Assessment Comments
Assessment is based on: (1) the results of ambient monthly water quality monitoring from January 2006 through December 2008 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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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 2006 through 2008 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 2006 through December 2008 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.
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 mean level of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2006 through 2008 (120 orgs/100ml) is slightly below the Iowa Class A1 water quality criterion of 126 orgs/100ml. Nine of the 22 samples (41%) 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 less than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Because the 2006-08 geometric mean is only slightly below the Class A1 geometric mean criterion, and because of the pre-existing bacterial impairment identified for this assessment segment as part of the 2008 listing cycle, this segment will not be proposed for de-listing for the current (2010) listing cycle. If, however, the 2008-2010 geometric mean also meets the Class A1 criterion, this segment will be proposed for de-listing for the 2012 cycle.
The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2006-2008 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 2006 through December 2008 showed no violations of Class B(WW1) water quality criteria for either conventional or toxic parameters. No violations occurred in the 34 samples analyzed for dissolved oxygen, pH, and ammonia-nitrogen, in the five 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 between 2004 and 2008 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).
Although these results suggest "full support" of the Class B(WW1) aquatic life uses, the results of water quality studies conducted in 1994 and 1995 for the Lehigh Portland Cement Company showed relatively low diversity of the fish community downstream from Mason City. The results from these studies continue to suggest the possibility of threats to full support of the aquatic life uses within the Mason City urban/industrial area. These studies are now quite old (over 10 years), and their ability to characterize current water quality conditions is doubtful. Follow-up monitoring is needed to better determine the status of the aquatic communities of this reach of the Winnebago River and to determine whether the Class B(WW1) uses may be impaired.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
