Dick Creek IA 05-CHA-1336

The (evaluated) assessment of the Class B(WW2) aquatic life uses was based on data collected in 2008 and 2009 by IDNR/SHL in support of SI/TMDL development.   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 2008 FIBI score was 26 (fair) and the 2008 BMIBI score was 26 (poor).   The 2009 FIBI score was 29 (fair) and the 2009 BMIBI score was 46 (fair).   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 from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The FIBI BIC for this ecoregion is 33 and the BMIBI BIC is 41.   This segment passed the BIBI BIC 0/2 times and passed the BMIBI BIC 1/2 times in the last seven years.

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2010-2014.  Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).  IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).  However, despite this change in assessment methodology and type, this waterbody moves from IR Category 5b-v to 5b-t and remains on Iowa’s 2010 Section 303(d) list of impaired waters.