Assessment Comments
Assessment based on: (1) IDNR/SHL biological sampling in 2012 and 2013, and (2) results of monitoring at two stations from May 2011 to July 2012: STORET station 15570001 at Cedar Rapids and STORET station 15570004 at Thomas Park.
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 presumptive Class A1 uses are assessed (monitored) as “partially supported” (IR 5p) due to levels of indicator bacteria that violate Class A1 criteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as "partially supported" (IR 5b-v) based on results of IDNR/SHL biological sampling in 2012 and 2013. Results of water quality monitoring from May 2010 to July 2011 do not suggest chemical/physical water quality impacts in this stream segment. The sources of data for this assessment remain (1) IDNR/SHL biological sampling in 2012 and 2013 and (2) the results of monitoring at two stations on Indian Creek sampled from May 2010 to July 2011: STORET station 15570001 at Cedar Rapids and STORET station 15570004 at Thomas Park.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria (E. coli) at two stations in the Cedar Rapids area. The geometric mean of indicator bacteria (E. coli) in the 12 samples collected at Station 15570001 near Cedar Rapids during the recreational season of 2010 (723 orgs/100 ml), and the geometric mean of the 12 samples collected during 2011 (564 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. Seventeen of the 23 samples (71%) collected at this station exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. Similarly, the geometric mean of indicator bacteria (E. coli) in the 11 samples collected at Station 15570004 at Thomas Park during the recreational season of 2010 (1,630 orgs/100 ml), and the geometric mean of the 12 samples collected during 2011 (1,669 orgs/100 ml) both far exceeded the Class A1 criterion of 126 orgs/100 ml. All 23 of the samples (100%) from this station 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 is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW-2) aquatic life uses are assessed (monitored) as "partially supported" based on results of IDNR/SHL biological (biocriteria) sampling in 2012 and 2013. 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 2012 FIBI score was 69 (good) and the BMIBI score was 62 (good). The 2013 FIBI score was 68 (good) and the BMIBI score was 65 (good). 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 1994-2008. The riffle habitat FIBI BIC for this ecoregion is 65 and the natural substrate BMIBI BIC for this ecoregion is 70. This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 0/2 times in the last five years (2009-2013).
This aquatic life assessment is now considered "monitored" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”.
Results of chemical/physical water quality monitoring from 2010 to 2011, however, suggest that the Class B(WW2) aquatic life uses should be assessed (monitored) as “fully supported.” No violations of Class B(WW2) water quality criteria for dissolved oxygen, pH, or temperature occurred in the 24 samples analyzed from May 2010 to July 2011 at station 15570001 and at station 15570004.
