Assessment Comments
Assessment remains based on: (1) results of IDNR/UHL TMDL-related water quality monitoring near Woolstock (STORET station 11400001) from May to September 2005 and (2) results of biological monitoring conducted by the IDNR Fisheries Bureau in 1998.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 and due to the results of an Use Attainability Analysis in 2007, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (evaluated) as "not supported" (IR Category 2b) based on results of ambient monitoring for indicator bacteria (E. coli) in 2005. The Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supporting” based on results of chemical water quality monitoring conducted in 2005 and in 2010. Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this assessment segment. The sources of data for this assessment are (1) results of IDNR/UHL TMDL-related water quality monitoring near Woolstock (STORET station 11400001) from May to September 2005 and (2) results of biological monitoring conducted by the IDNR Fisheries Bureau in 1998. Note: USGS conducted monitoring in this assessment segment at station 05480820 near Goldfield from March to October 2010. Samples were analyzed for dissolved oxygen and pH; no results for indicator or toxics were produced. This limited amount of data will be used to supplement the limited data from IDNR TMDL monitoring in 2005 in order to assess support of the Class B(WW1) uses.
EXPLANATION: The Class A1 uses remain assessed (evaluated) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the three samples collected in from May through September at the IDNR/UHL TMDL station near Woolstock (STORET station 11400001) (167 orgs/100ml) slightly exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Only one of the five samples (20%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). The amount of data available for this assessment (five samples) does not meet IDNR guidelines for Clean Water Act assessment and listing that require at least 10 samples be collected per site over a three-year period. Assessments based on data that do not meet IDNR assessment/listing guidelines are considered “evaluated” (i.e., of lower confidence); these assessments are not appropriate for adding waters to Iowa’s Section 303(d) list of impaired waters. Such assessments are, however, appropriate for addition of waters to IR subcategories 2b or 3b and to Iowa’s list of waters in need of further investigation.
The previous (2010) assessment of the Class B(WW2) aquatic life uses based on biological data is changed from “fully supporting” to “not assessed” due to age of the data upon which the assessment was based. The previous assessment was based on data collected in 1998 as part of an IDNR Fisheries sampling project; the Class B(WW2) aquatic life uses were assessed as “fully supporting.” Because the data upon which these assessment were based are now more than ten years old, the Class B(WW2) uses are now considered “not assessed.” As water quality data age, they are less able to represent current water quality conditions. 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.
The results of IDNR/UHL TMDL-related chemical/physical water quality monitoring conducted in 2005 at station 11400001 suggest good chemical water quality in this river segment. Results of this monitoring show no violations of Class B(WW1) water quality criteria for conventional parameters (dissolved oxygen or pH) or for ammonia in the five monthly samples collected from May to September 2005. The number of samples collected at this station (five) is relatively low and does not meet IDNR guidelines for developing a “monitored” (higher confidence) assessment (i.e., at least 10 samples collected over a three-year period). Thus, any assessment based on these data should be considered “evaluated” (of lower confidence). Results of limited monitoring conducted by USGS in this segment from March to October 2010 also suggest good water quality in this assessment segment with none of the five samples analyzed violating Class B(WW1) criteria for dissolved oxygen or pH.
Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.
