Gustafson Lake IA 06-LSR-1625

Buena Vista County S18T93NR36W 1 mi S of Sioux Rapids.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2012 - 2014
Stream/River Water Quality Data	CY 2012 - 2014
Lake Water Quality Data	CY 2010 - 2014
Biological Sampling Data	CY 2010 - 2014*
Fish Kill Data	CY 2010 - 2014
Fish Tissue Sampling Data	CY 2010 - 2014
Continuous Dissolved Oxygen Sampling Data	CY 2010 - 2014
*Biological sites sampled in both 2009 and 2013 were also assessed.

Open Segment Map
View assessment methodology in new window

Cycle: 2016
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Unknown
Trend: Unknown
Created: 5/31/2016 8:54:55 AM
Updated: 7/12/2016 11:54:30 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

Cause Magnitude

Slight

Status

Continuing

Source

Hydromodification: Erosion and Sedimentation

Source Confidence

Low

Cycle Added

2014

Impairment Rationale

Single-sample maximum criterion exceeded in significantly > 10% of samples

Data Source

Beach monitoring: Iowa DNR city/county

TMDL Priority

Tier II

Class BLW

Aquatic Life - Lakes and wetlands

Not Assessed

Class HH

Human Health -

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of the county beach monitoring program at Gabrielson Park beach at Gustafson Lake. The Class B(LW) aquatic life uses are "not assessed" due to a lack of information upon which to base an assessment. The fish consumption uses are also "not assessed" due to a lack of fish contaminant monitoring at this lake. Sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2012 through 2014.

Assessment Explanation

Results of IDNR beach monitoring from 2012 through 2014 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria at Gabrielson Park Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (12 samples), 2013 (14 samples) and 2014 (12 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 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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 Gabrielson Park Beach, the geometric means from 2012, 2013 and 2014 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 34 E. coli orgs/100 ml in 2012, 20 E. coli orgs/100 ml in 2013 and 101 E. coli orgs/100 ml in 2014. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 17% in 2012, 14% in 2013 and 17% in 2014. 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 "Fully Supported" of the Class A1 uses.

While the levels of indicator bacteria for Gabrielson Park Beach are not significantly greater than 10% of the samples and do not exceed the state's single season geometric mean criterion of 126 E. coli orgs/100 ml for the 2016 reporting cycle, Gabrielson Park Beach was listed as "partially supporting" the Class A1 uses for the 2014 reporting cycle due to indicator bacteria. Based on IDNR's assessment methodology, indicator bacteria violations must be not violation for two consecutive assessment cycles before a lake can be removed from the state’s Section 303(d) list (IR Category 5a). Therefore, Gabrielson Park Beach remains assessed as "partially supported" due to violations of the criterion for indicator bacteria for the 2016 assessment cycle.

Monitoring and Methods

Assessment Key Dates

5/29/2012

Fixed Monitoring Start Date

8/25/2014

Fixed Monitoring End Date

Methods

420

Indicator bacteria monitoring