Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program from 2004 through 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1997.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due violations of the state water quality standard for indicator bacteria. 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 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 from 2004 through 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1997.
EXPLANATION: Results of IDNR beach monitoring from 2004 through 2006 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at Red Haw Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2004 (16 samples), 2005 (17 samples), and 2006 (16 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 Red Haw Lake beach, the geometric mean of 1 thirty-day period during the summer recreation season of 2004 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. No geometric means violated the standard in 2005 or 2006. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was less than 10% in all three of the recreation seasons: 2004: 6%, 2005: 0%, 2006: 0%. 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 from the ISU and UHL lake surveys suggest that the Class A1 uses at Red Haw Lake are “fully supported.” Using the median values from these surveys from 2002 through 2006 (approximately 27 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 52, 53, and 56 respectively for Red Haw Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Red Haw 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. NOTE: A fishery renovation was completed in 2002, which has led to improved water clarity at Red Haw Lake.
The level of inorganic suspended solids is low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Red Haw Lake was 1.8 mg/L, which was the 15th lowest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a very small population of cyanobacteria exists at Red Haw Lake, which does not suggest impairment at this lake. These data show that cyanobacteria comprised only 40% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (2.2 mg/L) was the 12th lowest 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 results of physical/chemical monitoring associated with the IDNR beach monitoring program. The ISU and UHL lake surveys show that from 2002-2006 there were no violations of the Class B(LW) criterion for ammonia in 21 samples, one violation of the Class B(LW) criterion for dissolved oxygen in 27 samples (4%), and one violation of the Class A1,B(LW) criterion for pH in 27 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 of Red Haw Lake. Results of physical/chemical monitoring associated with the IDNR beach monitoring program also suggest “full support” of the Class B(LW) uses at Red Haw Lake. Data from this program from 2004-06 show no violation of the Class B(LW) criterion for dissolved oxygen in 49 samples and no violations of the Class A1,B(LW) criterion for pH in 49 samples.
The Class C (drinking water) uses remain "not assessed" due to lack of water quality information on which to base such an assessment. 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 very low at this lake (maximum value = 0.4 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 Red Haw 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 Red Haw 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.
