Assessment Comments
Assessment is based on 2005 and 2007 IDNR/UHL biological monitoring 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 July 2009 through November 2010 .
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 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 assessment segment. The Class B(WW1) aquatic life uses remain assessed (monitored) as "fully supported" based on results of biological (REMAP) monitoring in 2005 & 2007. 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 July 2009 through November 2010 and (2) results of IDNR/UHL biological monitoring 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 15 samples collected during the recreational season of 2009 at the Section 319 monitoring stations Tetes Des Morts Sites 6, 7, and 8 were 2,408, 1,410, and 1,765 orgs/100 ml, respectively, and the 2010 recreation season geometric means at these sites were 1,605, 1,520, and 1,295 orgs/100 ml, respectively. All of these recreation season geometric means far 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. Thirteen of the fourteen samples (93%) at Site 6 exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml, all 16 samples exceeded this criterion at Site 7, and 15 of 16 samples (94%) 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 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/UHL 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 six years. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.
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 2006-2010.
