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 2008 through December 2010 and on 2004 IDNR Fisheries Bureau fish sampling.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” based on results of monitoring for 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 2008 through December 2010 and IDNR Fisheries Bureau fish sampling in 2004.  

EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria during the recreational seasons of 2008-10.   The geometric means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at Otterville Access station were as follows:  the 2008 geometric mean was 105 orgs/100 ml, the 2009 geometric mean was 108 orgs/100 ml and the 2010 geometric mean was 248 orgs/100 ml.   The 2008 and 2009 geometric means are below the Class A1 criterion of 126 orgs/100 ml.   The results are consistent with the history of generally low levels of indicator bacteria in this river segments.   The 2010 geometric mean, however, exceeds this criterion.   Also, six of the 22 samples (27%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

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 33 samples collected at the IDNR station during the 2008-2010 period.   In addition, no violations of Class B(WW1) chronic criteria occurred in the three samples analyzed for toxic metals and for pesticides during the assessment period.  

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.