| Water Body Name: | Dry Creek (Napa County) |
| Water Body ID: | CAR2065005120000320121704 |
| Water Body Type: | River & Stream |
DECISION ID |
148774 |
Region 2 |
Dry Creek (Napa County) |
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| Pollutant: | Indicator Bacteria |
| Final Listing Decision: | List on 303(d) list (being addressed by USEPA approved TMDL) |
| Last Listing Cycle's Final Listing Decision: | New Decision |
| Revision Status | Revised |
| Sources: | See TMDL documentation |
| TMDL Name: | Napa River Pathogens |
| TMDL Project Code: | 60 |
| Date TMDL Approved by USEPA: | 02/29/2008 |
| 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 3.11 of the Listing Policy. Under this section when all other listing factors do not result in the listing of a water segment but information indicates non-attainment of standards, a water segment shall be evaluated to determine whether the weight of evidence demonstrates that water quality standard is not attained. If the weight of evidence indicates non-attainment, the water segment shall be placed on the CWA section 303(d) List. When making a listing decision based on the situation-specific weight of evidence, the Regional Water Board must justify its recommendation by: • Providing any data or information including current conditions supporting the decision; • Describing in fact sheets how the data or information affords a substantial basis in fact from which the decision can be reasonably inferred; • Demonstrating that the weight of evidence of the data and information indicate that the water quality standard is not attained; and • Demonstrating that the approach used is scientifically defensible and reproducible. Dry Creek is a tributary to Napa River. The Napa River and its tributaries, including Dry Creek, are impaired by indicator bacteria (pathogens) and subject to the Napa River Pathogen TMDL. The weight of evidence indicates that there is sufficient justification for placing this water segment-pollutant combination on the CWA section 303(d) List, specifically on the being addressed portion of the CWA section 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. Dry Creek is a tributary to Napa River which is impaired by pathogens. E. coli measured at several Napa River watershed locations including Dry Creek during the development of the Napa River Pathogen TMDL showed moderate but widespread exceedances of water quality objectives, indicating pathogen impairment of REC-1 and REC-2 beneficial uses throughout the watershed. The sources of pathogens include numerous onsite wastewater treatment systems, confined animal facilities, grazing lands and municipal runoff. These pathogen sources exist throughout the Napa River watershed, including the Dry Creek watershed. 2017 monitoring data indicate improvement is still needed throughout the watershed before TMDL targets are met. 2. The TMDL implementation plan states “The overall intent of this implementation plan is to restore and protect beneficial uses of the Napa River and its tributaries by reducing pathogen loadings. Potential pathogen sources in the watershed include: septic systems, sanitary sewer line failure, municipal runoff, livestock, and wildlife.” The TMDL implementation actions (e.g., the Conditional Waiver Program from Grazing Operations in the Napa River watershed and the NPDES general stormwater permit), were written to include the entire Napa River watershed. As such, the Napa River Pathogen TMDL already applies to the Dry Creek subwatershed. Sources of pathogens exist in the Dry Creek subwatershed and contribute to exceedances of E.coli objectives for water contact recreation. Current conditions indicate that water quality in the Creek is impaired. 3. Eighty-six out of two hundred thirty-four samples collected collectively in the Napa River tributaries during post-TMDL sampling exceeded E.coli objectives for REC-1. The water quality data are insufficient to determine that water quality have been improved and water quality objectives are met in the Napa River watershed in general and in Dry Creek subwatershed in particular. Therefore, based on the readily available data and information, the weight of evidence indicates that there is sufficient justification for placing this water segment-pollutant combination on the being addressed portion of the CWA section 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. 4. This process is scientifically defensible and reproducible. The Dry Creek subwatershed was included in the Napa River Pathogen TMDL assessment and determined to be a source of pathogens in the Napa River watershed. The TMDL assessment included a rigorous technical review, the public participation process, and approval by U.S. EPA. Additionally, the data analysis for the TMDL made use of the E. coli objectives that were in place at the time of TMDL development. Although these objectives have been subsequently updated, exceedances of the older objectives would also constitute exceedances of the revised (lower) objectives. |
