Gustafson Lake IA 06-LSR-1625

Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "partially supported."Levels of indicator bacteria at Gabrielson Park Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (12 samples) and 2016 (14 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 Gabrielson Park Beach, the geometric means from 2014 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 101 E. coli orgs/100 ml in 2014 and 19 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 17% in 2014 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.

While the levels of indicator bacteriaforGabrielson Park Beach are not significantly greater than 10% of the samples and do not exceed the state's single-season geometric mean criterion of 126 E. coli orgs/100 ml for the 2018reporting cycle, Gabrielson Park Beach was listed as "partially supporting" the ClassA1uses for the 2014reporting cycle due to indicator bacteria. Based on DNR's assessment methodology,(1)indicator bacteria violations must be not violation for two consecutive assessment cycles before a lake can be removed from the state’s Section 303(d) list (IR Category 5a),(2) 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 (3) not more than 10% of the samples during any one recreation season exceeds the state's single-sample maximum value of235 E. coli orgs/100 ml. Therefore, Gabrielson Park Beach remains assessed as "partially supported" due to violations of the criterion for indicator bacteria for the 2016 assessment cycle.

The Class B(LW) aquatic life uses of this lake are "not assessed" due to a lack of information upon which to base an assessment.

The fish consumption uses of this lake are “not assessed” due to the lack of fish contaminant information upon which to base an assessment.