Assessment Comments
Assessment is based on results of ambient water quality monitoring conducted at station 15570005 at Donnelly Park during July and August of 2005 as part of the Cedar Rapids intensive urban monitoring project.
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 (evaluated) as “not supported” due to high levels of indicator bacteria. Due to overwhelming evidence of impairment, the bacterial impairment in this segment is added to Category 5p of Iowa's 2008 Integrated Report. The Class B(WW2) aquatic life uses are “not assessed” due to the lack of water quality information upon which to base an assessments. The source of data for this assessment is the results of ambient water quality monitoring conducted at station 15570005 at Donnelly Park during July and August of 2005 as part of the Cedar Rapids intensive urban monitoring project.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses were assessed (evaluated) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. 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 A1 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 of E. coli in the 9 samples collected at the monitoring station on Dry Creek in July and August 2005 was 368 orgs/100 ml; this geometric mean exceeds Iowa’s Class A1 criterion of 126 orgs/100 ml. Eight of the nine samples (89%) 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 (nine) 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). Due, however, to the relatively high geometric mean (368 orgs/100 ml), and due to 100% of the nine 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 is added to Category 5p of Iowa's 2008 Integrated Report.
The Class B(WW2) aquatic life uses remain “not assessed” due to the lack of chemical or biological water quality information upon which to base an assessment.
