Twelvemile Creek IA 05-GRA-6572

from siltation pond (T3N R30W Sec27 Union Co.) to headwaters (T74N R31W Sec35 NE NE Adair Co.)

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.
Trend: Unknown
Created: 7/19/2019 9:16:54 AM
Updated: 7/19/2019 9:19:38 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

Fully Supported

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 (primary contact recreation) uses remain “not assessed” due to lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses remain assessed (monitored) as “fully supporting”. The sources of data for this assessment are the results of monitoring at STORET stations 13010001, 13880010, 13880008, 1388006, and 13880004 (Sites 12m-12, 12m-10, 12m-8, 12m-6, and 12m-4, respectively) conducted as part of a Clean Water Act Section 319 water quality project from 2012 to 2014.

Assessment Explanation

The presumptive Class B(WW1) aquatic life uses are assessed (monitored) as “fully supporting”.Monitoring at site 12m-4 showed no violations of Class B(WW1) water quality criteria for 7 Ammonia samples (maximum = 0.5 mg/L), or 21 Temperature samples (maximum = 27.2° c) occurred during monitoring from May 2012 to October 2014.Three of the 21 samples (14%) analyzed for Dissolved Oxygen (minimum = 1.4 mg/L) and one of the 21 samples (5%) analyzed for pH (range = 6 to 8.7) violated the Class B(WW1) criteria during the 2012-2014 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as Dissolved Oxygen, or pH suggests impairment of aquatic life uses. Because the frequency of violations for these parameters are not greater than 10 percent, these results do not suggest impairment and suggest "monitored/full support" of the Class B(WW1) aquatic life uses.

In contrast sites 12m-6, 12m-8, 12m-10, and 12m-12 do indicate the potential for impairment, however,2012 was a very stressful year. Subsequent years data at site 12m-4 showed improvement in dissolve oxygen conditions. Monitoring at site 12m-6 showed no violations of Class B(WW1) water quality criteria for 7 Ammonia samples (maximum = 0.1 mg/L), or 8 Temperature samples (maximum = 25.9° c) occurred during monitoring from May 2012 to August 2012.Four of the 8 samples (50%) analyzed for Dissolved Oxygen (minimum = 1.5 mg/L) and two of the 8 samples (25%) analyzed for pH (range = 4.6 to 8.2) violated the Class B(WW1) criteria during the 2012-2012 monitoring period. Monitoring at site 12m-8 showed no violations of Class B(WW1) water quality criteria for 7 Ammonia samples (maximum = 0.5 mg/L), or 8 Temperature samples (maximum = 27.4° c) occurred during monitoring from May 2012 to August 2012.Three of the 8 samples (38%) analyzed for Dissolved Oxygen (minimum = 1.5 mg/L) and two of the 8 samples (25%) analyzed for pH (range = 6 to 8.3) violated the Class B(WW1) criteria during the 2012 monitoring period.Monitoring at site 12m-10 showed no violations of Class B(WW1) water quality criteria for 8 pH samples (range = 6.5 to 8.4), or 8 Temperature samples (maximum = 29.5° c) occurred during monitoring from May 2012 to August 2012.One of the 7 samples (14%) analyzed for Ammonia (maximum = 9.4 mg/L) and four of the 8 samples (50%) analyzed for Dissolved Oxygen (minimum = 1.9 mg/L) violated the Class B(WW1) criteria during the 2012-2012 monitoring period. Monitoring at site 12m-12 showed no violations of Class B(WW1) water quality criteria for 7 Temperature samples (maximum = 28.6° c) occurred during monitoring from May 2012 to July 2012.Two of the 7 samples (29%) analyzed for Dissolved Oxygen (minimum = 1.3 mg/L) and two of the 7 samples (29%) analyzed for pH (range = 6.1 to 8.4) violated the Class B(WW1) criteria during the 2012-2012 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as Dissolved Oxygen, or pH suggests impairment of aquatic life uses. Because the frequency of violations for these parameters are greater than 10 percent, these results do suggest impairment of the Class B(WW1) aquatic life uses. However, due totheimproved dissolved conditions at site 12m-4 this site remains assessed (monitored) as “fully supporting”.

Monitoring and Methods

Assessment Key Dates

5/10/2012

Fixed Monitoring Start Date

10/27/2014

Fixed Monitoring End Date

Methods

220

Non-fixed station physical/chemical monitoring (conventional pollutant only)