Assessment Comments

Assessment is based on results of (1) monthly monitoring at the IDNR fixed ambient station near DeWitt from 2000-02, (2) LTRMP monitoring near the mouth of the Wapsipinicon River from 2000-02, and (3) EPA/IDNR fish tissue (RAFT) monitoring north of Donahue in Scott County in 2000 and 2002.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed (monitored) as "partially supported" due to high levels of indicator bacteria (fecal coliforms).   The Class B(WW) aquatic life were assessed (monitored) as "fully supported."  Fish consumption uses were assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2002.   The sources of data for this assessments were (1) the results of monthly monitoring at the IDNR fixed ambient station near DeWitt (station 10820001) from 2000-02, (2) results of LTRMP monitoring near the mouth of the Wapsipinicon River (station WP02.6M) in 2000, 2001, and 2001; and (3) results of EPA/IDNR fish tissue (RAFT) monitoring north of Donahue in Scott County in 2000 and 2002.  

EXPLANATION:  The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" due to high levels of indicator bacteria.   Of the 21 samples from the IDNR ambient monitoring station analyzed for indicator bacteria (fecal coliforms) during recreational seasons of 2000, 2001, and 2002, three samples were collected during conditions of high river flow.   These high flows resulted in monitoring at river discharges that exceeded the long-term monthly average flow plus one standard deviation of this average (flow statistics from Fischer et al.  1990 and Fischer and Eash 1998).   For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  The geometric mean level of indicator bacteria (fecal coliforms) in these 18 non-runoff-affected samples (87 orgs/100ml) was well below the Iowa Class A water quality criterion of 200 orgs/100ml.   Three of the 18 samples (17%), however, exceeded the U.S.  EPA-recommended single-sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "partially supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Thus, the Class A uses of this segment are assessed as “partially supported.”  

The Class B(WW) aquatic life uses were assessed as "fully supported" due to (1) the lack of violations of Iowa Class B(WW) water quality criteria for dissolved oxygen and ammonia-nitrogen in the approximately 36 samples collected from January 2000 through December 2002 at the IDNR fixed ambient station at DeWitt and in the 71 samples collected at the LTRMP station near the mouth of the river and (2) the lack of violations of Class B(WW) water quality criteria in the 9 samples from the IDNR ambient station analyzed for pesticides during the 2000-2001 biennial period.    

Fish consumption uses were assessed (monitored) as "fully supported."  EPA/DNR fish tissue (RAFT) monitoring conducted in 2002 north of Donahue in Scott County included sampling of whole-fish carp (RAFT trend monitoring) and sampling of fillets from channel catfish and flathead catfish (RAFT status monitoring).   Both trend and status monitoring were conducted at this site to determine whether the slightly elevated levels of chlordane seen in recent whole-fish carp samples (from 1998 and 2000 RAFT trend monitoring) were reflected in edible portions of fish from this site.     The composite sample of whole-fish common carp collected in 2002 from this site as part of RAFT trend monitoring had low levels of contaminants.   Similar to results of RAFT trend monitoring in 1998 and 2000 (see assessment for the 2002 report), this sample did contain a technical chlordane level that exceeded one-half the respective FDA AL and IDNR level of concern of 0.15 ppm.   Levels of primary contaminants in the sample were as follows: mercury: 0.095 ppm; total PCBs: 0.125 ppm; and technical chlordane: 0.190 ppm.   The composite samples of fillets from channel catfish and flathead catfish collected as part of RAFT status monitoring, however, had very low levels of contaminants.   Neither sample contained levels of contaminants that approached even one-half the respective FDA action levels or IDNR levels of concern.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.087 ppm; total PCBs: <0.09 ppm; and technical chlordane: 0.069 ppm.   Levels of primary contaminants in the composite sample of flathead catfish fillets were as follows: mercury: 0.036 ppm; total PCBs: <0.091 ppm; and technical chlordane: <0.03 ppm.   Thus, based on levels of contaminant in these fillet samples that are less than one-half the respective FDA action levels, the fish consumption uses are assessed (monitored) as “fully supported.”