Assessment Comments

Assessment is based on: (1) the results of IDNR/UHL ambient monthly monitoring during the 2004-2006 assessment period at STORET station 10440001 approximately 3 miles southwest of Oakland Mills in Henry County (formerly station number 821004) and (2) results of IDNR/UHL biological monitoring conducted in 2002 as part of the Iowa 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) and due to the completion of a Use Attainability Analysis prepared in 2007, this segment is also now 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 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 are assessed (evaluated) as "partially supported" based on results of biological monitoring conducted in 2002.   Fish consumption uses are “not assessed” due the lack of recent fish contaminant monitoring in this assessment segment.   The sources of data for this assessment include (1) the results of IDNR/UHL ambient monthly monitoring during the 2004-2006 assessment period at STORET station 10440001 approximately 3 miles southwest of Oakland Mills in Henry County (formerly station number 821004) and (2) results of IDNR/UHL biological monitoring conducted in 2002 as part of the Iowa stream biocriteria project.  

EXPLANATION:  The 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 (142 orgs/100ml) slightly exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Seven of the 24 samples (29%) exceed Iowa’s single-sample maximum value 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).   Also, according to U.S.  EPA guidelines for Section 305(b) reporting, if levels of E.  coli exceed the single-sample maximum value in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported” (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, the results for Cedar Creek suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, also suggesting that the Class A1 uses should be assessed as “partially supported/impaired.”  

Results of ambient chemical/physical water quality monitoring suggest “full support” of the Class B(WW1) aquatic life uses.   None of the approximately 35 samples collected during the 2004-2006 assessment period at the IDNR/UHL monthly station violated Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen; no violations occurred in the ten samples analyzed for toxic metals or in the seven samples analyzed for pesticides.  

Despite results of ambient chemical/physical monitoring that suggest “full support” of aquatic life uses, the results of biological monitoring conducted from 2000-2002 as part of the IDNR/UHL stream biocriteria project suggest only “partial support” of these uses.   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 fish species and benthic macroinvertebrate taxa that were collected in the stream sampling reach.   The biological metrics were combined to form a fish index of biotic integrity (FIBI) and a benthic macroinvertebrate index of biotic integrity (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 30.   The 2000-2002 BMIBI scores were 35, 40, 44, 36 (fair).   The BMIBI average was 38.8.   The aquatic life use support was assessed (evaluated) as partially supported (=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 1994-2004.   The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41.   This assessment is considered evaluated because the drainage area (529.3 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed the FIBI BIC (using the UAV +7) but failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.   Therefore, IDNR considers the aquatic life use impairments indicated by these data as “evaluated” assessments that are 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).

Fish consumption uses are “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.   Previous assessments were based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the NAWQA project.   These data are now considered too old (greater than 10 years) to accurately characterize current water quality conditions.