Assessment Comments
Assessment remains based on results of ambient water quality monitoring conducted at station 15570002 near Marion in summers of 2002 and 2005 as part of the Cedar Rapids intensive urban monitoring project.
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 uses remain assessed (monitored) as “not supported” due to high levels of indicator bacteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supported” based on results of ambient water quality monitoring conducted at station 15570002 near Marion in summers of 2002 and 2005 as part of the Cedar Rapids intensive urban monitoring project. The purpose of this project is to measure the daily variability of water quality through time in two urban streams in the Cedar Rapids area: McCloud Run and Indian Creek. Both streams are monitored by the City of Cedar Rapids Water Pollution Control as part of their storm water monitoring program. The daily monitoring is designed to supplement the storm water monitoring being conducted on these two streams by the City of Cedar Rapids.
EXPLANATION: The Class A1 (primary contact recreation) uses were assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. [Note: Because this assessment segment was first designated for Class A1 (primary contact recreation) uses in 2006, the data for E. coli collected as part of the 2002 sampling at station 15570001 were not used for previous Section 305(b) assessment cycles. With the addition of the Class A1 designation, these data have been used to assess the support of this beneficial use for the 2008 and subsequent assessment/listing cycles.] The geometric mean of E. coli in the 9 samples collected at the monitoring station on Indian Creek in July and August 2005 was 542 orgs/100 ml. Seven of the nine samples (78%) 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” (higher confidence) assessment (i.e., at least 10 samples collected over a three-year period). Thus, the assessment type should be 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). Addition of the three samples analyzed at the Marion station for E. coli in 2002, however, gives a sample size of 12 and an overall geometric mean of 715 orgs/100 ml. All three of the 2002 samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. These results suggest that the Class A1 primary contact recreation uses of this segment of Indian Creek should be assessed (monitored) as impaired due to high levels of indicator bacteria.
Despite impairment of the Class A1 uses, results of ambient water quality monitoring conducted in summer 2002 for the Cedar Rapids intensive urban monitoring project indicate good chemical water quality in this stream segment and “full support” of the Class B(WW2) aquatic life uses. In 2002, sampling was conducted daily on Indian Creek from about mid-May to mid August. Parameters monitored include pesticides, toxic organics, conventional parameters (including nutrients), and bacterial indicators (e.g., fecal coliforms and E. coli). In general—and in the context of the aquatic life uses designated for this stream—results of this monitoring show good water quality. The vast majority of the approximately 80 samples collected in summer 2002 did not violate the respective Class B(WW2) aquatic life criteria for dissolved oxygen, pH, or ammonia nitrogen. Monitoring for conventional parameters was not conducted as part of this study during the 2005 samplings.
One of 84 samples violated the Class B(WW2) criterion for dissolved oxygen: the sample collected on August 13, 2002 contained 4.7 mg/l of dissolved oxygen, thus violating the Class B(WW2) criterion of 5.0 mg/l. Two of 84 samples violated Class B(WW2) criteria for pH: samples collected on July 2 and August 13 had pH readings of 6.46 and 5.98 units, respectively. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), however, the percentages of violations for dissolved oxygen (1%) and pH (2%) at this station do not suggest a water quality impairment (the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated). Metals, pesticides, and other toxic organics were sampled on only three days during summer 2002: May 30, June 6 and June 8. None of the results approached the respective Class B(WW2) aquatic life criteria. Monitoring for toxic parameters was not conducted as part of this study during the 2005 samplings.
