Assessment Comments
Assessment is based on results of monitoring at five STORET stations from September 2010 to July 2011: (1) 13290003 (Cedar Creek at 130th Street, Site C), (2) 13290002 (135th St, Site B, (3) 13290006 (at Roosevelt Street, Site F), (4) 13440001 (near Danville), and (5) 13290001 (near US Hwy. 34, Site A).
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 from September 2010 through July 2011 at five stations on Cedar Creek upstream from Lake Geode: (1) 13290003 (Cedar Creek at 130th Street, Site C [NULL 016]), (2) 13290002 (135th St, Site B [NULL 017]), (3) 13290006 (at Roosevelt Street, Site F [NULL 018]), (4) 13440001 (near Danville [NULL 019]), and (5) 13290001 (near US Hwy. 34, Site A [NULL 020]). This monitoring was conducted as part of a Clean Water Act Section 319 water quality project.
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 means of indicator bacteria (E. coli) in the 16 to 17 samples collected during the recreation seasons of 2010 and 2011 at each of the five monitoring stations, as well as the percentages of samples that exceed the Class A1 single-sample maximum (SSMax) criterion of 235 orgs/100 ml, are as follows (arranged in approximate order from upstream (at Hwy 34) to downstream:
1. Site A (nr Hwy 34): 211 orgs/100 ml in 2010 and 199 orgs/100 ml in 2011 (7 of 16 (44%) > SSMax).
2. Site B (135th St.): 846 orgs/100 ml in 2010 and 276 orgs/100 ml in 2011 (11 of 16 (69%) > SSMax);
3. Site C (130th St): 6,112 orgs/100 ml in 2010 and 5,076 orgs/100 ml in 2011 (15 of 16 (94%) > SSMax);
3. Site F (Roosevelt St): 1,076 orgs/100 ml in 2010 and 1,310 orgs/100 ml in 2011 (17 of 17 (100%) > SSMax);
4. Nr Danville: 409 orgs/100 ml in 2010 and 388 orgs/100 ml in 2011 (11 of 17 (65%) > SSMax);
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 all five monitoring sites.
The presumptive Class B(WW1) aquatic life uses remain "not assessed". Other than indicator bacteria, the only other parameter monitored that is supported by Class B(WW1) crieria is temperature (there were no violations of the Class B(WW1) criterion for temperature in the combined 52 samples collected at the five station). Due to insufficient parameter coverage, the presumptive Class B(WW1) aquatic life uses remain "not assessed".
