 0.003 mg/l; this sample value does not exceed the MCL for atrazine.]

Despite the potential recent lowering of atrazine levels at Home Pond, the Class C (drinking water) uses will remain assessed as “not supported” for the current (2006) Section 305(b) reporting cycle due to average levels of atrazine that exceeded its MCL during the 2002-2004 period.

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