Assessment Comments
Assessment is based on results of IDNR/UHL ambient monthly monitoring near Hornick from 2006-08.
Basis for Assessment
[Note 1: For the 2002 report, the previous waterbody segment for the West Fork Little Sioux River (IA 06-LSR-0120-0), which extended 32 miles from its mouth to confluence with Mud Creek near Moville in Woodbury Co., was split into two subsegments: (1) mouth to confluence with an unnamed tributary 0.5 miles north of Climbing Hill (Woodbury Co. - this one) (IA 06-LSR-0120-1) and (2) unnamed tributary 0.5 miles north of Climbing Hill to Mud Creek near Moville, Woodbury Co. (IA 06-LSR-0120-2). See previous Section 305(b) from this subsegment for the assessments of the original 32-mile river reach.]
[Note 2: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" based on results of IDNR/UHL ambient water quality monitoring from 2006 through 2008. The extensive channel modifications on this river segment, however, remain a concern regarding the full support of aquatic life uses. This assessment is based on results of IDNR/UHL monthly ambient monitoring conducted during the 2006-2008 assessment period on West Fork Little Sioux River at the Highway 141 bridge approximately 1 mile east of Hornick in (STORET station 10970002).
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the 21 samples collected at the IDNR/UHL ambient monitoring station near Hornick during summer recreational seasons of 2006-2008 (1,156 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Eighteen of the 21 samples (86%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
Monitoring at the IDNR station east of Hornick showed no violations of Class B(WW2) water quality criteria in the 33 samples collected during the 2006-2008 assessment period for dissolved oxygen (minimum value = 7.2 mg/l), pH (range = 7.5 to 8.5 units), or ammonia-nitrogen (maximum value = 1.5). None of the two samples analyzed for toxic metals during the assessment period exceeded the respective Class B(WW2) criteria. These results suggest "full support" of the Class B(WW2) aquatic life uses. The extensive habitat alterations due to channel straightening in this stream system suggest a concern regarding full support of the aquatic life uses. This conclusion is based on a stream use assessment conducted by IDNR staff in 1995 (see assessments developed for the 1996, 1998, and 2000 reporting cycles for more information).
