Assessment Comments
Assessment is based on: (1) the results of ambient monthly water quality monitoring from January 2008 through December 2010 at the IDNR/UHL ambient city monitoring station located upstream from Mason City (STORET station 10170002) and (2) the results of biological monitoring conducted by the IDNR Fisheries Bureau near Fertile in 2000. The assessment is also based, in part, on historical water quality studies conducted for the Lehigh Portland Cement Company.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river 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 results of a Use Attainability Analysis, 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 are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported " based on results of (1) ambient water quality monitoring from 2008 through 2010 and (2) biological monitoring conducted by the IDNR Fisheries Bureau in 2000. Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment. The sources of data for this assessment include (1) the results of ambient monthly water quality monitoring from January 2008 through December 2010 at the IDNR/UHL ambient city monitoring station located upstream from Mason City (STORET station 10170002) and (2) the results of biological monitoring conducted by the IDNR Fisheries Bureau near Fertile in 2000.
EXPLANATION: The Class A1 primary contact recreation uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at station 10170002 upstream of Mason City were as follows: the 2008 geometric mean was 98 orgs/100 ml, the 2009 geometric mean was 132 orgs/100 ml and the 2010 geometric mean was 118 orgs/100 ml. The 2008 and 2010 geometric means are low and meet the Class A1 criterion of 126 orgs/100 ml. Only the 2009 geometric mean exceeds the Class A1 criterion. This violation of the Class A1 criterion is by only 6 orgs/100 ml and is probably not significantly different or higher than the criterion. Nonetheless, U.S. EPA has informed IDNR that any level of indicator bacteria above the criterion constitutes and impairment of the Class A1 uses. Six of the 22 samples (27%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.” Despite this impairment, this segment of the Winnebago River has very low levels of indicator bacteria relative to other Iowa rivers and relative to the Class A1 geometric mean criterion. If the 2009 geometric mean had been below the Class A1 criterion, this impairment would have been de-listed.
The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2008-2010 and on results of biological monitoring conducted in 2000. Results of monthly ambient water quality monitoring at the IDNR/UHL station upstream from Mason City from January 2008 through December 2010 showed no violations of Class B(WW1) water quality criteria for either conventional or toxic parameters. No violations occurred in the 33 samples analyzed for dissolved oxygen, pH, and ammonia-nitrogen, in the three samples analyzed for toxic metals, or in the three samples analyzed for pesticides.
The assessment is also partially based on data collected in 2000 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 2000 evaluated FIBI = 63 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The riffle habitat FIBI BIC for this ecoregion is 53. This segment passed the FIBI BIC 1/1 times in 2000.
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 over a five-year period to be considered “monitored”. This segment had a single sample collected in 2000. 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).
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
