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

Supporting Information

Regional Board 6 - Lahontan Region

Water Body Name:	Willow Creek (Lassen County)
Water Body ID:	CAR6372009520020603145810
Water Body Type:	River & Stream


DECISION ID	162184	Region 6
Willow Creek (Lassen County)

Pollutant:	Alkalinity as CaCO3
Final Listing Decision:	Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision:	New Decision
Revision Status	Revised
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162184, Alkalinity as CaCO3	Region 6
Willow Creek (Lassen County)

LOE ID:

341013

Pollutant:

Alkalinity as CaCO3

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

None

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed California Department Of Water Resources data for Willow Creek (Lassen County) to determine beneficial use support and results are as follows: 0 of 1 samples exceeded the water quality threshold for Alkalinity as CaCO3.

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances in concentrations that are toxic to, or that produce detrimental physiological responses in human, plant, animal, or aquatic life (Water Quality Control Plan, Lahontan Region).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

The USEPA recommended alkalinity criterion continuous concentration (CCC) for the protection of aquatic life in freshwater is a minimum value of 20,000 ug/L (4-day average).

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162184, Alkalinity as CaCO3	Region 6
Willow Creek (Lassen County)

LOE ID:

341012

Pollutant:

Alkalinity as CaCO3

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

The USEPA recommended alkalinity criterion continuous concentration (CCC) for the protection of aquatic life in freshwater is a minimum value of 20,000 ug/L (4-day average).

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162186	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available

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:	After review of the available data and information, SWRCB staff concludes that the water body-pollutant combination should not be placed on the section 303(d) list because it cannot be determined if applicable water quality standards are not being exceeded.

Line of Evidence (LOE) for Decision ID 162186, Aluminum	Region 6
Willow Creek (Lassen County)

LOE ID:

341030

Pollutant:

Aluminum

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

The aluminum criterion for the protection of aquatic life, is pH, total hardness, and dissolved organic carbon (DOC) dependent. When total hardness or DOC data were not available, default values based on the level III ecoregions developed by U.S EPA were substituted (EPA, 2018). When pH data were not available, the median pH value for the ecoregion, a pH value from a comparable waterbody, or a pH value from a local study in the same waterbody was used as a comparable surrogate.

Guideline Reference:

Final Aquatic Life Ambient Water Quality Criteria for Aluminum. EPA-822-R-18-001. Washington, D.C.: Office of Water, USEPA.

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162186, Aluminum	Region 6
Willow Creek (Lassen County)

LOE ID:

341033

Pollutant:

Aluminum

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed California Department Of Water Resources data for Willow Creek (Lassen County) to determine beneficial use support and results are as follows: 1 of 1 samples exceeded the water quality threshold for Aluminum.

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The California Secondary MCL that is incorporated by reference in the Water Quality Control Plan, Lahontan Region for aluminum is 0.2 mg/L (Water Quality Control Plan, Lahontan Region).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162186, Aluminum	Region 6
Willow Creek (Lassen County)

LOE ID:

341032

Pollutant:

Aluminum

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Final Aquatic Life Ambient Water Quality Criteria for Aluminum. EPA-822-R-18-001. Washington, D.C.: Office of Water, USEPA.

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162176	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162176, Arsenic	Region 6
Willow Creek (Lassen County)

LOE ID:

341120

Pollutant:

Arsenic

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The California Maximum Contaminant Level for arsenic incorporated by reference in the Basin Plan is 0.010 mg/L (Water Quality Control Plan, Lahontan Region).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162176, Arsenic	Region 6
Willow Creek (Lassen County)

LOE ID:

341094

Pollutant:

Arsenic

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The dissolved arsenic criterion continuous concentration (expressed as a 4-day average) to protect aquatic life in freshwater is 150 ug/L. The conversion factor used to convert the total fraction criterion for arsenic to dissolved fraction criterion is 1. Therefore all data was considered to be representative of the dissolved fraction. (California Toxics Rule, 2000)

Objective/Criterion Reference:

Water Quality Standards 2000. Establishment of numeric criteria for priority toxic pollutants for the State of California: Rules and regulations. Federal Register Vol. 65, No. 97. Washington, D.C.: Environmental Protection Agency

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162176, Arsenic	Region 6
Willow Creek (Lassen County)

LOE ID:

341073

Pollutant:

Arsenic

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The California Maximum Contaminant Level for arsenic incorporated by reference in the Basin Plan is 0.010 mg/L (Water Quality Control Plan, Lahontan Region).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162176, Arsenic	Region 6
Willow Creek (Lassen County)

LOE ID:

341080

Pollutant:

Arsenic

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	163693	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available

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:	After review of the available data and information, SWRCB staff concludes that the water body-pollutant combination should not be placed on the section 303(d) list because it cannot be determined if applicable water quality standards are not being exceeded.

