Assessment Comments
Assessment is based on results of IDNR/UHL chemical/physical water quality monitoring conducted from May 2004 to November 2006 at the Maple Valley Road crossing (STORET station 15960001) 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 also 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 exceed state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "partially supported" due to violations of criteria for dissolved oxygen. The source of data for this assessment is the results of IDNR/UHL chemical/physical water quality monitoring conducted from May 2004 to November 2006 at the Maple Valley Road crossing (STORET station 15960001) as part of the Yellow River Watershed Project.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. Results of IDNR/UHL monitoring suggest extremely high levels of indicator bacteria in this stream segment. 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 71 samples collected at the monitoring station at Maple Valley Road (station 15960001) during the recreational seasons of 2004 through 2006 was 4,494 orgs/100 ml. This geometric mean far exceeds the Class A1 criterion of 126 orgs/100 ml. Sixty-seven of the 71 samples (94%) 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 the IDNR/UHL water quality monitoring from 2004-2006 suggest impairment of the Class B(WW2) aquatic life uses. Results of this monitoring show 16 violations of the Class B(WW2) criteria for dissolved oxygen (5.0 mg/l) in the 80 samples collected for a violation frequency of 20%. The minimum level of dissolved oxygen was 2.9 mg/l. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), "partial support" of aquatic life uses is indicated if criteria are exceeded in from 11 to 25% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen). Based on IDNR’s assessment methodology, these results suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus suggest an impairment of the Class B(WW2) uses of this stream segment.
