Assessment Comments

Assessment is based on: (1) IDNR/UHL biological (REMAP) monitoring conducted in 2002, 2003, and 2004 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 assessment period at the Highway 141-175 bridge at Mapleton (STORET station 10670002 (formerly station 911040)).

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 the results of an Use Attainability Analysis, 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 uses are assessed (evaluated) as "partially supported” based on results of biological monitoring in 2002, 2003, and 2004.   Results of ambient water quality monitoring from 2004 through 2006 suggest relatively good water quality in this river segment.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/UHL biological (REMAP) monitoring conducted in 2002, 2003, and 2004 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 assessment period at the Highway 141-175 bridge at Mapleton (STORET station 10670002 (formerly station 911040)).  

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 at the IDNR/UHL ambient monitoring station near Mapleton during summer recreational seasons of 2004-2006 (1,006 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Twenty of the 24 samples (83%) 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).  

Regarding support of the Class B(WW1) aquatic life uses, results of ambient chemical/physical monitoring at the IDNR/UHL station at Mapleton showed no violations of Class B(WW1) water quality criteria during the 2004-2006 assessment period for dissolved oxygen (minimum value = 7.3 mg/l), ammonia nitrogen (maximum value = 0.84 mg/l) or pH (range = 7.8 to 8.6 units) in the 36 samples collected.   Levels of pesticides in the eight samples analyzed, and levels of toxic metals in the ten samples analyzed, were all below the analytical level of detection.   These results suggest “full support” of the Class B(WW1) aquatic life uses.

Despite results of ambient physical/chemical monitoring that suggest “full support” of aquatic life uses, results of biological monitoring suggest only “partial support” of these uses.   This assessment was based on biological data collected in 2002, 2003, and 2004 as part of the DNR/UHL stream REMAP project.   A series of biological metrics that 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 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 46 (fair).   The 2003 FIBI score was 9 (poor) and the 2003 BMIBI score was 55 (fair).   The 2004 FIBI score was 14 (fair) and the 2004 BMIBI score was 50 (fair).   The FIBI average was 11.5 and the BMIBI average was 50.3.  The aquatic life use support was assessed (evaluated) 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 1994-2004.   The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This assessment is considered “evaluated” because the drainage area (734 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 failed both the FIBI and BMIBI BICs, 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.   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).

Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river reach.