Assessment Comments
Assessment based on 2005 and 2007 IDNR/SHL biological sampling data (FIBI = 73 (excellent), BMIBI = 61, 73 (good). FIBI BIC = 52; BMIBI BIC = 61) and on results of a Clean Water Act Section 319 water quality project from August 2010 through November 2011.
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 Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” (IR 5a) due to violations of Iowa water quality criteria for indicator bacteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of biological (REMAP) sampling in 2005 & 2007 and based on results of water quality monitoring in 2011. The sources of data for this assessment include (1) results of monitoring at three sites (Tetes Des Morts Sites 6, 7, and 8)conducted as part of a Clean Water Act Section 319 water quality project from August 2010 to November 2011 and (2) results of IDNR/SHL biological sampling in 2005 and 2007.
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 mean of indicator bacteria (E. coli) in the 22 samples collected during the recreational season of 2010 at the Section 319 monitoring stations Tetes Des Morts Sites 6, 7, and 8 were 1,605, 1,520, and 1,295 orgs/100 ml, respectively, and the 2011 recreation season geometric means at these sites were 938, 613, and 630 orgs/100 ml, respectively. All 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 Class A1 primary contact recreation uses. Nineteen of the 22 samples (86%) at Site 6 exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml, 21 of 24 samples (88%) exceeded this criterion at Site 7, and 20 of 24 samples (83%) exceeded this criterion at Site 8. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1, the contact recreation uses are "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’s single-sample maximum criteria indicate impairment of Class A1 uses at all monitoring sites.
The assessment of the Class B(WW2) aquatic life uses remains based on data collected in 2005 and 2007 as part of the IDNR/SHL stream REMAP project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2005 FIBI score was 73 (excellent) and the BMIBI score was 61 (good). The 2007 BMIBI score was 73 (good). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI BIC 1/1 times and passed the BMIBI BIC 2/2 times in the last eight years. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. This aquatic life assessment is considered "evaluated" because even though there were two or more samples collected from this segment in multiple years over a five-year period, they were not collected during the most recent five-year period. Also, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Water quality data were also collected from April to October of 2011 at three Section 319 project sites: Site 6 at 266th Avenue (STORET station 13490005), Site 7 at 248th Avenue (STORET station 13490006), and Site 8 at 239th Avenue (STORET station 13490007). The results of this monitoring do not suggest impairment of the Class B(WW1) aquatic life uses. None of the 13 samples collected at each of these monitoring sites violated the Class B(WW2) criteria for dissolved oxygen or temperature. According to U.S. EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, these results suggest “full support” of the Class B(WW2) aquatic life uses.
