Lacey Keosauqua Lake IA 04-LDM-1008

Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria at Lacey-Keosauqua Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (15 samples), 2015 (17 samples) and 2016 (15 samples), as part of the DNR beach monitoring program. According to DNR’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 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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 Lacey-Keosauqua Beach, the geometric means from 2014, 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 18 E. coli orgs/100 ml in 2014, 45 E. coli orgs/100 ml in 2015 and 17 E. coli orgs/100 ml in 2016. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 13% in 2014, 18% in 2015 and 0% in 2016. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses.

Lacey-Keosauqua Beach was assessed as "partially supported" for the 2012 assessment/listing cycle. Based on DNR’s assessment methodology 2 consecutive assessment/listing cycles without violations of the geometric mean criterion and without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on bacteria violations. There were no violations of the geometric mean criterion for the 2016 or current 2018 assessment listing cycle and there were less than 10% of the samples exceeding the single-sample maximum criterion. Therefore, the impairment for indicator bacteria is suggested for delisting for the 2018 assessment/listing cycle.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lacey Keosauqua Lake are assessed (monitored) as "fully supported" based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 53, 44, and 47 respectively for Lacey Keosauqua Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lacey Keosauqua Lake in between the Mesotrophic and the Eutrophic categories. These values suggest extremely low levels of chlorophyll a and suspended algae in the water, very good water transparency, and extremely low levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was low at Lacey Keosauqua Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Lacey Keosauqua Lake (1.6 mg/L) was ranked 9th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a small population of cyanobacteria exists at Lacey Keosauqua Lake. These data show that cyanobacteria comprised 44% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (1.4 mg/L) was ranked 12th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and no violations of the criterion for pH in 15 samples(0%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Lacey Keosauqua Lake.

The Class C (drinking water) uses are not assessed due to the lack of recent information upon which to base an assessment. The only parameter collected as part of the ISU lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU surveys from 2012-2016 show that nitrate levels are extremely low at this lake (maximum value = 0.1 mg/l; median = 0 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.