Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2008-2012 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 "Iowa Voluntary Atrazine Monitoring Program" conducted by Syngenta Co. from 2010 through 2012, and (5) IDNR fish contaminant monitoring in 2013.
Basis for Assessment
SUMMARY: The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” (IR 5a) due to violations of the state’s dissolved oxygen criterion. [Note: this lake is not designated for Class A1 (primary contact recreation) uses in the Iowa Water Quality Standards.] The Class C (drinking water) uses are assessed (monitored) as "fully supported" (IR 2a) based on results of monitoring for atrazine from 2010 through 2012. Fish consumption uses are assessed as "fully supported" (IR 2a) based on results of fish contaminant monitoring in 2013. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2008-2012 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 "Iowa Voluntary Atrazine Monitoring Program" sponsored by Syngenta Co. from 2010 through 2012, and (5) IDNR fish contaminant monitoring in 2013.
Note: A TMDL for atrazine at West Lake Osceola was prepared by IDNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 through the 2010 Integrated Reporting cycles. Because atrazine levels had been low over the 2004-2012 monitoring period and had shown "full support" of the Class C uses for the 2008, 2010, 2012, and 2014 Integrated Reporting cycles, this impairment was removed, and the Class C uses were moved from Category 4a (impaired; TMDL not required) to Category 2a (fully supported) of Iowa's Integrated Report. Also, because the new impairment due to low levels of dissolved oxygen was not addressed by this TMDL, this waterbody was placed in Category 5a of Iowa's 2008 Integrated Report and remains in Category 5a for the 2014 Integrated Report.
EXPLANATION: The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” based on data from the ISU and UHL lake surveys. During 2008-2012 there were no violations of the Class B(LW) criterion for ammonia in 14 samples and one violation of the pH criterion in 14 samples. Based on IDNR's assessment methodology, the single violation of the pH criterion does not suggest a violation frequency significantly greater than 10%; therefore, this violation does not suggest impairment of the Class B(LW) uses. There were no violations of the dissolved oxygen criterion in 14 samples. However, there were 4 violations of the Class B(LW) uses criterion for dissolved oxygen in the dataset used for the previous (2012) assessment/listing cycle. Based on IDNR's methodology, no significant violations are required for 2 consecutive assessment/listing cycles to suggest de-listing. Therefore, West Lake will remain listed as "partially supported" and in IR Category 5a for the 2014 assessment/listing cycle.
Additional results from the ISU and UHL lake surveys show declining water quality at West 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 65, 63, and 74 respectively for West Lake. According to Carlson (1977) the Secchi depth and chlorophyll a values place West Lake in between the eutrophic and the hypereutrophic categories while the total phosphorus value places West Lake in the hypereutrophic category. These values suggest relatively low 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 is moderately high at West Lake and suggests that non-algal may contribute to impairment at this lake. The median inorganic suspended solids concentration at West Lake was 3.6 mg/L, and ranked 65th of the 134 monitored lakes.
Data from the 2008-2012 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at West Lake. These data show that cyanobacteria comprised 76% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (13.7 mg/L) and ranked 42nd of the 134 lakes sampled.
Information from the IDNR Fisheries Bureau suggests that West Lake Osceola does experience severe algae blooms during the summer. However, the Municipal Utilities treat the lake with copper sulfate to suppress the algae, which may affect sampling by the ISU and UHL surveys. Information from the IDNR Fisheries Bureau also suggests that common carp affect water quality at this lake.
The Class C (drinking water) uses are assessed (monitored) as "fully supported" based primarily on results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" from 2010 through 2012. Results of this monitoring showed no violations of Iowa’s Class C water quality criterion for atrazine of 3 ug/l in the 63 samples collected from 2010-12 (maximum value: 2.93 ug/l). Not surprisingly, none of the 63 moving annual averages for this monitoring period exceeded the Class C criterion (maximum moving annual average = 1.45 ug/l). Based on IDNR's assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported." In addition results of the ISU and UHL lake surveys from 2006-10 show that nitrate levels are very low at this lake (maximum value = 1.8 mg/l; median = 0.3 mg/l) relative to the MCL (10 mg/L).
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at West 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: 0.253 ppm. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.05 ppm; total PCBs: <0.15 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.
