Little Sioux River IA 06-LSR-1577

Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly city monitoring upstream of Spencer from 2002-04.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses remain assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2002 through 2004.   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 2002 through 2004 at the IDNR/UHL ambient city monitoring station located upstream from Spencer at the Highway 18 bridge northwest of Spencer (STORET station 10210002).  

EXPLANATION:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring.   Monitoring at the IDNR/UHL city station upstream from Spencer showed no violations of Class B(WW) water quality criteria for pH, or ammonia-nitrogen in the 36 samples collected, for toxic metals in the 32 samples analyzed, or for pesticides in the seven samples analyzed, during the 2002-2004 assessment period.   Monitoring results for dissolved oxygen, however, showed that one of the 36 samples analyzed (3%) violated the Class B(WW) water quality criterion for dissolved oxygen: the level of dissolved oxygen in the sample collected on February 10, 2004 (4.1 mg/l) was less than the Class B(WW) criterion of 5.0 mg/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), however, if 10% or less of samples exceed criteria for conventional parameters (e.g., dissolved oxygen and pH), aquatic life uses should be assessed as “fully supported”.   Thus, these results suggest “full support” of the Class B(WW) aquatic life uses.  

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring data for this river segment.