Line of Evidence (LOE) for Decision ID 163693, Chloride	Region 6
Willow Creek (Lassen County)

LOE ID:

343629

Pollutant:

Chloride

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed California Department Of Water Resources data to determine beneficial use support and results are as follows:
0 of 1 samples exceeded the water quality threshold for Chloride

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Basin Plan objective for Chloride in this water body is 6.6 (mg/L), (as a Mean).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: WILLOW C A RD A-27 NR LITCHFIELD (CALWR_WQX-G4200100)

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 163693, Chloride	Region 6
Willow Creek (Lassen County)

LOE ID:

343630

Pollutant:

Chloride

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Basin Plan objective for Chloride in this water body is 9.5 (mg/L), (as a Mean).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: WILLOW C A RD A-27 NR LITCHFIELD (CALWR_WQX-G4200100)

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162185	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162185, Chromium	Region 6
Willow Creek (Lassen County)

LOE ID:

341247

Pollutant:

Chromium

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The California Maximum Contaminant Level for total chromium incorporated by reference in the Water Quality Control Plan, Lahontan Region is 0.05 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162185, Chromium	Region 6
Willow Creek (Lassen County)

LOE ID:

341261

Pollutant:

Chromium

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The California Maximum Contaminant Level for total chromium incorporated by reference in the Water Quality Control Plan, Lahontan Region is 0.05 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162185, Chromium	Region 6
Willow Creek (Lassen County)

LOE ID:

341258

Pollutant:

Chromium

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The dissolved chromium (III) criterion continuous concentration (expressed as a 4-day average) to protect aquatic life in freshwater is is hardness dependent as described in Table 1 of paragraph (b)(1). The value calculated when using a default hardness of 100 mg/L is 180 ug/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162185, Chromium	Region 6
Willow Creek (Lassen County)

LOE ID:

341256

Pollutant:

Chromium

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162177	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162177, Copper	Region 6
Willow Creek (Lassen County)

LOE ID:

341302

Pollutant:

Copper

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The California Secondary Maximum Contaminant Level for total Copper incorporated by reference in the Water Quality Control Plan, Lahontan Region is 1.0 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162177, Copper	Region 6
Willow Creek (Lassen County)

LOE ID:

341296

Pollutant:

Copper

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The California Secondary Maximum Contaminant Level for total Copper incorporated by reference in the Water Quality Control Plan, Lahontan Region is 1.0 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162177, Copper	Region 6
Willow Creek (Lassen County)

LOE ID:

341279

Pollutant:

Copper

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The dissolved copper criterion continuous concentration (expressed as a 4-day average) to protect aquatic life in freshwater is hardness dependent. The criterion when calculated using a default hardness of 100 mg/L is 9 ug/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162177, Copper	Region 6
Willow Creek (Lassen County)

LOE ID:

341290

Pollutant:

Copper

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	70560	Region 6
Willow Creek (Lassen 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)(2016)
Revision Status	Revised
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.3 of the Listing Policy. Under section 3.3 a single line of evidence is necessary to assess listing status. Two lines of evidence are available in the administrative record to assess this pollutant. None of the samples exceeds the water quality objective. 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 section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. No quality assurance information is available to determine whether this dataset satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Samples were collected only in the summer and are not necessarily representative of year-round conditions. 3. None of three samples exceeded the water quality objective and 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:	This region was not assessed this cycle. All decisions have been carried over from the previous cycle and remain the same.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:	After review of this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 70560, Indicator Bacteria	Region 6
Willow Creek (Lassen County)

LOE ID:

6411

Pollutant:

Fecal Coliform

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

Water column surveys (e.g. fecal coliform)

Data Used to Assess Water Quality:

The U.S. Bureau of Land Management sampled Willow Creek in June and August 2002. Concentrations of fecal coliform bacteria in four samples ranged from 0 to 8 colonies per 100 mL. The objective was not violated. (Because the objective requires a minimum of five samples in a 30-day period, log means were not calculated.)

