Draft California 2016 Integrated Report (303(d) List/305(b) Report)

Supporting Information

Regional Board 2 - San Francisco Bay Region

Water Body Name:	Arroyo Las Positas
Water Body ID:	CAR2043008020010905115005
Water Body Type:	River & Stream


DECISION ID	44108	Region 2
Arroyo Las Positas

Pollutant:	Selenium
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)(2012)
Revision Status	Revised
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for placement on the section 303(d) list under section 3.1 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. Two of the samples exceed the water quality objective. Based on the readily available data and information, the weight of evidence indicates that there is not sufficient justification in favor of 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 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. The exceedances both occurred during the same season of the same year and do not provide evidence of impairment extending through time or over multiple seasons. 3. Selenium exceeded the Basin Plan chronic water quality objective in 2 spring samples out of 6 samples analyzed. Considering natural abundance of selenium in soils in the area and the fact that the data are more than 16 years old there is insufficient information to determine with confidence required by the Listing Policy that this water body is impaired. 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.

Line of Evidence (LOE) for Decision ID 44108, Selenium	Region 2
Arroyo Las Positas

LOE ID:

28928

Pollutant:

Selenium, Total

LOE Subgroup:

Pollutant-Water

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:

The Arroyo Las Positas Creek watershed was monitored as part of SWAMP assessment. Two of the six samples exceeded the chronic water quality objective for selenium, both during the spring sampling. ALP010 at 5.13 ug/L (1.02 chronic exceedence factor), and ALP100 at 8.6 ug/L (1.72 chronic exceedence factor).

Data Reference:

Water Quality Monitoring and Bioassessment in Nine San Francisco Bay Region Watersheds: Walker Creek, Lagunitas Creek, San Leandro Creek, Wildcat Creek/San Pablo Creek, Suisun Creek, Arroyo Las Positas, Pescadero Creek/Butano Creek, San Gregorio Creek, and Stevens Creek/Permanente Creek. Oakland, CA: Surface Water Ambient Monitoring Program, San Francisco Bay Regional Water Quality Control Board

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances that are lethal to or that produce other detrimental responses in aquatic organisms.
Table 3-4 in the Basin Plan (2007) lists freshwater water quality objectives for toxic pollutants: selenium 5 ug/L 4-day average (chronic) and 20 ug/L 1-hour (acute) WQOs.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Data were collected at three sampling locations on Arroyo Las Positas Creek - ALP010 (El Charro), ALP100 (Altamont Creek), and ALP110 (Arroyo Las Positas).

Temporal Representation:

Samples were collected at all three sites during spring and dry seasons of the 2001-2002 sampling season.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)


DECISION ID	43065	Region 2
Arroyo Las Positas

Pollutant:	Toxicity
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)(2012)
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 3.1 of the Listing Policy. Under section 3.1 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. Four of six samples exceed the guideline. A 2007 SWAMP study identified 1500 microSiemens per centimeter as an electrical conductivity (EC) limit for Selenastrum capricornutum in standard toxicity tests and recommended that sample waters exceeding this EC level be tested against high EC controls of similar salinity to differentiate actual toxicity from reductions in growth due to elevated EC. This protocol was not in effect for the data collected in 2001 and 2002. Specific conductance exceeded 1500 microSiemens per centimeter in three of the five samples that showed significant S. capricornutum growth reductions in laboratory tests (Spring sample at 204ALP010 and dry season and Spring samples at 204APL100). It is highly likely that the algae growth results for up to three samples would be reported as not significantly toxic under the updated testing guidelines. Thus, the SWAMP data do not present a reasonable basis for this proposed listing and are deemed insufficient information. Based on the readily available data and information, the weight of evidence indicates that there is not sufficient justification in favor of 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 do not satisfy the data quality requirements of section 6.1.4 of the Policy (see above). 2. The data used satisfies the data quantity requirements of section 6.1.5 of the Policy. 3. Four of six samples exceed the guideline and this exceeds the allowable frequency listed in Table 3.1 of the Listing Policy. 4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.

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

Line of Evidence (LOE) for Decision ID 43065, Toxicity	Region 2
Arroyo Las Positas

LOE ID:

28993

Pollutant:

Toxicity

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

TOXICITY TESTING

Data Used to Assess Water Quality:

Six samples were collected in 2001 to evaluate water toxicity at two monitoring locations in Arroyo Las Positas Creek. The toxicity tests included survival and reproduction of Ceriodaphnia, survival and growth of fathead minnow, and growth of Selenastrum. Selenastrum growth was significantly lower than the control in four out of six samples (all spring samples and one of the dry season samples). Growth ranged between 55.6 and 79.5 percent of the control for these samples.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances that are lethal to or that produce other detrimental responses in aquatic organisms.
There shall be no chronic toxicity in ambient waters. Chronic toxicity is a detrimental biological effect on growth rate, reproduction, fertilization success, larval development, population abundance, community composition, or any other relevant measure of the health of an organism, population, or community.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Water toxicity was evaluated according to the SWAMP methodology. The U.S.EPA whole effluent toxicity protocol (U.S.EPA 1994) was used to test the effect of water samples on three freshwater test organisms. Statistical evaluation (alpha = 0.05) and a default threshold of 80% of the control value were used to establish whether water exhibited significant toxicity adversely impacting aquatic organisms.

