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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf) 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" based on results of ambient monitoring for indicator bacteria (E. coli) in 2005. The Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supporting” based on results of biological monitoring in 1998. 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.
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 assessment of the Class B(WW1) aquatic life uses remains based on data collected in 1998 as part of an IDNR Fisheries stream sampling project: Manchester research station. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1998 evaluated FIBI score was 61 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The non-riffle site FIBI BIC for this ecoregion is 32 and this segment passed the FIBI BIC 1/1 times in 1998.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”. This segment had a single sample collected in 1998. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Despite this change in assessment methodology and type, this waterbody remains in IR Category 2b based on the bacteria data.
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).
Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.
