Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly monitoring near Milford in 2000 & 2001.

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody segment for the Little Sioux River (IA 06-LSR-0040-1), which extended 44 miles from the confluence with the Ocheyedan River at Spencer (Clay Co.) to confluence with the West Fork Little Sioux River in Dickinson Co., was split into two subsegments:  (1) Ocheyedan River at Spencer to confluence with Milford Creek (Dickinson Co.) (IA 06-LSR-0040-1) and (2) Milford Creek to confluence with West Fork Little Sioux River (Dickinson Co.) (IA 06-LSR-0040-2).   See subsegment IA 06-LSR-0040-1 for previous Section 305(b) assessments of the original 44-mile river reach.   In addition, due to splitting of the of that segment, the previous waterbody segment for the Little Sioux River (IA 06-LSR-0040-2), which extends approximately 8 miles from the confluence with the West Fork Little Sioux River in Dickinson Co.  to the Iowa/Minnesota state line, was renumbered to IA 06-LSR-0040-3.]

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported / threatened" based on results of ambient chemical/physical water quality monitoring that show occasional violations of state water quality criteria for dissolved oxygen.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of IDNR/UHL monthly ambient monitoring conducted during the 2000-2002 assessment period near Milford (STORET station 10300001 (formerly station 920450)); this station is located approximately 1.2 miles west of Milford and is approximately 0.5 miles upstream from the confluence with Milford Creek.  

EXPLANATION:  Monitoring at the IDNR station near Milford showed no violations of Class B(WW) water quality criteria during the 2000-2002 assessment period for pH (range = 7.6 to 8.9 units) or ammonia-nitrogen (maximum value = 1.30) in the 36 samples analyzed.   Levels of pesticides in the nine samples analyzed were all below the analytical level of detection.   Levels of dissolved oxygen in two of the 36 samples (6%), however, violated the Class B(WW) criterion of 5.0 mg/l.   The sample collected on January 9, 2001, contained 4.1 mg/l, and the sample collected on March 13, 2001 contained 2.4 mg/l (the March 13th sample also contained the maximum level of ammonia-nitrogen for the biennial period (1.3 mg/l)).   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b:  page 3-17), a violation frequency for conventional parameters (including dissolved oxygen) of 10% or less does not suggest an impairment of aquatic life uses.   Regardless, the relatively poor water quality indicated by results of monitoring on March 13, 2001 (dissolved oxygen = 2.4 mg/l; ammonia-nitrogen = 1.3 mg/l) suggests a potential water quality problem in this river segment.   Thus, the Class B(WW) aquatic life uses were assessed as "fully supported / threatened."  

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