Pilot Branch IA 05-NSH-1424

Assessment Comments

Assessment remains based on 1996, 2002 and 2009 IDNR/SHL biological sampling data: FIBI = 42, 30 (fair) and 51 (good), BMIBI = 63 (good), 49 (fair) and 63 (good). FIBI BIC = 31, BMIBI BIC = 54.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses.   According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters.   Thus, for the current (2014) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are "not assessed" (IR Category 3a) due to the lack of information upon which to base an assessment.   The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as "fully supported" (IR Category 2a) based on results of IDNR/SHL biological sampling in 1996, 2002, and 2009.   The assessment type is considered "evaluated" (relatively lower confidence assessment) due to the uncertainty of using biological assessment methods developed for larger wadeable streams for assessing aquatic life conditions in small headwater stream segments.

EXPLANATION:  The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as "fully supported" based on data collected in 1996, 2002 and 2009 as part of the IDNR/SHL stream biocriteria project.   The 1996 FIBI score was 42 (fair) and the BMIBI score was 63 (good).   The 2002 FIBI score was 30 (fair) and the BMIBI score was 49 (fair).   The 2009 FIBI score was 51 (good) and the BMIBI score was 63 (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 from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This segment passed the FIBI BIC 2/3 times and passed the BMIBI BIC 2/3 times in the last 17 years.  

Even though this site passed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.