Assessment Comments

Assessment is based on: (1) the results of monthly monitoring at the IDNR fixed ambient station near DeWitt (station 10820001) from 2010-12, (2) results of LTRMP ambient water quality monitoring near the mouth of the Wapsipinicon River (station WP02.6M) from 2010 to 2012; (3) results of USGS ambient monitoring near DeWitt from 2010 to 2012 (station 05422000); (4) results of EPA/IDNR fish tissue (RAFT) trend monitoring north of McCausland in 2008 and 2010, and (5) IDNR/SHL biological sampling in 2011 and 2012.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 5a) due to levels of indicator bacteria (E.  coli) that slightly exceed Class A1 criteria.   The Class B(WW1) aquatic life are assessed (evaluated) as "not supported" (IR 3b-u) based on the results of IDNR/SHL biological sampling in 2011 and 2012.   Fish consumption uses remain assessed (monitored) as "fully supported" (IR 2a) 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 2010 through December 2012, (2) results of LTRMP ambient water quality monitoring near the mouth of the Wapsipinicon River (station WP02.6M) from January 2010 to November 2012; (3) results of USGS ambient monitoring near DeWitt from February 2010 to December 2012 (station 05422000); (4) results of EPA/IDNR fish tissue (RAFT) trend monitoring north of McCausland in 2008 and 2010, and (5) IDNR/SHL biological sampling in 2011 and 2012.   Note:  part of 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 "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at IDNR ambient station near DeWitt were as follows:  the 2010 geometric mean was 318 orgs/100 ml, the 2011 geometric mean was 140 orgs/100 ml and the 2012 geometric mean was 75 orgs/100 ml.   Two of the three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml; the third (2012) geometric mean is well below the Class A1 criterion.   Seven of the 24 samples (29%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  

The geometric means of indicator bacteria (E.  coli) in the 23 samples collected during the recreational seasons of 2010 through 2012 at the USGS station near DeWitt were as follows:  the 2010 geometric mean was 373 orgs/100 ml, the 2011 geometric mean was 348 orgs/100 ml, and the 2012 geometric mean was 64 orgs/100 ml.   Similar to the results from IDNR ambient station at DeWitt, two of the three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Seven of the 23 samples (30%) 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 should be assessed as "impaired" (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.”  

Based on the water quality sampling in this segment, the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported" due to the lack of violations during the 2010-12 monitoring period of Iowa Class B(WW1) water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in (1) the approximately 35 samples collected from at the IDNR fixed ambient station at DeWitt or (2) in the approximately 30 samples from the USGS ambient monitoring station at DeWitt.   None of the 33 samples analyzed for chloride and sulfate and the IDNR ambient station exceed the respective Class B(WW1) aquatic life criteria.   The only violation of a Class B(WW1) criterion in the in the 41 samples collected during the 2010-2012 period at the LTRMP station near the mouth of the river was for pH, with one of the 41 samples (2%) exceeding the high pH criterion of 9.0 pH units.   According to IDNR’s assessment methodology and U.S.  EPA’s assessment guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as pH and dissolved oxygen does not suggest impairment of aquatic life uses.   Thus, the violation frequency for pH (2%) does not suggest impairment of the aquatic life uses.   No violations of dissolved oxygen or ammonia occurred in the 41 samples collected over this period by the LTRMP.   In addition, no violations of Class B(WW1) water quality criteria for the pesticides DDT, dieldrin, or chlorpyrifos occurred during the 2010-2012 period in the 33 samples from the USGS ambient monitoring station at DeWitt.  

In contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the aquatic life uses are "not supporting" (IR 3b-u).   This evaluated biological assessment was based on data collected in 2011 and 2012 as part of the IDNR/SHL large river sampling project.   A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach.   The biological metrics were combined a benthic macroinvertebrate index (BMIBI).   The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2011 BMIBI score was 22 (poor) and the 2012 BMIBI score was 28 (poor).  The aquatic life use support was assessed (evaluated) as not supporting (=NS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008.   The BMIBI BIC for this ecoregion is 51.   This assessment is considered evaluated because the drainage area (2334 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site failed the BMIBI BIC (twice), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.   According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).   IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).  

Fish consumption uses remain assessed as "fully supported" based on results of 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.   This site was scheduled for RAFT trend sampling in 2012, but drought-related low water conditions prevented sample collection.   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.