Related by context. Frequent words. (Click for all words.) 54 hydrocarbons 52 contaminating groundwater 52 harmful contaminants 52 elemental mercury 52 PCBs polychlorinated biphenyls 52 petroleum distillates 51 fracking fluids 51 frac sand 51 biogenic 51 chlorinated solvents 50 MtBE 50 chemicals 49 phosphine 49 disinfection byproducts 49 toxic chemicals 49 hydrocarbon 49 polychlorinated biphenyls PCBs 49 chemical solvents 49 contaminants 49 ethylbenzene 48 additive MTBE 48 sludges 48 fracking fluid 48 CO2 sequestration 48 petroleum hydrocarbons 48 hazardous substances 48 evaporation ponds 48 fracking chemicals 47 hydrogen sulphide 47 substances 47 hydrofluoric acid 47 carcinogenic chemicals 47 frac fluid 47 Hydrogen sulfide 47 xylene 47 flammable gases 47 residues 47 hexane 47 chlordane 47 toxicants 47 potentially carcinogenic 47 hazardous chemicals 47 solvents 47 polluted groundwater 46 carbon tetrachloride 46 naturally occurring radioactive 46 contaminate groundwater 46 furans 46 suspected carcinogen 46 flammable vapors 46 flame retardant chemicals 46 methane 45 THAI TM 45 radiological contamination 45 coal tar 45 sulfur oxide 45 polybrominated diphenyl ethers 45 Toxic chemicals 45 hydraulic fracturing 45 radioactive contaminants 45 pollutants 45 absorbents 45 harmful substances 45 acrolein 45 PAHs 45 Methyl 45 Controlled burns 45 sulfur 45 mercury arsenic 45 H2S 45 methylene chloride 45 hexavalent chromium 45 pollutant 45 perchlorethylene 45 contaminant 45 sorbents 45 arsenic 45 pollutants emitted 44 toxic pollutants 44 ecologically sensitive areas 44 dissolved solids 44 subsurface 44 polychlorinated biphenyls 44 tailing ponds 44 toxic substances 44 gaseous fuels 44 toluene 44 benzene 44 Residues 44 wellheads 44 trichlorethylene TCE 44 manganese 44 extraction 44 propane butane 44 diazinon 44 methyl tertiary butyl ether 44 Sulfate 44 fumigants 44 sulfur hexafluoride 44 furan 44 condensate