Assessment Comments
Assessment based on 2009 and 2010 IDNR/SHL biological sampling data: FIBI = 66 (good), BMIBI = 78, 79 (excellent). Riffle habitat FIBI BIC = 65 and natural substrate BMIBI BIC = 70. Assessment is also based on results of water quality monitoring at 52nd St. Dr. from May 2010 to July 2011.
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. This stream segment is also designated as an "outstanding Iowa water" in the Iowa Water Quality standards.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” (IR 5p) due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this segment. The source of data for this assessment is the results of chemical, physical, and bacterial monitoring at 52nd St. Dr. (STORET station 15060002) from May 2010 to July 2011. The Class B(WW2) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of IDNR/SHL biological (biocriteria) sampling in 2009 and 2010.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 11 samples at 52nd St. Dr. (STORET station 15060002) collected during the recreational season of 2010 (495 orgs/100 ml), and the geometric mean of the 12 samples collected during the recreation season of 2011 (1,079 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. Twenty-one of the combined 23 samples (91%) 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 are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW2) aquatic life uses remain assessed (monitored) as "fully supporting" based on biological data collected in 2009 and 2010 as part of the IDNR/SHL stream biocriteria project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological 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 2009 FIBI score was 66 (good) and the BMIBI score was 79 (excellent). The 2010 FIBI score was unavailable and the BMIBI score was 79 (excellent). The aquatic life use support was assessed as fully supported (=FS), 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 1/1 times and BMIBI BICs 2/2 times in the last five years (2008-2012). This assessment is considered "monitored" because there were two or more samples collected from this segment in multiple years from 2008-2012.
The results of chemical/physical monitoring at 52nd St. Dr. in 2010 and 2011 indicate good chemical water quality in this stream segment and “full support” of the Class B(WW2) aquatic life uses; thus, these results are consistent with the biological assessment for this segment. No violations of Class B(WW2) water quality criteria for dissolved oxygen, pH or temperature occurred in the 23 samples analyzed from May 2010 to July 2011. These results suggest that the Class B(WW2) aquatic life uses should be assessed (monitored) as “fully supported.”
