Saylorville Reservoir IA 04-UDM-1213

Assessment Comments

Assessment is based on results of monitoring at Saylorville Res. conducted by Iowa State Univ. in 2000-01 as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.

Basis for Assessment

SUMMARY:  Continue to assess support of the Class A (primary contact recreation) uses as "fully supported."  The Class B(WW) aquatic life uses were assessed as "fully supported / threatened," and the fish consumption uses were assessed as "fully supported."  EXPLANATION:  The assessments of support of the beneficial uses are based on results of water quality monitoring conducted by Iowa State University (under contract with the U.S.  Army Corps of Engineers) as part of the Des Moines River Water Quality Study (see Lutz et al.  1999 and Lutz 2000).   ISU/ACOE monitoring of levels of indicator bacteria (fecal coliforms) during summers of 1998 and 1999 at mid-lake near the dam and at three locations at each of the two swimming beaches (Sandpiper and Oak Grove) showed that geometric mean levels of indicator bacteria were far below the state water quality criterion of 200 orgs/100 ml.   Geometric means for the 1998-99 period were as follows:  3 orgs/ 100 ml at the mid-lake station (18 sampling events; max = 58 orgs/100 ml); 6 orgs/100 ml at Oak Grove Beach (17 sampling events; max daily mean = 51 orgs/100 ml); 10 orgs/100 ml at Sandpiper Beach (17 sampling events; max daily mean = 733 orgs/100 ml).   Only two of the combined 120 samples exceeded the U.S.  EPA recommended single-sample maximum value of 400 organisms/100 ml; both of these high levels (880 and 1,040 orgs/100 ml) occurred at Sandpiper Beach during the July 7, 1998 sampling event.   These high levels at Sandpiper Beach did not result any 30-day geometric means greater than the WQ criterion of 200 orgs/100 ml, with the worst-case 30-day period from June 2 to July 7, 1998 (n=4) having a geometric mean of 88 orgs/100 ml.   The Class B(WW) aquatic life uses were assessed as "fully supported / threatened."  Two of the 33 samples from the mid-lake (surface) station during the biennial period exceeded the Class B(WW) WQ criterion for dissolved oxygen of 5.0 mg/l.   These violations occurred on August 31 (4.54 mg/l) and September 7, 1999 (4.88 mg/l).   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations at the mid-lake station (6%) does not suggest a water quality impairment.   No violations occurred for the other Class B(WW) WQ parameters (pH, ammonia) in the 33 samples analyzed for at this station.   Due to the violations of the WQ criterion for dissolved oxygen in reservoir surface samples in 1998, the assessment of support of the Class B(WW) aquatic life uses was downgraded from "fully supported" to fully supported / threatened.   This change in assessment presumes a minor water quality impact and does not indicate a declining trend in water quality.   Fish contaminant monitoring conducted in Saylorville Reservoir by ISU/ACOE in 1998 and 1999 showed that levels of contaminants (dieldrin, chlordane, alachlor, trifluralin, and chlorpyrifos) in composite samples of whole fish common carp were all less than ½ of the respective FDA action levels or DNR levels of concern.   Thus, fish consumption uses were assessed as fully supported.   For more information on ISU/ACOE water quality monitoring at Saylorville Reservoir, see Lutz et al.  (1999) and Lutz (2000).