Assessment Comments
Assessment remains based on 2000 and 2009 IDNR/SHL biological sampling data: FIBI = 58, 64 (good), BMIBI = 57, 56 (good) (non-riffle habitat FIBI BIC = 44; artificial substrate BMIBI BIC = 52) and is also based on results of water quality monitoring from the Turkey River Watershed project from May 2011 to November 2012.
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 (2014) 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 “partially supported” due to levels of indicator bacteria that exceed state water quality criteria (IR 5p). This is a new impairment for this assessment segment. The Class B(WW-2) aquatic life uses remain assessed (evaluated) as "fully supported" (IR 2a) based on results of IDNR/SHL biological sampling in 2000 and 2009 and based on results of water quality monitoring in 2011 and 2012. The sources of data for this assessment include (1) results of IDNR/SHL biological monitoring in 2000 and 2009 and (2) results of water quality monitoring from the Turkey River Watershed project from May 2011 to November 2012 at station CRA50 at A6/150th Street (STORET station 15450013).
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed as "partially supported" based on levels of indicator bacteria that slightly exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2011 and 2012 at monitoring station 15450013 were as follows: the 2011 geometric mean of seven samples was 146 orgs/100 ml and the 2012 geometric mean of eight samples was 404 orgs/100 ml. Both geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. Nine of the 15 samples (60%) exceeded the 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported based on biological data collected in 2000 and 2009 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 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 score was 64 (good) and the BMIBI score was 56 (good). The 2009 FIBI score was 58 (good) and the BMIBI score was 57 (good). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The non-riffle habitat FIBI BIC is 44 and the artificial substrate BMIBI BIC is 52. This segment passed the FIBI and BMIBI BICs 2/2 times in the last 10 years. The biological impairment criteria were determined from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. This aquatic life assessment is now considered "evaluated" 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 over a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 12 years (2000-2012); however, the samples were not collected during a five-year period. However, despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.
Results of chemical/physical water quality monitoring conducted as part of the Turkey River Watershed project at station 15450013 from 2011 to 2012 also suggest “full support of the Class B(WW1) aquatic life uses. No violations of Class B(WW1) water quality criteria for ammonia, pH, or temperature occurred in the 15 samples analyzed from May 2011 to November 2012. Three of the 15 samples analyzed for dissolved oxygen (20%), however, violated the Class B(WW1) criterion of 5 mg/l. The sample collected on June 4, 2012 contained 4 mg/l, the sample collected on August 1, 2012 contained 3 mg/l, and the sample collected on September 5 of 2012 contained 2 mg/l of dissolved oxygen, and all three of these samples violated the Class B(WW2) standard of 5 mg/l (note: dissolved oxygen values were reported to the nearest mg/l). According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as pH and dissolved oxygen suggests impairment of aquatic life uses. Based on IDNR’s assessment methodology, however, these results suggest that the frequency of violations is not significantly greater than 10 percent; thus, these results do not suggest impairment of the Class B(WW2) aquatic life uses. Thus, these monitoring results suggest that the Class B(WW2) aquatic life uses should be assessed (monitored) as “fully supported”.
