Assessment Comments
Assessment is based on: (1) results of IDNR/UHL biological monitoring in 2006 & 2007 conducted as follow-up sampling and (2) results of IDNR/UHL water quality monitoring from January 2006 to September 2008 at station 15960002 (107th Avenue crossing) as part of the Yellow River watershed 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 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that far exceed state water quality criteria. The assessment of the Class B(WW2) aquatic life uses of this stream segment remains “partially supported” for the current (2010) cycle based on the biological data. New data indicate that the previous aquatic life impairment due to low levels of dissovled oxygen no longer exists; thus, this impairment is de-listed for the current (2010) cycle. The sources of data for this assessment include (1) results of IDNR/UHL biological monitoring in 2006 and 2007 conducted as part of the IDNR/UHL stream biological sampling, (2) results of IDNR/UHL water quality monitoring from January 2006 to June 2008 at station 15960002 (107th Avenue crossing) as part of the Yellow River watershed project, and (3) results of IDNR bacteria monitoring from January 2006 to September 2008 at station 15960002.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 27 samples collected at IDNR/UHL station 15960002 during the recreational seasons of 2006 through 2008 was 3,665 orgs/100 ml. This geometric mean far exceeds the Class A1 criterion of 126 orgs/100 ml. Twenty-six of the 27 samples (96%) exceeded Iowa’s Class A1 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 applicable state criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Thus, because the geometric mean for IDNR/UHL station 15960002 exceeds the Class A1 criterion, the primary contact recreation uses are assessed as “not supported.”
The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” due to the lack of violations of Class B(WW2) criteria. Although 17 of 76 samples (22%) collected at IDNR station 15960002 during the previous assessment cycle contained levels of dissolved oxygen that violated this criterion, none of the 53 samples collected from January 2006 through June 2008 violated this criterion. The average level of dissolved oxygen in the 53 samples was 10.5 mg/l with 95% of the values greater than 6.4 mg/l; the minimum level was 5.4 mg/l on July 20, 2006. None of the 32 samples collected at this station from January 2006 through June 2006 violated Iowa’s chronic criteria for ammonia (early life stages present). According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and IDNR’s assessment/listing methodology, these results suggest full support of the Class B(WW2) aquatic life uses.
However, the results of biological monitoring in 2006 and 2007 suggest "partial support" of the aquatic life uses in this segment. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data collected 2006. 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 2006 FIBI score was 46 (fair) and the BMIBI score was 74 (good). The 2007 FIBI scores were 48, 49 (fair) and 58 (good) and the 2007 BMIBI scores was 71 (good). 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 FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI BIC 1/4 times and passed the BMIBI BIC 2/2 times in the last five years.
This aquatic life use assessment is considered "monitored" because there were two or more samples collected in multiple years from 2004-2008.
