Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (3) results of the IDNR beach monitoring program in 2010-2012 and (4) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to high levels of indicator bacteria. The chlorophyll a impairment at this lake is suggested for de-listing. The Class B(LW) aquatic life uses are assessed (monitored) as “fully supported.” The Class C (drinking water) uses remain “not assessed” due to a lack of information upon which to base an assessment. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring at this lake. Sources of data for this assessment include: (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (3) results of the IDNR beach monitoring program in 2010-2012, and (4) information from the IDNR Fisheries Bureau. Note: this lake was drained and its fishery was renovated by IDNR in 2006, and watershed improvements were also made (e.g., installation of silt-retention structures). Positive changes in water quality may result from this renovation which will affect future assessments.
EXPLANATION: Results of IDNR beach monitoring from 2010-2012 suggest that the Class A1 uses are “fully supported." Levels of indicator bacteria at Viking Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2010 (16 samples), 2011 (15 samples), and 2012 (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 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 Viking 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 75 E. coli orgs/100 ml in 2010, 26 E. coli orgs/100 ml in 2011, and 17 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 19% in 2010, 7% in 2011 and 13% in 2012. These results suggest "full support" of the Class A1 uses. However, Viking Lake was listed as "partially supporting" the Class A1 uses for the 2012 assessment/listing cycle due to the number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2009. According to IDNR’s assessment, 2 consecutive cycles without significant violations are required to suggest de-listing, therfore, Viking Lake will remain assessed as “partially supporting” its Class A1 uses.
Results from the ISU and UHL lake surveys suggest the Class A1 uses at Viking Lake should be assessed as “fully supported.” The chlorophyll a impairment at this lake is suggested for de-listing. Using the median values from these surveys from 2008 through 2012 (approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 60, 60, and 57 respectively for Viking Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Viking Lake in between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and relatively low levels of phosphorus in the water column.
The level of inorganic suspended solids is low at Viking Lake and suggests that non-algal turbidity does not contribute to the impairment at this lake. The median inorganic suspended solids concentration at Viking Lake was 2.1 mg/L, which and ranked 12th of the 134 monitored lakes.
Data from the 2008-2012 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Viking Lake, which does not cause an impairment due to nuisance aquatic life. These data show that cyanobacteria comprised 68% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (23.3 mg/L) and ranked 65th of the 134 lakes sampled.
NOTE: Extensive in-lake and watershed restoration work was completed at Viking Lake between 2000-2006, with over 10 detention basins being built in the watershd to reduce nutrient and sediment loads to the lake. Water quality improvements at Viking Lake can be attributed to these efforts.
The Class B(LW) (aquatic life) uses at Viking Lake are assessed (monitored) as “fully supported.” Information from the IDNR Fisheries Bureau suggests that since the fishery renovation in 2006 the water quality and fishery at this lake are greatly improved although algae still remains a problem at this lake. Results from the ISU and UHL lake surveys show moderately good chemical water quality at Viking Lake. During 2008-2012 there were no violations of the Class B(LW) criterion for ammonia in 14 samples, no violations of the pH criterion in 14 samples, and no violations of the dissolved oxygen criterion in 14 samples.
The Class C (drinking water) uses remain “not assessed” due to lack of water quality information upon which to base such 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 the ISU and UHL surveys from 2008-2012 show that nitrate levels are very low at this lake (maximum value = 0.25 mg/l; median = 0.2 mg/l) relative to the 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 "not assessed" due to the lack of fish contaminant monitoring in this lake.
