Assessment Comments
Assessment is based on results of IDNR/UHL ambient monthly water quality monitoring north of Independence from 2002-04.
Basis for Assessment
SUMMARY: Class A (primary contact recreation) uses are assessed (monitored) as “partially supported” due to high levels of indicator bacteria (E. coli). The Class B(WW) 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 2002 through December 2004.
EXPLANATION: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria from 2002-04. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 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 39 samples collected was 108 orgs/100 ml; this geometric mean is below the Iowa water quality standard of 126 orgs/100 ml and suggests generally low levels of bacteria in this river reach. Eight of the 39 samples (20%), however, exceeded the EPA-recommended single-sample maximum value 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 value 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 value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”.
The Class B(WW) aquatic life uses were assessed as "fully supported" due to the lack of violations of state water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the approximately 34 samples collected at the IDNR station during the 2002-2004 period. In addition, no violations of Class B(WW) chronic criteria occurred in the 10 samples analyzed for pesticides and toxic metals during the assessment period.
The fish consumption uses remain “not assessed” due to the lack of recent fish tissue monitoring in this river segment.
