Draft California 2026 Integrated Report (303(d) List/305(b) Report)

Supporting Information

Regional Board 5 - Central Valley Region

Water Body Name:	Cow Creek (Tuolumne County)
Water Body ID:	CAR5344105020101028161426
Water Body Type:	River & Stream


DECISION ID	161520	Region 5
Cow Creek (Tuolumne County)

Pollutant:	Indicator Bacteria
Final Listing Decision:	Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision:	Do Not List on 303(d) list (TMDL required list)(2020)
Revision Status	Revised
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for placement on the CWA section 303(d) List under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. Nine lines of evidence are available in the administrative record to assess this pollutant. Historical bacteria LOEs (pre-2010 data) have been removed and data has been compared to the newer E. coli bacteria water quality objective. Zero of nine samples, calculated as geometric means and two of 36 samples, calculated as Statistical Threshold Values (STVs) for E. coli exceed the E. coli bacteria objective for REC-1. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing this water segment-pollutant combination on the CWA section 303(d) List. This conclusion is based on the staff findings that: 1. The data used satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The data used satisfies the data quantity requirements of section 6.1.5 of the Policy. 3. Zero of nine samples, calculated as geometric means and two of 36 samples, calculated as Statistical Threshold Values (STVs) for E. coli exceed the E. coli bacteria objective for REC-1. This does not exceed the allowable frequency listed in Table 3.2 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.

Regional Board Decision Recommendation:	After review of the available data and information, RWQCB staff concludes that the water body-pollutant combination should not be placed on the section 303(d) list. The readily available data and information is insufficient to determine, with the power and confidence of the Listing Policy, the applicable beneficial use support rating.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194902

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed data for Cow Creek (Tuolumne County) to determine beneficial use support and the results are as follows: 1 of the 3 samples exceeded the Statistical Threshold Value (STV) water quality threshold for E. coli. The STV is based on a 10% exceedance rate that is calculated monthly.

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective applicable to all waters, except Lake Tahoe, where the salinity is less than 10 parts per thousand (ppth) 95 percent or more of the time is a STATISTICAL THRESHOLD VALUE (STV) of 320 cfu/100 mL not to be exceeded more than 10 percent of the time (calculated monthly).

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): HC20-UCD-Tate

Temporal Representation:

The samples were collected between the days of 2016-07-13 and 2016-09-20 .

Environmental Conditions:

QAPP Information:

Kenneth W. Tate, Ph.D., CRM. 2011. UC Davis - US Forest Service Grazing Allotment Water Quality Monitoring Quality Assurance Project Plan (QAPP)., Kenneth W. Tate, Ph.D., CRM. 2016. UC Davis - US Forest Service Grazing Allotment E. coli Monitoring Quality Assurance Project Plan (QAPP).

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment E. coli Monitoring Quality Assurance Project Plan (QAPP)

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment Water Quality Monitoring Quality Assurance Project Plan (QAPP)

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194534

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed data for Cow Creek (Tuolumne County) to determine beneficial use support and the results are as follows: 0 of the 6 samples exceeded the geomean water quality threshold for E. coli. This is a six week rolling geomean that is calculated weekly.

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective applicable to all waters, except Lake Tahoe, where the salinity is less than 10 parts per thousand (ppth) 95 percent or more of the time is a six-week rolling GEOMETRIC MEAN (GM) of Escherichia coli (E. coli) not to exceed 100 colony forming units per 100 milliliters (cfu/100 mL) (calculated weekly).

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): CC_BR

Temporal Representation:

The samples were collected between the days of 2011-07-26 and 2017-08-23 .

Environmental Conditions:

QAPP Information:

Central Sierra Environmental Resource Center. 2010. QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest., Central Sierra Environmental Resource Center. 2016. QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest., Central Sierra Environmental Resource Center (CSERC). 2017. QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest., Central Sierra Environmental Resource Center. 2018. QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest.

