Assessment Comments

Assessment is based on: (1) results of IDNR/UHL monthly ambient chemical/physical water quality monitoring conducted during the 2004-2006 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 current (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 also now 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 (monitored) as "fully supported” based on (1) results of ambient chemical/physical water quality monitoring from 2004-2006 and (2) results of biological monitoring for fish and aquatic macroinvertebrates in 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 2004-2006 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.  

EXPLANATION:  The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected at the IDNR/UHL ambient monitoring station NE of Missouri Valley during summer recreational seasons of 2004-2006 (776 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Sixteen of the 24 samples (67%) 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).  

Both types of monitoring conducted in this river segment suggest “full support” of the Class B(WW1) aquatic life uses.   Monitoring at the IDNR/UHL ambient water quality monitoring station near Pisgah showed no violations of Class B(WW1) water quality criteria during the 2004-2006 assessment period for dissolved oxygen (minimum value = 6.6 mg/l), pH (range = 7.9 to 8.5 units), or ammonia-nitrogen (maximum value = 0.78 mg/l) in the 36 samples analyzed.   In addition, levels of toxic metals in the ten samples analyzed, and levels of pesticides in the eight samples analyzed, were all below Class B(WW1) chronic criteria.   These results suggest "full support" of the Class B(WW1) aquatic life uses

Results of IDNR/UHL biological monitoring in 2000 and 2002 also suggest “full support” of the aquatic life uses of this stream.   This assessment was based on data collected in 2000/2002 as part of the DNR/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 2002 BMIBI score was 51 (fair) and the 2000 FIBI score was 39 (fair).   The aquatic life use support was assessed (evaluated) as fully 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 is considered FS because the FIBI score was greater than the FIBI BIC and the BMIBI score plus the UAV (8) was greater than the BMIBI BIC.

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