Assessment Comments

Assessment is based on: (1) the results of monthly monitoring at the IDNR fixed ambient station near DeWitt (station 10820001) from 2008-10, (2) results of LTRMP ambient water quality monitoring near the mouth of the Wapsipinicon River (station WP02.6M) from 2008 to 2010; (3) results of USGS ambient monitoring near DeWitt from 2008 to 2010 (station 05422000), and (4) results of EPA/IDNR fish tissue (RAFT) trend monitoring north of McCausland in 2008 and 2010.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to high levels of indicator bacteria (E.  coli).   The Class B(WW1) aquatic life are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2008-10.   Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring.   The sources of data for this assessments are (1) the results of monthly monitoring at the IDNR fixed ambient station near DeWitt (station 10820001) from January 2008 through December 2010, (2) results of LTRMP ambient water quality monitoring near the mouth of the Wapsipinicon River (station WP02.6M) from January 2008 to November 2010; (3) results of USGS ambient monitoring near DeWitt from February 2008 to December 2010 (station 05422000), and (4) results of EPA/IDNR fish tissue (RAFT) trend monitoring north of McCausland in 2008 and 2010.   Note:  this assessment is also used for the next upriver segment, IA 01-WPS-0010-2.  

EXPLANATION:  The Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at IDNR ambient station near DeWitt were as follows:  the 2008 geometric mean was 335 orgs/100 ml, the 2009 geometric mean was 166 orgs/100 ml and the 2010 geometric mean was 318 orgs/100 ml.   All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Nine of the 21 samples (43%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  

The geometric means of indicator bacteria (E.  coli) in the 15 samples collected during the recreational seasons of 2009 and 2010 at the USGS station near DeWitt were as follows:  the 2009 geometric mean was 418 orgs/100 ml and the 2010 geometric mean was 373 orgs/100 ml.   Both seasonal geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Seven of the 15 samples (47%) 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 recreation season geometric means exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" due to the lack of violations during the 2008-10 monitoring period of Iowa Class B(WW1) water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in (1) the approximately 30 samples collected from at the IDNR fixed ambient station at DeWitt, (2) in the 41 samples collected at the LTRMP station near the mouth of the river, and (3) in the approximately 30 samples from the USGS ambient monitoring station at DeWitt.   In addition, no violations of Class B(WW1) water quality criteria for the pesticides DDT, dieldrin, or chlorpyrifos occurred during this period in the 30 samples from the USGS ambient monitoring station at DeWitt.  

Fish consumption uses are assessed as "fully supported" based on the 2008 and 2010 EPA/IDNR fish tissue (RAFT) sampling on the Wapsipinicon River north of McCausland.   This site has been sampled for whole-fish common carp since 1994 on an every-other-year basis as part of RAFT trend monitoring.   The results from the 2008 and 2010 samplings show low levels of the primary contaminants (chlordane, PCBs and mercury) in the composite whole-fish samples of common carp.     In the 2008 samples, the levels were as follows: mercury: 0.0959 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.042 ppm.   In the 2010 sample, the levels of contaminants were as follows: mercury: 0.0768 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.052 ppm.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   The fish contaminant data generated from the 2008 and 2010 RAFT sampling conducted at this river segment show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.