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Lahontan Basin Plan's water quality objective for coliform bacteria states: "Waters shall not contain concentrations of coliform organisms attributable to anthropogenic sources, including human and livestock waste.

The fecal coliform concentration during any 30-day period shall not exceed a log mean of 20/100 ml, nor shall more than 10 percent of all samples collected during any 30-day period exceed 40/100 ml. The log mean shall ideally be based on a minimum of not less than five samples collected a evenly spaced as practicable during any 30-day period. However, a log mean concentration exceeding 20/100 ml for any 30-day period shall indicate violation of this objective even if fewer than five samples were collected."

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Three stations were sampled.

Temporal Representation:

Two sampling runs were made. All three stations were sampled on August 20, 2002. Station W-8, "Willow Creek at Sheep Bridge" was also sampled on June 6, 2002.

Environmental Conditions:

Willow Creek is a tributary of the Susan River. It is designated for both the Warm Freshwater Habitat and Cold Freshwater Habitat beneficial uses, and for the Spawning, Reproduction and Development uses. Site specific water quality objectives are designated for certain constituents for two stations on Willow Creek in Basin Plan Table 3-9. Both stations with objectives are upstream of the USBLM sampling sites.

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):

Line of Evidence (LOE) for Decision ID 70560, Indicator Bacteria	Region 6
Willow Creek (Lassen County)

LOE ID:

6413

Pollutant:

Fecal Coliform

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

Water column surveys (e.g. fecal coliform)

Data Used to Assess Water Quality:

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Three stations (USBLM Nos. W-1, W-4 and W-8) were sampled.

Temporal Representation:

Two sampling runs were made. All three stations were sampled on August 20, 2002. Station W-8, "Willow Creek at Sheep Bridge" was also sampled on June 6, 2002.

Environmental Conditions:

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):


DECISION ID	162178	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162178, Iron	Region 6
Willow Creek (Lassen County)

LOE ID:

341379

Pollutant:

Iron

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances in concentrations which are toxic to, or which produce detrimental physiological responses in, human, plant, animal, or aquatic life (Water Quality Control Plan, Lahontan Region).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

The Red Book states that based on field observations principally, a criterion of 1.0 mg/L iron for freshwater aquatic life is believed to be adequately protective.

Guideline Reference:

Quality Criteria for Water. USEPA Office of Water and Hazardous Materials. Washington, D.C

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162178, Iron	Region 6
Willow Creek (Lassen County)

LOE ID:

341388

Pollutant:

Iron

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Lahontan Regions Objective for Municipal and Domestic Supply uses of inland surface waters states that waters designated as MUN shall not contain concentrations of chemical constituents in excess of the maximum contaminant level (MCL) or secondary maximum contaminant level (SMCL). This is based upon drinking water standards specified in the following provisions of Title 22 of the California Code of Regulations which are incorporated by reference into the Water Quality Control Plan: Table 64431-A of Section 64431 (Inorganic Chemicals), Table 64431-B of Section 64431 (Fluoride), Table 64444-A of Section 64444 (Organic Chemicals), Table 64449-A of Section 64449 (Secondary Maximum Contaminant Levels-Ranges). The maximum contaminant level listed in Table 64449-A for Iron is 0.3 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162178, Iron	Region 6
Willow Creek (Lassen County)

LOE ID:

341378

Pollutant:

Iron

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

The Red Book states that based on field observations principally, a criterion of 1.0 mg/L iron for freshwater aquatic life is believed to be adequately protective.

Guideline Reference:

Quality Criteria for Water. USEPA Office of Water and Hazardous Materials. Washington, D.C

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162178, Iron	Region 6
Willow Creek (Lassen County)

LOE ID:

341389

Pollutant:

Iron

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162178, Iron	Region 6
Willow Creek (Lassen County)

LOE ID:

341370

Pollutant:

Iron

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

The Red Book states that based on field observations principally, a criterion of 1.0 mg/L iron for freshwater aquatic life is believed to be adequately protective.

Guideline Reference:

Quality Criteria for Water. USEPA Office of Water and Hazardous Materials. Washington, D.C

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162178, Iron	Region 6
Willow Creek (Lassen County)

LOE ID:

341393

Pollutant:

Iron

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

The Red Book states that based on field observations principally, a criterion of 1.0 mg/L iron for freshwater aquatic life is believed to be adequately protective.