Guideline Reference:

Revised approach to toxicity test acceptability criteria using a statistical performance assessment. Environmental Toxicology and Chemistry, vol. 16, No. 6, pp 1322?1329

Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms. EPA/600/4-91/002. Third Edition. July 1994

Spatial Representation:

Data were collected at three sampling locations, ALP010, (El Charro), ALP100 (Altamont Creek), and ALP110 (Arroyo Las Positas) representing the mainstem of Arroyo Las Positas Creek.

Temporal Representation:

SWAMP samples were collected during winter wet season, spring season, and dry season of 2001.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)

Line of Evidence (LOE) for Decision ID 43065, Toxicity	Region 2
Arroyo Las Positas

LOE ID:

28831

Pollutant:

Sediment Toxicity

LOE Subgroup:

Pollutant-Sediment

Matrix:

Sediment

Fraction:

None

Beneficial Use:

Warm Freshwater Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Toxicity testing of sediments

Data Used to Assess Water Quality:

Data used to evaluate sediment toxicity comprise one sediment sample collected by the SWAMP in 2001. No toxicity or adverse affects were exhibited for Hyallela azteca.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Sediment toxicity was evaluated according to the SWAMP methodology. Sample toxicity was determined by comparing mean organism response in samples and in negative controls. Statistical evaluation (alpha = 0.05) and a default threshold of 80% of the control value were used to establish whether the sediment exhibited significant toxicity adversely impacting aquatic organisms.

Guideline Reference:

Revised approach to toxicity test acceptability criteria using a statistical performance assessment. Environmental Toxicology and Chemistry, vol. 16, No. 6, pp 1322?1329

Spatial Representation:

One sediment sample was collected at a "watershed integrator" site located close to the mouth of Arroyo Las Positas Creek at El Charro.

Temporal Representation:

Sample was collected in 2001.

Environmental Conditions:

QAPP Information:

Samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)


DECISION ID	43430	Region 2
Arroyo Las Positas

Pollutant:	Ammonia (Unionized) \| Nitrogen, ammonia (Total Ammonia)
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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	These pollutants are being considered for placement on the section 303(d) list under section 3.1 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 these pollutants. 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. 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. None of the twelve samples exceeded the water quality objectives (Basin Plan) and US EPA's Lifetime Health advisory criteria and this does not exceed the allowable frequency listed in Table 3.1 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 43430, Multiple Pollutants	Region 2
Arroyo Las Positas

LOE ID:

28065

Pollutant:

Ammonia (Unionized) | Nitrogen, ammonia (Total Ammonia)

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:

Twelve water samples were assessed for total ammonia and un-ionized ammonia. None of them exceeded the evaluation criteria.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

The San Francisco Bay Regional Water Quality Board Basin Plan stated that the discharge of wastes shall not cause receiving water to contain concentrations of un-ionized ammonia in excess of 0.025mg/l annual median.

For Total Ammonia: EPA's Lifetime Health advisory level for total ammonia is 30.0 mg/L as stated on page 8 of the 2006 edition of the drinking water standards and health advisories. This Advisory Level is defined as "the concentration of a chemical in drinking water that is not expected to cause any adverse noncarcinogenic effects for up to ten days of exposure."

Objective/Criterion Reference:

2006 edition of the drinking water standards and health advisories. EPA 822-R-03-013

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Twelve samples from four monitoring locations (ALP010, ALP100, ALP110 and ALP140) were assessed.

Temporal Representation:

Samples were collected during three seasons: dry, spring and wet season of 2001.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):


DECISION ID	43706	Region 2
Arroyo Las Positas

Pollutant:	Anthracene \| Benzo(a)anthracene \| Benzo(a)pyrene (3,4-Benzopyrene -7-d) \| Chlordane \| Chrysene (C1-C4) \| DDD (Dichlorodiphenyldichloroethane) \| DDE (Dichlorodiphenyldichloroethylene) \| DDT (Dichlorodiphenyltrichloroethane) \| Dieldrin \| Endrin \| Fluoranthene \| Fluorene \| Heptachlor epoxide \| Lindane/gamma Hexachlorocyclohexane (gamma-HCH) \| Naphthalene \| PAHs (Polycyclic Aromatic Hydrocarbons) \| PCBs (Polychlorinated biphenyls) \| Phenanthrene \| Pyrene
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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for placement on the section 303(d) list under section 3.1 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. 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. Concentrations of organic pollutants analyzed in one sample did not exceed the Sediment Quality Guideline and this does not exceed the allowable frequency listed in Table 3.1 of the Listing Policy. There is insufficient number of samples to asses this pollutant. 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 43706, Multiple Pollutants	Region 2
Arroyo Las Positas

