Assessment Comments
Assessment is based on (1) 1998 IDNR/UHL biological monitoring data: FIBI = 48 (fair); FIBI BIC = 36 and (2) 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 are assessed (monitored) as “not supported” based on data from Iowa Geological Survey snapshot monitoring from 2004-2008. The Class B(WW-2) aquatic life are assessed (evaluated) as "fully supported" based on results of biological monitoring conducted in 1998 as part of the IDNR/UHL stream biocriteria project. The sources of data for this assessment include (1) results for E. coli 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 and (2) IDNR/UHL biological (biocriteria) monitoring in 1998 (note: the 1998 sampling data are now greater than five years old; therefore, this biological assessment is now considered "evaluated" instead of "monitored").
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. The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported.”
EXPLANATION: The Class A1 uses are 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).
The Class B(WW-2) aquatic life uses remain assessed (evaluated) as “fully supporting” based on biological data collected in 1998 as part of the IDNR/UHL stream biocriteria project. The 1998 FIBI score was 48 (fair) and not enough data was available to calculate the BMIBI score. The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 36.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