Guideline Reference:

Quality Criteria for Water. USEPA Office of Water and Hazardous Materials. Washington, D.C

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162179	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162179, Lead	Region 6
Willow Creek (Lassen County)

LOE ID:

341403

Pollutant:

Lead

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

California Maximum Contaminant Levels (MCLs) apply to ambient waters under the Lahontan Basin Plan's 'Chemical Constituents' objective. The MCL for lead is 15 ug/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162179, Lead	Region 6
Willow Creek (Lassen County)

LOE ID:

341405

Pollutant:

Lead

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The dissolved lead criterion continuous concentration (expressed as a 4-day average) to protect aquatic life in freshwater is hardness dependent. The criterion when calculated using a default hardness of 100 mg/L is 2.5 ug/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162179, Lead	Region 6
Willow Creek (Lassen County)

LOE ID:

341399

Pollutant:

Lead

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162180	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162180, Manganese	Region 6
Willow Creek (Lassen County)

LOE ID:

341433

Pollutant:

Manganese

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162180, Manganese	Region 6
Willow Creek (Lassen County)

LOE ID:

341417

Pollutant:

Manganese

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	170628	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available

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:	After review of the available data and information, SWRCB staff concludes that the water body-pollutant combination should not be placed on the section 303(d) list because it cannot be determined if applicable water quality standards are not being exceeded.

Line of Evidence (LOE) for Decision ID 170628, Mercury	Region 6
Willow Creek (Lassen County)

LOE ID:

341456

Pollutant:

Mercury

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Commercial or recreational collection of fish, shellfish, or organisms

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Mercury criteria for the protection of human health from consumption of organisms only is 0.051 ug/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 170628, Mercury	Region 6
Willow Creek (Lassen County)

LOE ID:

341451

Pollutant:

Mercury

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The mercury criteria for the protection of human health from the consumption of water and organisms is 0.050 ug/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 170628, Mercury	Region 6
Willow Creek (Lassen County)

LOE ID:

341443

Pollutant:

Mercury

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

National Recommended Water Quality Criteria Continuous Concentrations (4-day average concentrations) for freshwater aquatic organisms exposure to total mercury is 0.77 ug/L.

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 170628, Mercury	Region 6
Willow Creek (Lassen County)

LOE ID:

341460

Pollutant:

Mercury

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

National Recommended Water Quality Criteria Continuous Concentrations (4-day average concentrations) for freshwater aquatic organisms exposure to total mercury is 0.77 ug/L.

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162181	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162181, Nickel	Region 6
Willow Creek (Lassen County)

LOE ID:

341566

Pollutant:

Nickel

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The dissolved nickel criterion continuous concentration (expressed as a 4-day average) to protect aquatic life in freshwater is hardness dependent. The criterion when calculated using a default hardness of 100 mg/L is 52 ug/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162181, Nickel	Region 6
Willow Creek (Lassen County)

LOE ID:

341568

Pollutant:

Nickel

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Lahontan Region?s Objective for Municipal and Domestic Supply uses of inland surface waters states that waters designated as MUN shall not contain concentrations of chemical constituents in excess of the maximum contaminant level (MCL) or secondary maximum contaminant level (SMCL). This is based upon drinking water standards specified in the following provisions of Title 22 of the California Code of Regulations which are incorporated by reference into the Water Quality Control Plan: Table 64431-A of Section 64431 (Inorganic Chemicals), Table 64431-B of Section 64431 (Fluoride), Table 64444-A of Section 64444 (Organic Chemicals), Table 64449-A of Section 64449 (Secondary Maximum Contaminant Levels-Ranges). The maximum contaminant level listed in Table 64431-A for nickel is 0.1 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162181, Nickel	Region 6
Willow Creek (Lassen County)

LOE ID:

341545

Pollutant:

Nickel

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162181, Nickel	Region 6
Willow Creek (Lassen County)

LOE ID:

341573

Pollutant:

Nickel

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Commercial or recreational collection of fish, shellfish, or organisms

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The nickel criterion for the protection of human health from consumption of organisms only is 4.6 mg/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162181, Nickel	Region 6
Willow Creek (Lassen County)

LOE ID:

341572

Pollutant:

Nickel

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Commercial or recreational collection of fish, shellfish, or organisms

