Assessment Comments
Assessment is based on results of (1) monitoring of USGS water quality monitoring June 2008 to August 2010 near Marengo and (2) daily IDNR/UHL monitoring for dissolved oxygen and temperature at Marengo from May-August 2000.
Basis for Assessment
SUMMARY: The assessment of the Class A1 (primary contact recreation) uses is changed from "evaluated/not supported" (IR Category 2b) to "not assessed" (IR Category 3a) for the 2012 Integrated Reporting cycle. The previous assessment was based on levels of indicator bacteria from USGS monitoring from 1996-98 that exceed state water quality standards. Because these data are now more than 10 years old, and thus are of marginal use for characterizing curren water quality conditions, the assessment is changed to "not assessed". The Class B(WW1) uses remain assessed (evaluated) as "fully supported" based on results of ambient chemical/physical monitoring. Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this assessment segment. The source of data for this assessment is the results of ambient water quality monitoring conducted by USGS at station 05453100 at Marengo from June 2008 through August 2010.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed "not assessed." Only one sample was analyzed for indicator bacteria (E. coli) during the 2008-10 assessment period. According to IDNR’s assessment/listing methodology, this amount of data is not sufficient for developing an assessment of the degree to which the Class A1 uses are supported.
Regarding support of the Class B(WW1) aquatic life uses, results of USGS monitoring at Marengo showed no violations of Class B(WW1) criteria for ammonia, pH, or dissolved oxygen in the approximately 12 samples collected during the 2008-10 period. These results suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as “fully supporting.”
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment. Previous assessments of the fish consumption uses for this segment ("fully supported") were based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the NAWQA project. These data are now considered too old (greater than 10 years) to accurately characterize current water quality conditions.
