Rock Creek IA 02-CED-528

mouth (S33 T87N R11W Black Hawk Co.) to Benton/Tama county line (west line S6 T85N R12W Benton Co.) (reach designated as B(w) prior to 1990).

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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

Open Segment Map
View assessment methodology in new window

Cycle: 2024
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: 11/1/2023 8:13:18 AM
Updated: 1/29/2024 2:52:46 PM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

WINOFI

Bacteria: Indicator Bacteria- E. coli

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2022

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Watershed project monitoring

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

Fully Supported

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 use was assessed as “WINOFI” based on levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The presumptive Class BWW1 use was assessed as "fully supported" based on water quality monitoring data.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
CRWQ	23	WQ	CY 2020-2022	99990046	Rock Creek

Presumptive Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2020/ 2021/2022)

2020 Geometric Mean

2021 Geometric Mean

2022 Geometric Mean

Violates Annual Geometric Mean?

# 2020 SSM violations / SSM Violations needed for impairment

# 2021 SSM violations / SSM Violations needed for impairment

# 2022 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

99990046

5/5/5

879

589

282

YES

5 / NA

4 / NA

YES

Evaluated

WINFOI

Presumptive Class A1 – pH:

Site ID	Data Source ID	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
99990046	23	13 / 3	6.68	9.23	8.07	1	4	NO	Mon	Full

Presumptive Class BWW1 - Binomial Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	# Acute / Chronic Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
99990046	23	Chloride	15 / 3	13.8	21.4	17	NA	0 / 0	4	NO	Mon	Full
99990046	23	Dissolved Oxygen	15 / 3	7.6	14.3	10	0	NA / NA	4	NO	Mon	Full
99990046	23	pH	13 / 3	6.68	9.23	8.07	1	NA / NA	4	NO	Mon	Full
99990046	23	Sulfate	15 / 3	15.1	25.6	19.4	0	NA / NA	4	NO	Mon	Full
99990046	23	Temperature	15 / 3	7.1	27.3	17.6	0	NA / NA	4	NO	Mon	Full

Monitoring and Methods

Assessment Key Dates

6/3/2020

Monitoring Start

8/23/2022

Monitoring End

Methods

200

Physical/Chemical Monitoring

420

Indicator bacteria monitoring

860

Other Agencies/Organizations provided monitoring data