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The nickel criterion for the protection of human health from consumption of organisms only is 4.6 mg/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162181, Nickel	Region 6
Willow Creek (Lassen County)

LOE ID:

341567

Pollutant:

Nickel

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162182	Region 6
Willow Creek (Lassen County)

Pollutant:	Sodium
Final Listing Decision:	Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision:	New Decision
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. Two lines of evidence are available in the administrative record to assess this pollutant, one that assesses for MUN and one that assesses for AGR. One of one samples exceed the objective for MUN, and zero of one sample exceed the guideline for AGR. 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. One of one samples exceed the objective for MUN, and zero of one sample exceed the guideline for AGR and 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 because applicable water quality standards are not being exceeded.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:

Line of Evidence (LOE) for Decision ID 162182, Sodium	Region 6
Willow Creek (Lassen County)

LOE ID:

341773

Pollutant:

Sodium

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Per the Drinking Water Standards and Health Advisories (USEPA 2012), the health advisory for sodium for individuals on a sodium-restricted diet is 20 mg/l.

Guideline Reference:

2012 Edition of the Drinking Water Standards and Health Advisories

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162182, Sodium	Region 6
Willow Creek (Lassen County)

LOE ID:

341788

Pollutant:

Sodium

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Agricultural Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Water Quality for Agriculture, published by the Food and Agriculture Organization of the United Nations in 1985, contains criteria protective of various agricultural uses of water, including irrigation of various types of crops and stock watering. At or below the sodium threshold of 69 mg/L, agricultural uses of water should not be limited.

Guideline Reference:

Water Quality for Agriculture, Food and Agriculture Organization of the United Nations - Irrigation and Drainage Paper No. 29, Rev 1, Rome (1985)

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	163695	Region 6
Willow Creek (Lassen County)

Pollutant:	Total Dissolved Solids
Final Listing Decision:	Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision:	New Decision
Revision Status	Revised
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available

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:	After review of the available data and information, SWRCB staff concludes that the water body-pollutant combination should not be placed on the section 303(d) list because it cannot be determined if applicable water quality standards are not being exceeded.

Line of Evidence (LOE) for Decision ID 163695, Total Dissolved Solids	Region 6
Willow Creek (Lassen County)

LOE ID:

343699

Pollutant:

Total Dissolved Solids

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Basin Plan objective for Total Dissolved Solids in this water body is 310 (mg/L), (as a Mean).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: WILLOW C A RD A-27 NR LITCHFIELD (CALWR_WQX-G4200100)

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 163695, Total Dissolved Solids	Region 6
Willow Creek (Lassen County)

LOE ID:

343698

Pollutant:

Total Dissolved Solids

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Basin Plan objective for Total Dissolved Solids in this water body is 200 (mg/L), (as a Mean).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: WILLOW C A RD A-27 NR LITCHFIELD (CALWR_WQX-G4200100)

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 163695, Total Dissolved Solids	Region 6
Willow Creek (Lassen County)

LOE ID:

343705

Pollutant:

Total Dissolved Solids

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Basin Plan objective for Total Dissolved Solids in this water body is 310 (mg/L), (as a Mean).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: WILLOW C A RD A-27 NR LITCHFIELD (CALWR_WQX-G4200100)

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 163695, Total Dissolved Solids	Region 6
Willow Creek (Lassen County)

LOE ID:

343704

Pollutant:

Total Dissolved Solids

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Basin Plan objective for Total Dissolved Solids in this water body is 200 (mg/L), (as a Mean).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: WILLOW C A RD A-27 NR LITCHFIELD (CALWR_WQX-G4200100)

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	162183	Region 6
Willow Creek (Lassen County)

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

Regional Board Conclusion:	Insufficient information is available to determine beneficial use support for this waterbody-pollutant combination with the statistical power and confidence required by the Listing Policy. Beneficial use support will be reassessed in a future cycle, if more data are available.