LOE ID:

28498

Pollutant:

LOE Subgroup:

Pollutant-Sediment

Matrix:

Sediment

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:

Concentrations of Anthracene, fluorene, napthalene, phenanthrene, benz(a)anthracene, benzo(a)pyrene, chrysene, fluoranthrene, pyrene, PAH (total), PCB (total), chlordane, dieldrin, DDD/DDE/DDT, endrin, heptachlor epoxide, and HCH, gamma in one sediment sample collected in spring 2005 did not exceed the sediment quality guidelines.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances that are lethal to or that produce other detrimental responses in aquatic organisms.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Sediment Quality Guidelines (MacDonald et al., 2000): PEC (probable effect concentration) Anthracene - 845 ug/kg; Fluorene - 536 ug/kg; Naphthalene - 561 ug/kg;
Phenanthrene -1170 ug/kg; Benz(a)anthracene - 1050 ug/kg; Benzo(a)pyrene - 1450 ug/kg; Chrysene - 1290 ug/kg; Fluoranthene - 2230 ug/kg; Pyrene - 1520 ug/kg; PAH (total) - 22800 ug/kg; PCB (total) - 676 ug/kg; Chlordane - 17.6 ug/kg; Dieldrin - 61.8 ug/kg; DDD (sum op + pp) - 28 ug/kg; DDE (sum op + pp) - 31.3 ug/kg; DDT (sum op + pp) - 62.9 ug/kg; DDT (total) - 572 ug/kg; Endrin - 207 ug/kg; Heptachlor epoxide - 16 ug/kg; HCH, gamma - 4.99 ug/kg.

Guideline Reference:

Development and evaluation of consensus-based sediment quality guidelines for freshwater ecosystems. Environmental Contamination and Toxicology. 39: 20-31

Spatial Representation:

One sediment sample was collected at a "watershed integrator" site located close to the mouth of Arroyo Las Positas Creek.

Temporal Representation:

Sediment sample was collected in 2001-2002 sampling season.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):


DECISION ID	43416	Region 2
Arroyo Las Positas

Pollutant:	Arsenic \| Cadmium \| Copper \| Lead \| Mercury \| Zinc
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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for placement on the section 303(d) list under section 3.1 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. 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. None of one sample exceeded the Sediment Quality Guidelines and this does not exceed the allowable frequency listed in Table 3.1 of the Listing Policy. There were not enough samples taken to satisfy the requirements of Table 3.1. 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 43416, Multiple Pollutants	Region 2
Arroyo Las Positas

LOE ID:

28631

Pollutant:

LOE Subgroup:

Pollutant-Sediment

Matrix:

Sediment

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:

Concentrations of arsenic, cadmium, copper, lead, mercury and zinc in one sediment sample collected in spring 2005 did not exceed the sediment quality guidelines.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances that are lethal to or that produce other detrimental responses in aquatic organisms.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Sediment Quality Guidelines (MacDonald et al., 2000): PEC (probable effect concentration) arsenic - 33 mg/kg dw; cadmium - 4.98 mg/kg dw; chromium - 111 mg/kg dw; copper - 149 mg/kg dw; lead - 128 mg/kg dw; mercury - 1.06 mg/kg dw; nickel - 48.6 mg/kg dw; zinc - 459 mg/kg dw.

Guideline Reference:

Development and evaluation of consensus-based sediment quality guidelines for freshwater ecosystems. Environmental Contamination and Toxicology. 39: 20-31

Spatial Representation:

One sediment sample was collected at a "watershed integrator" site located close to the mouth of Arroyo Las Positas watershed at El Charro.

Temporal Representation:

Sediment sample was collected in April of 2005.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):


DECISION ID	44261	Region 2
Arroyo Las Positas

Pollutant:	Arsenic \| Chromium (total) \| Copper \| Lead \| Nickel \| Silver \| Zinc
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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under section 3.1 a single line of evidence is necessary to assess listing status. One line of evidence are 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. 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. None of 6 samples exceeded the water quality objectives and this does not exceed the allowable frequency listed in Table 3.1 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 44261, Multiple Pollutants	Region 2
Arroyo Las Positas

LOE ID:

28927

Pollutant:

LOE Subgroup:

Pollutant-Water

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:

The Arroyo Las Positas Creek watershed was monitored as part of SWAMP assessment. None of the six samples exceeded the water quality objectives for arsenic, chromium VI, copper, lead, nickel, silver and zinc.
Concentrations of total dissolved chromium were well below the objective for chromium VI.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances that are lethal to or that produce other detrimental responses in aquatic organisms.
Table 3-4 in the Basin Plan (2007) lists freshwater water quality objectives for toxic pollutants: arsenic- 150 ug/L, chromium VI- 11 ug/L, copper - 9.0 ug/L, lead - 2.5 ug/L; nickel - 52 ug/L, silver-3.4 ug/L and zinc - 120 ug/L.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Data were collected at three sampling locations on Arroyo Las Positas Creek - ALP010 (El Charro), ALP100 (Altamont Creek), and ALP110 (Arroyo Las Positas).

