Unnamed Tributary to Twelvemile Creek IA 05-GRA-6583

from mouth (T73N R30W Sec7 Union Co.) to headwaters (T73N R31W Sec1 Union 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 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: 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
Trend: Unknown
Created: 9/22/2016 11:14:39 AM
Updated: 9/22/2016 11:14:39 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” (IR 3a) due to lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supporting” (IR 2a) due to lack of violations of the criterion for dissolved oxygen, pH, and ammonia in the samples collected. The source of data for this assessment is the results of monitoring at STORET station 13880009 (Site 12m-9) conducted as part of a Clean Water Act Section 319 water quality project from May to August 2012.

Assessment Explanation

The presumptive Class A1 uses remain “not assessed” due to lack of monitoring for indicator bacteria (E. coli) in this assessment segment.

The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supporting”. Seven samples were analyzed for dissolved oxygen at Site 12m-9 in summer 2012 with only 1 sample (14%) violating the Class B(WW1) criterion for dissolved oxygen of 5 mg/l. Similarly, seven samples were analyzed for pH with only one sample (14%) violating the Class A/B(WW1) criterion of 6.5 pH units (no samples collected as part of the Twelvemile water quality project exceeded the upper pH criterion of 9.0 pH units). This type of violation for pH is not uncommon in headwater streams in southern Iowa during low-flow or no-flow conditions of mid to late summer. The only other parameter monitored at this station that has corresponding Class B(WW1) criteria is ammonia. None of the seven samples analyzed for ammonia violated Class B(WW1) chronic criteria (early life stages presumed present). In general, violations of the temperature/pH-dependent Class B(WW1) chronic criteria (early life states presumed present) were very rare during the Twelvemile project.

[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are presumptively designated as Class A1 and Class B(WW1) waters. Thus, for the current assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]

Monitoring and Methods

Assessment Key Dates

5/10/2012

Fixed Monitoring Start Date

7/26/2012

Fixed Monitoring End Date

Methods

220

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