Mormon Trail Lake IA 05-NOD-1404
Adair County S17T76NR31W 1.5 mi SE of Bridgewater.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 10/16/2018 9:33:41 AM
- Updated
- 6/6/2019 3:08:30 PM
The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported” (IR 2a). The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported" (IR 2a). Fish consumption uses, however, remain assessed (monitored) as “partially supported” due to the issuance of a fish consumption advisory at this lake. Sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2014 through 2016, (2) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) results of the EPA/DNR fish contaminant monitoring program (RAFT) in 2008, 2009, and 2015.
Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria at Mormon Trail Park Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (13 samples), 2015 (14 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). Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/DNR fish contaminant (RAFT) monitoring at Mormon Trail Lake in 2008, 2009, and 2015. 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. Sampling was conducted at Mormon Trail Lake in 2008; samples of largemouth bass and walleye were collected. The level of mercury in the sample of largemouth bass was 0.22 ppm, which was below the one meal per week consumption advisory. The level of mercury in the sample of walleye, however, was 0.361 ppm, which was above the one meal per week advisory level. Follow-up sampling was again conducted in 2009. The level of mercury in a sample of walleye (0.245 ppm) was below the advisory level, however, the level of mercury in a sample of largemouth bass (0.341 ppm) again exceeded the advisory trigger level.Sampling was again conducted in 2015. The level of mercury in a sample oflargemouth bass (0.274 ppm)was below the advisory level, however,according to Iowa DNR’s assessment listing methodology, if two consecutive samplings show that contaminant levels are below the consumption advisory threshold, the impairment of the Human Health designated use can be removed.Therefore, the fish consumption advisory remained at Mormon Trail Lake, and the fish consumption uses for this lake have remained assessed as "partially supported."
In addition, turtle tissue sampling was conducted at Mormon Trail Lake in 2009. Levels of primary contaminants in the shoulder tissue sample of snapping turtle were as follows: mercury: 0.138 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. These results indicate low levels of primary contaminants in turtle tissue.