Draft California 2024 Integrated Report (303(d) List/305(b) Report)

Supporting Information

Regional Board 4 - Los Angeles Region

Water Body Name:	Stokes Creek
Water Body ID:	CAR4042202019990201161555
Water Body Type:	River & Stream


DECISION ID	150336	Region 4
Stokes Creek

Pollutant:	Indicator Bacteria
Final Listing Decision:	Do Not Delist from 303(d) list (being addressed with USEPA approved TMDL)
Last Listing Cycle's Final Listing Decision:	List on 303(d) list (being addressed by USEPA approved TMDL)(2018)
Revision Status	Revised
Sources:	Nonpoint Source
TMDL Name:	Malibu Pathogens (47 in part)
TMDL Project Code:	236
Date TMDL Approved by USEPA:	01/24/2006
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for removal on the CWA section 303(d) List under sections 2.2 and section 4.3 of the Listing Policy. Under section 4.3 of the Policy, a minimum of one line of evidence is needed to assess listing status. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against removing this water segment-pollutant combination from the CWA section 303(d) List. There is sufficient justification to place it in the Being Addressed portion of the CWA 303(d) List because a TMDL has been completed and approved by RWQCB and USEPA, and is expected to result in attainment of the standard. 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. 3.7 of 9 samples exceeded the geometric mean for E. coli and these exceed the allowable frequency listed in Table 4.3 of the Listing Policy. 4. The Malibu Creek Watershed Bacteria TMDL was approved by USEPA on January 24, 2006. 5. Pursuant to section 4.11 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 removed from the section 303(d) list because applicable water quality standards for the pollutant are being exceeded.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:

Line of Evidence (LOE) for Decision ID 150336, Indicator Bacteria	Region 4
Stokes Creek

LOE ID:

2261

Pollutant:

Coliform Bacteria

LOE Subgroup:

Pollutant-Water

Matrix:

Not Specified

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

Not Specified

Data Used to Assess Water Quality:

Unspecified--This LOE is a placeholder to support a 303(d) listing decision made prior to 2006.

Data Reference:

Placeholder reference 2006 303(d)

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Temporal Representation:

Environmental Conditions:

QAPP Information:

QA Info Missing

QAPP Information Reference(s):

Line of Evidence (LOE) for Decision ID 150336, Indicator Bacteria	Region 4
Stokes Creek

LOE ID:

302994

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

STV

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed LA County MS4 data for Stokes Creek to determine beneficial use support and the results are as follows: 4 of the 7 samples exceeded the Statistical Threshold Value (STV) water quality threshold for E. coli. The STV is based on a 10% exceedance rate that is calculated monthly.

Data Reference:

WQ data from the MS4 database assembled for the 2024 Integrated Report in Region 4.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

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

Objective/Criterion Reference:

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

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): MCW-CIMP 6 (Stokes Creek in Malibu Creek State Park behind the administration building.).

Temporal Representation:

The samples were collected between the days of 2017-01-10 and 2019-04-16 .

Environmental Conditions:

QAPP Information:

Municipal Separate Storm Sewer System (MS4)

QAPP Information Reference(s):

Municipal Separate Storm Sewer System (MS4)

Line of Evidence (LOE) for Decision ID 150336, Indicator Bacteria	Region 4
Stokes Creek

LOE ID:

303081

Pollutant:

Escherichia coli (E. coli)

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

GeoMean

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed LA County MS4 data for Stokes Creek to determine beneficial use support and the results are as follows: 7 of the 9 samples exceeded the geomean water quality threshold for E. coli. This is a six week rolling geomean that is calculated weekly.

Data Reference:

WQ data from the MS4 database assembled for the 2024 Integrated Report in Region 4.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective to protect the REC-1 beneficial use for waters where the salinity is equal to or less than 1 part per thousand 95 percent or more of the time applies a rolling six-week geometric mean of E. coli, not to exceed 100 cfu/100 mL (ISWEBE 2018).

Objective/Criterion Reference:

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

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): MCW-CIMP 6 (Stokes Creek in Malibu Creek State Park behind the administration building.).

Temporal Representation:

The samples were collected between the days of 2017-01-10 and 2019-04-16 .