| Regional Board Decision Recommendation: | After review of the available data and information, RWQCB staff concludes that the water body-pollutant combination should be placed on the section 303(d) list because applicable water quality standards are exceeded and a pollutant contributes to or causes the problem. |
| State Board Review of Regional Board Conclusion and Recommendation: | Therefore, based on the readily available data and information, the weight of evidence indicates that there is sufficient justification for placing this water segment-pollutant combination on the being addressed portion of the CWA section 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. 4. This process is scientifically defensible and reproducible. The Dry Creek subwatershed was included in the Napa River Pathogen TMDL assessment and determined to be a source of pathogens in the Napa River watershed. The TMDL assessment included a rigorous technical review, the public participation process, and approval by U.S. EPA. Additionally, the data analysis for the TMDL made use of the E. coli objectives that were in place at the time of TMDL development. Although these objectives have been subsequently updated, exceedances of the older objectives would also constitute exceedances of the revised (lower) objectives. |
| State Board Decision Recommendation: | |
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| LOE ID: | 300548 | ||||
| Pollutant: | Escherichia coli (E. coli) | ||||
| LOE Subgroup: | Pollutant-Water | ||||
| Matrix: | Water | ||||
| Fraction: | STV | ||||
| Beneficial Use: | Water Contact Recreation | ||||
| Number of Samples: | 5 | ||||
| Number of Exceedances: | 1 | ||||
| Data and Information Type: | PATHOGEN MONITORING | ||||
| Data Used to Assess Water Quality: | Water Board staff assessed SWAMP RWB2 Monitoring data for Dry Creek (Napa County) to determine beneficial use support and the results are as follows: 1 of the 5 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: | Field, Habitat, Tissue, Toxicity, WQ data from the California Environmental Data Exchange Network assembled for the 2024 Integrated Report in Region 2. | ||||
| SWAMP Data: | 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): 206DRY100 (Dry Creek at Solano Avenue). | ||||
| Temporal Representation: | The samples were collected between the days of 2017-01-11 and 2017-07-27 . | ||||
| Environmental Conditions: | |||||
| QAPP Information: | SWRCB. 2018. This is a placeholder reference for data that was collected after QAPP requirements were developed, but exempt from the requirements.. | ||||
| QAPP Information Reference(s): | This is a placeholder reference for data that was collected after QAPP requirements were developed, but exempt from the requirements. | ||||
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| LOE ID: | 300497 | ||||
| Pollutant: | Escherichia coli (E. coli) | ||||
| LOE Subgroup: | Pollutant-Water | ||||
| Matrix: | Water | ||||
| Fraction: | GeoMean | ||||
| Beneficial Use: | Water Contact Recreation | ||||
| Number of Samples: | 1 | ||||
| Number of Exceedances: | 0 | ||||
| Data and Information Type: | PATHOGEN MONITORING | ||||
| Data Used to Assess Water Quality: | Water Board staff assessed SWAMP RWB2 Monitoring data for Dry Creek (Napa County) to determine beneficial use support and the results are as follows: 0 of the 1 samples exceeded the geomean water quality threshold for E. coli. This is a six week rolling geomean that is calculated weekly. | ||||
| Data Reference: | Field, Habitat, Tissue, Toxicity, WQ data from the California Environmental Data Exchange Network assembled for the 2024 Integrated Report in Region 2. | ||||
| SWAMP Data: | 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): 206DRY100 (Dry Creek at Solano Avenue). | ||||
| Temporal Representation: | The samples were collected between the days of 2017-01-11 and 2017-07-27 . | ||||
| Environmental Conditions: | |||||
| QAPP Information: | SWRCB. 2018. This is a placeholder reference for data that was collected after QAPP requirements were developed, but exempt from the requirements.. | ||||
| QAPP Information Reference(s): | This is a placeholder reference for data that was collected after QAPP requirements were developed, but exempt from the requirements. | ||||
DECISION ID |
100050 |
Region 2 |
Dry Creek (Napa County) |
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| 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. Three lines of evidence are available in the administrative record. The CSCI scores for this site are all above 0.92. However, Regional Board staff are concerned about water quality issues related to sediment in this water body.
