| S | Analytical Sensitivity; Standard Deviation |
| s g | Sigma g |
| S1S Hardboard | Smooth-One-Side Hardboard |
| S2S Hardboard | Smooth-Two-Sides Hardboard |
| SA | Supply Air; System Administrator |
| SAAP | Special Appropriations Act Project |
| SAB | Science Advisory Board |
| SACM | Superfund Accelerated Cleanup Model |
| SAED | Selected area electron diffraction |
| Safety Data Sheet | Federal reporting requirement |
| SAN | Styrene Acrylonitrile Resin |
| SAP | FIFRA Science Advisory Panel; Sampling and Analysis Plan; Serum Alkaline Phosphatase |
| SAPU | Secondary Aluminum Processing Unit |
| SAR | Supplied-Air Respirator |
| SARA | Superfund Amendment and Reauthorization Act; Superfund Amendments & Reauthorization Act |
| SASW | Spectral analysis of surface waves |
| SAV | Submerged Aquatic Vegetation |
| SAV Habitat | Submerged Aquatic Vegetation Habitat |
| SBC | System Benefits Charges |
| SBE | Small Business Enterprise |
| SBRA | Small Business Rural Area |
| SBS | Sick Building Syndrome |
| SCADA System | Supervisory Control and Data Acquisition System |
| SCAL | Secondary Calibration Standard (turbidity) |
| SCANNING | IMAGE SCANNING |
| SCBA | Self-Contained Breathing Apparatus |
| SCC | Somatic Cell Count; Source Classification Code |
| SCD | Soil Conservation District |
| SCDM | Superfund Chemical Data Matrix |
| SCLP | Straight Chain Lepidopteran Pheromone |
| SCM | Stated Choice Method |
| SCR | Selective Catalytic Reduction |
| SCS | Soil Conservation Service; Supplementary Control System |
| SD | Arithmetic Standard Deviation |
| SDF | Structure Data Format |
| SDMP | Scientific Data Management Plan |
| SDO | Standards developing organization |
| SDT | Smelt Dissolving Tank |
| SDWA | Safe Drinking Water Act |
| SDWIS | Safe Drinking Water Identification System |
| SE | Secretary of Energy |
| SEA | State/EPA Agreement |
| Sealed EAF | Sealed Electric Arc Furnace |
| SEB | Skeleton Eroding Band Disease |
| SEE Program | Senior Environmental Employee Program |
| SEER | Seasonal energy efficiency ratio |
| SELDI ToF Mass Spectrometry | Surface-Enhanced Laser Desorption Ionization Time of Flight Mass Spectrometry |
| SEM | Scanning Electron Microscopy |
| Senior NEPA Agency official | Senior National Environmental Policy Act Agency Official |
| SEP | Supplemental Environmental Projects |
| Separated MSW | Separated Municipal Solid Waste |
| Separated RIN | Separated Renewable Identification Number |
| SERC | State Emergency Response Commission |
| SERS | Surface Enhanced Raman Spectroscopy |
| SES | Socio-economic status; Socioeconomic Status |
| SF | STANDARD FORM; Superfund |
| SF6 | Sulfur Hexafluoride |
| SF₆ | Sulfur Dexafluoride |
| SFC | Supercritical Fluid Chromatography |
| SFTP | Supplemental Federal Test Procedure |
| SG | specific gravity |
| SGOT | Serum Glutamic-Oxaloacetic Transaminase |
| SGPT | Serum Glutamic-Pyruvic Transaminase |
| Short Term RfC | Short Term Reference Concentration |
| Short Term RfD | Short Term Reference Dose |
| SI | Site Inspection; Site table; Stressor Identification |
| SIC | Standard Industrial Classification (code) |
| SIC Code | Standard Industrial Classification (code) |
| SIC codes | Standard Industrial Classification codes |
| SIC Solution | Spectral Interference Check Solution |
| SIDS | Sudden Infant Death Syndrome |
| SIMEX | Simulation Extrapolation |
| SIO | Senior Information Officer |
| SIP | State Implementation Plans |
| SIPs | Structurally insulated panels |
| SIR | Self-Insured Retention |
| SITE Program | Superfund Innovative Technology Evaluation Program |
| SIU | Significant Industrial User |
| SLAMS | State; Local Air Monitoring Station |
| SLC | Subscriber Line Charge |
| SLN | Special Local Need |
| SLS | Sodium Lauryl Sulfate |
| SM | Site Manager; Standard Methods for the Examination of Water and Wastewater |
| SMA | Streamside Management Area |
| Small CAFO | Small Concentrated Animal Feeding Operation |
| Small HMIWI | Small Hospital/Medical/Infectious Waste Incinerator |
| Small Rural HMIWI | Small Rural Hospital/Medical/Infectious Waste Incinerator |
| Small SI Engine | Small Spark-Ignition Engine |
| SMATV | Satellite Master Antenna Television |
| SMCL | Secondary Maximum Contaminant Level (regulatory) |
| SMCLs | Secondary Maximum Contaminant Levels |
| SMDP | Scientific Management Decision Point |
