Assessment Comments
The source of data for this assessment remains the results of monitoring from March 2006 through October 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 (2012) 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" 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” based on chemical/physical water quality monitoring conducted from 2006-2008. The source of data for this assessment remains the results of monitoring from March 2006 through October 2008 conducted by the National Laboratory for Agriculture and the Environment (NLAE), Ames, IA (*formerly, National Soil Tilth Laboratory), at station SF400 approximately 2 miles NNE of Buckeye. This assessment is the same as that developed for the adjacent upstream segment (IA 02-IOW-0280_4). Data for the current (2008-2010) assessment period for this assessment segment were requested from NLAE in October 2011. The IDNR request was acknowledged by NLAE, but the data were not received and were thus were not used for this assessment.
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 63 samples collected at station SF400 (1,626 orgs/100 ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Fifty-five of the 63 samples (87%) 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 SF400 is based on raw data for the 63 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 18 independent measurements of E. coli is 728 orgs/100 ml with 14 of the 18 samples (78%) exceeding Iowa’s single-sample maximum criterion. Thus, whether raw data or averaged data are used, the results of monitoring at this station suggested “nonsupport” of the presumptive Class A1 (primary contact recreation) uses.
Monitoring by the NLAE approximately 2 miles NNE of Buckeye (station SF400) from 2007-08 included continuous monitoring for dissolved oxygen, pH, and water temperature. Data for daily maximum, mean, and minimum values were provided to Iowa DNR. Three of the 458 daily maximum values for pH (0.7%) exceeded the Class B(WW1) pH criteria of 9.0; the maximum pH reported for this period was 9.07 units). None of the daily minimum values violated the pH criterion of 6.5 pH units (minimum daily value = 6.7 units). None of the 477 daily maximum values for water temperature exceeded Iowa’s added heat criterion of 32C. Of the 469 daily minimum values for dissolved oxygen, four values (0.9%) were below Iowa’s Class B(WW1) criterion for dissolved oxygen of 5.0 mg/l (minimum value = 4.39 mg/l). These minimum values tended to occur in the late night or early morning hours during summer months (August and September). 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 and pH suggest "full support" of aquatic life uses.
