Assessment Comments
Assessment remains based on results of monitoring near from 2006 through 2008 conducted by the National Laboratory for Agriculture and the Environment, Ames, IA.
Basis for Assessment
[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.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supported” (IR 2a) based on results of water quality monitoring from 2006-2008 (results of biological monitoring in 1999 used for previous assessments are now too old (>10 years) to be useful for assessment purposes). The source of data for this assessment is the results of water quality monitoring near the mouth of Tipton Creek from 2006 through 2008 conducted by the National Laboratory for Agriculture and the Environment (NLAE), Ames, IA (formerly, National Soil Tilth Lab), at station TC325 approximately 3.5 miles NNW of New Providence, Hardin County.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean of E. coli in the 56 samples collected at station TC325 (2,109 orgs/100 ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Forty-eight of the 56 samples (86%) 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 "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Note: the geometric mean of E. coli at station TC325 is based on raw data for the 56 samples collected during the recreational seasons of 2006 through 2008. If daily duplicate samples and other serially correlated samples collected on consecutive days are averaged, the geometric mean of the resulting 20 independent measurements of E. coli is 1,137 orgs/100 ml with 15 of the 20 samples (75%) exceeding Iowa’s single-sample maximum criterion. Thus, whether raw data or averaged data are used, the results of monitoring at this station suggest geometric mean levels of E. coli far above the water quality criterion and thus indicate “nonsupport” of the presumptive Class A1 (primary contact recreation) uses.
The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supported” based on results of monitoring by the NLAE approximately 2 miles NNE of Buckeye (station SF400) from 2007-08. 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. Six of the 521 daily maximum values for pH (1.2%) exceeded the Class B(WW1) pH criteria of 9.0; the maximum pH reported for this period was 9.09 units. None of the daily minimum values violated the pH criterion of 6.5 pH units (minimum daily value = 7.2 units). Five of the 631 daily maximum values for water temperature (0.8%) exceeded Iowa’s added “heat criterion” of 32C. Of the 626 daily minimum values for dissolved oxygen, twenty-nine values (4.6%) were below the 5.0 mg/l Class B(WW1) criterion, but only two values (0.3%) were below Iowa’s Class B(WW2) criterion for a minimum dissolved oxygen of 4.0 mg/l during any 24-hour period (minimum value = 3.7 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.
