Assessment Comments

Assessment is based on results of IDNR/UHL monthly ambient water quality monitoring conducted on the Wapsipinicon R. just north of Independence at the Otterville Access (STORET station 10100001) during the period from January 2004 through December 2006 and on 2004 IDNR Fisheries Bureau fish sampling.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to high levels of indicator bacteria (E.  coli).   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported."  Fish consumption uses were not assessed due to the lack of fish contaminant monitoring in this river reach.   The source of data for this assessment is results of IDNR/UHL monthly ambient water quality monitoring conducted on the Wapsipinicon R.  just north of Independence at the Otterville Access (STORET station 10100001) during the period from January 2004 through December 2006 and IDNR Fisheries Bureau fish sampling in 2004.    

EXPLANATION:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria from 2004-06.   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 the 2006 Section 305(b) assessments and Section 303(d) listings.  

The geometric mean of E.  coli in the 70 samples collected was 123 orgs/100 ml; this geometric mean is slightly below the Iowa water quality standard of 126 orgs/100 ml and suggests generally low levels of bacteria in this river reach.   Seventeen of the 70 samples (24%), however, exceeded the EPA-recommended single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed the single-sample maximum criterion for indicator bacteria, 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, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired.”  

Due to the availability of weekly bacteria data for the recreation seasons of 2004 and 2005 at the IDNR/UHL ambient station (10100001), the thirty-day/five-sample geometric means were calculated for these two recreation seasons (in 2006, the sampling frequency at this monitoring station returned to monthly).   In the 2004 recreation season, 13 of the 31 thirty-day geometric means exceeded Iowa’s Class A1 criterion of 126 orgs/100 ml.   In the 2005 recreation season, 17 of the 31 geometric means exceeded the Class A1 criterion.   As noted above, U.S.  EPA guidelines for Section 305(b) reporting and the IDNR assessment/listing methodology state that a single geometric mean greater than the state criterion of 126 orgs/100 ml.  suggests that the Class A1 uses are “not supported.”  Thus, when assessed on the basis of thirty-day/5-sample geometric means, the data for indicator bacteria at this station suggest nonsupport of the Class A1 uses.  

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" due to the lack of violations of state water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the approximately 36 samples collected at the IDNR station during the 2004-2006 period.   In addition, no violations of Class B(WW1) chronic criteria occurred in the 10 samples analyzed for pesticides and toxic metals during the assessment period.  

In addition, the results of the 2004 IDNR Fisheries Bureau fish sampling suggest this segment is fully supporting (evaluated) its aquatic life uses.   This evaluated biological assessment was based on data collected in 2004 by the IDNR Fisheries Bureau.   A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data.   The biological metrics are based on the numbers and types of fish species collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2004 FIBI score was 48 (fair).  The aquatic life use support was assessed (evaluated) as Fully Supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The non-riffle FIBI BIC for this ecoregion is 44.   This assessment is considered evaluated because the drainage area (905 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, 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.

The fish consumption uses remain “not assessed” due to the lack of recent fish tissue monitoring in this river segment.