Assessment Comments
Assessment remains based on results of bacterial monitoring conducted as part of Iowa Geological Survey snapshot monitoring from 2006-2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (monitored) as “not supported” (IR 4a) based on data from Iowa Geological Survey snapshot monitoring from 2004-2008. The Class B(WW-2) aquatic life remain “not assessed” (IR 3a) due to lack of recent biological data upon which to base an assessment. The source of data for this assessment is the results for E. coli monitoring from 2006-2008 at two monitoring stations sampled as part of Iowa Geological Survey Watershed Snapshot monitoring: station 977102 in West Des Moines at the road crossing on 73rd Street and station 977111 in West Des Moines at the road crossing on NW 114th Street. The IDNR/SHL biological sampling from 1998 are now considered too old (greater than 10 years) to characterize current water quality conditions.
Note: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by IDNR and approved by EPA in June 2008. Thus, this impairment is placed into Category 4a of Iowa’s Integrated Report.
EXPLANATION: The Class A1 uses remain assessed (monitored) as “not supported” due to levels of indicator bacteria (E. coli) that exceed state water quality criteria. The geometric mean levels of indicator bacteria (E. coli) in the 10 recreational season samples collected at each station as part of snapshot monitoring events from 2006-2008 (983 orgs/100ml at station 977102 and 1,107 orgs/100 ml at station 977111) both far exceed the Iowa Class A1 water quality criterion of 126 orgs/100ml. All 10 samples at each station exceeded the Iowa single-sample maximum Class A1 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).
Although previously assessed as “fully supporting”, the Class B(WW-2) aquatic life uses are now considered “not assessed” due to the age of the biological data (greater than 10 years) upon which the previous assessments were based.