Environmental Conditions:

QAPP Information:

Municipal Separate Storm Sewer System (MS4)

QAPP Information Reference(s):

Municipal Separate Storm Sewer System (MS4)


DECISION ID	137643	Region 4
Stokes Creek

Pollutant:	Nitrate/Nitrite (Nitrite + Nitrate as N)
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 137643, Nitrate/Nitrite (Nitrite + Nitrate as N)	Region 4
Stokes Creek

LOE ID:

243927

Pollutant:

Nitrate/Nitrite (Nitrite + Nitrate as N)

LOE Subgroup:

Pollutant-Water

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 data from the Los Angeles County MS4 Permit to determine beneficial use support. The results are as follows: 0 out of 2 samples exceed the criterion for Nitrate + Nitrite as N.

Data Reference:

WQ data from the MS4 database assembled for the 2024 Integrated Report in Region 4.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Los Angeles Region gives a site specific objective for Nitrate + Nitrite as N in Stokes Creek of 10 (mg/L).

Objective/Criterion Reference:

Water Quality Control Plan Los Angeles Region R4 Basin Plan

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Station MCW-CIMP 6 (34.09815, -118.712467), located in Stokes Creek in Malibu Creek State Park behind the administration building..

Temporal Representation:

The water samples were taken between 1/12/2019 - 1/31/2019, per the monitoring requirements listed in the Los Angeles County Municipal Separate Storm Sewer Permit.

Environmental Conditions:

QAPP Information:

The work was performed in accordance with the provisions of the Los Angeles Municipal Separate Storm Sewer System quality control and quality assurance procedures listed in coordinated integrated monitoring plan.

QAPP Information Reference(s):

Municipal Separate Storm Sewer System (MS4)


DECISION ID	149951	Region 4
Stokes Creek

Pollutant:	Nitrogen, Nitrate
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 149951, Nitrogen, Nitrate	Region 4
Stokes Creek

LOE ID:

302505

Pollutant:

Nitrogen, Nitrate

LOE Subgroup:

Pollutant-Water

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 LA County MS4 data for Stokes Creek to determine beneficial use support and results are as follows: 0 of 1 samples exceeded the water quality threshold for Nitrate as N.

Data Reference:

WQ data from the MS4 database assembled for the 2024 Integrated Report in Region 4.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Los Angeles Region (page 3-34) states that: Waters shall not exceed 10 mg/L as nitrate-nitrogen (NO3-N).

Objective/Criterion Reference:

Water Quality Control Plan Los Angeles Region R4 Basin Plan

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: MCW-CIMP 6 (Stokes Creek in Malibu Creek State Park behind the administration building.).

Temporal Representation:

The samples were collected between the dates of 2019-01-31 and 2019-01-31

Environmental Conditions:

QAPP Information:

Municipal Separate Storm Sewer System (MS4)

QAPP Information Reference(s):

Municipal Separate Storm Sewer System (MS4)

Line of Evidence (LOE) for Decision ID 149951, Nitrogen, Nitrate	Region 4
Stokes Creek

LOE ID:

302546

Pollutant:

Nitrogen, Nitrate

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Not Recorded

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 LA County MS4 data for Stokes Creek to determine beneficial use support and results are as follows: 0 of 1 samples exceeded the water quality threshold for Nitrate as N.

Data Reference:

WQ data from the MS4 database assembled for the 2024 Integrated Report in Region 4.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Los Angeles Region (page 3-34) states that: Waters shall not exceed 10 mg/L as nitrate-nitrogen (NO3-N).

Objective/Criterion Reference:

Water Quality Control Plan Los Angeles Region R4 Basin Plan

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: MCW-CIMP 6 (Stokes Creek in Malibu Creek State Park behind the administration building.).

Temporal Representation:

The samples were collected between the dates of 2019-01-12 and 2019-01-12

Environmental Conditions:

QAPP Information:

Municipal Separate Storm Sewer System (MS4)

QAPP Information Reference(s):

Municipal Separate Storm Sewer System (MS4)

Line of Evidence (LOE) for Decision ID 149951, Nitrogen, Nitrate	Region 4
Stokes Creek

LOE ID:

302478

Pollutant:

Nitrogen, Nitrate

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Not Recorded

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 LA County MS4 data for Stokes Creek to determine beneficial use support and results are as follows: 0 of 1 samples exceeded the water quality threshold for Nitrate as N.

