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) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program in 2010-2012, and (5) results of the EPA/DNR fish contaminant monitoring program (RAFT) in 1994, 2006, 2008, and 2009.
Basis for Assessment
SUMMARY: 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 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) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program in 2010-2012, and (5) results of the EPA/DNR fish contaminant monitoring program (RAFT) in 1994, 2006, and 2008.
EXPLANATION: Results of IDNR city/county beach monitoring from 2010-2012 suggest that the Class A1 uses are “fully supported." Levels of indicator bacteria at Mormon Trail Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2010 (12 samples), 2011 (14 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 Mormon Trail 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 17 E. coli orgs/100 ml in 2010, 14 E. coli orgs/100 ml in 2011, and 6 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 0% in 2010, 0% in 2011, and 0% in 2012. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “full support” of the Class A1 uses.
Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Mormon Trail Lake be assessed as "fully supported." 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 58, 55, and 52 respectively for Mormon Trail Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Mormon Trail Lake in the eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, relatively good water transparency, and low levels of phosphorus in the water column.
The level of inorganic suspended solids is relatively low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Mormon Trail Lake was 2.5 mg/L, and ranked 38th of the 134 monitored lakes.
Data from the 2008-2012 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Mormon Trail Lake, which does not contribute to impairment at this lake. These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (17.0 mg/L) and ranked 61st of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on results from the ISU and UHL lake surveys. The ISU and UHL lake surveys show that during 2008-2012 there were no violations of the Class B(LW) criterion for ammonia in 14 samples and no violations of the Class B(LW) criterion for dissolved oxygen in 14 samples and no violations of the Class A1, B(LW) criterion for pH in 14 samples.
Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Mormon Trail Lake in 1994, 2006, 2008, and 2009. 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. Levels of primary contaminants in 1994 were generally low in the fish samples collected. The level of mercury in the sample of largemouth bass (0.34 ppm), however, exceeded the IDNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Follow up sampling was conducted in 2006 at Mormon Trail Lake. The level of mercury in the 2006 sample of largemouth bass was 0.565 ppm. This again exceeded the IDNR/IDPH trigger level; therefore a one meal per week consumption advisory was issued for Mormon Trail Lake. Follow up sampling was conducted again 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. Therefore, the fish consumption advisory remained at Mormon Trail Lake, and the 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.
