Assessment Comments
Assessment is based on results of IDNR/UHL ambient water quality monitoring from 2004 through 2006 near Palo.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to levels of indicator bacteria that exceed state criteria. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring. Fish consumption uses remain not assessed due to the lack of fish contaminant monitoring in this river segment. The source of data for this assessment is the results of monthly monitoring from January 2004 through December 2006 at the IDNR ambient city monitoring station located at County Road E36 east of Palo (STORET station 10570002).
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria (E. coli) at the IDNR/UHL ambient monitoring station on the Cedar River east of Palo. 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 25 samples collected (56 orgs/100ml) is well below the Iowa Class A1 water quality criterion of 126 orgs/100ml. Five of the 25 samples (20%), however, exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if levels of E. coli exceed the single-sample maximum criterion 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, 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”. Note: one less violation of the single-sample maximum criterion for E. coli during the 2004-2006 period would have resulted in an assessment of “fully supported” for the Class A1 uses.
The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of water quality monitoring from the IDNR ambient station near Palo. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen or ammonia-nitrogen in the approximately 35 samples analyzed, or for toxic metals in the approximately 15 samples analyzed during this assessment period. The level of pH, however, in two of the 36 samples from the IDNR/UHL station violated the Class B(WW1) criterion of 9.0 pH units. Because these violations are more likely related to natural conditions than to a pollutant, the occurrence of the high level of pH in this river segment is not seen as a water quality impairment. In addition, the frequency of pH violations does not suggest impairment: according to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as pH suggest "full support" of aquatic life uses. Thus, the percentages of violations of the pH criterion at the IDNR station (6%) does not suggest an impairment of aquatic life uses.
Fish consumption uses remain “not assessed” due to lack of recent fish tissue monitoring in this river segment.
