Assessment Comments
Assessment is based on water quality monitoring at Elkader from May to November 2011 and at Highway 13 from April to November 2012.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (evaluated) as partially supporting (IR Category 3b) based on bacterial monitoring in 2011 and 2012. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR Category 2a) based on results of water quality monitoring in 2011 and 2012. Fish consumption uses remain “not assessed” (IR Category 3a) due to the lack of monitoring data upon which to base an assessment. Sources of data for this assessment include results of water quality monitoring from (1) May to November 2011 at Elkader (STORET station 15220021, aka, TR30) and (2) April to November 2012 at Hwy. 13 (STORET station 15220045, aka, TR28).
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (evaluated) as "partially supported" based on levels of indicator bacteria that potentially exceed state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the seven monthly samples collected during the recreational season of 2011 at the monitoring station at Elkader (90 orgs/100 ml), however, was well below the Class A1 geometric mean criterion of 126 orgs/100 ml. Similarly, the geometric mean of the eight samples collected during the recreation of 2012 at Hwy. 13 (109 orgs/100 ml) was below the Class A1 criterion. These results suggest “full support” of the Class A1 (primary contact recreation) uses. Two of the seven samples collected in 2011 (29%), and two of the eight samples collected in 2012 (25%), however, exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to IDNR’s assessment/listing methodology, if at least 10 samples are collected during the recreation season, and if significantly greater than 10% of these samples exceed Iowa’s single sample maximum criterion of 235 orgs/100 ml, the Class A1 uses should be assessed as impaired. Because, however, less than 10 samples were collected at these sites, the confidence level in the assessment is relatively low, and thus this assessment is appropriate for placement on Iowa’s list of waters in need of further investigation (IR Category 3b). The fact that the geometric means from both sites in both years met the Class A1 criterion, however, suggests relatively low levels of indicator bacteria in this assessment segment.
Results of chemical/physical water quality monitoring in 2011 and 2012 do not suggest impairment of the Class B(WW1) aquatic life uses. Monitoring at stations at Elkader and Hwy. 13 showed no violations of Class B(WW1) water quality criteria for ammonia, dissolved oxygen, or pH in the approximately 7 samples analyzed at each station. Thus, the Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported”.
The previous assessment of the Class B(WW1) uses in this segment (fully supported/evaluated) was based on biological data collected in 2000 as part of an IDNR Fisheries stream sampling project. Because the biological data upon which this assessment was based are now more than ten years old, these data are no longer useful for purposes of water quality assessment. As data age beyond ten years, their ability to represent current water quality conditions is increasing suspect. Additional monitoring is needed in this assessment segment to update status of its aquatic communities. Thus, the current (2014) assessment of the Class B(WW1) uses will be based on the results of chemical/physical water quality monitoring conducted in 2011 and 2012 in this river segment.
Fish consumption uses remain “not assessed” due to the lack of monitoring data upon which to base an assessment.
