Assessment Comments
Assessment remains 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 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, 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 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 remain assessed (monitored) as “not supported” (IR 5p) due to high levels of indicator bacteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) although this stream suffers from naturally-occurring problems with flow stability (i.e., intermittency). The source of data for this assessment remains the results of IDNR/UHL ambient water quality monitoring conducted from May 2004 through September 2006 at IDNR station 10340002 near Greene. IDNR/UHL ambient monitoring at this station was terminated in September 2006. This assessment is the same as that developed for the previous (2008 through 2012) assessment/listing cycles.
EXPLANATION: The presumptive Class A1 uses remain assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). 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.
