In hydrologic terms, a geologic formation which has no interconnected openings and cannot hold or transmit water.
                                                            
                                                     
                        
                                                
                        
                        
                            A geologic formation that has no interconnected openings and hence cannot receive or transmit water.
                                                            
                                                     
                        
                                                
                        
                        
                            an impermeable formation neither containing nor transmitting water