Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in the summer of 2008 and 2012, (2) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), and (4) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (evaluated) as “not supported” due to algal and non-algal turbidity. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “fully supported.” The Class C (drinking water) uses remain “not assessed” due to a lack of information upon which to base an assessment. Fish consumption uses are “not assessed” due to a lack of recent fish contaminant monitoring at this lake. Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2008 and 2012, (2) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), and (4) information from the IDNR Fisheries Bureau.
Note: This assessment is considered an "evaluated" assessment because there were too few samples collected to support a "monitored" assessment. Restoration work completed throughout the assessment period limited the number of samples collected between 2008-2012. For the 2012 assessment/listing cycle, Green Valley Lake was assessed (monitored) as "partially supporting" its designated uses due to aesthetically objectionable conditions from algal and non-algal turbidity.
EXPLANATION: Results of IDNR beach monitoring from 2008 and 2012 suggest that the Class A1 uses are assessed (evaluated) as “fully supported." Levels of indicator bacteria at Green Valley Lake beach were monitored once per week during the primary contact recreation season (May through September) of 2008 (7 samples) and 2012 (4 samples) as part of the IDNR beach monitoring program. This assessment is considered an "evaluated" assessment because there were too few samples collected to support a "monitored" assessment. 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 Green Valley Lake beach, the geometric mean from 2008 and 2012 was below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 16 E. coli orgs/100 ml in 2008. 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 14% in 2008 and was 0% in 2012. These results are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “full support” of the Class A1 uses.
Results of the ISU and UHL lake surveys suggest that the Class A uses are "not supported" at Creen Castle Lake due to aestheticially objectionable conditions caused by high algal and non-algal turbidity. Using the median values from these surveys from 2008-2012 (approximately 8 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 71, and 85 respectively for Green Valley Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Green Valley Lake in the hypereutrophic category. These values suggest very high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column. This assessment is considered an "evaluated" assessment because there were too few samples collected to support a "monitored" assessment. Restoration work completed throughout the assessment period limited the number of samples collected between 2008-2012. For the 2012 assessment/listing cycle, Green Valley Lake was assessed (monitored) as "partially supporting" its Class A1 and Class B(LW) uses based on monitoring data collected by the ISU and UHL surveys in 2006-2010.
Data from 2008-2012 suggest moderately high populations of cyanobacteria exist at Green Valley Lake, which may contribute to aesthetically objectionable conditions at this lake. Thus, this lake is added to Iowa's list of waters in need of further investigation (IR 3b). These data show that cyanobacteria comprised 77% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.4 mg/L) and ranked 67th of the 134 lakes sampled.
The levels of inorganic suspended solids at this lake were high and may contribute to the non-algal turbidity impairment. The median level of inorganic suspended solids in Green Valley Lake (9.3 mg/L) and ranked 105th of the 134 lakes sampled by the ISU and UHL programs.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “fully supported.” The ISU and UHL lake surveys data from 2008-2012 show no violations of the Class B(LW) criteria for ammonia in 8 samples, two violations of the Class B(LW) dissolved oxygen criterion in 8 samples (25%), and no violations of the Class A1,B(LW) pH criterion in 8 samples. Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the Class B(LW) uses of Green Valley Lake.
Note: A fishery renovation was completed in 2008. Watershed improvements are being installed and other a sediment removal project is scheduled for the winter of 2009/2010. Water quality improvements are expected as this project progresses and the lake is filled. Because of the water quality improvement project activities throughout the assessment period, a limited number of samples were collected in 2008-2012.
The Class C (drinking water) uses remain "not assessed" due to a lack of water quality information upon which to base an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU and UHL survey from 2008-2012 show that nitrate levels are low at this lake (maximum value = 4.1 mg/l; median = 0.2 mg/l) relative to the MCL (10 mg/L), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses are assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Green Valley in 2011. The composite samples of fillets from largemouth bass and channel catfish had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0541 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.200 ppm. 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 2011 RAFT sampling conducted at this lake show that 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.