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 162183, Zinc	Region 6
Willow Creek (Lassen County)

LOE ID:

342000

Pollutant:

Zinc

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Total

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Lahontan Region Objective for Municipal and Domestic Supply uses of inland surface waters states that waters designated as MUN shall not contain concentrations of chemical constituents in excess of the maximum contaminant level (MCL) or secondary maximum contaminant level (SMCL). This is based upon drinking water standards specified in the following provisions of Title 22 of the California Code of Regulations which are incorporated by reference into the Water Quality Control Plan: Table 64431-A of Section 64431 (Inorganic Chemicals), Table 64431-B of Section 64431 (Fluoride), Table 64444-A of Section 64444 (Organic Chemicals), Table 64449-A of Section 64449 (Secondary Maximum Contaminant Levels-Ranges). The maximum contaminant level listed in Table 64449-A for Zinc is 5 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162183, Zinc	Region 6
Willow Creek (Lassen County)

LOE ID:

342006

Pollutant:

Zinc

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162183, Zinc	Region 6
Willow Creek (Lassen County)

LOE ID:

342003

Pollutant:

Zinc

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The dissolved zinc criterion continuous concentration (expressed as a 4-day average) to protect aquatic life in freshwater is hardness dependent. The criterion when calculated using a default hardness of 100 mg/L is 120 ug/L (California Toxics Rule, 2000).

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.

Line of Evidence (LOE) for Decision ID 162183, Zinc	Region 6
Willow Creek (Lassen County)

LOE ID:

341998

Pollutant:

Zinc

LOE Subgroup:

Ancillary Line of Evidence

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: CALWR_WQX-G4200100 (WILLOW C A RD A-27 NR LITCHFIELD).

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

No QAPP Received. Data will be assessed as ancillary evidence.

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	69948	Region 6
Willow Creek (Lassen County)

Pollutant:	Dissolved oxygen saturation
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)(2016)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the 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. One of evidence is available in the administrative record to assess this pollutant. One of the samples exceed the water quality objective. 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 section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. No quality assurance information is available to determine whether this dataset satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. One of three samples exceeded the water quality objective and 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:	This region was not assessed this cycle. All decisions have been carried over from the previous cycle and remain the same.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:	After review of this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 69948, Dissolved oxygen saturation	Region 6
Willow Creek (Lassen County)

LOE ID:

6419

Pollutant:

Dissolved oxygen saturation

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Fixed station physical/chemical (conventional plus toxic pollutants)

Data Used to Assess Water Quality:

The U.S. Bureau of Land Management sampled Willow Creek on June 6 2002 and August 20, 2002. Percent saturation of dissolved oxygen at three different stations ranged from 78 to 85.7 percent. One of three samples was in violation of the objective.

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Lahontan Basin Plan's regionwide narrative objective states that percent saturation shall not be depressed by more than 10 percent and minimum dissolved oxygen concentration shall not be less than 80 percent saturation.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Three stations were sampled.

Temporal Representation:

Station W-8 was sampled on June 6, 2002. All three stations were sampled on August 20, 2002. .

Environmental Conditions:

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):


DECISION ID	70619	Region 6
Willow Creek (Lassen County)

Pollutant:	Oxygen, Dissolved
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)(2016)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the 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. One line of evidence is available in the administrative record to assess this pollutant. Three of the samples exceed the water quality objective. 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 section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. No quality assurance information was available to determine whether the dataset used satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The dataset used does not satisfy the data quantity requirements of section 6.1.5 of the Policy. All samples were collected on one date. 3. Three of three samples exceeded the water quality objective and 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:	This region was not assessed this cycle. All decisions have been carried over from the previous cycle and remain the same.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:	After review of this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 70619, Oxygen, Dissolved	Region 6
Willow Creek (Lassen County)

LOE ID:

6418

Pollutant:

Oxygen, Dissolved

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Fixed station physical/chemical (conventional plus toxic pollutants)

Data Used to Assess Water Quality:

The U.S. Bureau of Land Management sampled Willow Creek on August 20, 2002. Concentrations of dissolved oxygen at three different stations ranged from 7.42 to 7.78 mg/L.

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The water quality objective (Lahontan Basin Plan Table 3-6) is a one-day minimum dissolved oxygen concentration of 8 mg/L.

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Three stations were sampled.

Temporal Representation:

All three stations were sampled on August 20, 2002. .

