Assessment Comments

Assessment is based on results of IDNR ambient monthly water quality monitoring near James in 2000 & 2001.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported / threatened."  Fish consumption uses remain "not assessed."  This assessment is based on results of IDNR monthly (plus) ambient monitoring conducted during the 2000-2001 biennial period at the County Road C-70 bridge north of Sioux City (station 10750001 (formerly station 950110)).   EXPLANATION:  Monitoring at the IDNR station north of Sioux City showed no violations of Class B(WW) water quality criteria for pH in the 32 samples analyzed, for toxic metals in the four samples analzlyed, or for pesticides in the 10 samples analyzed during the 2000-2001 biennial period.   Levels of dissolved oxygen and ammonia-nitrogen, however, did violate the Class B(WW) criteria during the biennial period.   The sample collected on April 1, 2001, contained 4.7 mg/l of dissolved oxygen, thus violating the Class B(WW) criterion of 5.0 mg/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violation for dissolved oxygen at this station (3.1%) does not suggest a water quality impairment.   These guidelines allow up to 10% violations of conventional parameters such as dissolved oxygen before impairment of water quality is indicated.   In addition, the sample collected on March 19, 2001 contained 1.5 mg/l of ammonia-nitrogen; this level exceeded the Class B(WW) chronic criterion of 1.10 mg/l for the water temperature and pH of that sample.   According to U.S.  EPA guidelines for Section 305(b) reporting, if, for a dataset where at least 10 samples have been collected over a three-year period, upto one sample can exceed a criterion with indicating impairment (see pg 3-18 of U.S.  EPA 1997b).   Based on IDNR modifications to the U.S.  EPA guidelines, the occurrence of one violation of a chronic criterion for a toxic parameter suggests that the aquatic life uses should be assessed as "fully supporting / threatened."  Data from this station suggest a period of relatively high levels of ammonia-nitrogen from early March through late April of 2001.   The levels of ammonia-nitrogen in the six samples collected during this period were as follows:  1.2 mg/l on March 6, 1.5 mg/l on March 19, 1.3 mg/l on March 28, 0.6 mg/l on April 3, 2.3 mg/l on April 12, and 0.8 mg/l on April 24.   Levels before and after this period were much lower (e.g., from <0.01 to 0.2 mg/l).   The high levels of ammonia-nitrogen seen in March and April 2001 at the Floyd River monitoring station are atypical for Iowa rivers, and their occurrence suggests a potential water quality problem in this river reach.   Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river reach (see assessment developed for the 2000 report).