Cedar River IA 02-CED-472

Assessment Comments

Assessment is based on results of IDNR ambient monthly monitoring near Janesville from 2000-02.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses were 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 2000 through December 2002 at the IDNR ambient monthly monitoring station located near Janesville in Bremer Co.  (STORET station 10090001).  

EXPLANATION:  The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station near Janesville from 2000 through 2002.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 36 samples collected or for pesticides in the nine samples analyzed during this assessment period.   Levels of pH, however, occasionally violated the Class B(WW) criterion of 9.0 pH units.   Two of the 36 samples had pH values greater than 9.0 units, with a maximum value of 9.1 units.   Both violations occurred on days when dissolved oxygen levels were well above 100% saturation:  April 12, 2000 (pH=9.1; % DO saturation=125%); May 4, 2000 (pH=9.1; DO saturation=140%).   These conditions suggest that high levels of primary productivity resulted in the high levels of pH.   Because these violations are more related to natural conditions than to pollution, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.   Fish consumption uses were not assessed due to the lack of recent fish tissue monitoring in this river segment.