Assessment Comments
Assessment is based on: (1) results of IDNR/UHL TMDL-related monitoring from June 2006 through June 2007 at TMDL station NuCr1 (STORET station 11330001) and (2) results of IDNR/UHL biological monitoring in 2006 and 2008.
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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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 (2010) 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 are assessed (monitored) as "not supported" due to levels of indicator bacteria that exceeded state water quality criteria. The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supported" based on results of (1) IDNR/UHL biological (biocriteria) sampling in 2006 & 2008 (2) IDNR/UHL TMDL-related water quality monitoring from June 2006 to June 2007. The sources of data for this assessment include (1) results of IDNR/UHL TMDL-related monitoring from June 2006 through June 2007 at TMDL station NuCr1 (STORET station 11330001) and (2) results of 2006 & 2008 IDNR/UHL biological monitoring.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses were assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 14 samples collected during the 2006 and 2007 recreational seasons (March 15 to November 15) at TMDL station NuCr1 was 4,087 orgs/100 ml.; ten of the 14 samples (71%) exceeded Iowa’s 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 the geometric mean 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).
The results of IDNR/UHL water quality monitoring at TMDL station NuCr1 from June 2006 to 2007 suggest “full support” of the Class B(WW2) aquatic life uses. None of the 13 samples collected violated the Class B(WW2) criteria for dissolved oxygen, pH, or ammonia.
This assessment is also based on biological data collected in 2006 & 2008 as part of the IDNR/UHL stream biocriteria project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were 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 2006 FIBI scores were 68 (good), 50 (fair) and the BMIBI scores were 74 (good), 52 (fair). The 2008 FIBI score was 55 (good) and the BMIBI score was 74 (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 biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI and BMIBI BICs 2/3 times in the last five years.
This aquatic life use assessment is considered "monitored" because there were two or more samples collected in multiple years from 2004-2008.
