Assessment Comments
Assessment is based on: (1) IDNR/UHL biological (biocriteria) sampling in 2000, and (2) results of monitoring at two stations on Indian Creek sampled in 2002 and 2005 as part of the Cedar Rapids Intensive Urban Water Quality Study: station 15570001 at Cedar Rapids and station 15570004 at Thomas Park.
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 (monitored) as “not supported” due to high levels of indicator bacteria. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of IDNR/UHL biological (biocriteria) sampling in 2000. Results of water quality monitoring for pesticides and toxic metals from late May through mid-August 2002 at IDNR stations 15570001 do not suggest toxic-related water quality impacts in this stream segment. The source of data for this assessment is the results of monitoring at two stations on Indian Creek sampled in 2002 and 2005 as part of the Cedar Rapids Intensive Urban Water Quality Study: station 15570001 at Cedar Rapids and station 15570004 at Thomas Park.
EXPLANATION: The Class A1 uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E. coli) at two stations in the Cedar Rapids Intensive Urban Water Quality Study. [Note: Because this assessment segment was only recently designated for Class A1 (primary contact recreation) uses, the data for E. coli collected as part of the 2002 sampling at station 15570001 have not been used for previous Section 305(b) assessment cycles. With the addition of the Class A1 designation, these data can now be used to assess the support of this beneficial use.]
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 A 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 A1 uses for purposes of Section 305(b) assessments and Section 303(d) listings.
Daily samples were analyzed for E. coli at the Cedar Rapids station (15570001) from May 29 to August 18, 2002. Using the E. coli data from these 78 samples, fifty-one 30-day geometric means were calculated for summer 2005. All of the 51 geometric means exceeded Iowa’s Class A1 water quality criterion of 126 orgs/100 ml; the minimum 30-day geometric mean was 237 orgs/100 ml. In addition, the geometric means of the nine samples collected in summer 2005 at the Cedar Rapids (338 orgs/100 ml) and Thomas Park (1,209 orgs/100 ml) stations both exceeded the Class A1 criterion. Fifty-four of the 78 samples collected in summer 2002 exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. In 2005, five of nine samples (56%) exceeded this criterion at the Cedar Rapids station, and seven of nine samples (78%) exceed this criterion at the Thomas Park station. According to U.S. EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, if the geometric mean level 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). In addition, significantly more than 10% of the samples at both stations exceeded Iowa’s single-sample maximum criterion of 235 E. coli orgs/100 ml. These results suggest impairment of the Class A1 uses of this stream segment.
The Class B(WW-2) aquatic life uses continued to be assessed (evaluated) as "partially supported" based on results of DNR/UHL biological (biocriteria) monitoring in 2000. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2000 FIBI scores were 36 (fair) and 66 (good); the BMIBI scores were 45 (fair) and 63 (good). The FIBI average was 51 and the BMIBI average was 54. The aquatic life use support was assessed (evaluated) as Partially Supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The non-riffle habitat FIBI BIC for this ecoregion is 44 and the natural substrate BMIBI BIC for this ecoregion is 70. The 2000 sampling data are now greater than five years old; therefore, this aquatic life use assessment is now considered "evaluated" instead of "monitored".
Results of water quality monitoring conducted in 2002 at IDNR station 15570001 at Cedar Rapids suggest levels of toxic contaminants are low in Indian Creek. This monitoring was conducted as part of the Cedar Rapids intensive urban water quality study. During the 10-week period from late May to mid-August 2002, 78 samples were collected and analyzed for the following toxic contaminants: cadmium, chlorpyrifos, chromium, copper, DDD, DDE, DDT, dieldrin, lead, nickel, and zinc. Single violations for copper and lead were reported: the sample collected on May 29, 2002 contained 80 ug/l of total copper, thus exceeding the Class B(WW2) criterion of 55 ug/l. The May 29, 2002 sample also contained 100 ug/l of total lead, thus exceeding the Class B(WW2) criterion of 80 ug/l. These single violations of Class B(WW2) water quality criteria, however do not indicate impairment of the aquatic life uses: according to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-18), one violation of a water quality criterion for a toxic pollutant in an abundant data set (at least 10 samples over at three-year period) does not indicate an impairment of aquatic life uses. Monitoring for toxic parameters was not conducted as part of this study during the 2005 samplings.
