Assessment Comments
Assessment is based on: (1) results of monthly monitoring from 2006 through 2008 at the IDNR/UHL ambient city monitoring station located downstream from Mason City (STORET station 10170003) and (2) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring east of Mason City in 2004. 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 ambient water quality monitoring from 2008 through 2010. Fish consumption uses remain assessed (evaluated) as "fully supported" based on results of fish contaminant monitoring in 2004. The sources of data for this assessment include (1) results of monthly monitoring from 2008 through 2010 at the IDNR/UHL ambient city monitoring station located downstream from Mason City (STORET station 10170003) and (2) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring east of Mason City in 2004. 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 means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at station 10170003 downstream from Mason City were as follows: the 2008 geometric mean was 371 orgs/100 ml, the 2009 geometric mean was 328 orgs/100 ml and the 2010 geometric mean was 255 orgs/100 ml. All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. Thirteen of the 22 samples (59%) 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.”
The Class B(WW1) aquatic life uses are assessed as “fully supported” based on results of IDNR/UHL water quality monitoring downstream from Mason City (STORET station 10170003). Monitoring at this station from January 2008 through December 2010 showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 38 samples collected, for pesticides in the three samples collected, or for toxic metals in the three samples collected. 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 (approaching 20 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 assessed as "fully supported" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring east of Mason City in 2004. Because this monitoring was conducted over five years ago, the assessment type is changed from “monitored” (higher confidence assessment) to “evaluated” (lower confidence assessment). The composite samples of fillets from common carp and northern pike had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.136 ppm; total PCBs: 0.101 ppm; and technical chlordane: < 0.03 ppm. Levels of primary contaminants in the composite sample of northern pike fillets were as follows: mercury: 0.16 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The levels of contaminants in the samples collected east of Mason City in 2004 do not exceed any of Iowa’s advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
