Assessment Comments
Assessment is based on results of (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) water quality, fish tissue, and beach indicator bacteria monitoring conducted as part of the UI/ACOE "Coralville Water Quality Study” from 2006-08.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to aesthetically objectionable conditions caused by poor water transparency due to inorganic turbidity. The Class B(WW1) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) water quality, fish tissue, and beach indicator bacteria monitoring conducted as part of the UI/ACOE "Coralville Water Quality Study” from 2006-08.
EXPLANATION: Results of UI/ACOE beach monitoring at Sugar Bottom beach from 2006 through 2008 suggest that the Class A1 uses are "fully supported." Levels of indicator bacteria at Sugar Bottom beach were monitored once per week during the primary contact recreation seasons (May through September) of 2006 (20 samples), 2007 (19 samples), and 2008 (10 samples) as part of the UI/ACOE monitoring program. 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) all thirty-day geometric means for 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 5-sample, 30-day 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).
At Sugar Bottom beach, the geometric means of all 37 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 were below Iowa water quality standard of 126 E. coli orgs/100 ml. Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was not significantly greater than 10% in any of the following recreation seasons: 2006: 5% and 2007: 0%, and 2008: 0%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results do not suggest impairment of the Class A1 (primary contact recreation) uses.
Results of UI/ACOE beach monitoring at Sandy beach from 2006 through 2008 also suggest that the Class A1 uses are "fully supported." At Sandy beach, the geometric means of all 28 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 were below Iowa water quality standard of 126 E. coli orgs/100 ml. Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was not significantly greater than 10% in 2006: 0% or 2007: 7%. The percentange of samples exceeding Iowa's single-sample maximum criterion was significantly greater than 10% in 2008 (33%). However, there were only 9 samples collected in 2008 due to severe flooding. Only 3 samples exceeded the single sample maximum and two of these samples occurred in July immediately after sampling resumed when water levels began to recede. Because these samples were likely influenced by the severe flooding that occurred and the geometric mean values remained low (maximum = 59 E. coli orgs/100 ml), it is determined that bacteria does not cause an impairment of the primary contact recreation uses at this reservoir.
Results of UI/ACOE beach monitoring at West Overlook beach from 2006 through 2008 suggest that the Class A1 uses are "fully supported." At West Overlook beach, the geometric means of all 40 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 were below Iowa water quality standard of 126 E. coli orgs/100 ml. Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was not significantly greater than 10% in any of the following recreation seasons: 2006: 0% and 2007: 18%, and 2008: 0%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results do not suggest impairment of the Class A1 (primary contact recreation) uses.
Results from the ISU and UHL statewide surveys of Iowa lakes from 2004-08, however, suggest that the Class A1 uses be assessed (monitored) as “partially supported” due to high levels of inorganic turbidity. Using the median values from these surveys from 2004 through 2008 (approximately 24 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus are 67, 62, and 79, respectively for Coralville Reservoir. According to Carlson (1977), the index values for Secchi depth and chlorophyll a place Coralville Reservoir in between the eutrophic and hypereutrophic categories, while the total phosphorus value places this reservoir in the hypereutrophic category. These index values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and extremely high levels of phosphorus in the water column.
Results from ACOE monitoring at the main lake basin also suggest that algae does not cause an impairment at this reservoir. (NOTE: Secchi depth measurements are not collected as part of the ACOE monitoring at Coralville Reservoir.) Using median values from this survey from 2006 through 2008 (approximately 35 samples, Carlson's (1977) trophic state indices for chlorophyll a and total phosphorus are 64 and 80, respectively. These results suggest moderately high levels of chlorophyll a and suspended algae in the water and extremely high levels of phosphorus in the water column.
The levels of inorganic suspended solids were very high at this lake and suggest that non-algal turbidity contributes to poor water transparency and the impairment at Coralville Reservoir. The median level of inorganic suspended solids in Coralville Reservoir (10.7 mg/L) was the 20th highest concentration among the 132 lakes sampled by the ISU and UHL lake surveys.
Data from the 2004-2008 ISU and UHL surveys suggest a small population of cyanobacteria exists at Coralville Reservoir. These data show that cyanobacteria comprised 26% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (2.4 mg/L) was the 13th lowest of the 132 lakes sampled.
The Class B(WW1) (aquatic life) uses of Coralville Reservoir are assessed (monitored) as "fully supported" based on results from the UI/COE water quality study, results from the ISU and UHL lake surveys, and information from the IDNR Fisheries Bureau. None of the 56 samples collected during the 2006-2008 period as part of ACOE monitoring violated Class B(WW1) criteria for ammonia or the Class A1,B(WW1) criteria for pH. Three of 56 samples (5%) violated the Class B(WW1) criterion for dissolved oxygen. According to 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(WW1) uses of Coralville Reservoir.
The ISU and UHL lake surveys data from 2004-2008 show no violations of the Class B(WW1) criterion for ammonia or dissolved oxygen in 24 samples. The data for pH, however, show 2 violations of the Class A,B(WW1) criterion for pH in 24 samples (8%). Based on IDNR’s assessment methodology, these violations are not significantly greater than 10% and therefore do not constitute an impairment of the Class A1 or Class B(WW1) uses of Coralville Reservoir.
Fish consumption uses are assessed (monitored) as "fully supporting." Fish contaminant monitoring conducted in Coralville Reservoir in 2006, 2007 and 2008 as part of the Coralville Reservoir Water Quality Study showed that levels of organochlorine contaminants (chlordane, dieldrin, and heptachlor epoxide) in composite samples of whole-fish carp were very low. 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 fish contaminant data generated from the 2006, 2007, or 2008 ACOE fish contaminant monitoring conducted at Coralville Reservoir show that the levels of contaminants do not exceed any of the advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody. Analysis of fish tissue for the ACOE monitoring program, however, does not include analysis for mercury or PCBs.
