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 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 (IR 5a) and pH (IR 4a) that exceed Iowa’s water quality standards. The Class B(LW) uses are assessed (monitored) as “partially supported” due to violations of the state’s pH (IR 4a) and dissolved oxygen criteria (IR 5a). The Class C (drinking water) uses remain “not assessed” (IR 3a) due to a lack of information on which to base an assessment. Fish consumption uses remain 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 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, mercury, and dissolved oxygen), however, are addressed in the TMDL. Thus, this waterbody remains in Category 5a (impaired; TMDL required) for the 2014 assessment/listing cycle.
EXPLANATION: Results of IDNR beach monitoring from 2010-2012 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 2010 (15 samples), 2011 (18 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 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 306 E. coli orgs/100 ml in 2010, 85 E. coli orgs/100 ml in 2011, and 122 E. coli orgs/100 ml in 2012. 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 47% in 2010, 33% in 2011 and 31% in 2012. The results from all three years 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 2008-2012 (approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 59, 58, and 66 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 relatively low levels of chlorophyll a and suspended algae in the water, relatively 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. Because the median TSI values are less than or equal to 63 for a second assessment and listing cycle, the algae impairment at Lake Keomah is suggested for de-listing for the 2014 Integrated Report.
The level of inorganic suspended solids was moderately high at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Keomah was 2.9 mg/L, and ranked 56th of the 134 lakes sampled.
Data from the 2008-2012 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Lake Keomah. These data show that cyanobacteria comprised 60% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (17.0 mg/L) and ranked 62nd 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 and dissolved oxygen. Based on data from the ISU and UHL lake surveys from 2008-2012, there was two violations of the Class B(LW) criterion for ammonia in 14 samples (14%). 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. There were also no violations to the Class B(LW) and A1 for pH in 14 samples. However, pH was assessed as "partially supporting" in the 2012 assessment/listing cycle. Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose delisting based on pH violations. Therefore, Lake Keomah will remain assessed as "partially supporting" the Class A1 and B(LW) uses for the 2014 assessment/listing cycle. Data from the ISU and UHL surveys show 4 violations of the Class B(LW) criterion for dissolved oxygen in 14 samples (29%). 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 2008-2012 show that nitrate levels at Lake Keomah (maximum value = 1.5 mg/l; median = 0.3 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 remain 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 showed that levels of mercury were sufficiently high for concern and thus justified follow-up monitoring. While levels of mercury, total PCBs, and technical chlordane in the 2009 composite samples of channel catfish fillets were all below the advisory trigger level, results from this sampling showed that the level of mercury in the sample of largemouth bass fillets (0.464 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 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 were assessed as “partially supported.” This assessment remains for the 2014 IR cycle.
