Assessment Comments
Assessment is based on: (1) results of IDNR/UHL biological monitoring in 2006 conducted as follow-up sampling and (2) results of IDNR/UHL water quality monitoring from May 2004 to November 2006 at station 15960002 (107th Avenue crossing) as part of the Yellow River watershed project.
Basis for Assessment
[Note: Prior to the current (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 (2008) 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 far exceed state water quality criteria. The Class B(WW2) aquatic life uses of this stream segment are assessed (monitored) as “partially supported” due to violations of state water quality criteria for dissolved oxygen. The sources of data for this assessment include (1) results of IDNR/UHL biological monitoring in August 2006 conducted as part of the IDNR/UHL stream biological sampling and (2) results of IDNR/UHL water quality monitoring from May 2004 to November 2006 at station 15960002 (107th Avenue crossing) as part of the Yellow River watershed project.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of Iowa’s water quality criteria for indicator bacteria. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.
The geometric mean of E. coli in the 69 samples collected at IDNR/UHL station 15960002 during the recreational seasons of 2004 through 2006 was 6,383 orgs/100 ml. This geometric mean far exceeds the Class A1 criterion of 126 orgs/100 ml. All 69 samples (100%) 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 the geometric mean of E. coli is greater than the applicable state criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Thus, because the geometric mean for IDNR/UHL station 15960002 exceeds the Class A1 criterion, the primary contact recreation uses are assessed as “not supported.”
The Class B(WW2) aquatic life uses are assessed (monitored) as “partially supported” due to violations of the Class B(WW2) criterion for dissolved oxygen. Seventeen of the 76 samples (22%) collected at IDNR station 15960002 from May 2004 through November 2006 contained levels of dissolved oxygen that violate this criterion. Sixteen of the 17 violations occurred from June to September, 2005. The average level of dissolved oxygen in the 16 samples collected during this period was 3.3 mg/l. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and IDNR’s assessment/listing methodology, these results suggest impairment of the Class B(WW2) aquatic life uses. That is, significantly more than 10% of the samples (17 of 76 samples; 22% violation) violated the Class B(WW2) criterion of 5.0 mg/l. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed the criterion for a conventional pollutant, the aquatic life uses should be assessed "partially supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the results from Yellow River station 15960002 suggest that significantly greater than 10% of the samples violate Iowa’s Class B(WW2) water quality criterion for dissolved oxygen, thus suggesting that these uses should be assessed as “impaired.”
Despite results of chemical/physical water quality monitoring that suggest poor water quality conditions, results of biological monitoring in 2006 suggest relatively good biological integrity in this assessment segment. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data collected 2006. 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 score was 46 (fair) 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. This site met the FIBI BIC with the use of the FIBI UAV of 7 points. 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.
