Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program in summers of 2004, 2005, and 2006, (2) results from the IDNR-county voluntary beach monitoring program in 2004, 2005, and 2006, (3) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (4) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (5) information from the IDNR Fisheries Bureau, and (6) EPA/DNR fish contaminant (RAFT) monitoring in 2004.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of the state water quality criteria for indicator bacteria at Marble Beach. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” 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 (evaluated) as “fully supported.” Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2004, 2005, and 2006, (2) results from the IDNR-county voluntary beach monitoring program in 2004, 2005, and 2006, (3) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (4) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (5) information from the IDNR Fisheries Bureau, and (6) EPA/DNR fish contaminant (RAFT) monitoring in 2004.
EXPLANATION: Results of IDNR beach monitoring at Crandall’s Beach on Big Spirit Lake from 2004 through 2006 suggest that the Class A1 uses should be assessed (monitored) as “fully supported." Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2004 (22 samples), 2005 (23 samples), and 2006 (28 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) all thirty-day geometric means for 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 5-sample, 30-day 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).
At Crandall’s beach, the geometric means of all 61 thirty-day periods during the summer recreation seasons of 2004, 2005 and 2006 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. These results suggest generally low levels of indicator bacteria at this lake. Also, the number of samples exceeding the one-time maximum criteria of 235 orgs/100 ml was below 10% for all years (2004: 5%, 2005: 4%, 2006: 7%). Thus, these results do not suggest an impairment of the Class A1 uses of Big Spirit Lake.
Results of IDNR beach monitoring from 2004 through 2006 at Marble Beach suggest that the Class A1 uses are "not supported." At Marble beach, the geometric means of 2 thirty-day periods during the summer recreation seasons of 2004, 2005 and 2006 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml: 0 of 18 geometric means violated in 2004, 0 of 19 geometric means violated in 2005, and 2 of 24 geometric means violated in 2006. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was less than 10% in all recreation seasons: 2004: 0%, 2005: 4%, 2006: 7%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest impairment (nonsupport) of the Class A1 (primary contact recreation) uses.
Results of IDNR-county beach monitoring from 2004 through 2006 suggest that the Class A1 uses are assessed (evaluated) as "partially supported." Levels of indicator bacteria at Orleans Beach at Big Spirit Lake were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (4 samples), 2005 (16 samples), and 2006 (16 samples) as part of the IDNR county beach monitoring program. At Orleans beach, the geometric means of all 19 thirty-day periods during the summer recreation seasons of 2004, 2005 and 2006 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was significantly greater than 10% in 2004: 67%. The percentage of samples exceeding Iowa’s single-sample maximum criterion was not significantly greater than 10% in 2005 (6%) or 2006 (13%). According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest partial support (evaluated) of the Class A1 (primary contact recreation) uses.
Results from the ISU and UHL lake surveys, however, suggest that the Class A1 uses of Big Spirit Lake are “fully supported.” Using the median values from these surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 52, 56, and 58 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 relatively 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 (3.0 mg/L) was the 39th lowest median concentration among the 132 lakes sampled by the ISU and UHL lake surveys.
Data from the 2002-2006 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Big Spirit Lake, which does not suggest an impairment at this lake. These data show that cyanobacteria comprised 63% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (28.0 mg/L) was the 44th highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau, results from the ISU and UHL lake surveys and physical and chemical results associated with IDNR’s beach monitoring program. The ISU and UHL lake survey results show good chemical water quality at Big Spirit Lake. During 2002-2006 there were no violations of the Class B(LW) criterion for ammonia (17 samples), or dissolved oxygen (23 samples), and only one violation of the pH criterion in 22 samples. Based on IDNR’s assessment methodology, the one violation of the pH criterion does not constitute an impairment of the Class A1,B(LW) uses at Big Spirit Lake. The physical/chemical data associated with the beach monitoring data from 2004 through 2006 show 5 violations of the Class B(LW) criteria for dissolved oxygen in 138 samples (4%) and 6 violations of the Class A1,B(LW) criterion for pH in 136 samples (4%). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) 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 2002-06 show that nitrate levels are extremely low at this lake (maximum value = 0.6 mg/l; median = 0.1 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Big Spirit Lake in 1997. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 1997 RAFT sampling conducted at this lake show that levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.