Temporal Representation:

Samples were collected at all three sites during spring and dry seasons of the 2001-2002 sampling season.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)


DECISION ID	43584	Region 2
Arroyo Las Positas

Pollutant:	Chlorpyrifos \| Dacthal \| Diazinon \| Disulfoton \| Endosulfan \| Lindane/gamma Hexachlorocyclohexane (gamma-HCH) \| Methyl Parathion \| PCBs (Polychlorinated biphenyls) \| Thiobencarb/Bolero
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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	These pollutants are being considered for placement on the section 303(d) list under section 3.1 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. The data used satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The data used satisfies the data quantity requirements of section 6.1.5 of the Policy. 3. Zero of two samples exceeded the water quality objective and this does not exceed the allowable frequency listed in Table 3.1 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 43584, Multiple Pollutants	Region 2
Arroyo Las Positas

LOE ID:

28984

Pollutant:

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:

The Arroyo Las Positas Creek watershed was monitored as part of SWAMP assessment. Neither sample exceeded the water quality objectives for Chlorpyrifos, Dacthal, diazinon, disulfoton, endosulfan, Lindane/gamma Hexachlorocyclohexane (gamma-HCH), methyl parathion, thiobencarb.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

PCBs - 0.014 ug/L freshwater continuous Concentration; Chlorpyrifos - 0.015 ug/L (chronic); Dacthal (DCPA) - 14300 ug/L (acute); Disulfoton (Disyston) - 0.05 ug/L (acute); Endosulfan - 0.056 ug/L (chronic)/0.22 ug/L (acute); HCH, gamma-(gamma BHC, Lindane) - 0.95 ug/L (acute); methyl parathion - 0.08 ug/L (acute); Thiobencarb - 3.1 ug/L (acute).

Guideline Reference:

Spatial Representation:

Data were collected at one sampling location (ALP010/El Charro) in the Arroyo Las Positas Creek.

Temporal Representation:

Samples were collected at one location during spring and dry seasons of the 2001 - 2002 sampling season.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)


DECISION ID	43417	Region 2
Arroyo Las Positas

Pollutant:	Chromium
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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for placement on the section 303(d) list under section 3.1 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. One sample 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. 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 sample exceeded the Sediment Quality guidelines and this does not exceed the allowable frequency listed in Table 3.1 of the Listing Policy. However, the sample frequency was too low to meet the requirements of Table 3.1. 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 43417, Chromium	Region 2
Arroyo Las Positas

LOE ID:

28752

Pollutant:

Chromium (total)

LOE Subgroup:

Pollutant-Sediment

Matrix:

Sediment

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:

Concentration of chromium in one sediment sample collected in fall 2001 exceeded the sediment quality guidelines.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances that are lethal to or that produce other detrimental responses in aquatic organisms.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Sediment Quality Guidelines (MacDonald et al., 2000): PEC (probable effect concentration) chromium - 111 mg/kg dw.

Guideline Reference:

Development and evaluation of consensus-based sediment quality guidelines for freshwater ecosystems. Environmental Contamination and Toxicology. 39: 20-31

Spatial Representation:

One sediment sample was collected at a "watershed integrator" site located close to the mouth of Arroyo Las Positas watershed at El Charro. The PEC was exceeded for chromium, with a sample concentration of 133 mg/kg dw.

Temporal Representation:

Sediment sample was collected in September of 2001.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):


DECISION ID	39675	Region 2
Arroyo Las Positas

Pollutant:	Nickel
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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for placement on the section 303(d) list under section 3.1 of the Listing Policy. Under this section 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 sample 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. 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 sample exceeded the water quality objective, but this sample size is insufficient to determine with the power and confidence of the Listing Policy if standards are not met. A minimum of two samples are needed for application of table 3.1. 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 39675, Nickel	Region 2
Arroyo Las Positas

LOE ID:

28753

Pollutant:

Nickel

LOE Subgroup:

Pollutant-Sediment

Matrix:

Sediment

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:

Concentration of nickel in one sediment sample collected in fall 2001 exceeded the sediment quality guidelines.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances that are lethal to or that produce other detrimental responses in aquatic organisms.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Sediment Quality Guidelines (MacDonald et al., 2000): PEC (threshold effect concentration) nickel - 48.6 mg/kg dw.

Guideline Reference:

Development and evaluation of consensus-based sediment quality guidelines for freshwater ecosystems. Environmental Contamination and Toxicology. 39: 20-31

Spatial Representation:

One sediment sample was collected at a "watershed integrator" site located close to the mouth of Arroyo Las Positas watershed at El Charro. The PEC was exceeded for nickel, with a sample concentration of 109 mg/kg dw.

