Assessment Comments
Assessment is based on results of monitoring at two stations during the 2010-2012 period: (1) STORET station 13030004 near Dorchester Drive & Waterloo Creek Drive (Site Arch 1) and (2) STORET station 13030006 at Waterloo Creek Drive (Site Waterloo 4).
Basis for Assessment
[Note: Prior to the 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, 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 presumptively designated as Class A1 and Class B(WW1) waters. Thus, for the current assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” (IR 5p) due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this previously unassessed segment. The presumptive Class B(WW1) aquatic life uses remain “not assessed” (IR 3a) due to the lack of sufficient water quality information upon which to base an assessment. The source of data for this assessment is the results of monitoring at two stations monitored as part of an IDNR water quality project: (1) STORET station 13030008 (Site Waterloo 4) from April through November 2010 [NULL 071] and (2) STORET station 13030004 (Site Arch1) from June to September 2011 [NULL 118].
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as “not supported" (IR 5p) due to levels of indicator bacteria (E. coli) that exceed the Class A1 geometric mean criterion. The geometric mean of indicator bacteria (E. coli) in the 18 samples collected at Station 13030006 (Waterloo 4) during the recreation season of 2010 was 1,640 orgs/100 ml. Seventeen of the 18 samples (94%) exceeded the Class A1 single sample maximum criterion of 235 orgs/100 ml. Similarly, the geometric mean of indicator bacteria (E. coli) in the 11 samples collected at Station 13030004 (Arch1) during the recreation season of 2011 was 829 orgs/100 ml. Ten of the 11 samples (91%) exceeded the 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 a recreation season geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). In addition, the percentage of samples with levels of E. coli that exceeded Iowa single-sample maximum criteria indicates impairment of presumptive Class A1 uses at this monitoring site.
Although parameter coverage was limited, results of chemical/physical water quality monitoring at Station 13030004 from June to November 2011 suggest that the presumptive Class B(WW1) aquatic life uses could be assessed as "fully supporting". No violations of Class B(WW1) water quality criteria for dissolved oxygen or temperature occurred in the 11 samples analyzed.
