Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, (5) results of a fish kill investigation in August 2009, and (6) results of U.S EPA/IDNR fish contaminant monitoring in 2009.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to violations of the state water quality criteria for indicator bacteria at Crandall's Beach. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on results of a fish kill investigation in August 2009. The Class C (drinking water) uses are “not assessed” due to a lack of recent information upon which to base an assessment. Fish consumption uses are assessed (monitored) as "fully supported" based on results of fish tissue data in 2009. Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, (5) results of a fish kill investigation in August 2009, and (6) results of U.S EPA/IDNR fish contaminant monitoring in 2009.
EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Crandall's beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (27 samples), 2009 (26 samples), and 2010 (14 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 2012 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 Crandall's beach, the geometric means from 2008, 2009, and 2010 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 20 E. coli orgs/100 ml in 2008, 17 E. coli orgs/100 ml in 2009, and 65 E. coli orgs/100 ml in 2010. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 0% in 2008, 8% in 2009 and 29% in 2010. The percentage of samples exceeding the single-sample maximum criterion was significantly greater than 10% of the samples in 2010 and therefore suggests impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “partial support” of the Class A1 uses.
Results of IDNR beach monitoring from 2008 through 2010 at Marble Beach suggest that the Class A1 uses are "fully supported." At Marble beach, the geometric means from 2008, 2009, and 2010 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 2008, 17 E. coli orgs/100 ml in 2009, and 28 E. coli orgs/100 ml in 2010. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 0% in 2008, 4% in 2009 and 7% in 2010. 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 of Big Spirit Lake are assessed (monitored) as “fully supported." Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 54, 55, and 57 respectively for Big Spirit Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Big Spirit Lake in the eutrophic category. These values suggest low levels of chlorophyll a and suspended algae in the water, very good water transparency, and relatively low levels of phosphorus in the water column.
The levels of inorganic suspended solids were relatively low at this lake and do not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Big Spirit Lake (2.0 mg/L) was the 6th lowest median concentration among the 134 lakes sampled by the ISU and UHL lake surveys.
Data from the 2006-2010 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Big Spirit Lake. These data show that cyanobacteria comprised only 47% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (25.3 mg/L) was the 57th lowest cyanobacteria mass among the 134 lakes sampled by the ISU and UHL lake surveys. These results do not suggest an impairment due to nuisance aquatic life.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on results of a fish kill investigation in August 2009. The kill occurred on or before August 13, 2009. Approximately 600 walleye were killed along the southeast shoreline of Spirit Lake. Results of the investigation indicate that low levels of dissolved oxygen likely caused by algae and aquatic plant decomposition caused the kill. This is the same assessment as the 2010 assesment. According to the IDNR assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2008-2011) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys suggest that the Class B(LW) uses should be assessed as "fully supported." The ISU and UHL lake survey results show good chemical water quality at Big Spirit Lake. During 2006-2010 there were no violations of the Class B(LW) criterion for ammonia (22 samples), dissolved oxygen (22 samples), or pH (22 samples). Based on IDNR’s assessment methodology, these results suggest "full support" of the Class B(LW) aquatic life uses at Big Spirit Lake.
The Class C (drinking water) uses are “not assessed” due to the lack of recent information upon which to base an assessment. In previous 305(b) assessment cycles, the Class C uses were assessed as "fully supported" based on results of sampling conducted by UHL in January 1995 (see assessment for the 1996 and 1998 reports). However, these data are now considered too old (greater than ten years) to characterize current water quality conditions. 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 2006-10 show that nitrate levels are extremely low at this lake (maximum value = 0.6 mg/l; median = 0.2 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Big Spirit Lake in 2009. The composite samples of fillets from common carp and yellow perch had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.0343 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of yellow perch fillets were as follows: mercury: 0.043 ppm. 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. The fish contaminant data generated from the 2009 RAFT sampling conducted at this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
