Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2004, 2005, and 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2000.
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, violations of the state criterion for pH, and aesthetically objectionable conditions caused by algae blooms. Cyanobacteria populations also cause a potential impairment due to nuisance aquatic life. The Class B(LW) uses are assessed (monitored) as “partially supported” due to violations of the state’s pH criterion. The Class C (drinking water) uses are “not assessed” due to a lack of information on which to base an assessment. Fish consumption uses remain assessed (evaluated) as “fully supported.” Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2004, 2005, and 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2000.
Note: A TMDL for siltation at Lake Keomah was prepared by IDNR and approved by EPA in 2002; thus, this lake was placed into IR Category 4a for the 2004 assessment/listing cycle. Not all of the section 303(d) impairments identified for the 2006 or the current (2008) assessment/listing cycle (indicator bacteria, algal growth, and pH), however, are addressed in the TMDL. Thus, this waterbody remains in Category 5a (impaired; TMDL required) for the 2008 assessment/listing cycle.
EXPLANATION: Results of IDNR beach monitoring from 2004 through 2006 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at Lake Keomah beach were monitored once per week during the primary contact recreation seasons (May through September) of 2004 (16 samples), 2005 (23 samples), and 2006 (28 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) 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 Lake Keomah beach, the geometric means of 6 thirty-day periods during the summer recreation season of 2006 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. No geometric means violated this criterion in 2004 or 2005. 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: 2004: 13%, 2005: 9%, and 2006: 14%. According to IDNR’s assessment methodology and U.S. EPA guidelines, the violations of the geometric mean criterion suggest impairment (nonsupport) of the Class A1 (primary contact recreation) uses.
Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Lake Keomah are assessed (monitored) as “partially supported” due to violations of Iowa’s pH criterion, algal blooms, and nuisance cyanobacteria populations. Using the median values from these surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 61, 68, and 70 respectively for Lake Keomah. According to Carlson (1977) the Secchi depth, and chlorophyll a values place Lake Keomah in between the eutrophic and hypereutrophic categories, while the total phosphorus value places Lake Keomah in the hypereutrophic category. These values suggest high 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 was relatively low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Keomah was 3.0 mg/L, which was the 44th lowest of the 132 monitored lakes. Although this lake was indentified as impaired by non-algal turbidity for the 2006 listing cycle, identification of this impairment was an error: data for ISS have never suggested that water transparency problems at this lake were due to ISS. Thus, the turbidity impairment is de-listed for this (2008) listing cycle.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at Lake Keomah, which contributes to impairment at this lake. These data show that cyanobacteria comprised 92% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (50.8 mg/L) was also the 23rd highest of the 132 lakes sampled. This median is in the worst 25% of the 132 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values from 2002-2006. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to a high frequency of violations of Iowa’s criterion for pH. Based on data from the ISU and UHL lake surveys from 2002 through 2006, there were no violations of the Class B(LW) criterion for ammonia in 17 samples and one violation of the Class B(LW) criterion for dissolved oxygen in 23 samples (4%). Based on IDNR’s assessment methodology, the violation of the Class B(LW) criterion for dissolved oxygen is not significantly greater than 10% of the samples and therefore does not constitute an impairment of the aquatic life uses of Lake Keomah. Data from the ISU and UHL surveys, however, show nine violations of the Class A1,B(LW) criterion for pH in 23 samples (39%). Based on IDNR’s assessment methodology these results are significantly greater than 10% of the samples and therefore constitute an impairment (partial support/monitored) of the Class B(LW) uses of Lake Keomah. Results of physical/chemical monitoring associated with the IDNR-UHL beach monitoring program also suggest “partial support” of the Class B(LW) uses of Lake Keomah. Results from 2004 through 2006 show only one violation of the Class B(LW) criterion for dissolved oxygen in 62 samples (2%). These data show 22 violations of the Class A1,B(LW) criterion for pH in 63 samples (35%). These violations are significantly greater than 10% of the samples and therefore support the impairment (partial support/monitored) of the Class A1,B(LW) uses at Lake Keomah.
Drinking water (Class C) uses were not assessed due to the 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 these surveys from 2002-06 show that nitrate levels at Lake Keomah (maximum value = 0.5 mg/l; median = 0.1 mg/l) are very low relative to the drinking water 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 Lake Keomah in 2000. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. 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 2000 RAFT sampling conducted at Lake Keomah 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.
