Unnamed Tributary to Twelvemile Creek IA 05-GRA-6577

from mouth (T73N R30W Sec27 Union Co.) to headwaters (T73N R30W Sec15 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 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: 3 - Insufficient data exist to determine whether any designated uses are met.
Trend: Unknown
Created: 7/19/2019 8:28:03 AM
Updated: 7/19/2019 8:28:39 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

WINOFI

Organic Enrichment: Low Dissolved Oxygen

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2014

Impairment Rationale

Potential Impairment

Data Source

Watershed project monitoring

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 are assessed (evaluated) as “partially supporting” due to violations of the criterion for dissolved oxygen. The source of data for this assessment is the results of monitoring at STORET station 13880005 (Site 12m-5) conducted as part of a Clean Water Act Section 319 water quality project from May to August 2012.

Assessment Explanation

The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supporting” based on violations of the Class B(WW1) criterion for dissolved oxygen. Five samples were analyzed for dissolved oxygen at Site 12m-5 in summer 2012 with two samples (40%) violating the Class B(WW1) criterion for dissolved oxygen of 5 mg/l. This assessment is considered evaluated (of lower confidence)—and thus not appropriate for Section 303(d) listing—for two reasons:(1) the Iowa DNR assessment/listing methodology requires that at least 10 samples be collected over the three-year assessment period (in this case, from 2010 through 2012) in order to develop a “monitored” (i.e., higher confidence) assessment that is appropriate for Section 303(d) listing and (2) all violations of dissolved oxygen criteria occurred in this headwater stream segment in the exceptionally warm and dry mid-to late summer period of 2012; that is, violations of Class B(WW1) water quality criteria for dissolved oxygen would be expected in headwater streams during the warm and low-flow conditions that occurred throughout Iowa during summer of 2012. Levels of pH also occasionally violated the Class A/B(WW1) criterion of 6.5 units with pH values occurring below this level. Five samples were analyzed for pH with one sample (20%) 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. As with the case for dissolved oxygen, too few samples were analyzed for pH during the 2010-12 period to meet requirements of Iowa’s assessment/listing methodology for a “monitored” (higher confidence) assessment that would be appropriate for Section 303(d) listing. The only other parameter monitored at this station that has corresponding Class B(WW1) criteria is ammonia. Five samples were analyzed for ammonia at site 12m-5 with not samples violating 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.

Monitoring and Methods

Assessment Key Dates

5/10/2012

Fixed Monitoring Start Date

6/28/2012

Fixed Monitoring End Date

Methods

220

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