Environmental Conditions:

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):


DECISION ID	70010	Region 6
Willow Creek (Lassen County)

Pollutant:	Sediment
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)(2016)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: The Lahontan Basin Plan's narrative water quality objective is an antidegradation based objective that provides that there shall be no increases in suspended sediment concentrations or loads. This pollutant is being considered for placement on the section 303(d) list under section 3.10 of the Listing Policy, which deals with trends in water quality. Under section 3.2 a single line of evidence is necessary to assess listing status. One line of evidence, based on quarterly sampling, is available in the administrative record to assess this pollutant. It consists of a single sample. Suspended sediment concentrations and loads are dependent on flows and can change rapidly over a short time during storm or snowmelt runoff events. Quarterly samples are insufficient to capture these short term events and therefore are insufficient to define natural background suspended sediment concentrations and loads, or to detect trends. Listing Policy Section 3.10 requires that natural background conditions be established. 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 section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. No quality assurance information was submitted with this dataset. 2. Sampling frequency was insufficient to establish natural background conditions and therefore does not meet the requirements of Listing Policy Section 3.10. 3. 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:	This region was not assessed this cycle. All decisions have been carried over from the previous cycle and remain the same.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:	After review of this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 70010, Sediment	Region 6
Willow Creek (Lassen County)

LOE ID:

6416

Pollutant:

Sediment

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Fixed station physical/chemical (conventional plus toxic pollutants)

Data Used to Assess Water Quality:

The U.S. Bureau of Land Management collected one suspended sediment sample from Willow Creek on June 6, 2002. There is insufficient information to document background conditions or allow evaluation of change.

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Lahontan Basin Plan's regionwide water quality objective states: "The suspended sediment load and suspended sediment discharge rate of surface waters shall not be altered in such a manner as to cause nuisance or adversely affect the water for beneficial uses."

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

One station, Willow Creek at Sheep Bridge, was sampled.

Temporal Representation:

Station W-8, "Willow Creek at Sheep Bridge" was sampled on June 6, 2002.

Environmental Conditions:

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):


DECISION ID	70133	Region 6
Willow Creek (Lassen County)

Pollutant:	Specific Conductance
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)(2016)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the section 303(d) list under section 3.2 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. None of the samples exceed the water quality objective. 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 section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. No quality assurance information is available to determine whether the dataset used satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. None of four samples exceeded the water quality objective and 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:	This region was not assessed this cycle. All decisions have been carried over from the previous cycle and remain the same.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:	After review of this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 70133, Specific Conductance	Region 6
Willow Creek (Lassen County)

LOE ID:

6405

Pollutant:

Specific Conductance

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Municipal & Domestic Supply

Number of Samples:

Number of Exceedances:

Data and Information Type:

Fixed station physical/chemical (conventional plus toxic pollutants)

Data Used to Assess Water Quality:

The U.S. Bureau of Land Management sampled Willow Creek in June and August 2002. Specific conductance values in four samples ranged from 195 to 450 uS/cm. The MCL was not exceeded.

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

California Maximum Contaminant Levels (MCL) apply to ambient surface waters under the Lahontan Basin Plan's "Chemical Constituents" objective. The MCL for specific conductance is 900 microsiemens per centimeter (uS/cm).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Three stations were sampled.

Temporal Representation:

Two sampling runs were made. All three stations were sampled on August 20, 2002. Station W-8, "Willow Creek at Sheep Bridge" was also sampled on June 6, 2002.

Environmental Conditions:

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):


DECISION ID	163694	Region 6
Willow Creek (Lassen County)

Pollutant:	Sulfates
Final Listing Decision:	Do Not List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision:	New Decision
Revision Status	Original
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. One line of evidence is available in the administrative record to assess this pollutant. One of one samples exceeds the objective. 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. One of one samples exceeds the objective and 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 because applicable water quality standards are not being exceeded.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:

Line of Evidence (LOE) for Decision ID 163694, Sulfates	Region 6
Willow Creek (Lassen County)

LOE ID:

343684

Pollutant:

Sulfates

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed California Department Of Water Resources data to determine beneficial use support and results are as follows:
1 of 1 samples exceeded the water quality threshold for Sulfate

Data Reference:

WQX from the NWQMP for the 2026 Integrated Report in Region 6

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Basin Plan objective for Sulfate in this water body is 0.4 (mg/L), (as a Mean).

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: WILLOW C A RD A-27 NR LITCHFIELD (CALWR_WQX-G4200100)

Temporal Representation:

The samples were collected between the dates of 2012-09-10 and 2012-09-10

Environmental Conditions:

QAPP Information:

QAPP Information Reference(s):

The data included in this LOE does not have a QAPP, but was collected after the QAPP requirements had been developed, and thus was assessed as an ancillary line of evidence.


