Morris Lake IA 04-LDM-1071

Lucas County S26T72NR21W approx 3 mi E of Chariton.

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 2014 - 2016
Stream/River Water Quality Data	CY 2014 - 2016
Lake Water Quality Data	CY 2012 - 2016
Biological Sampling Data	CY 2012 - 2016*
Fish Kill Data	CY 2012 - 2016
Fish Tissue Sampling Data	CY 2012 - 2016
Continuous Dissolved Oxygen Sampling Data	CY 2012 - 2016
*Biological sites sampled in both 2011 and 2015 were also assessed.

Open Segment Map
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Cycle: 2018
Release Status: Final
Overall IR: 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
Trophic: Unknown
Trend: Unknown
Created: 6/11/2019 1:23:06 PM
Updated: 6/11/2019 1:23:26 PM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

Not Assessed

Class C

Drinking Water -

Fully Supported

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 B(LW) aquatic life uses and fish consumption uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. The Class C (drinking water) uses are assessed (monitored) as "fully supported" due to continued decrease in average levels of atrazine. The source of data for this assessment is the results of the Iowa Voluntary Atrazine Monitoring Program conducted from 2008 and 2009 by Syngenta Crop Protection, Inc.

Assessment Explanation

The Class B(LW) uses remain not assessed due to the lack of water quality information needed to assess these uses.

The Class C (drinking water) uses are assessed (monitored) as “fully supported” based on results of the Syngenta “Iowa Voluntary Atrazine Monitoring Program” from 2008 and 2009. This monitoring showed that the time-weighted mean levels of atrazine in the samples were well below the MCL of 3.0 ug/L. The mean and median atrazine concentrations over this three-year period (N= 40) were 1.3 ug/L and 0.6 ug/L, respectively. The maximum value for this period was 5.2 ug/L. None of the 9 moving annual averages for atrazine for 2008 and 2009 at Morris Lake exceeded the MCL of 3.0 ug/L. Based on DNR’s assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C uses of the source water should be assessed as “fully supported.”

NOTE: The Class C (drinking water) uses were assessed as “not supported” for the 2004 assessment/listing cycle based on results of sampling conducted as part of the Iowa Voluntary Atrazine Monitoring Program in 2000, 2001, and 2002 by Syngenta Crop Protection, Inc. Results of this program from 2000 through 2002 showed that seven of the 47 moving annual averages calculated for this period were above the MCL of 3 ug/l. These elevated running annual averages resulted from high levels of atrazine that occurred from May through September of 2001. Based on DNR's Section 305(b) assessment methodology, the Class C (drinking water) uses of Lake Morris were assessed as "not supported" for the 2004 reporting cycle.Data used for the 2006 assessment/listing cycle suggested that levels of atrazine were below the MCL and suggested “full support” of the Class C uses. Morris Lake, however, remained on the 303d list to ensure that atrazine levels were consistently below the MCL. Results from 2004-2006 again suggested that annual average levels of atrazine have not exceeded the MCL. Therefore, based on continued low levels of atrazine at Morris Lake, the Class C uses were assessed as “fully supported” and the lake was proposed for removal from the state’s 303d list in 2008.

Monitoring and Methods

Assessment Key Dates

1/24/2008

Fixed Monitoring Start Date

8/10/2009

Fixed Monitoring End Date

Methods

270

PWS chemical monitoring (ambient water)