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 CSCI scores for this site are all above 0.92. Additionally, this water body passed several screening criteria and was identified as a reference water body for the purposes of developing the CSCI. The State Water Board has redefined the Integrated Reporting categories in order to make them more reflective of actual water quality conditions in the State. This revision allows for the inclusion of minimally disturbed data reference sites that were identified in the development of the California Stream Condition Index (CSCI) tool into Category 1. Reference sites are the core of the State¿s statewide biological and habitat assessment program and set the benchmark for biological conditions expected when human activity in the landscape is absent or minimal. Unless there is any additional data showing that beneficial uses in a water body are not being supported, these reference water bodies along with any other bioassessment data sets showing a score of 0.92 or higher will be placed in Category 1 (all core beneficial uses are supported). However, Regional Board staff are concerned about water quality issues related to sediment in this water body and do not feel it should be placed in Category 1 at this time.. 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. |
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| LOE ID: | 96005 | ||||
| Pollutant: | Benthic-Macroinvertebrate Bioassessments | ||||
| LOE Subgroup: | Population/Community Degradation | ||||
| Matrix: | Water | ||||
| Fraction: | None | ||||
| Beneficial Use: | Cold Freshwater Habitat | ||||
| Number of Samples: | 3 | ||||
| Number of Exceedances: | 0 | ||||
| Data and Information Type: | Benthic macroinvertebrate surveys | ||||
| Data Used to Assess Water Quality: | The CSCI scores for these sites are 0.983922, 1.244608, 1.23922 and is therefore meeting the water quality objective for this water body. This water body passed several screening criteria and was identified as a reference water body for the purposes of developing the CSCI. Reference sites where human disturbance is absent or minimal are used to set benchmark expectations for healthy streams. A large set of nearly 600 reference sites representing the broad diversity of natural stream types found across California was used to develop the CSCI. | ||||
| Data Reference: | RWB2 Reference Study Monitoring 2008 | ||||
| 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 Basin (Region 2) | ||||
| Evaluation Guideline: | The California Stream Condition Index (CSCI) is a biological scoring tool that helps aquatic resource managers translate complex data about benthic macroinvertebrates found living in a stream into an overall measure of stream health. The CSCI score is calculated by comparing the expected condition with actual (observed) results (Rhen, A.C. et al., 2015). CSCI scores range from 0 (highly degraded) to greater than 1 (equivalent to reference). CSCI scoring of biological condition are as follows (per the scientific paper supporting the development of the CSCI scoring tool): greater than or equal to 0.92 = likely intact condition, 0.91 to 0.80 = possibly altered condition, 0.79 to 0.63 = likely altered condition, less than or equal to 0.62 = very likely altered condition. Sites with scores below 0.79 are considered to have exceeded the water quality objective for the aquatic life beneficial use. | ||||
| Guideline Reference: | Bioassessment in complex environments: designing an index for consistent meaning in different settings | ||||
| Spatial Representation: | Sampling was done at to following station:206DRY040, 206DRY060, 206DRY100 | ||||
| Temporal Representation: | Sampling was done on 4/23/2001 (at sites 206DRY040 and 206DRY060), and 5/3/2000 at 206DRY100 | ||||
| Environmental Conditions: | |||||
| QAPP Information: | Data collected following SWAMP QA protocols. | ||||
| QAPP Information Reference(s): | Surface Water Ambient Monitoring Program Quality Assurance Program Plan | ||||