Assessment Comments

Basis for Assessment

Fish consumption uses not assessed due to lack of monitoring.   No violations of Class B(WW) WQ criteria for conventional pollutants occurred in the 46 samples collected during the 1996-97 period.   Over a three year period (October 1994-September 1997), the following violation of Class B(WW) toxics occurred at this station:  1 of 12 samples violated the chronic criterion for copper, and 10 of 11 samples violated the chronic criterion for mercury.   Section 305(b) reporting guidelines allow one violation of chronic or acute criteria for toxic metals in 10 or more samples collected over at 3-year period in waters assessed as FST.   Thus, the 1 violation of the criterion for copper does not suggest an impaired condition.  The high percentage of samples that violate the chronic Class B(WW) criterion for mercury (91%) suggests a water quality impairment.   However, due to concerns with validity of data for trace levels of metals (especially mercury), and due to lack of high levels of mercury in fish tissue samples collected both upstream and downstream from this reach, the data for mercury were not considered for this assessment.   Based on this information, assess support of the Class B(WW) aquatic life uses as FST due to known threats form agricultural nonpoint sources.