Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2010-2012, (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), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 1996, 2006, 2008 and 2009.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 4a) due to high levels of bacteria that exceed the Class A1 standard. High levels of pH that exceed the state water quality criterion also contribute to an impairment (IR 4a) at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” (IR 4a) due to high pHs that exceed the state water quality criterion. The Class C (drinking water) uses remain “not assessed” (IR 3a) due to a lack of information upon which to base an assessment. Fish consumption uses are assessed (monitored) as “partially supported” (IR 5a) due to the issuance of a fish consumption advisory at this lake. Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2010-2012, (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), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 1996, 2006, 2008 and 2009.
Note: A TMDL for bacteria and pH at Geode Lake was prepared by IDNR and approved by EPA in 2009. Because not all of the Section 303(d) impairments identified for the 2012 assessment/listing cycle (mercury) are addressed by the TMDL, this waterbody remains in IR Category 5a (impaired; TMDL required) for the 2014 assessment/listing cycles.
EXPLANATION: Results of IDNR beach monitoring from 2010-2012 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Geode Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2010 (17 samples), 2011 (16 samples), and 2012 (18 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 Geode Lake beach, the geometric means from 2010-2012 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 81 E. coli orgs/100 ml in 2010, 74 E. coli orgs/100 ml in 2011, and 38 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 24% in 2010, 31% in 2011 and 16% in 2012. Results from 2010 and 2011 are significantly greater than 10% of the samples and therefore suggest impairment of the Class A1 uses at Lake Geode. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “partial support” of the Class A1 uses.
Results from the ISU lake survey and the UHL ambient lake monitoring program suggest that the Class A1 (primary contact recreation) uses for Lake Geode be assessed (monitored) as “partially supported” for the 2014 reporting cycle due to high levels of pH. Other than high pH, the ISU and UHL data show good water quality for Lake Geode. 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 49, 51, and 56 respectively for Lake Geode. According to Carlson (1977) the total phosphorus and chlorophyll a values place Lake Geode in the eutrophic category, while the Secchi depth value places Lake Geode in the mesotrophic. These values suggest low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and relatively low levels of phosphorus in the water column.
The level of inorganic suspended solids were relativelyl low at Lake Geode and do not suggest an impairment due to non-algal turbidity. Based on data from the ISU and UHL surveys in 2008-2012, the median concentration of inorganic suspended solids at Lake Geode was 2.5 mg/L, which ranked 19th of the 134 lakes monitored by these programs.
Data from the 2008-2012 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Lake Geode. These data show that cyanobacteria comprised 86% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (15.4 mg/L) and ranked 51st of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “partially supported” based on results from the ISU and UHL lake surveys. The ISU and UHL lake surveys data from 2008-2012 show no violations of the Class B(LW) criteria for ammonia in 14 samples or dissolved oxygen in 14 samples. The data, however, show 2 violations of the criterion for pH in 14 samples (14%). Lake Geode was assessed as "partially supporting" in the 2012 assessment/listing cycle due to significant violations of the pH crterion. Based on IDNR's methodology, 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violation the criterion are necessary to propose de-listing based on pH violations. Thus, the Class B(LW) (aquatic life) uses will remain listed as "partially supporing" for the 2014 IR cycle.
The Class C (drinking water) uses remain "not assessed" due to the lack of water quality information. 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 these surveys from 2008-2012 show that nitrate levels at this lake are low relative to the drinking water MCL (10 mg/l) (maximum sample value = 4.8 mg/l; median = 2.125 mg/l), these data are not sufficient for developing a valid assessment of the Class C uses.
Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish tissue monitoring in 1996, 2006, 2008 and 2009. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 1996 RAFT sampling conducted at Lake Geode showed that levels of mercury were sufficiently high for concern and thus justified follow-up monitoring. Results from the 1996 sampling showed that the level of mercury in the sample of largemouth bass fillets (0.348 ppm) exceeded the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warranted issuance of an advisory nor indicated impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Follow-up sampling conducted in 2006 showed that levels of mercury in largemouth bass (0.51 ppm) again exceeded the 1 meal/week trigger level (0.30 ppm). Thus a one meal per week fish consumption advisory was issued for Lake Geode, and the fish consumption uses were assessed as “partially supported.” Follow-up sampling was conducted in 2008. The level of mercury in the sample of largemouth bass fillets (0.267 ppm) was less than the 1 meal/week advisory trigger level (0.30 ppm). Because the level of mercury was less than the advisory trigger level in 2008, follow-up sampling was conducted again in 2009. The level of mercury in the sample of largemouth bass fillets (0.437 ppm) was again above the advisory trigger level. Therefore the fish consumption advisory remains at Geode Lake, and the lake remains assessed as "partially supported" for the 2014 assessment/listing cycle.
In addition to fish tissue, turtle tissue from Lake Geode was also analyzed for levels of primary contaminants. The composite samples of shoulder tissue from snapping turtle had low levels of contaminants. Levels of primary contaminants in the composite sample of snapping turtle shoulder tissue were as follows: mercury: 0.284 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.
