Assessment Comments
Assessment is based on results of monitoring at Site 32 (STORET station 191910016) conducted as part of monitoring by the Northeast Iowa RC&D from April 2010 to October 2012.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are presumptively designated as Class A1 and Class B(WW1) waters. Thus, for the current assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this previously unassessed segment. The Class B(WW1) aquatic life uses are assessed as "fully supporting" (IR 2a) based on results of chemical/physical water quality monitoring. The source of data for this assessment is the results of monitoring at Site 32 (STORET station 191910016) conducted as part of monitoring by the Northeast Iowa RC&D from April 2010 to October 2012.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as “not supported due to levels of indicator bacteria (E. coli) that exceed the Class A1 geometric mean criterion. The geometric means of indicator bacteria (E. coli) in the __ samples collected during the recreational seasons of 2010, 2011, and 2012 at the Site 32 were 634, 624, and 659 orgs/100 ml, respectively. All three of these recreation season geometric means exceed Iowa’s Class A1 geometric mean criterion of 126 E. coli orgs/100 ml, thus indicating nonsupport of the presumptive Class A1 primary contact recreation uses. Seventeen of the 20 samples (85%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). In additional, the percentage of samples with levels of E. coli that exceeded Iowa single-sample maximum criteria indicate impairment of Class A1 uses at this monitoring site.
In terms of comparison to Iowa's Class A2 (secondary contact) criteria, the results of monitoring at Site 32 suggst very slight impairment. Two of the annual geometric means (2010 at 634 orgs/100 ml and 2012 at 659 orgs/100 ml) very slightly exceede the Class A2 geometric mean criterion of 630 orgs/100 ml. The 2011 geometric mean (624 orgs/100 ml) was just slightly below this criterion. Only three of the 20 samples (15%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if an annual geometric mean is greater than the Class A2 criterion (630 orgs/100 ml), the secondary contact recreation uses should be assessed as "not supported". Thus, if designated for Class A2 uses, this stream would be considered "slightly impaired" and placed on the state's Section 303(d) list.
Results of chemical/physical monitoring at Site 32 from 2010 to 2012 suggest "full support" of the presumptive Class B(WW1) aquatic life uses. None of the 14 samples analyzed from April to October 2011 violated the Class B(WW1) criteria for dissolved oxygen or temperature, None of the 20 samples collected violated the Class B(WW1) criteria for ammonia: all level of ammonia were reported as less than detection (0.05 mg/l) Only one of six samples (17%) violated the Class A1 & B(WW1) criterion for pH. The lack of sufficient data quantity to develop an assessment (at least 10 samples over a three-year period) and the single violation do not suggest a pH impairment in thi stream segment. Based on IDNR’s assessment methodology, these results suggest good water quality and "full support" of the presumptive Class B(WW1) aquatic life uses.
