Assessment Comments
Assessment is based on results of IDNR/UHL ambient water quality monitoring conducted from May 2004 through September 2006 at IDNR station 10340002 near Greene.
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 uses are assessed (monitored) as “not supported” due to high levels of indicator bacteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" although this stream suffers from naturally-occurring problems with flow stability (i.e., intermittency). The source of data for this assessment is the results of IDNR/UHL ambient water quality monitoring conducted from May 2004 through September 2006 at IDNR station 10340002 near Greene.
EXPLANATION: The presumptive Class A1 uses are assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). 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 A 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 level of indicator bacteria (E. coli) in the 23 samples collected during the recreational seasons of 2004 through 2006 (213 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Eight of the 23 samples (35%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level 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 Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” based on results of routine ambient water quality monitoring. This stream is known to be prone to intermittency; the causes of this intermittency are believed to be naturally-occurring. Despite this problem, results of ambient water quality monitoring conducted by IDNR/UHL near Greene, Iowa, during the 2004-2006 assessment period continue to suggest “full support” of the Class B(WW2) aquatic life uses. None of the samples collected violated state criteria for dissolved oxygen (25 samples), temperature (25 samples), pH (24 samples), or ammonia-nitrogen (22 samples); none of the six samples analyzed for pesticides and toxic metals contained levels above the Class B(WW2) criteria. The results of this monitoring suggest that, when Flood Creek has sufficient water, the water quality is relatively good.
