Cedar River IA 02-CED-455

Assessment Comments

Assessment is based on results of WQ monitoring conducted through contract w/ Duane Arnold Energy Center at Palo; this monitoring network was discontinued in 1999.

Basis for Assessment

SUMMARY:  Class A (primary contact recreation) uses were assessed as "fully supporting," Class B(WW) aquatic life uses were assessed as "fully supporting," and Class C (drinking water) uses were assessed as "fully supporting / threatened."  Fish consumption uses were assessed as "fully supporting."  EXPLANATION:  The assessments of support of the beneficial uses are based primarily on results of water quality monitoring conducted by the University of Iowa Hygienic Laboratory as part of the Cedar River Baseline Ecological Study sponsored by the Duane Arnold Energy Center at Palo, Iowa (see McDonald 1999, 2000).   Of the 26 sampling events for indicator bacteria at the four DAEC monitoring stations in this reach of river during summer periods of 1998 and 1999, only 10 sampling events were conducted at river flows that were not materially affected by surface runoff.   Higher than normal precipitation in Iowa, and especially in northeastern Iowa, during water year 1999 resulted in higher than normal river flows at many USGS gauging stations in Iowa, including the station on the Cedar River at Cedar Rapids (see pages 3 to 8 and 180 to 181 "Water Resources Data, Iowa, Water Year 1999" (Nalley et al.  2000)).   These high flows resulted in monitoring at river discharges that exceeded the long-term monthly average flow plus one standard deviation of this average (flow statistics from Fischer et al.  1990).   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 during these conditions of high runoff and river flow.   Geometric mean (GM) levels of fecal coliform bacteria for the 10 non-runoff-affected samples at each of the four monitoring stations were below the Iowa WQ standard of 200 orgs/100 ml (from upstream to downstream in Linn County):  (1) Lewis Access:  GM=88 orgs/100 ml with 1 sample (=10%) greater than the U.S.  EPA's recommended single sample maximum level of 400 orgs/100 ml; (2) upstream from Duane Arnold EC:  GM=69 orgs/100 ml, with no samples greater than the single sample maximum value; (3) downstream from Duane Arnold EC:  GM=90 orgs/100 ml with no samples greater than the single sample maximum value; (4) 0.5 miles downstream from Duane Arnold EC:  GM=63 orgs/100 ml with no samples greater than the single sample maximum value.   Based on U.S.  EPA methods for making use support decisions (EPA 1997b, pages 3-33 to 3-35), these results suggest full support of the primary contact recreation uses.   Class B(WW) aquatic life uses were assessed as "fully supporting" due to the lack of violations of water quality criteria for conventional and toxic parameters (dissolved oxygen, pH, and ammonia-nitrogen) in the 46 samples collected at each of the four monitoring stations (total of 184 samples) during the 1998-1999 biennial period.   Class C (drinking water) uses were assessed as "fully supporting / threatened" due to the relatively few violations of the U.S.  EPA MCL for nitrate.   At each of the four monitoring stations in this river reach, 5 of the 46 samples collected during the 1998-1999 biennial period exceeded the 10 mg/l MCL.   The maximum level of nitrate in the 184 samples was 13.0 mg/l.   MCL violations tended to occur in only two months:  April and June.   Mean nitrate values at the four stations (N=46) ranged from 7.0 to 7.3 mg/l, with standard deviations ranging from 2.4 to 2.5 mg/l).   Based on DNR's assessment methodology for Section 305(b) reporting, the frequency of violation at each of the four stations (= 11%) suggests that the drinking water uses should be assessed as "fully supported / threatened."  Fish consumption uses were assessed as "fully supporting" based on results from EPA/DNR fish tissue (RAFT) monitoring in 1996 that showed levels of organochlorine contaminants and toxic metals in composite samples of fillets from channel catfish and freshwater drum were below ½ of the respective FDA action levels and DNR levels of concern.