Assessment Comments
Assessment remains based on monitoring conducted at the mouth of Sand Creek (STORET station 15280005) as part of the Lake Delhi watershed assessment from April to June, 2006.
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 Class A1 (primary contact recreation) uses remain assessed (evaluated) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” based on results of water quality monitoring conducted in 2006. The source of data used for this assessment is monitoring conducted at the mouth of Sand Creek (STORET station 15280005) as part of the Lake Delhi watershed assessment from April to June, 2006. This is the same assessment as that developed for the previous Integrated Reporting cycles.
EXPLANATION: The Class A1 (primary contact recreation) uses were 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 7 samples collected during the 2006 recreation season at the monitoring station at the mouth of Sand Creek was 383 orgs/100 ml. Five of the seven samples (71%) 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). Although these results indicate impairment of the primary contact recreation uses designated for this stream segment, the number of samples is relatively low and does not meet IDNR guidelines for developing a “monitored” (i.e., higher confidence) assessment. Thus, the assessment type is considered “evaluated” (lower confidence). While lower confidence assessments are not appropriate for addition to the state’s Section 303(d) list of impaired waters (IR Category 5), this assessment is appropriate for addition to the state list of waters in need of further investigation (IR Categories 2b or 3b).
Results of monitoring from the Lake Dehli watershed assessment station at the mouth of Sand Creek suggest that the Class B(WW2) aquatic life uses should be assessed (evaluated) as “fully supported.” The seven samples collected at this station from April to June, 2006, show no violations of Class B(WW2) criteria for dissolved oxygen, pH, or ammonia. Other than ammonia, toxic pollutants were not analyzed at this monitoring station. Although these results indicate “full support” of the aquatic life uses of this stream segment, the number of samples is relatively low and does not meet IDNR guidelines for developing a “monitored” (i.e., higher confidence) assessment. Thus, the assessment type is considered “evaluated” (lower confidence).
