| t½ | Half-life |
| TAB | Technical Assistance to Brownfields Communities |
| Table 10 HAP | Table 10 Hazardous Air Pollutant |
| TAG | Technical Assistance Grants |
| TARA | Technical Approach for Risk Assessment |
| Target HAP | Target Hazardous Air Pollutant |
| Target HAP Containing Coating | Target Hazardous Air Pollutant Containing Coating |
| Target HAP Containing Material | Target Hazardous Air Pollutant Containing Material |
| TASC | Technical Assistance Services for Communities |
| TBA | Tertiary Butyl Alcohol |
| TBEL | Technology Based Effluent Limitation |
| TBT | Tributyl Tin |
| TC | Technical coordinator; Toxic Concentration; Toxicity Characteristic |
| TCC | Tagliabue Closed Cup |
| TCDD | 2,3,7,8-Tetrachlorodibenzo-p-Dioxin |
| TCE | Trichloroethane; Trichloroethene; Trichloroethylene |
| TCF Bleaching | Totally Chlorine-Free Bleaching |
| TCLP | Toxicity Characteristic Leaching Procedure |
| TCM | Transportation Control Measure |
| TCMs | Transportation Control Measures |
| TCP/IP | Transmission Control Protocol/Internet Protocol |
| TCR | T Cell Receptor |
| TCU | Towering Cumulus |
| TD | Technical director; Toxic Dose |
| T-D Transfer Station | Transmission-Distribution Transfer Station |
| TD-GC/MS | Thermal Desorption-Gas Chromatography/Mass Spectrometry |
| TDH | Total Dynamic Head |
| TDL | Target Distance Limit |
| TDL for the Surface Water Migration Pathway | Target Distance Limit for the Surface Water Migration Pathway |
| TDR | Time domain reflectometry |
| TDS | Total Dissolved Solids |
| TEA | terminal electron acceptor; Tribal Environmental Agreement |
| TEA (Chemical) | Triethanolamine Zirconate |
| TEC | Threshold Effects Concentration |
| TEL | Threshold Effects Level |
| TEM | Transient Electromagnetics; Transmission Electron Microscopy |
| TENORM | Technologically Enhanced Naturally Occurring Radioactive Material |
| TEQ | Toxicity Equivalence |
| TERA | TSCA Experimental Release Application |
| Tetra-EG | Tetraethylene Glycol |
| TEU | Twenty-Foot Equivalent Unit |
| TEV | total economic value |
| TF1 | Total Fluorides |
| TGA | Technical-Grade Active Ingredient |
| THC | Thermohaline Circulation; Total Hydrocarbons |
| THC (Hydrocarbons) | Total Hydrocarbon Emission; Total Hydrocarbons Measurement |
| THCE | Total Hydrocarbon Equivalent |
| Thermal System Insulation ACM | Thermal System Insulation Asbestos-Containing Material |
| THM | Trihalomethanes |
| THMs | Total Trihalomethanes |
| TI | Technical Impracticability; Therapeutic Index |
| TIE | Toxicity Identification and Evaluation; Toxicity Identification Evaluation |
| Tier 4 | Emission Standard Tier 4 |
| TIFF | Tagged Image File Format |
| TIM | Technical Information Manager |
| TIO | Technology Innovation Office |
| TIP | Tribal Implementation Plan |
| TIP (Transportation) | Transportation Improvement Program |
| TLC | Thin Layer Chromatography |
| TLV | Threshold Limit Value; Total Lung Volume |
| TLVs | Threshold Limit Values |
| TMDL | Total Maximum Daily Loads |
| TMDL Process | Total Maximum Daily Load Process |
| TMR | Total Mixed Ration |
| TMRC | Theoretical Maximum Residue Contribution |
| TMY | Typical Meteorological Year |
| TNCWS | Transient Non-Community Water Systems |
| TO | Task Order |
| TOA | Trace Organic Analysis |
| TOC | Tagliabue Open Cup; Total Organic Carbon; Total Organic Compounds |
| TOD | Transit-Oriented Development |
| TOF Mass Spectrometry | Time-of-Flight Mass Spectrometry |
| TOSC | Technical Outreach for Communities |
| Total Metal HAP | Total Metal Hazardous Air Pollutant |
| Total Non-Vinyl Chloride Organic HAP | Total Non-Vinyl Chloride Organic Hazardous Air Pollutant |
| Total SO2 Equivalent | Total Sulfur Dioxide Equivalent |
| TOU | Time-of-Use Pricing |
| ToxFAQs | Frequently Asked Questions About Contaminants Found at Hazardous Waste Sites |
| TP | Total Phosphorus |
| TPC | Third-Party Certifier |
| TPH | total petroleum hydrocarbons |
| TPLIF | Two-Photon Laser-Induced Fluorescence |
| TPPU | Thermoplastic Product Process Unit |
| TPQ | Threshold Planning Quantity |
| TQ | Threshold Quantity |
| TQM | Total quality management |
| Transmission Company Interconnect M & R Station | Transmission Company Interconnect Metering and Regulating Station |
| TRE | Toxicity Reduction Evaluation |
| TRE Index Value | Total Resource Effectiveness Index Value |
| TRI | Toxic Release Inventory; Toxics Release Inventory |
| TRI chemicals | Toxics Release Inventory chemicals |
| TRI facilities | Toxics Release Inventory facilities |
| TRI Facility | Toxics Release Inventory Facility |
| TRI ID | Toxic Release Inventory Identification Number |
| Tri-EG | Triethylene Glycol |
| TRI-ME | Toxics Release Inventory - Made Easy |
| tRNA | Transfer RNA |
| TRO | Temporary Restraining Order |
| TRPH | total recoverable petroleum hydrocarbons |
| TRRL | Tire Rolling Resistance Level |
| TRS | Total Reduced Sulfur |
| TRS (Telecommunications) | Telecommunications Relay Service |
| TRU | Transuranic |
| TRW | Technical Review Workgroup for Lead |
| TSA | Technical Systems Audit |
| TSCA | Toxic Substances Control Act |
| TSD | Technical Support Document; Treatment, Storage, and Disposal Facility |
| TSDF | Treatment, Storage, Disposal Facilities |
| TSFE | Exposure duration |
| TSI | Thermal System Insulation; Timber Stand Improvement |
| TSP | Total Suspended Particles; Total Suspended Particulates |
| TSS | Total Suspended Solids |
| TSSMS | Time Sharing System Management System |
| TT | Technology Transfer; Text Telephone; Treatment Technique Requirement (regulatory) |
| TTE | Temporary Total Enclosure |
| TTFMS | Two-Tone Frequency-Modulated Spectroscopy |
| TTO | Total Toxic Organics |
| TTY | Teletypewriter; Text Telephones |
| TUs | Temporary Units |
| TVH | Total Volatile Hydrocarbon |
| TWA | Time-Weighted Average |
| TWF | Time weighting factor |
| TWS | Transient Non-Community Water System; Transient Water System |
| TWTDS | Treatment Works Treating Domestic Sewage |
| TZ | Treatment Zone |