Related by context. Frequent words. (Click for all words.) 69 arsenic 67 groundwater 61 contaminants 59 contaminant 59 groundwater contamination 59 nitrates 58 Groundwater 58 Arsenic 56 nitrate 56 aquifers 56 hexavalent chromium 56 pollutants 56 coliform bacteria 55 fecal coliform 55 contaminated groundwater 55 perchlorate 55 contamination 55 aquifer 54 sediment 53 ppb 53 radium 53 turbidity 52 chromium 52 polluted 52 toxic chemicals 52 selenium 52 mercury contamination 52 radon 52 silt 51 E. coli bacteria 51 PCBs 51 contaminated 51 manganese 51 reservoirs 51 chloride 51 soils 50 tritium 50 mercury 50 hydrogen sulfide 50 septic systems 50 salinity 49 wastewater 49 Drinking Water 49 watersheds 49 effluent 49 pollution 48 toxins 48 phosphorus 48 contaminated soil 48 pollutant 48 benzene 48 sedimentation 48 chlorination 48 phosphorous 48 pesticides 48 pesticide residues 48 contaminates 48 sediments 48 bacterial contamination 47 Contamination 47 septic tanks 47 tributaries 47 water 47 fluoride 47 Aquifer 47 sewage 47 sulfate 47 dioxins 46 Superfund site 46 lakes 46 polychlorinated biphenyls 46 harmful chemicals 46 bacteria 46 chlorine 46 Safe Drinking Water 46 potable 46 drainages 46 Superfund sites 46 potable water 46 waterways 46 E. coli 45 stormwater runoff 45 suspended solids 45 rivers 45 atrazine 45 mercury pollution 45 sewage treatment 45 E. Coli 45 cadmium 45 pesticide 45 untreated sewage 45 hazardous chemicals 45 Contaminated 45 leachate 45 dioxin 45 air pollution 45 seepage 45 PFCs 45 brackish water 45 headwaters 44 hydrogen sulphide