Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (biocriteria) sampling in 2000 and (2) IDNR/UHL monitoring for pesticides and toxic metals in 2002.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) 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 station 15570001, however, do not suggest toxic-related water quality impacts in this stream segment.
EXPLANATION: The Class B(LR) aquatic life uses continued to be assessed 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 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 site FIBI BIC for this ecoregion is 44 and the natural substrate BMIBI BIC for this ecoregion is 70.
Results of water quality monitoring conducted 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(LR) criterion of 55 ug/l. The May 29, 2002 sample also contained 100 ug/l of total lead, thus exceeding the Class B(LR) criterion of 80 ug/l. These single violations of Class B(LR) 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.
