Assessment Comments

Assessment is based on results of (1) IDNR/SHL monthly ambient chemical/physical water quality monitoring conducted during the 2010-2012 assessment period at the County Road F20 bridge west of Pisgah (STORET station 10430002 (formerly station 950032)) and (2) IDNR/SHL biological monitoring conducted in 2000, 2002 and 2012 as part of the stream biocriteria project.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW1) aquatic life uses, including fish consumption 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 presumptively designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported” (IR 3b-c) based on results of biological sampling in 2000, 2002 and 2012.   Results of ambient water quality monitoring suggest "full support" of the Class B(WW1) uses.   Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river segment.   The sources of data used for this assessment include (1) results of IDNR/SHL monthly ambient chemical/physical water quality monitoring conducted during the 2010-2012 assessment period at the County Road F20 bridge west of Pisgah (STORET station 10430002 (formerly station 950032)) and (2) results of IDNR/SHL biological sampling conducted in 2000, 2002 and 2012 as part of the stream biocriteria project.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) are assessed 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 24 samples collected during the recreational seasons of 2010 through 2012 at Soldier River near Pisgah were as follows:  the 2010 geometric mean was 750 orgs/100 ml, the 2011 geometric mean was 234 orgs/100 ml and the 2012 geometric mean was 395 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Twelve of the 24 samples (50%) 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 are "not supported" (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.”  

Monitoring at the IDNR/SHL ambient water quality monitoring station near Pisgah showed no violations of Class B(WW1) water quality criteria during the 2010-2012 assessment period for dissolved oxygen (minimum value = 7.2 mg/l), pH (range = 7.8 to 8.5 units), temperature (maximum = 30.2C), or ammonia-nitrogen (maximum value = 0.57 mg/l) in the 36 samples analyzed.   Levels of chloride and sulfate were below their respective Class B(WW1) criteria in all 36 samples analyzed.   These results suggest "full support" of the Class B(WW1) aquatic life uses.  

However, the results of IDNR/SHL biological monitoring in 2000, 2002 and 2012 suggest “partial support” of the aquatic life uses of this stream.   This assessment was based on data collected in 2000, 2002 and 2012 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 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 2000 FIBI score was 39 (fair).   The 2002 BMIBI score was 51 (fair) and the 2012 BMIBI score was 33 (fair).   The aquatic life use support was assessed (evaluated) as "partially supporting”, 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 FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This segment passed the FIBI BIC in 2000 and passed the BMIBI BIC 0/2 times in the last 11 years.

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 years in a recent five year period to be considered “monitored”.   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 remains in IR Category 5p based on the bacteria data.

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.