| Water Body Name: | Mormon Slough (San Joaquin County; outside Delta Boundary) |
| Water Body ID: | CAR5313000020021209142456 |
| Water Body Type: | River & Stream |
DECISION ID |
165312 |
Region 5 |
Mormon Slough (San Joaquin County; outside Delta Boundary) |
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| Pollutant: | Indicator Bacteria |
| Final Listing Decision: | Do Not Delist from 303(d) list (TMDL required list) |
| Last Listing Cycle's Final Listing Decision: | Do Not Delist from 303(d) list (TMDL required list)(2018) |
| Revision Status | Revised |
| Sources: | A Source Unknown |
| TMDL Priority: | Low |
| Impairment from Pollutant or Pollution: | Pollutant |
| Regional Board Conclusion: | This pollutant is being considered for removal from the CWA section 303(d) List under section 4.2 of the Listing Policy. Under this section 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. Historical bacteria LOEs (pre-2010 data) have been removed and data has been compared to the newer E. coli bacteria water quality objective. Three of the 6 samples exceed the objective for REC-1. This waterbody was originally listed based on pre-2010 data and the USEPA recommended objective of 235 MPN/100 mL for single sample maximum allowable density of E. coli in freshwater designated beach areas. The newer E. coli data is insufficient to determine if the REC-1 beneficial use are fully supported; therefore, the final listing decision will remain Do Not Delist from 303(d) list (TMDL required list). Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification against removing this water segment-pollutant combination from the CWA section 303(d) List. 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. Three of the 6 samples exceed the objective for REC-1. This waterbody was originally listed based on pre-2010 data and the USEPA recommended objective of 235 MPN/100 mL for single sample maximum allowable density of E. coli in freshwater designated beach areas. The newer E. coli data is insufficient to determine if the REC-1 beneficial use are fully supported; therefore, the final listing decision will remain Do Not Delist from 303(d) list (TMDL required list). 4. Pursuant to section 4.11 of the Listing Policy, no additional data and information are available indicating that standards are met. |
| Regional Board Decision Recommendation: | After review of the available data and information, RWQCB staff concludes that the water body-pollutant combination should not be removed from the section 303(d) list because applicable water quality standards for the pollutant are being exceeded. |
| State Board Review of Regional Board Conclusion and Recommendation: | |
| State Board Decision Recommendation: | |
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| LOE ID: | 4484 | ||||
| Pollutant: | Pathogens | ||||
| LOE Subgroup: | Pollutant-Water | ||||
| Matrix: | Water | ||||
| Fraction: | Not Recorded | ||||
| Beneficial Use: | Water Contact Recreation | ||||
| Number of Samples: | 0 | ||||
| Number of Exceedances: | 0 | ||||
| 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 pre-2006 303(d) | ||||
| SWAMP Data: | Non-SWAMP | ||||
| Water Quality Objective/Criterion: | Unspecified | ||||
| Objective/Criterion Reference: | Placeholder reference pre-2006 303(d) | ||||
| Evaluation Guideline: | Unspecified | ||||
| Guideline Reference: | Placeholder reference pre-2006 303(d) | ||||
| Spatial Representation: | Unspecified | ||||
| Temporal Representation: | Unspecified | ||||
| Environmental Conditions: | Unspecified | ||||
| QAPP Information: | Unspecified | ||||
| QAPP Information Reference(s): | |||||
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| LOE ID: | 329430 | ||||
| Pollutant: | Escherichia coli (E. coli) | ||||
| LOE Subgroup: | Pollutant-Water | ||||
| Matrix: | Water | ||||
| Fraction: | STV | ||||
| Beneficial Use: | Water Contact Recreation | ||||
| Number of Samples: | 6 | ||||
| Number of Exceedances: | 3 | ||||
| Data and Information Type: | PATHOGEN MONITORING | ||||
| Data Used to Assess Water Quality: | Water Board staff assessed City of Stockton & San Joaquin Co. Rec Water Mont. data for Mormon Slough (San Joaquin County; outside Delta Boundary) to determine beneficial use support and the results are as follows: 3 of the 6 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, Toxicity, WQ from the City of Stockton and San Joaquin County Stormwater Program receiving water monitoring for the 2026 Integrated Report in Region 5 | ||||
| SWAMP Data: | Non-SWAMP | ||||
| Water Quality Objective/Criterion: | The bacteria water quality objective to protect the REC-1 beneficial use where the salinity is less than 1 parts per thousand 95 percent or more of the time applies a statistical threshold value to E. coli of 320 cfu/100 mL, not to be exceeded by more than 10 percent of samples within a calendar month (ISWEBE 2018). | ||||
| Objective/Criterion Reference: | Inland Surface Waters, Enclosed Bays, and Estuaries Plan. Part 1: Trash Provisions; Part 2: Tribal Subsistence Beneficial Uses and Mercury Provisions; Part 3: Bacteria Provisions and Variance Policy | ||||
| Evaluation Guideline: | |||||
| Guideline Reference: | |||||
| Spatial Representation: | The samples were collected at 1 monitoring site(s), station(s): MR-2R (Mormon Slough receiving water MR-2R (Commerce Street)). | ||||
| Temporal Representation: | The samples were collected between the days of 2019-08-27 and 2020-06-02 . | ||||
| Environmental Conditions: | |||||
| QAPP Information: | Stockton NPDES QAPP - City of Stockton & San Joaquin Co. Rec Water Mont. | ||||
| QAPP Information Reference(s): | SWRCB - Region5 - Stockton NPDES QAPP - City of Stockton & San Joaquin Co. Rec Water Mont. - 402686 | ||||