Assessment Comments

Assessment is based on: (1) results of IDNR/UHL monthly ambient chemical/physical water quality monitoring conducted during the 2006-2008 assessment period at the County Road F20 bridge west of Pisgah (STORET station 10430002 (formerly station 950032)) and (2) results of IDNR/UHL biological monitoring conducted in 2000 and 2002 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" 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” based on (1) results of ambient chemical/physical water quality monitoring from 2006-2008 and (2) results of biological monitoring for fish and aquatic macroinvertebrates in 1999, 2000 and 2002.   Fish consumption uses remain "not assessed" 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/UHL monthly ambient chemical/physical water quality monitoring conducted during the 2006-2008 assessment period at the County Road F20 bridge west of Pisgah (STORET station 10430002 (formerly station 950032)) and (2) results of IDNR/UHL biological monitoring conducted in 1999, 2000 and 2002 as part of the stream biocriteria project.  

EXPLANATION:  The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   The geometric mean level of indicator bacteria (E.  coli) in the 21 samples collected at the IDNR/UHL ambient monitoring station near Pisgah during summer recreational seasons of 2006-2008 (1065 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Seventeen of the 21 samples (81%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E.  coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

Monitoring at the IDNR/UHL ambient water quality monitoring station near Pisgah showed no violations of Class B(WW1) water quality criteria during the 2006-2008 assessment period for dissolved oxygen (minimum value = 6.6 mg/l), pH (range = 7.6 to 8.5 units), or ammonia-nitrogen (maximum value = 0.93 mg/l) in the 33 samples analyzed.   In addition, levels of toxic metals in the two samples analyzed were all below Class B(WW1) chronic criteria.   (NOTE: Pesticides were not monitored at this site from 2006 through 2008.)  These results suggest "full support" of the Class B(WW1) aquatic life uses.  

However, the results of IDNR/UHL biological monitoring in 1999, 2000 and 2002 suggest “partial support” of the aquatic life uses of this stream.   This assessment was based on data collected in 1999, 2000 and 2002 as part of the IDNR/UHL 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 1999 BMIBI score was 34 (fair).   The 2002 BMIBI score was 51 (fair) and the 2000 FIBI score was 39 (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 1994-2004.   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 10 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 between 2004 and 2008 to be considered “monitored”.   This segment had multiple BMIBI samples collected in the previous 10 years (1999-2008); however, the multiple samples were not collected during 2004-2008 and/or were not collected in multiple years.   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 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.