Draft 2008 California 303(d)/305(b) Integrated Report

Supporting Information

Regional Board 2 - San Francisco Bay Region

Water Body Name: Arroyo Mocho
Water Body ID: CAR2043008020010905115519
Water Body Type: River & Stream
 
DECISION ID
7571
 
Pollutant: Temperature, water
Final Listing Decision: List on 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision: New Decision
Revision Status Revised
Sources: Channelization | Habitat Modification | Removal of Riparian Vegetation
Expected TMDL Completion Date: 2021
Impairment from Pollutant or Pollution: Pollutant
 
Weight of Evidence: This pollutant is being considered for listing under section 3.2 of the Listing Policy. Under section 3.2 a single line of evidence is necessary to assess listing status. One line of evidence is available in the administrative record to assess this pollutant. A sufficient number of samples exceed the water quality objective.

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 were collected as part of the SWAMP and 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. Temperature measurements at 6 out of 12 continuous deployments exceeded the 17 °C evaluation guideline for steelhead used to interpret the water quality objective for waters designated as cold water habitat and this exceeds the allowable frequency listed in Table 3.2 of the Listing Policy.

4. Pursuant to section 3.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.
 
RWQCB Board Decision / Staff Recommendation: After review of the available data and information, Water Board staff concludes that the water body-pollutant combination should be added to the section 303(d) list because applicable water quality standards are exceeded and a pollutant contributes to or causes the problem.
 
SWRCB Board Decision / Staff Recommendation:
 
USEPA Decision:
 
 
Lines of Evidence (LOEs) for Decision ID 7571
 
LOE ID: 4789
 
Pollutant: Temperature, water
LOE Subgroup: Pollutant-Water
Matrix: Water
Fraction: None
 
Beneficial Use: Cold Freshwater Habitat
Aquatic Life Use: Wildlife Habitat
 
Number of Samples: 12
Number of Exceedances: 6
 
Data and Information Type: PHYSICAL/CHEMICAL MONITORING
Data Used to Assess Water Quality: Comprehensive water quality assessment was conducted at the Arroyo Mocho watershed as part of SWAMP assessment. 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 five locations throughout the watershed.

The measured temperatures ranged from 6.1°C to 27.72 °C and varied with season and location. The 17 °C criterion for steelhead was exceeded in 6 out of 12 deployments.

High water temperatures exceeding 24 °C, that is a maximum short exposure temperature for survival of salmonids (EPA 1977) were also measured at three monitoring locations at lower and upper reaches of the Creek during spring and summer seasons. At the monitoring site in the lower reach of the Arroyo Mocho Creek high temperature persisted for up to 5.75 hours during spring while at the middle and upper reach it lasted from 5 to more than 9 hours.
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
 
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 Water Board that such alteration in temperature 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: San Francisco Bay Basin (Region 2) Water Quality Control Plan (Basin Plan)
 
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 the 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) suggests that temperatures exceeding the above thresholds will cause 10% reduction in average fish 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 five sites located on the mainstem of Arroyo Mocho Creek. The highest temperatures were recorded at the monitoring location southeast of Livermore in August 2004. High temperatures also occurred in the lower reach of the Creek during the spring season of 2004.
Temporal Representation: In 2004 and 2005 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 (5 sites), spring (5 sites), and summer dry season (2 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)