Assessment Comments
Assessment remains based on results of IDNR/UHL water quality monitoring conducted as part of TMDL development from April through September 2005 at station 11380009.
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 (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 (2010) 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 primary contact recreation uses are assessed (evaluated) as “not supported” due to high levels of indicator bacteria. Based on overwhelming evidence of impairment, this impairment is added to Category 5p of Iowa's 2008 Integrated Report. The Class B(WW2) aquatic life uses are assessed (evaluated) as “fully supported” based on results of chemical/physical water quality monitoring during 2005. The source of data for this assessment is the results of IDNR/UHL water quality monitoring conducted as part of TMDL development from April through September 2005 at station 11380009. No additional monitoring has been conducted at this station since 2005.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (evaluated) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the seven samples collected at TMDL station 11380009 (495 orgs/100 ml) exceeded Iowa’s Class A1 criterion of 126 orgs/100 ml. All seven samples (100%) exceeded Iowa’s 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 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). The number of samples collected at this station (7) is relatively low and does not meet IDNR guidelines for developing a “monitored” (higher confidence) assessment (i.e., at least 10 samples collected over a three-year period). Thus, the assessment type is considered “evaluated” (lower confidence). Due, however, to the relatively high geometric mean (495 orgs/100 ml), and due to 100% of the samples exceeding Iowa's single-sample maximum criterion, these results strongly indicate impairment of the primary contact recreation uses presumptively designated for this stream segment. Thus, based on strong evidence of impairment, this stream segment was added to Category 5p of Iowa's 2008 Integrated Report and remains in Category 5p of Iowa’s 2010 IR.
The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” based on results of IDNR/UHL water quality monitoring conducted at station 11380009. Results of this monitoring show no violations of Class B(WW2) water quality criteria for conventional parameters dissolved oxygen or pH) or for ammonia in the seven monthly samples collected from April-September 2005. As with the assessment of support of the Class A1 uses for this segment, too few samples were collected over the 2004-2006 assessment period to allow development of a high-confidence (i.e., “monitored”) assessment.
