Assessment Comments
Assessment is based on results of (1) IDNR/UHL ambient monthly water quality monitoring from 2000-02 and (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1994.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported / threatened" due to a single violation of state water quality criteria for ammonia-nitrogen. The Class C (drinking water) uses are assessed (monitored) as "fully supported / threatened" due to a violation of state water quality criteria for atrazine. Fish consumption uses are assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring in 1994. This assessment is based on (1) results of IDNR monthly ambient monitoring conducted during the 2000-2002 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)) and (2) results of U.S. EPA / IDNR fish contaminant (RAFT) monitoring in 1994.
EXPLANATION: Monitoring at the IDNR station near Shambaugh showed no violations of Class B(WW) water quality criteria during the 2000-2002 assessment period for dissolved oxygen 5(minimum value = 8.4 mg/l) or pH (range = 7.5 to 8.8 units) in the 36 samples collected. The sample collected on October 1, 2001, however, contained a level of ammonia-nitrogen (1.5 mg/l) that violated pH-dependent chronic criterion of 0.65 mg/l. Levels of pesticides in the nine samples analyzed were all below the analytical level of detection. These results suggest "full support" of the Class B(WW) aquatic life uses. According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), uses are “fully supported” if chronic criteria for a toxic pollutant (for example, ammonia) are exceeded in up to one sample from a dataset based on monthly monitoring. IDNR assessment guidelines, however, specify that one violation of a toxic parameter (e.g., ammonia) indicates a “threat” to full support of the designated uses.
The Class C (drinking water) uses were assessed as "fully supported / threatened" due to a single violation of the state water quality criterion for atrazine. One of 36 samples analyzed exceeded the MCL for atrazine of 3.0 ppb (mean atrazine = 0.7 ppb; maximum = 18 ppb). According to IDNR guidelines for Section 305(b) assessments, these results do not suggest an impairment of drinking water uses due to atrazine but do suggest a “threat” to full support of the drinking water uses. Results of IDNR ambient monthly monitoring near Shambaugh show no violations of the nitrate MCL in the 36 samples collected during the 2000-2002 assessment period (mean=2.2 mg/l; maximum=10.0 mg/l).
Fish consumption uses remain assessed (evaluated) as "fully supported" based on results of the U.S. EPA/IDNR fish tissue (RAFT) monitoring near Shambaugh in 1994. However, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively low confidence). This site was again monitored as part of the 2003 RAFT program; the results from this monitoring, however, are not yet available.
