Assessment Comments
Assessment is based on results of monthly monitoring from 2006 through 2008 at the IDNR/UHL ambient city monitoring station located upstream from Spencer at the Highway 18 bridge northwest of Spencer (STORET station 10210002).
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW1) aquatic life uses, including fish consumption 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) and the results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The 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(WW1) aquatic life uses remain assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2006 through 2008. 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 2006 through 2008 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 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 upstream from Spencer during summer recreational seasons of 2006-2008 (363 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Eleven of the 21 samples (52%) 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).
The Class B(WW1) 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(WW1) water quality criteria for pH, or ammonia-nitrogen in the 32 samples collected, or for toxic metals in the 2 samples analyzed during the 2006-2008 assessment period. Monitoring results for dissolved oxygen showed that one of the 33 samples analyzed (3%) violated the Class B(WW1) water quality criterion for dissolved oxygen: the level of dissolved oxygen in the sample collected on August 14, 2007 (4.8 mg/l) was less than the Class B(WW1) 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 the Class B(WW1) aquatic life uses should be assessed as “fully supported.”
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring data for this river segment.
