Briggs Woods Lake IA 04-UDM-1255

Results of DNR county beach monitoring from 2004 through 2005 suggest that the Class A1 uses are assessed (evaluated) as "partially supported."Levels of indicator bacteria at Briggs Woods Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (22 samples) and 2005 (23 samples) as part of the DNR county beach monitoring program. Because only two years of data were collected as part of this program these data are considered not sufficient to accurately characterize current water quality conditions, therefore the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). According to DNR’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 Briggs Woods Lake beach, the geometric mean of 1 thirty-day period during the summer recreation seasons of 2004 and 2005 exceeded the Iowa water quality standard of 126 E.coli orgs/100 ml: 0 of 6 geometric means violated in 2004, and 1 of 12 geometric means violated in 2005. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E.coli orgs/100 ml) was not significantly greater than 10% in either of the following recreation seasons: 2004: 14%, 2005: 13%. According to DNR’s assessment methodology and U.S.EPA guidelines, these results suggest impairment (nonsupport/evaluated) of the Class A1 (primary contact recreation) uses.

An indicator bacteria impairment at Briggs Woods Lake was incorrectly identified for the 2016 IR cycle. As noted in previous assessments for this lake, indicator bacteria data should be considered not sufficient to accurately characterize current water quality conditions, therefore the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Thus, this impairment is proposed for de-listing for the 2018 cycle and be place in category 3b.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Briggs Woods Lake are assessed (monitored) as "not supported" due to frequent violations of the state criterion for pH based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 62, 64, and 62 respectively for Briggs Woods Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Briggs Woods Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column. The data show 6 violations of the Class A1 criterion for pH in 15 samples (40%).

The level of inorganic suspended solids was moderately high at Briggs Woods Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Briggs Woods Lake (3.1 mg/L) was ranked 70th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderate population of cyanobacteria exists at Briggs Woods Lake. These data show that cyanobacteria comprised 62% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (9.5 mg/L) was ranked 43rd of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "not supported" due to violations of the Class A1,B(LW) criterion for pH.A fish kill occurred on June 1,2005and was attributed to low levels of dissolved oxygen related to the excessive growth of submergent aquatic vegetation in the lake. An estimated 1,000 bluegill of a variety of sizes were killed. Because the kill affected immature as well as adult fish, the kill was attributed to an oxygen sag rather than spawning stress. This was only a partial kill: many live fish were observed and anglers were catching fish during the DNR investigation. This is the same assessment as that developed for the 2010 and 2012 assessment/listing cycles. The continuance of the IR Category 2b listing is based on DNR's 2014 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 orwaterbodyreach during the most recent assessment period (2010-2012) 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 DNR 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 2014 Integrated Report.

Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and 6 violations of the criterion for pH in 15 samples(40%). Based on DNR's assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (not supported/monitored) of the Class B(LW) uses of Briggs Woods Lake.

The level of support of the Class HH-fish consumption uses is “not assessed” due to the age of the data upon which the previous assessment was based. The previous assessments were based on results of U.S. EPA / DNR fish tissue (RAFT) monitoring at Briggs Woods Lake in 2005. 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: mercury: 0.0194 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.0568 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. 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 the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2005 RAFT sampling conducted in this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.

Note: The DNR TMDL prepared for impairments due to algae and low dissolved oxygen (organic enrichment) was approved by U.S.EPA in July 2012. Thus, these impairments are moved from IR Category 5a (impaired; TMDL required) to Category 4a (impaired; TMDL approved). Because not all the impairments identified for this lake are covered by this TMDL (pH), this lake remains in IR Category 5a.