Temporal Representation:

Sediment sample was collected in September of 2001.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):


DECISION ID	43733	Region 2
Arroyo Las Positas

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)(2012)
Revision Status	Original
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for listing under sections 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. Temperature measurements exceed the water quality objective in 7 out of 13 deployments. Based on the readily available data for this water body, the weight of evidence indicates that there is insufficient justification for 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 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. Temperature measurements at 7 out of 13 continuous deployments exceeded the 17oC evaluation guideline used to interpret the water quality objective for waters designated as cold water habitat. Although the number of exceedances exceeds the allowable frequency listed in Table 3.2 of the Listing Policy there is insufficient information to determine that the standards are not met. The maximum 7-day mean temperature exceeded 20oC on five occasions during dry summer period (June/July) only. The range of exceedances was from 17.2 to 23.1oC. These highest temperatures were detected in Altamont Creek that has intermittent flows in upstream portions and in the most upstream reach of Arroyo Las Positas Creek that has limited flows during dry summer months and these conditions are known to be difficult to monitor. Also, the creak survey in 1999 determined that Arroyo Las Positas and its tributaries had no spawning/rearing potential for rainbow trout. Thus, the temperature levels during summer months may reflect natural conditions in the creek and would not pose impairment on salmonides to which the evaluation guidelines apply. 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, Water Board staff concludes that the water body-pollutant combination should not be placed on the section 303(d) list because there is insufficient information to determine that the standards are not met.

Line of Evidence (LOE) for Decision ID 43733, Temperature, water	Region 2
Arroyo Las Positas

LOE ID:

30213

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:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Water quality assessment was conducted at the Arroyo Las Positas watershed as part of SWAMP study in 2002. Continuous field monitoring at 15 minute increments of temperature, dissolved oxygen, pH and specific conductance was conducted to determine temporal variability in basic water quality at three locations. Continuous monitoring sondes were deployed 13 times at 3 or 5 monitoring locations during winter wet, spring wet and summer dry seasons. The measured temperatures ranged from 3.89oC to 32.1oC and varied with season and location. The 7-day mean temperature threshold for steelhead of 17 ?C was exceeded during 7 out of 13 deployments. The 7-day moving average was consistently high (above 20oC) at all 5 monitoring locations during summer sampling season only (June-July 2002).

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

Temperature objectives for enclosed bays and estuaries are specified in the "Water Quality Control Plan for Control of Temperature in the Coastal and Interstate Waters and Enclosed Bays of California" including any revisions to the plan. In addition, the following temperature objectives apply to surface waters: The natural receiving water temperature of intrastate waters shall not be altered unless it can be demonstrated to the satisfaction of the Regional Board that such an alteration does not adversely affect beneficial uses. The temperature of any cold or warm freshwater habitat shall not be increased by more than 5?F (2.8?C) above natural receiving water temperature.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Sullivan et al. (2000) reviewed a wide range of studies incorporating information from laboratory-based research, field observations, and risk assessment approaches and developed criteria for assessing temperature risk to aquatic life. The 7-day mean temperature (maximum value of a 7-day moving average of the daily mean temperature) of 14.8?C was established as the upper threshold criterion for coho salmon and 17.0?C for steelhead trout. The risk assessment approach used by Sullivan et al. (2000)suggest that temperatures exceeding the above thresholds will cause a 10% reduction in average growth compared to optimal conditions.

Guideline Reference:

An Analysis of the Effects of Temperature on Salmonids of the Pacific Northwest with Implications for Selecting Temperature Criteria

Spatial Representation:

Temperature was measured at three or five sites in the Arroyo Las Positas watershead. Four monitoring sites are located in the mainstream of Arroyo Las Positas Creek while one site (ALP105) is located in Altamont Creek that is believed to be intermittent in the upstream section.

Temporal Representation:

In 2002 the SWAMP Program performed continuous monitoring of temperature at 15 minute intervals for periods of 1-2 weeks in each of three different seasons: winter (3 sites), spring (5 sites), and summer dry season (5 sites).

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)