| SME | Subject Matter Experts |
| SMOA | Superfund Memorandum of Agreement |
| SMOKE | Sparse Matrix Operator Kernel Emissions modeling system |
| SMR | Standardized Mortality Ratio |
| SMSA | Standard Metropolitan Statistical Area |
| S/N | Signal-to-Noise Ratio |
| SNARL | Suggested No Adverse Response Level |
| SNG | Synthetic natural gas |
| SNP | Single Nucleotide Polymorphism |
| SNUN | Significant New Use Notice |
| SO₂ | Sulfur Dioxide |
| SOA | Secondary Organic Aerosol; Service-Oriented Architecture |
| SOAP | Simple Object Access Protocol |
| SOC | Synthetic Organic Chemical |
| SOCs | Synthetic Organic Chemicals |
| SOD | Sediment Oxygen Demand |
| Soluble HAP | Soluble Hazardous Air Pollutant |
| SOM | Soil Organic Matter |
| SOP | Standard Operating Procedure |
| SOPs | Standard Operating Procedures |
| SoR | System of Registries |
| SOUR | Specific Oxygen Uptake Rate |
| SOW | Statement of Work |
| SOX | Sulfur Oxides |
| SP | Self potential |
| SPA | State Program Advisory |
| SPCC | Spill Prevention Control and Countermeasure Plan; Spill Prevention Control and Countermeasures |
| SPCC Plan | Spill Prevention Control and Countermeasure Plan |
| SPCC/FRP | Spill Prevention Control and Countermeasure and Facility Response Plan |
| SPCP | Spill Prevention, Containment, and Countermeasures Plan |
| SPE | Solid-Phase Extraction |
| SPECS | Specifications |
| SPF | Polyurethane Spray Foam |
| SPM | Species Pattern Marker |
| SPM Station | Special Purpose Monitor Station |
| SPMD | Semi-Permeable Membrane Device |
| SPP | Small Power Producer |
| SPP Toxicity | Suspended Particulate Phase Toxicity |
| SPPD | Sector Policies and Programs Division |
| Spreader Stoker Coal/RDF Mixed Fuel-Fired Combustor | Spreader Stoker Coal/Refuse-Derived Fuel Mixed Fuel-Fired Combustor |
| SQG | Small Quantity Generator |
| SQL | Sample Quantitation Limit |
| SRF | State Revolving Fund |
| SRI | Solar Reflectance Index |
| SRI/FS | Supplemental Remedial Investigation / Feasibility Study |
| SRM | Standard Reference Material; Standard Reference Method |
| SRM-Equivalent PRM | Standard Reference Material-Equivalent Compressed Gas Primary Reference Material |
| SRO | Spill Response Organization |
| SRP | soluble reactive phosphorus |
| SS | Settleable Solids; Stationary Source; Suspended Solids |
| SSA | Sole Source Aquifer |
| SSAB | Site-Specific Advisory Board |
| SSC | School Siting Committee; Scientific Support Coordinators; Shared Schema Components; Superfund State Contract |
| SSCV Standard | Second Source Calibration Verification Standard |
| SSL | Secure Sockets Layer |
| SSMP | Startup, Shutdown, and Malfunction Plan |
| SSO | Sanitary Sewer Overflows |
| SSRC | Shared Services Resource Catalog |
| SSS | Stock Standard Suspension |
| SSTS | Section Seven Tracking System |
| S&T | Screening and Testing |
| Stand-Alone PFPR Facility | Stand-Alone Pesticide Formulating, Packaging, and Repackaging Facility |
| Statewide GHG Cap | Statewide Greenhouse Gas Cap |
| Statewide GHG Target | Statewide Greenhouse Gas Target |
| StATS | State Authorization Tracking System |
| STED | Stimulated Emission Depletion Microscopy |
| STEG Collection System | Septic Tank Effluent Gravity Collection System |
| STEL | Short-Term Exposure Limit |
| STEP Collection System | Septic Tank Effluent Pump Collection System |
| STM | Scanning Tunneling Microscopy |
| STN Station | Speciation Trends Network Station |
| STORET | Storage and Retrieval of Water-Related Data |
| STROLE | Superfund Enhanced State and Tribal Role Initiative |
| STS | Secondhand Tobacco Smoke |
| Subchronic RfC | Subchronic Reference Concentration |
| Subchronic RfD | Subchronic Reference Dose |
| SUPERJTI | Superfund Job Training Initiative |
| SUR | Surrogate Analyte |
| Surfacing ACM | Surfacing Asbestos Containing Material |
| SUV | Sport Utility Vehicle |
| SUVA | Specific Ultraviolet Absorption |
| Sv | Sievert |
| SVE | Soil Vapor Extraction |
| SVOC | Semi-Volatile Organic Compound; Semivolatile Organic Compound |
| S/W | Software |
| SW | Solid Waste |
| SWCD | Soil and Water Conservation District |
| SWDA | Solid Waste Disposal Act |
| SWM | Solid Waste Management |
| SWMU | Solid Waste Management Unit |
| SWPA | Source Water Protection Area |
| SWPB Process | Side-Worked Prebake Process |
| Synthetic Minor HAP Source | Synthetic Minor Hazardous Air Pollutant Source |