Assessment Comments

Assessment is based on results of IDNR ambient monthly monitoring downstream from Sac City in 2000-01 and 2001 (evaluated) Biocriteria data: Fish IBI= 54 (good); BM-IBI= 51 (fair).

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody subsegment for the North Raccoon River (IA 04-RAC-0040-2), which extended 38 miles from Highway 286 near Lanesboro in Carroll County to Cedar Creek in Sac County, was split into three subsegments:  (1) Highway 286 near Lanesboro to Camp Cr.  in Calhoun Co.  (IA 04-RAC-0040-4), (2) Camp Cr.  to Indian Cr.  northeast of Lake View in Sac Co.  (IA 04-RAC-0040-5), and (3) Indian Cr.  to Cedar Cr.  approximately 1 mile south (downstream) from Sac City (IA 04-RAC-0040-6, this one).   See IA 04-RAC-0040_5 for previous Section 305(b) assessments of the original 38-mile subsegment of the North Raccoon River.]

SUMMARY:  The Class A (primary contact recreation) uses are assessed as "not supported;" the Class B(WW) aquatic life uses are assessed as "fully supported /threatened."  Support of fish consumption uses remains "not assessed."  The source of data for this assessment is the results from the IDNR ambient monthly monitoring station downstream from Sac City in Sac County (station 10810001 (formerly station 423014)) located approximately 5 miles south of Sac City.   EXPLANATION:  The Class A uses are assessed as "not supported."  For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  Sixteen of the 21 samples collected from the Sac City station during the 2000 and 2001 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 16 non-runoff-affected samples (228 orgs/100ml) is above the Iowa Class A water quality criterion of 200 orgs/100ml; four of the 16 samples (25%) exceeded the U.S.  EPA-recommended single-sample maximum value of 400 orgs/100 ml (these results are nearly identical to those from the IDNR ambient monitoring station downstream on the North Raccoon River near Jefferson (10370001)).   According to U.S.  EPA guidelines for Section 305(b) reporting, geometric means for fecal coliforms that exceed 200 organisms/100 ml indicate nonsupport of primary contact recreation uses (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   The Class B(WW) uses are assessed (monitored) as "fully supported / threatened."  Results of monitoring at the Sac City station during the 2000-2001 biennial period show no violations of Class B(WW) (aquatic life) water quality criteria in the 32 samples analyzed for dissolved oxygen and pH, in the four samples analyzed for toxic metals, or in the 10 samples analyzed for pesticides and other toxic organic compounds.   The sample collected on March 19, 2001, however, contained 4.1 mg/l of ammonia-nitrogen and thus violated the Class B(WW) chronic water quality criterion.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), this one violation of a water quality criterion for a toxic parameter in an "abundant" data set does not suggest an impairment of the aquatic life uses.   Based on IDNR's assessment methodology for Section 305(b) reporting, however, this violation suggests that the Class B(WW) aquatic life uses should be assessed as "fully supported/threatened."  Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment (see IA 04-RAC_0040_5 assessment developed for the 2000 report).

The Class B(WW) aquatic life uses were also assessed (evaluated) using biological data collected in 2001 as part of the ambient water monitoring project and the DNR/UHL stream biocriteria project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (F-IBI) and a benthic macroinvertebrate index (BM-IBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2001 evaluated Fish IBI score was 54 (good) and 2001 evaluated BM-IBI score was 51 (fair), respectively.  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report.  The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.   The reason this site was evaluated instead of monitored for this cycle was because of the size of the waterbody.   The FIBI and BMIBI criteria were based and calibrated on wadeable streams and rivers.   This waterbody is on the upper end of being classified as a wadeable site; therefore, the criteria used to assess this may not accurately reflect the condition of the biological community.