DECISION ID	34169	Region 2
Arroyo Las Positas

Pollutant:	Eutrophication
Final Listing Decision:	List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision:	List on 303(d) list (TMDL required list)(2012)
Revision Status	Original
Sources:	Source Unknown
Expected TMDL Completion Date:	2021
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	This pollutant is being considered for listing under sections 3.2 and 3.11 of the Listing Policy. Under section 3.11, water segments shall be evaluated to determine whether the weight of evidence demonstrates that a water quality standard is not attained. Four lines of evidence are available in the administrative record to assess this pollutant: (1) low dissolved oxygen measurements from continuous dissolved oxygen records, (2) supersaturated dissolved oxygen measurements from continuous dissolved oxygen records, (3) measurements of nitrate as N concentrations in water, and (4) samples of benthic macroinvertebrate assemblages. Based on the readily available data for this water body, the weight of evidence indicates that there is sufficient justification available in favor of adding this water segment-pollutant combination to the section 303(d) list in the Water Quality Limited Segments category. This conclusion is based on the staff findings that: 1. The data concerning current conditions and supporting the listing decision satisfy the data quality requirements of section 6.1.4 of the Policy. 2. The data used satisfy the data quantity requirements of section 6.1.5 of the Policy. 3. Minimum dissolved oxygen measurements were below the warm-water water quality objective of 5 mg/L in 4 out of 9 sampling events. Using table 3.2 of the listing policy, a minimum of 5 exceedances are needed to list this water body on the 303(d) list with a minimum sample size of 5. However, additional water quality information indicates that this water body is impaired by low dissolved oxygen levels as a result of widespread eutrophic conditions. Under section 3.11, these additional factors shall be considered in a weight of evidence approach in the decision to list a water body as impaired. 4. Supersaturated dissolved oxygen levels greater than 200% were observed in 5 out of 9 deployments, including a maximum value of 395%, indicating tremendous oxygen production by algae (eutrophication). 5. Eight out of 8 nitrate samples had concentrations greater than the guideline of 0.5 mg/L to prevent nuisance algae growth. Additionally, 8 out of 8 nitrate samples had concentrations greater than the guideline of 2.0 mg/L to protect aquatic life from nitrate toxicity. These high nitrate concentrations can promote the growth of periphyton that can cause nuisance and adversely affect beneficial uses. 6. Twelve out of 13 samples exceeded the recommended pH level of 8.5. The measured exceedances ranged from 8.52 to 8.99 with one maximum pH of 9.24. 7. Benthic macroinvertebrate (BMI) assemblages were significantly altered relative to reference conditions, indicating that controllable water quality factors have resulted in significant alterations in the community ecology of receiving waters. These alterations are most likely the result of low levels of dissolved oxygen, which is a result of eutrophication. Of the 6 sites where BMI were sampled, dissolved oxygen was also measured at 4 sites. Three of these sites had dissolved oxygen levels <5 mg/L. 8. 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 is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 34169, Eutrophication	Region 2
Arroyo Las Positas

LOE ID:

4813

Pollutant:

Benthic-Macroinvertebrate Bioassessments

LOE Subgroup:

Population/Community Degradation

Matrix:

-N/A

Fraction:

None

Beneficial Use:

Warm Freshwater Habitat

Aquatic Life Use:

Wildlife Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

Benthic macroinvertebrate surveys

Data Used to Assess Water Quality:

Benthic macroinvertebrates were sampled from 7 sites in the Arroyo Las Positas watershed in April 2001 by the SWAMP program. Benthic macroinvertebrate assemblage metrics were well outside the range of scores for minimally disturbed reference sites. Taxa richness scores at all 7 sampled sites in the Arroyo Las Positas watershed ranged from 11 to 16 taxa, whereas taxa richness values at reference sites ranged from 28 to 59. No taxa that are sensitive to pollution were present in any of the samples, indicating that pollution has resulted in significant alterations of community ecology.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances in concentrations that are lethal to or that produce significant alterations in population or community ecology or receiving water biota. In addition, the health and life history characteristics of aquatic organisms in waters affected by controllable water quality factors shall not differ significantly from those for the same waters in areas unaffected by controllable water quality factors.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Benthic macroinvertebrate assemblage metric scores that are outside the range of scores for minimally disturbed reference sites indicate significant alterations in community ecology. Taxa richness values at reference sites sampled by the SWAMP program between 2001 and 2003 ranged from 28 to 59.

Guideline Reference:

Spatial Representation:

Benthic macroinvertebrates were sampled from 7 sites throughout the watershed. Five sites were sampled on the main stem of Arroyo Las Positas, and 2 sites were sampled on Altamont Creek, the major perennial tributary of Arroyo Las Positas.

Temporal Representation:

Benthic macroinvertebrates were sampled once in April, 2001.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)

Line of Evidence (LOE) for Decision ID 34169, Eutrophication	Region 2
Arroyo Las Positas

LOE ID:

4811

Pollutant:

Dissolved oxygen saturation

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Warm Freshwater Habitat

Aquatic Life Use:

Wildlife Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data used to evaluate dissolved oxygen was collected by SWAMP. Supersaturated dissolved oxygen levels greater than 200% were observed in 5 out of 9 deployments, including a maximum value of 395%, indicating tremendous oxygen production by algae (eutrophication). Supersatured conditions always occurred during the daylight hours. The maximum diurnal range in dissolved oxygen was greater than 30 mg/L, higher than any values ever reported in the literature (Kent et al. 2005).

Data Reference:

Algal productivity and nitrate assimilation in an effluent dominated concrete lined stream. Journal of the American Water Resources Association: 41: 1109-1128

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

All waters shall be maintained free of toxic substances in concentrations that are lethal to or that produce significant alterations in population or community ecology or receiving water biota.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Dissolved oxygen supersaturation above 200 percent results in mortality of fish due to gill and skin lesions from gas bubble disease (Woodbury 1942, Renfro 1963, Weitkamp and Katz 1980).

