Assessment Comments
Assessment is based on results of WQ monitoring conducted by Duane Arnold Energy Center at Palo, by IDNR near Palo, and by Cedar Rapids Water Dept. See attached document for details.
Basis for Assessment
[Note: For the 2002 report, the previous waterbody segment IA 02-CED-0030-0, which extended 57 miles from Prairie Creek at Cedar Rapids to Wolf Creek at LaPorte City, was split into four subsegments: (1) Prairie Creek to McCloud Run at Cedar Rapids (IA 02-CED-0030-1), (2) McCloud Run to Bear Creek near Palo (IA 02-CED-0030-2), (3) Bear Creek to Hinkle Creek near Vinton (IA 02-CED-0030-3), and (4) Hinkle Creek to Wolf Creek (IA 02-CED-0030-4). See assessment information for segment IA 02-CED-0030_1 for previous Section 305(b) assessments for the original 57-mile river reach. Also note that the ambient water quality monitoring network sponsored by the Duane Arnold Energy Center near Palo was terminated in December 1999. Monitoring as part of the IDNR ambient water quality monitoring network began in November 1999 at the county road E-36 bridge east of Palo. This new site is downriver from the Duane Arnold facility and is downriver from all four of the former DAEC sites.]
SUMMARY: The Class A (primary contact recreation) uses and the Class B(WW) aquatic life uses were assessed as "fully supported." The Class C (drinking water) uses were assessed as "fully supported/threatened" with a declining water quality trend. Fish consumption uses were not assessed. The sources of data for this assessment are (1) the results of monthly monitoring from October 1999 through September 2001 at the IDNR ambient city monitoring station located at County Road E36 east of Palo and (2) the results of ambient monitoring of the Cedar River for nitrate by the Cedar Rapids Water Department during 2000 and 2001. EXPLANATION: The Class A uses were assessed as "fully 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." Seven of the 9 samples collected from the Palo 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 seven non-runoff-affected samples (24 orgs/100ml) is well below the Iowa Class A water quality criterion of 200 orgs/100ml. In addition, none of the seven samples contained a level of fecal coliform bacteria that exceeded the U.S. EPA-recommended single-sample maximum value of 400 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if the geometric mean is less than 200 orgs/100ml, and less than 10% or less of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "fully supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Because less than 10 non-flow affected samples were available for this assessment, the assessment type is considered "evaluated"; thus, this assessment is not of sufficient quality to support a Section 303(d) listing or de-listing. Nonetheless, the assessment for the 2000 report (above) was based on at least 10 non-flow affected samples (i.e., a "monitored" assessment), and, consequently, this assessment is appropriate for Section 303(d) listing/de-listing. Thus, on the basis on a monitored assessment in 2000 suggesting full support of Class A uses, and with the supporting "evaluated" assessment for the 2002 report, this river segment is fully supporting its Class A use and should not be included on Iowa's Section 303(d) list. The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station near Palo in 2000 and 2001. Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen, ammonia-nitrogen, or for toxic metals and toxic organic compounds in the 14 samples analyzed during this biennial period. The level of pH, however, in one of the 14 samples violated the Class B(WW) criterion of 9.0 pH units in one sample. The sample collected on October 9, 2000 had a pH level of 9.2 units which is greater than the Iowa water quality standard of 9.0 pH units. This violation occurred on a day with an extremely high level of dissolved oxygen (19.2 mg/l) and a percent DO saturation of > 140%. These conditions suggest that the high level of primary productivity resulted in the high level of pH. Because this violation is more related to natural conditions than to pollution, the occurrence of the high level of pH in this river segment is not seen as a water quality impairment. The Class C (drinking water) uses were assessed as "fully supported/threatened" with a declining water quality trend due to violations of the MCL for nitrate. Results of IDNR ambient monthly monitoring at the Palo station show only one violation of the nitrate MCL in the 14 samples collected during the 2000-2001 biennial period (mean=4.8 mg/l; maximum=11.0 mg/l). Monitoring of the Cedar River by the Cedar Rapids Water Department near their water supply intake in 2000 and 2001 supports this assessment: 56 of the 420 samples collected during 2000 and 2001 (13.3%) had levels of nitrate above the nitrate MCL of 10 mg/l (mean=5.9 mg/l; maximum=13.2 mg/l). All 56 violations occurred during the spring and early summer with the majority of violations (40 of 56) occurring during June of 2000 and 2001. According to IDNR's assessment guidelines, both these datasets suggest that full support of the Class C use is "threatened." That is, if the MCL is exceeded during the biennial period, but no more than 15% of samples exceed the MCL, the full support of drinking water uses is considered "threatened." Additional information supplied by the Cedar Rapids Water Department shows evidence of increasing nitrate levels over time. This increasing trend in nitrate suggests that less than full support is likely within the next few years. According to IDNR assessment guidelines, waterbodies assessed as "fully supported with a declining water quality trend are considered "impaired" and are candidates for Section 303(d) listing. This assessment is consistent both with previous assessment (see assessments of Class C uses for the 2000 and 1998 reports above) and with placement of this river segment on Iowa's 1998 Section 303(d) list of impaired waters. Fish consumption uses were not assessed due to lack of recent fish tissue monitoring in this river segment.
