Assessment Comments
Assessment is based on results of chemical/physical/bacterial water quality monitoring conducted on Dry Run Creek from June 2005 through September 2006 at three stations sampled as part of the Dry Run Creek Watershed Project: Site DRC5 at University Avenue (STORET station 1507003), at Site DRC8 at Greenhill Road (STORET station 15070005), and Site DRC10 at Viking Road (STORET station 11070007).
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. 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. This waterbody has not been assessed for Section 305(b)/303(d) purposes prior to the current (2008) assessment/listing cycle.]
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 presumptive Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of chemical/physical monitoring in 2005 and 2006. The sources of data for this assessment include the results of chemical/physical/bacterial water quality monitoring conducted on Dry Run Creek from June 2005 through September 2006 at three stations sampled as part of the Dry Run Creek Watershed Project: Site DRC5 at University Avenue (STORET station 1507003), at Site DRC8 at Greenhill Road (STORET station 15070005), and Site DRC10 at Viking Road (STORET station 11070007).
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. 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 overall (2005-2006) geometric means of E. coli in the samples collected at all three monitoring stations in this assessment segment exceeded Iowa’s Class A1 criterion of 126 orgs/100 ml. These geometric means and the number of samples collected from June 2005 to November 2006 are as follows: 2,093 orgs/100 ml at Site DRC5 (33 samples); 389 orgs/100 ml at Site DRC8 (35 samples); and 386 orgs/100 ml at Site DRC10 (34 samples). The percentages of samples at these stations that exceeded Iowa’s single-sample maximum criterion are as follows: Site DRC5: 29 of 33 samples (88% violated); Site DRC8: 24 of 35 samples (69% violated), and Site DRC10: 23 of 34 samples (68% violated). 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).
Due to the availability of weekly bacteria data for a portion of the 2005 recreational season at all three stations, seven 30-day/5-sample geometric means were calculated for each station and compared to the Class A1 criterion of 126 orgs/100 ml. All 21 of the 30-day geometric means were greater than the Class A1 criterion; the minimum 30-day geometric mean was 583 orgs/100 ml at Station DRC10. Thus, whether based on an overall summary of the data or on weekly data from 2005, the results of bacterial monitoring at these three stations suggest that the presumptive Class A1 uses should be assessed as “not supported.”
The presumptive Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported” based on results of chemical/physical monitoring conducted for the Dry Run Creek Watershed project from June 2005 through December 2006. No violations of Class B(WW1) criterion for ammonia or pH occurred in the approximately 19 samples analyzed at each station over this period. One of the approximately 35 samples (~2% violation at each station) analyzed for dissolved oxygen at stations DRC5 and DRC10 violated the Class B(WW1) criterion for dissolved oxygen. The violations at both stations occurred on July 21, 2005. According to U.S. EPA assessment guidelines, if less than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as fully supported (see pgs 3-17 of U.S. EPA 1997b). Thus, the minor violations for dissolved oxygen at stations DRC5 and DRC10 do not suggest a water quality impairment.