Guideline Reference:

A sudden mortality of fishes acoompanying a supersaturation of oxygen in Lake Waubesa, Wisconsin. Trans. Am. Fish. Soc. 71: 112-117

A review of dissolved gas supersaturation literature. Trans. Am. Fish. Soc. 109:659-702

Gas-bubble mortality of fishes in Galveston Bay, Texas. Trans. Am. Fish Soc. 92:320-322

Spatial Representation:

Dissolved oxygen was measured at five sites. Three of these sites were located on the mainstem of Arroyo Las Positas, while one site each was located on the major tributary. The highest dissolved oxygen levels were measured at site ALP105 on Altamont Creek, a major tributary to Arroyo Las Positas.

Temporal Representation:

The SWAMP Program performed continuous monitoring of dissolved oxygen at 15 minute intervals for periods of 1-2 weeks in each of three different seasons: winter (March 2002; 3 sites, 1 site meeting quality assurance requirements), spring (April 2002; 5 sites, 4 sites meeting quality assurance requirements), and summer (late June and late July 2002; 5 sites, 4 sites meeting quality assurance requirements).

Environmental Conditions:

Arroyo Las Positas flows west through the eastern Livermore valley before its confluence with Arroyo Mocho in eastern Pleasanton. The lower and middle sections of Arroyo Las Positas and Altamont Creek flow through the northern portion of the city of Livermore, a city of 82,000 people. The upper watershed is primarily used for cattle grazing. The lowest and highest dissolved oxygen levels were measured in a section of Altamont Creek that contained very high amounts of benthic algae and was located downstream of a golf course and small eutrophic pond. The main stem of Arroyo Las Positas is almost completely devoid of riparian vegetation as a result of extensive channel alteration and incision.

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)

Line of Evidence (LOE) for Decision ID 34169, Eutrophication	Region 2
Arroyo Las Positas

LOE ID:

28987

Pollutant:

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 quality assessment was conducted at the Arroyo Las Positas Creek watershed as part of SWAMP study in 2001-2002. Continuous field monitoring at 15 minute increments of temperature, dissolved oxygen, pH and specific conductance was conducted to determine temporal variability in basic water quality at three locations. Continuous monitoring sondes were deployed 13 times at 3 or 5 monitoring locations during wet, spring and dry seasons. The pH ranged from 7.58 to 8.99. The upper level of 8.5 was exceeded in 12 of the 13 sampling location over the three seasons.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

The pH shall not be depressed below 6.5 nor raised above 8.5. This encompasses the pH range usually found in waters within the basin. Controllable water quality factors shall not cause changes greater than 0.5 units in normal ambient pH levels.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Comprehensive water quality assessment was conducted at Arroyo Las Positas Creek watershed as part of SWAMP assessment in 2002. Continuous field monitoring of temperature, dissolved oxygen, pH, and specific conductance to determine temporal variability in basic water quality at three or five locations, throughout Arroyo Las Positas Creek watershed. The pH ranged from 7.58 to 8.99 and varied with season.

Guideline Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Spatial Representation:

pH was measured at three to five sites located on the mainstream of Arroyo Las Positas Creek that are representative of the entire creek length.

Temporal Representation:

In 2002 the SWAMP Program performed continuous monitoring of pH at 15 minute intervals for periods of 1-2 weeks in each of three different seasons: winter (3 sites), spring (5 sites), and summer dry season (5 sites).

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB, 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)

Line of Evidence (LOE) for Decision ID 34169, Eutrophication	Region 2
Arroyo Las Positas

LOE ID:

4812

Pollutant:

Nitrate

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Dissolved

Beneficial Use:

Warm Freshwater Habitat

Aquatic Life Use:

Wildlife Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Eight out of 8 nitrate samples had concentrations greater than 0.5 mg/L. Eight out of 8 nitrate samples also had concentrations greater than 2.0 mg/L. The highest concentrations (8.04 mg/L and 6.52 mg/L) occurred at the same site (ALP110; Arroyo Las Positas, just upstream of Altamont Creek) in January and April 2002, and were among the highest nitrate concentrations measured by SWAMP in the SF Bay Region.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

Waters shall not contain biostimulatory substances in concentrations that promote aquatic growths to the extent that such growths cause nuisance or adversely affect beneficial uses

All waters shall be maintained free of toxic substances in concentrations that are lethal to or that produce significant alterations in population or community ecology or receiving water biota.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

1. Total nitrogen levels greater than 0.5 mg/L can result in large masses of nuisance algae unless other factors limit algae growth (Bowie et al. 1985; Biggs 2000). Since nitrate is one component of total nitrogen in water, nitrate levels should also be less than 0.5 mg/L.
2. Nitrate (NO3-N) concentrations above 2.0 mg/L can cause toxicity in a variety of freshwater organisms (Camargo et al. 2005).

