Assessment Comments
Assessment is based on results of (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) monitoring of water quality, fish contaminants, and indicator bacteria at beaches conducted from 2010-2012 by Iowa State University as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses of Saylorville Reservoir are assessed (monitored) as "not supported” due to violations of the state water quality standard for indicator bacteria. The Class B(WW-1) (aquatic life) uses are assessed (monitored) as "fully supported." Fish consumption uses were assessed (monitored) as "fully supported" based on ACOE-sponsored annual fish contaminant monitoring from 2010-12. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) monitoring of water quality, fish contaminants, and indicator bacteria at beaches conducted from 2010-12 by Iowa State University as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
EXPLANATION: Results of ACOE beach monitoring at Oak Grove and Sandpiper beaches in 2012 suggest that the Class A1 uses are (evaluated) "partially supported." Levels of indicator bacteria at Oak Grove beach were monitored approximately three times per month during the primary contact recreation season (May through September) 2012 (11 samples) as part of the ACOE beach monitoring program. No samples were collected in 2010 or 2011 due to high water at the beach, therefore this assessment is considered "evaluated" or of lower confidence. According to IDNR’s assessment methodology two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) the geometric mean of the samples from each recreation season of the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10% of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. If a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
NOTE: Based on consultation with EPA Region 7 staff in 2011, IDNR’s methodology for assessing impairments based on the geometric mean water quality criterion was changed. Prior to the 2012 listing cycle, IDNR calculated geometric means for lakes based on a 30-day periods within the recreational season. Any violation of one of these 30-day periods within 3 years resulted in an impairment of the Class A1 uses of that lake. Because water quality standards do not identify a 30 day period but instead a recreational season, Region 7 concurred that the approach used for rivers and streams with less frequent bacteria data (seasonal geometric means) would be appropriate for identifying §303(d) impairments at lake beaches. Thus, for the 2014 listing cycle, IDNR identified primary contact recreation impairments for lakes when the geometric mean of all samples from the recreation season of a given year exceeded the geometric mean criterion. This does not impact the way IDNR assesses beaches for closure to protect the recreating public in the short term.
At Oak Grove beach, the geometric mean from 2012 was below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 11 E. coli orgs/100 ml in 2012. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 0% in 2012. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “full support” of the Class A1 uses.
Results of ACOE beach monitoring at Sandpiper beach from 2012 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Sandpiper beach were monitored approximately three times per month during the primary contact recreation season (May through September) of 2012 (11 samples) as part of the ACOE monitoring program. No samples were collected in 2010 and 2011 due to high water at the beach, therefore this assessment is considered "evaluated" or of relatively lower confidence. At Sandpiper beach, the geometric mean from 2012 (66 orgs/100 ml) was below the Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 27% in 2012. These results are significantly greater than 10% of the samples and therefore suggest impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest "partial support." Because data were only collected in one year since the 2012 assessment, Saylorville Reservoir will remain assessed as "not supported" due to indicator bacteria until more data are collected that suggest de-listing.
Results of monitoring at the ISU/ACOE long-term station on the main reservoir near the dam and results of the ISU and UHL surveys suggest that the Class A1 uses should be assessed (monitored) as "fully supporting." Using the median values from these surveys from 2008 through 2012 (approximately 100 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus are 61, 55, and 71, respectively. According to Carlson (1977), the index value for total phosphorus places this reservoir in the hypereutrophic category, the index values for Secchi depth places this reservoir in between the eutrophic and hypereutrophic categories, and the index value for chlorophyll a places this reservoir in the eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and very high levels of phosphorus in the water column.
The level of inorganic suspended solids is moderately high at this lake and suggests that non-algal turbidity may cause water quality problems at this lake. The median inorganic suspended solids concentration at Saylorville Reservoir was 7.0 mg/L, and ranked 95th of the 134 monitored lakes.
Data from the 2008-2012 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Saylorville Reservoir, which does not suggest an impairment at this lake. These data show that cyanobacteria comprised 77% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (10.3 mg/L) and ranked 27th of the 134 lakes sampled. According to the ISU/ACOE annual monitoring reports (e.g., Lutz and Esser 2002, Lutz and Cummings 2003, Lutz 2004, and Lutz et al. 2005), blooms of cyanobacteria typically occur during July and August, especially under elevated pool conditions. These reports contain a summary of when these blooms have occurred at Saylorville Reservoir since 1990.
The Class B(WW-1) (aquatic life) uses of Saylorville Reservoir are assessed as "fully supported" although dissolved oxygen remains a concern at this lake. Four of the 100 dissolved oxygen samples collected during the sampling period as part of ISU/ACOE, ISU, and UHL monitoring programs violated the Class B(LW) criterion for dissolved oxygen. There were no violations to the Class A1,B(WW-1) criterion for pH (102 samples) or the Class B(WW-1) criterion for ammonia (102 samples). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(WW-1) uses at Saylorville Reservoir.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of ACOE/ISU fish contaminant monitoring at Saylorville Lake in 2010-2012. The composite samples of whole-fish common carp had low levels of contaminants (the ACOE/ISU samples are not analyzed for mercury or PCBs). Levels of total chlordane in the composite samples were as follows: 2008: 6.6 ppb; 2009: 16.0 ppb; 2010: 1.8 ppb. None of these levels approach the advisory trigger level of 600 ppb for chlordane. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. 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.
