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

Supporting Information

Regional Board 1 - North Coast Region

Water Body Name:	Irish Beach
Water Body ID:	CAC1136300020181220045391
Water Body Type:	Coastal & Bay Shoreline


DECISION ID	170531	Region 1
Irish Beach

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)(2018)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	In accordance with section 6.1.5.3 of the Listing Policy, data should be representative of the critical timing that the pollutant is expected to impact the waterbody. Lacking constant inputs, indicator bacteria do not persist in the environment for a long period and effects are of relatively short duration. As a result, the historic levels of bacteria in the waterbody may be a poor indicator of current risks to human health, particularly when more recent data are available to sufficiently assess the water quality standard. Historic lines of evidence for data collected prior to October 21, 2012 were evaluated pursuant to these considerations and were not used to assess water quality standards attainment because they do not meet the temporal representation requirements of section 6.1.5.3 of the Listing Policy. No data has been collected from on or after October 21, 2012 and so the existing decision will carry-over. 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 170531, Indicator Bacteria	Region 1
Irish Beach

LOE ID:

133710

Pollutant:

Enterococcus

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed Beachwatch_Mendocino County data for Irish Beach to determine beneficial use support and the results are as follows: 0 of the 2 samples exceeded the Statistical Threshold Value (STV) water quality standard for Enterococcus. The STV is based on a 10% exceedance rate that is calculated monthly. This data is for an AB411 beach. This LOE specifically corresponds with dry weather samples and only includes samples collected between April 1 and October 31 of each year.

Data Reference:

Mendocino County Beachwatch data reformatted and renamed to match CEDEN fields.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective to protect the REC-1 beneficial for all waters where the salinity is equal to or greater than 10 ppth 95 percent or more of the time, is a Statistical Threshold Value (STV) of 110 cfu/100 mL not to be exceeded more than 10 percent of the time (calculated monthly).

Objective/Criterion Reference:

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

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

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

Temporal Representation:

The samples were collected between the days of 2003-06-11 and 2009-05-05 .

Environmental Conditions:

QAPP Information:

Data exempt from QAPP requirement. Draft QAPP for Mendocino County Beachwatch data used instead. Represents data collection procedure prior to development of a formal QAPP.

QAPP Information Reference(s):

Draft QAPP for Mendocino County Beachwatch. Represents data collection procedure prior to development of a formal QAPP.

Line of Evidence (LOE) for Decision ID 170531, Indicator Bacteria	Region 1
Irish Beach

LOE ID:

133637

Pollutant:

Enterococcus

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

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

Data Reference:

Mendocino County Beachwatch data reformatted and renamed to match CEDEN fields.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

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

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

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

Temporal Representation:

The samples were collected between the days of 2003-03-19 and 2009-05-05 .

Environmental Conditions:

QAPP Information:

Data exempt from QAPP requirement. Draft QAPP for Mendocino County Beachwatch data used instead. Represents data collection procedure prior to development of a formal QAPP.

QAPP Information Reference(s):

Draft QAPP for Mendocino County Beachwatch. Represents data collection procedure prior to development of a formal QAPP.

Line of Evidence (LOE) for Decision ID 170531, Indicator Bacteria	Region 1
Irish Beach

LOE ID:

133587

Pollutant:

Enterococcus

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed Beachwatch_Mendocino County data for Irish Beach to determine beneficial use support and the results are as follows: 0 of the 1 samples exceeded the Statistical Threshold Value (STV) water quality standard for Enterococcus. The STV is based on a 10% exceedance rate that is calculated monthly.

Data Reference:

Mendocino County Beachwatch data reformatted and renamed to match CEDEN fields.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

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

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

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

Temporal Representation:

The samples were collected between the days of 2003-03-19 and 2003-03-19 .

Environmental Conditions:

QAPP Information:

Data exempt from QAPP requirement. Draft QAPP for Mendocino County Beachwatch data used instead. Represents data collection procedure prior to development of a formal QAPP.

QAPP Information Reference(s):

Draft QAPP for Mendocino County Beachwatch. Represents data collection procedure prior to development of a formal QAPP.