Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 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 2009 and 2010.
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. 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 are assessed (monitored) as "partially supported" 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 2008, 2009, and 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 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 2009 and 2010.
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. In September 2012, IDNR received EPA approval of a TMDL for the impariments of the Class A1 and Class B(LW) uses caused by algae and pH. Thus, these impairments were moved to IR Category 4a for the current (2012) IR cycle. Not all of the section 303(d) impairments identified for the current (2012) assessment/listing cycle (indicator bacteria and mercury), however, are addressed in the TMDL. Thus, this waterbody remains in Category 5a (impaired; TMDL required) for the 2012 assessment/listing cycle.
EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 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 2008 (22 samples), 2009 (25 samples), and 2010 (15 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 2012 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 Lake Keomah beach, the geometric mean from 2010 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 21 E. coli orgs/100 ml in 2008, 71 E. coli orgs/100 ml in 2009, and 306 E. coli orgs/100 ml in 2010. The results from 2010 suggest impairment of the Class A1 uses at Lake Keomah. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 5% in 2008, 28% in 2009 and 47% in 2010. The results from 2009 and 2010 were significantly greater than 10% of the samples and therefore suggest impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “nonsupport” of the Class A1 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. Using the median values from these surveys from 2006 through 2010 (approximately 24 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 52, 52, and 65 respectively for Lake Keomah. According to Carlson (1977) the Secchi depth, and chlorophyll a values place Lake Keomah in the eutrophic category, while the total phosphorus value places Lake Keomah in between the eutrophic and the hypereutrophic categories. These values suggest low levels of chlorophyll a and suspended algae in the water, very good water transparency, and high levels of phosphorus in the water column.
Lake Keomah was assessed as "partially supporting" its Class A1 primary contact recreation uses for the 2010 assessment/listing cycle due to aesthetically objectionable conditions due to algae (2010 median chlorophyll TSI = 67). Based on IDNR's assessment methodology two consecutive assessment/listing cycles with TSI values for Secchi depth and chlorophyll a values less than or equal to 63 are necessary to suggest de-listing of the algae impairment at this lake. Therefore Lake Keomah will remain assessed as "partially supported" due to algae blooms. If chlorophyll a levels remain low for the 2014 assessment/listing cycle, the algae impairment will be suggested for de-listing.
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 2.0 mg/L, which was the 26th 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 was de-listed for the 2008 assessment/listing cycle.
Data from the 2006-2010 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Lake Keomah. These data show that cyanobacteria comprised 49% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (10.0 mg/L) was also the 23rd lowest of the 134 lakes sampled.
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 2006 through 2010, there was one violation of the Class B(LW) criterion for ammonia in 24 samples (4%) and two violations of the Class B(LW) criterion for dissolved oxygen in 24 samples (8%). Based on IDNR’s assessment methodology, these violations are not significantly greater than 10% of the samples and therefore do not constitute an impairment of the aquatic life uses of Lake Keomah. Data from the ISU and UHL surveys, however, show 5 violations of the Class A1,B(LW) criterion for pH in 24 samples (21%). 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.
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 2006-10 show that nitrate levels at Lake Keomah (maximum value = 1.4 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 (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Keomah in 2009 and 2010. 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 2009 RAFT sampling conducted at Lake Keomah show that levels of mercury are sufficiently high for concern and thus justify follow-up monitoring. Results from the 2009 sampling show that the level of mercury in the sample of largemouth bass fillets (0.464 ppm) exceeds 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 warrants issuance of an advisory nor indicates 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 2010 showed that levels of mercury in largemouth bass (0.432 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 Keomah and the fish consumption uses are assessed as “partially supported.” Levels of mercury, total PCBs, and technical chlordane in composite samples of channel catfish fillets were all below the advisory trigger level.