Data Reference:

WQ data from the MS4 database assembled for the 2024 Integrated Report in Region 4.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Los Angeles Region (page 3-34) states that: Waters shall not exceed 10 mg/L as nitrate-nitrogen (NO3-N).

Objective/Criterion Reference:

Water Quality Control Plan Los Angeles Region R4 Basin Plan

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: MCW-CIMP 6 (Stokes Creek in Malibu Creek State Park behind the administration building.).

Temporal Representation:

The samples were collected between the dates of 2019-01-12 and 2019-01-12

Environmental Conditions:

QAPP Information:

Municipal Separate Storm Sewer System (MS4)

QAPP Information Reference(s):

Municipal Separate Storm Sewer System (MS4)

Line of Evidence (LOE) for Decision ID 149951, Nitrogen, Nitrate	Region 4
Stokes Creek

LOE ID:

302492

Pollutant:

Nitrogen, Nitrate

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:

Water Board staff assessed LA County MS4 data for Stokes Creek to determine beneficial use support and results are as follows: 0 of 1 samples exceeded the water quality threshold for Nitrate as N.

Data Reference:

WQ data from the MS4 database assembled for the 2024 Integrated Report in Region 4.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The Water Quality Control Plan for the Los Angeles Region (page 3-34) states that: Waters shall not exceed 10 mg/L as nitrate-nitrogen (NO3-N).

Objective/Criterion Reference:

Water Quality Control Plan Los Angeles Region R4 Basin Plan

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site: MCW-CIMP 6 (Stokes Creek in Malibu Creek State Park behind the administration building.).

Temporal Representation:

The samples were collected between the dates of 2019-01-31 and 2019-01-31

Environmental Conditions:

QAPP Information:

Municipal Separate Storm Sewer System (MS4)

QAPP Information Reference(s):

Municipal Separate Storm Sewer System (MS4)


DECISION ID	99314	Region 4
Stokes Creek

Pollutant:	Benthic Community Effects
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:	Benthic Community Effects is being considered for placement on the CWA section 303(d) List under sections 3.9 of the Listing Policy. Under section 3.9, an additional line of evidence associating the Benthic Community Effects with a water or sediment concentration of pollutants is necessary to assess listing status. The one sample collected had an IBI score above 40. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against placing Benthic Community Effects in this water segment 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.The one sample collected had an IBI score above 40. However, this sample size is insufficient to determine with the power and confidence of the Listing Policy if standards are 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:	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 this Regional Board decision, SWRCB staff recommend the decision be approved by the State Board.

Line of Evidence (LOE) for Decision ID 99314, Benthic Community Effects	Region 4
Stokes Creek

LOE ID:

89455

Pollutant:

Benthic-Macroinvertebrate Bioassessments

LOE Subgroup:

Population/Community Degradation

Matrix:

Water

Fraction:

Not Recorded

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Benthic macroinvertebrate surveys

Data Used to Assess Water Quality:

The one sample collected had an IBI score above 40. The score at site STC16 was 51.

Data Reference:

Data for abundance calculations, taxa list and IBI scores in Malibu Creek Watershed, 2006-2009.

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 or animal, or aquatic life. Compliance with this objective will be determined by use of indicator organisms, analysis of species diversity, population density, growth anomalies, bioassays of appropriate duration or other appropriate methods as specified by the State or Regional Board. Region 4 Basin Plan.

Objective/Criterion Reference:

Water Quality Control Plan Los Angeles Region R4 Basin Plan

Evaluation Guideline:

The IBI is a multi-metric assessment that employs biological metrics that respond to a habitat or water quality impairment. Each of the biological metrics measured at a site are converted to an IBI score then summed. These cumulative scores are then ranked. For the Southern California IBI, sites with scores below 40 are considered to have impaired conditions.

Guideline Reference:

Development of a Benthic Index of Biotic Integrity (B-IBI) for Wadeable Streams in Northern Coastal California and its Application to Regional 305(b) Assessment

Spatial Representation:

The sample was collected at station STC16 Stokes Creek outlet, Malibu Creek State Park.

Temporal Representation:

The sample was collected in the fall 2006.

Environmental Conditions:

QAPP Information:

Data was collected in compliance with California Stream Bioassessment Procedure. Collection procedures were audited by California Department of Fish and Game in 2006.

QAPP Information Reference(s):