Their simple construction provides little or no protection against possible ground water contamination. Injection wells may not only upset the natural recharge volume to aquifers, but may also introduce both thermally and chemically distinct fluids into ground water resources. It is estimated that more than 1 million of these wells exist nationwide. Although similar in their basic function, there are many different types of injection wells. Common examples of Class V wells are industrial wastewater disposal into septic systems, and septic systems connected to automotive service station bays.
Injection wells vary in their potential to contaminate ground water.
The risk depends on various factors including the types of waste fluids injected, well construction, local geology, and well location in proximity to local water supply. Class V shallow injection wells have the greatest potential to adversely impact drinkable ground water. Shallow injection wells are mainly used for drainage, discharge, or disposal of unwanted fluids. The broad definition of an injection well, which is basically any hole in the ground whose depth is greater than its largest surface dimension, brings a number of underground systems under this classification. Except for disposal systems serving single families or systems serving less than 20 persons, sumps, septic systems, cesspools, and drain fields are classified as injection wells.