North Fork Black Hawk Creek IA 02-CED-551

mouth (T87N R15W Sec1 Grundy County) to confluence with South Fork Black Hawk Creek(T88N R15W Sec8 Grundy County)

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: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 8/2/2019 1:22:05 PM
Updated: 8/2/2019 1:23:08 PM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.

Cause Magnitude

High

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study

TMDL Priority

Tier III

Class BWW2

Aquatic Life - Warm Water Type 2

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 assessed as “not supported” due to high levels of indicator bacteria. The Class B(WW2) aquatic life uses remain assessed as “fully supported” based on results of chemical/physical water quality monitoring during 2005. The sources of data for this assessment remain (1) the results of Section 319 bacteria monitoring at station BHC-14 from June 2009 through November 2010 and (2) the results of DNR/SHL water quality monitoring conducted as part of TMDL development from April through September 2005 at station 11380009. No additional monitoring has been conducted at this station since 2005. This is the same assessment as developed for previous IR cycles.

Assessment Explanation

The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2009 and 2010 at Section 319 site BHC-14 were as follows: the 2009 geometric mean was 932 orgs/100 ml and the 2010 geometric mean was 962 orgs/100 ml. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Nineteen of the 20 samples (95%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).

The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” based on results of DNR/SHL water quality monitoring conducted at TMDL station 11380009. Results of this monitoring show no violations of Class B(WW2) water quality criteria for dissolved oxygen, pH, or ammonia in the seven monthly samples collected from April-September 2005. Too few samples were collected to allow development of a high-confidence (i.e., “monitored”) assessment.

Monitoring and Methods

Assessment Key Dates

4/21/2005

Fixed Monitoring Start Date

9/12/2005

Fixed Monitoring End Date

6/18/2009

Fixed Monitoring Start Date

11/2/2010

Fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

220

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

420

Indicator bacteria monitoring