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194844

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): HC1-UCD-Tate

Temporal Representation:

The samples were collected between the days of 2016-07-13 and 2016-09-20 .

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment E. coli Monitoring Quality Assurance Project Plan (QAPP)

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment Water Quality Monitoring Quality Assurance Project Plan (QAPP)

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194894

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed data for Cow Creek (Tuolumne County) to determine beneficial use support and the results are as follows: 0 of the 1 samples exceeded the geomean water quality threshold for E. coli. This is a six week rolling geomean that is calculated weekly.

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): HC20-UCD-Tate

Temporal Representation:

The samples were collected between the days of 2016-07-13 and 2016-09-20 .

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment E. coli Monitoring Quality Assurance Project Plan (QAPP)

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment Water Quality Monitoring Quality Assurance Project Plan (QAPP)

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

329443

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

STV

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed Stanislaus Forest:Bacteria Contamination,Livestock data for Cow Creek (Tuolumne County) to determine beneficial use support and the results are as follows: 0 of the 8 samples exceeded the Statistical Threshold Value (STV) water quality threshold for E. coli. The STV is based on a 10% exceedance rate that is calculated monthly.

Data Reference:

WQ from the Stanislaus National Forest CSERC for the 2026 Integrated Report in Region 5

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective to protect the REC-1 beneficial use where the salinity is less than 1 parts per thousand 95 percent or more of the time applies a statistical threshold value to E. coli of 320 cfu/100 mL, not to be exceeded by more than 10 percent of samples within a calendar month (ISWEBE 2018).

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): CC_BR (Cow Creek downstream of Bull Run).

Temporal Representation:

The samples were collected between the days of 2020-06-23 and 2021-09-24 .

Environmental Conditions:

QAPP Information:

CSERC_QAPP_2021 - Stanislaus Forest:Bacteria Contamination,Livestock

QAPP Information Reference(s):

SWRCB - Region5 - CSERC_QAPP_2021 - Stanislaus Forest:Bacteria Contamination,Livestock - 402645

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194519

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed data for Cow Creek (Tuolumne County) to determine beneficial use support and the results are as follows: 0 of the 19 samples exceeded the Statistical Threshold Value (STV) water quality threshold for E. coli. The STV is based on a 10% exceedance rate that is calculated monthly.

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): CC_BR

Temporal Representation:

The samples were collected between the days of 2011-07-26 and 2017-08-23 .

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

QAPP Information Reference(s):

QAPP for Surface Water Ambient Monitoring Project in the Stanislaus National Forest

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194761

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): CHC2-UCD-Tate

Temporal Representation:

The samples were collected between the days of 2016-07-13 and 2016-09-20 .

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment E. coli Monitoring Quality Assurance Project Plan (QAPP)

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment Water Quality Monitoring Quality Assurance Project Plan (QAPP)

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194933

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed data for Cow Creek (Tuolumne County) to determine beneficial use support and the results are as follows: 0 of the 3 samples exceeded the Statistical Threshold Value (STV) water quality threshold for E. coli. The STV is based on a 10% exceedance rate that is calculated monthly.

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): CHC2-UCD-Tate

Temporal Representation:

The samples were collected between the days of 2016-07-13 and 2016-09-20 .

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment E. coli Monitoring Quality Assurance Project Plan (QAPP)

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment Water Quality Monitoring Quality Assurance Project Plan (QAPP)

Line of Evidence (LOE) for Decision ID 161520, Indicator Bacteria	Region 5
Cow Creek (Tuolumne County)

LOE ID:

194745

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Data Reference:

Water data for the 2020/2022 integrated report in Region 5.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): HC1-UCD-Tate

Temporal Representation:

The samples were collected between the days of 2016-07-13 and 2016-09-20 .

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment E. coli Monitoring Quality Assurance Project Plan (QAPP)

QAPP Information Reference(s):

UC Davis - US Forest Service Grazing Allotment Water Quality Monitoring Quality Assurance Project Plan (QAPP)