The presence of a potentially hazardous material on or in the ground does not necessarily imply groundwater contamination. Release of the material into the groundwater is required.Acid-base typical reactions involve the transfer of hydrogen ions (H) among solutes dissolved in water, and they affect the effective concentrations of dissolved chemicals by using changes in the H concentration in water. A brief notation for H concentration (activity) is pH, which represents a harmful logarithmic scale of the H concentration. Smaller values of pH represent larger concentrations of H, and larger values of pH represent smaller concentrations of H. Many metals stay dissolved when pH values are small; increased pH causes these metals to precipitate from solution.