Assessment Comments
Assessment is based on results of (1) the IDNR-county beach monitoring program from 2008, 2009, and 2010, (2) fish kill investigations in April 2005 and August 2006, and (3) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2008.
Basis for Assessment
SUMMARY: The Class A1 primary contact recreation uses are assessed (monitored) as "fully supported" based on indicator bacteria data from the IDNR county beach monitoring program. The Class B(LW) aquatic life uses of this waterbody are assessed (evaluated) as “partially supported” due to a fish kill in April 2005 and a fish kill in August 2006. Both kills were attributed to natural causes. This impairment is appropriate for Class 2b of the integrated report. The fish consumption uses are assessed (monitored) as "fully supported." Sources of data for this assessment include: (1) the IDNR-county beach monitoring program from 2008, 2009, and 2010, (2) fish kill investigations in April 2005 and August 2006, and (3) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2008.
EXPLANATION: Results of IDNR city/county beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “fully supported." Levels of indicator bacteria at Grays Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (10 samples), 2009 (12 samples), and 2010 (10 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 Grays Lake 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 38 E. coli orgs/100 ml in 2008, 10 E. coli orgs/100 ml in 2009, and 38 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 20% in 2008, 0% in 2009 and 0% 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.
The Class B(LW) aquatic life uses, however, are assessed (evaluated) as "partially supported" due to fish kills at Grays Lake. The first kill occurred on or before April 14, 2005. The kill was attributed to “unknown/natural” causes. IDNR field staff investigated this kill. An estimated 30 fish were killed (all largemouth bass); no estimate of the value of the fish killed was provided. The dead largemouth bass were found from west of the beach to the northwest boat launch. Most of the bass were about 6 inches long; a few were up to 9 inches, and a couple were about 2 inches in length. A light wind was blowing from the southeast and likely concentrated the dead fish at this end of the lake. Water quality testing did not identify any obvious causes of the kill. The IDNR Fisheries Bureau suggested that the kill could have been caused by a virus or may have even resulted from winterkill.
The second fish kill occurred on or before August 16, 2006. The kill was attributed to "unknown/natural" causes. The total number of fish killed was 89. The estimated value of these fish was $589.94. No evidence was found to indicate the cause of this fish kill.
The fish kill portion of this assessment is the same as that developed for the 2008 and 2010 assessment/listing cycle. The continuance of the IR Category 2b listing is based on IDNR's 2012 assessment methodology that states the following: 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” and will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. Thus, this assessment segment will remain in Category 2b of Iowa’s 2012 Integrated Report.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Grays Lake in 2008. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: total PCBs: 0.094 ppm; and technical chlordane: 0.055 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.089 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 2008 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.
