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[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses.  Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses.  The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses).  Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.] 

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli).  The geometric mean of E. coli in the seven samples collected at station TC325 during the recreation season of 2010 (308 orgs/100 ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.  Four of the seven samples (57%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b).    

The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supported” based on results of monitoring at station TC325 during 2010 by the NLAE.  This monitoring included continuous monitoring for dissolved oxygen, pH, and water temperature.  Data for daily maximum, mean, and minimum values were provided to Iowa DNR.  None of the 104 daily maximum values for pH exceeded the Class B(WW2) pH criteria of 9.0; the maximum pH reported for this period was 8.5 units.  Similarly, none of the daily minimum values violated the pH criterion of 6.5 pH units (minimum daily value = 6.8 units).  None of the 162 daily maximum values for water temperature exceeded Iowa’s added “heat criterion” of 32C.  Of the 144 daily minimum values for dissolved oxygen, none were below the either the 5.0 mg/l Class B(WW2) criterion or the 4.0 mg/l criterion which applies during any 24-hour period (minimum value = 5.39 mg/l).  According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen, pH, and temperature suggest "full support" of aquatic life uses. 

For previous assessments, results of biological sampling conducted in 1999 as part of the IDNR/SHL stream biocriteria project were used to assess the aquatic life uses of this stream as “fully supported”.  As both chemical and biological water quality data age, however, they are less able to represent current water quality conditions.  As data age beyond ten years, their ability to represent current water quality conditions is increasing suspect.  Thus, because the biological data collected in 1999 are well over 10 years old, these data are not being used for the current assessment.  Additional biological monitoring is needed in this assessment segment to update status of its aquatic communities.