Guideline Reference:

Eutrophication of streams and rivers: dissolved nutrient-chlorophyll relationships for benthic algae. J. N. Am. Benthol. Soc. 19:17-31

Rates, Constant, and Kinetics Formulations in Surface Water Quality Modeling, 2nd Edition. EPA/600/3-85/040. USEPA Environmental Research Laboratory, Athens, GA

Nitrate toxicity to aquatic animals: a review with new data for freshwater invertebrates. Chemosphere 58:1255-67

Spatial Representation:

Nitrate was sampled at four sites in the watershed, including two main stem sites and two sites on Altamont Creek, an important tributary.

Temporal Representation:

Water samples were collected for nitrate analyses during three sampling events. The same four sites were sampled during each sampling event. Data are evaluated from the January 2002 and April 2002 sampling events only. Laboratory methods used on samples collected during September 2001 did not meet quality assurance requirements, so this data has not been considered.

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)

Line of Evidence (LOE) for Decision ID 34169, Eutrophication	Region 2
Arroyo Las Positas

LOE ID:

4810

Pollutant:

Low Dissolved Oxygen

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Warm Freshwater Habitat

Aquatic Life Use:

Wildlife Habitat

Number of Samples:

Number of Exceedances:

Data and Information Type:

PHYSICAL/CHEMICAL MONITORING

Data Used to Assess Water Quality:

Data used to evaluate dissolved oxygen were collected by SWAMP in 2002. In 4 out of 9 deployments, minimum dissolved oxygen levels fell below the objective of 5 mg/L. Minimum values were nearly anoxic (0.56 mg/L) at one site in the summer season. Low dissolved oxygen concentrations generally occurred during the night and early morning hours.
Continuous depressed levels of dissolved oxygen (< 5.0 mg/L) lasted from over 5 hours (dry season, downstream location) to 12 hours and 45 minutes (dry season, Altamont Creek upstream of confluence with Arroyo Las Positas).

Dissolved oxygen levels fell below 5 mg/L during one additional deployment in the upstream section of Arroyo Las Positas. The longest duration of suppressed oxygen levels lasted for over 12 hours and the patterns of dissolved oxygen concentrations at this location followed closely that of Altamont Creek. Although these measurements support the listing decision and indicate that dissolved oxygen levels are the cause of the impairment, they cannot be used directly because of the marginal (by +/- 0.4%) exceedance of the quality assurance requirements.

Data Reference:

SWAMP Data:

SWAMP

Water Quality Objective/Criterion:

The numeric water quality objective for dissolved oxygen is 5.0 mg/L minimum for waters designated as warm freshwater habitat. The median dissolved oxygen concentration for any three consecutive months shall not be less than 80 percent of the dissolved oxygen content at saturation.

Objective/Criterion Reference:

Water Quality Control Plan (Basin Plan) - San Francisco Bay Region (Region 2)

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

Dissolved oxygen was measured at five sites. Three of these sites were located on the mainstem of Arroyo Las Positas, while one site each was located on Altamont Creek and Arroyo Seco, two major tributaries. The lowest dissolved oxygen levels were measured at site ALP105 on Altamont Creek. Low dissolved oxygen levels also occurred in the mainstem of Arroyo Las Positas during the summer season.

Temporal Representation:

Environmental Conditions:

QAPP Information:

All samples were collected and analyzed using procedures comparable with the SWAMP Quality Assurance Management Plan (SWRCB 2002).

QAPP Information Reference(s):

Quality Assurance Management Plan for the State of California's Surface Water Ambient Monitoring Program. Sacramento, CA. State Water Resources Control Board. SWAMP. December 2002 (1st version)


DECISION ID	34081	Region 2
Arroyo Las Positas

Pollutant:	Diazinon
Final Listing Decision:	List on 303(d) list (being addressed by USEPA approved TMDL)
Last Listing Cycle's Final Listing Decision:	List on 303(d) list (being addressed by USEPA approved TMDL)(2012)
Revision Status	Original
Sources:	Urban Runoff/Storm Sewers
TMDL Name:	San Francisco Bay Urban Creeks Diazinon
TMDL Project Code:	9
Date TMDL Approved by USEPA:	05/16/2007
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	303(d) listing decisions made prior to 2006 were not held in an assessment database. The Regional Boards will update this decision when new data and information become available and are assessed. The USEPA final decision on the 2006 303(d) list was to move this listing to the being addressed by a USEPA approved TMDL portion of the 303(d) list, because the San Francisco Bay Urban Creeks Diazinon TMDL was approved by USEPA on 5/16/07 (USEPA, 2007).

Regional Board Decision Recommendation:	This is a decision previously approved by the State Water Resources Control Board and the USEPA. No new data were assessed by the Regional Board for the current. The decision has not changed.

Line of Evidence (LOE) for Decision ID 34081, Diazinon	Region 2
Arroyo Las Positas

LOE ID:

1797

Pollutant:

Diazinon

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

None

Beneficial Use:

Cold Freshwater Habitat

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):