DECISION ID	68200	Region 6
Willow Creek (Lassen County)

Pollutant:	Temperature, water
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)(2016)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: This pollutant is being considered for placement on the 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. One line of evidence is available in the administrative record to assess this pollutant. The water quality objective for temperature is anti-degradation based, and there are insufficient samples to establish background temperature conditions, to document trends, or to determine whether changes in violation of the objective have occurred.. 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 section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. No quality assurance information is available to determine whether the dataset used satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. There are insufficient background/trend data available to determine whether the objective is being exceeded under Section 3.10 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:	This region was not assessed this cycle. All decisions have been carried over from the previous cycle and remain the same.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:	After review of this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 68200, Temperature, water	Region 6
Willow Creek (Lassen County)

LOE ID:

6423

Pollutant:

Temperature, water

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Fixed station physical/chemical (conventional plus toxic pollutants)

Data Used to Assess Water Quality:

The U.S. Bureau of Land Management sampled Willow Creek in June and August 2002. Temperatures in four samples ranged from 17.48 to 23 degrees Celsius.

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The relevant language from the Lahontan Basin Plan's temperature objective states: "The natural receiving water temperature of all waters shall not be altered unless it can be demonstrated to the satisfaction fo the Regional Board that such an alteration in temperature does not adversely affect the water for beneficial uses.

For waters designated WARM, water temperature shall not be altered by more than five degrees Fahrenheit ... above or below the natural temperature. For waters designated COLD, the temperature shall not be altered."

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Three stations were sampled.

Temporal Representation:

Two sampling runs were made. All three stations were sampled on August 20, 2002. Station W-8, "Willow Creek at Sheep Bridge" was also sampled on June 6, 2002.

Environmental Conditions:

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):


DECISION ID	72290	Region 6
Willow Creek (Lassen County)

Pollutant:	pH
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)(2016)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	Regional Board Conclusion: This pollutant was considered for placement on the section 303(d) list in a previous assessment cycle. No new information was reviewed for this current assessment cycle. Therefore, the previous conclusion remains unchanged, and is as follows: One line of evidence is available in the administrative record to assess this pollutant. The Lahontan Basin Plan's narrative pH objective is a non-degradation objective for waters designated for the Cold Freshwater Habitat beneficial use, and sample numbers are insufficient to establish baseline conditions or detect trends as required under Listing Policy Section 3.10. 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 section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data used satisfy the data quality requirements of section 6.1.4 of the Policy. No quality assurance information was submitted with the dataset. 2. The data used do not satisfy the data quantity requirements of section 6.1.5 of the Policy. Only one sample is available. 3. It is not possible to determine whether the narrative pH objective was exceeded because the requirements of Listing Policy Section 3.10 were not met. 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:	This region was not assessed this cycle. All decisions have been carried over from the previous cycle and remain the same.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:	After review of this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 72290, pH	Region 6
Willow Creek (Lassen County)

LOE ID:

6407

Pollutant:

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Fixed station physical/chemical (conventional plus toxic pollutants)

Data Used to Assess Water Quality:

The U.S. Bureau of Land Management sampled Willow Creek in June and August 2002. Values of pH in four samples rranged from 7.42 to 9.02. Two samples had pH values above 8.5. There is insufficient information to document background conditions or allow evaluation of change.

Data Reference:

Water quality data for surface waters on U.S Bureau of Land Management lands in Lassen and Modoc Counties

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The regionwide pH objective in the Lahontan Basin Plan states: "In fresh waters with designated beneficial uses of COLD or WARM, changes in normal ambient pH levels shall not exceed 0.5 pH units. For all other waters of the region, the pH shall not be depressed below 6.5 nor raised above 8.5 units.

The Regional Board recognizes that some waters of the Region may have natural pH levels outside of the 6.5 to 8.5 range. Compliance with the pH objective for these waters will be determined on a case-by-case basis."

Objective/Criterion Reference:

Water Quality Control Plan for the Lahontan Region (as amended)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Three stations were sampled.

Temporal Representation:

Two sampling runs were made. All three stations were sampled on August 20, 2002. Station W-8, "Willow Creek at Sheep Bridge" was also sampled on June 6, 2002.

Environmental Conditions:

QAPP Information:

No quality assurance information was submitted with the data.

QAPP Information Reference(s):