Assessment is based on: (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, (4) results from the IDNR-county voluntary beach monitoring program from 2010-2012, and (5) IDNR fish contaminant monitoring.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed Iowa’s water quality standard. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are assessed as "fully supported." 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, (4) results from the IDNR-county voluntary beach monitoring program from 2010-2012, and (5) IDNR fish contaminant monitoring in 2013.
EXPLANATION: Results of IDNR city/county beach monitoring from 2010-2012 suggest that the Class A1 uses are “not supported." Levels of indicator bacteria at Hickory Grove Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2010 (11 samples), 2011 (14 samples), and 2012 (16 samples) as part of the IDNR beach 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) 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 Hickory Grove Lake beach, the geometric mean from 2010 was below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric means for 2011 and 2012, however, were above the state criterion of 126 E.coli orgs/100 ml. The geometric mean was 52 E. coli orgs/100 ml in 2010, 143 E. coli orgs/100 ml in 2011, and 187 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 18% in 2010, 43% in 2011 and 50% in 2012. The percentage of samples exceeding the single-sample maximum was significantly greater than 10% in 2011 and 2012 and therefore indicates impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest that the Class A1 uses are “not supported.”
Results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program, however, show good water quality at Hickory Grove Lake. Using the median values from these surveys from 2008-2012 (approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 61, 62, and 63 respectively for Hickory Grove Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Hickory Grove Lake in between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were relatively low and do not suggest an impairment due to non-algal turbidity. The median level of inorganic suspended solids in Hickory Grove Lake (2.5 mg/L) and ranked 29th of the 134 lakes sampled by the ISU and UHL programs.
Data from the 2008-2012 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Hickory Grove Lake, which does not contribute to impairment at this lake. These data show that cyanobacteria comprised 62% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (15.7 mg/L) and ranked 54th of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on results from the ISU and UHL lake surveys. The data from these surveys from 2008-2012 show no violations of the Class B(LW) criteria for ammonia in 11 samples, or pH in 14 samples. There was one violation of the Class A1,B(LW) criterion for dissolved oxygen in 14 samples (7%). Based on IDNR’s assessment methodology this violation is not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses at Hickory Grove Lake.
Information from the IDNR Fisheries Bureau suggests that high levels of nutrients enter the lake during rain events and that a restoration project is beginning.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Hickory Grove Lake in 2013. 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 largemouth bass fillets were as follows: mercury: 0.239 ppm. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: total PCBs: <0.6 ppm; and technical chlordane: <0.2 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 2013 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.