Assessment Comments

Assessment is based on (1) results of a DNR biocriteria sampling in 1998 and (2) results IDNR ambient monitoring NE of Statford in 2000 & 2001.

Basis for Assessment

[NOTE:  For the 2002 report, the previous waterbody segment for the Boone River (IA 04-UDM-0180-1), which extended 25 miles from its mouth to the confluence with Brewers Creek at Webster City in Hamilton County was split into two subsegments:  (1) mouth to state Highway 17 south of Webster City (IA 04-UDM-0180-1) and (2) from Highway 17 to confluence with Brewers Creek at Webster City (IA 04-UDM-0180-2).   See above for previous Section 305(b) assessments for the original 25-mile river segment of the Boone River.]

SUMMARY:  Class A (primary contact recreation) uses were assessed as "fully supported."  The Class B(WW) aquatic life uses were assessed as "fully supported / threatened."  Fish consumption uses are assessed as "fully supported."  The sources of data used for this assessment include (1) results of IDNR monthly ambient water quality monitoring conducted on the Boone River northeast of Stratford (Station 10400001 (formerly Station 438056)), (2) results of IDNR/UHL biocriteria monitoring in 1998, and (3) results of U.S.  EPA / IDNR fish tissue (RAFT) monitoring in 2000.   EXPLANATION:  The Class A (primary contact recreation) uses were assessed as "fully supported."  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."  Of the 15 samples from this station analyzed for indicator bacteria (fecal coliforms) during summers of 2000 and 2001, only one sample was 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).   For purposes of Section 305(b) assessments only, IDNR 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 of fecal coliform bacteria in the 14 non-runoff-affected samples was 71orgs/100 ml; one of the 14 samples (7%) exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   The geometric mean (71 orgs/100 ml) is well-below the state water quality criterion of 200 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if the geometric mean is less than 200 orgs/100ml, and less than 10% of samples exceed the single-sample maximum value of 400 orgs/ 100 ml, the primary contact recreation uses are "fully supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Thus, the Class A (primary contact recreation) uses are assessed as "fully supported."  The Class B(WW) aquatic life uses were assessed as "fully supported / threatened."  The only violation of Class B(WW) criteria for conventional parameters was in one of the 24 samples analyzed for pH during the 2000-2001 biennial period.   The sample collected on March 14, 2000, had a pH level of 9.3 units; this level violated the Class B(WW) (and Class A) criterion of 9.0 units.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations for pH at this station (4%) does not suggest a water quality impairment (the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated).   Levels of dissolved oxygen and ammonia-nitrogen did not violate the respective Class B(WW) criteria in the 24 samples analyzed during the biennial period; no violations of Class B(WW) chronic criteria occurred in the four samples analyzed for toxic metals or in the six samples analyzed for pesticides.   Results of IDNR/UHL biocriteria monitoring in 1998 suggest that the Class B(WW) uses are "fully supported / threatened" (see assessment for the 2000 report above).   Thus, despite lack of violations of Class B(WW) numeric aquatic life criteria during the 2000-2001 biennial period, the Class B(WW) aquatic life uses were assessed as "fully supported / threatened."  Fish consumption uses were assessed as "fully supported" based on results of U.S.  EPA / IDNR fish tissue (RAFT) monitoring in July 2000.   This monitoring showed that levels of all contaminants in the composite samples of fillets from channel catfish and smallmouth bass were well-below ½ of the respective FDA action levels and IDNR levels of concern.