Region 1: EPA New England

Underground Injection Control Program

Selected Terms

Any geologic formation or group of formations, or part of a formation that is capable of economically yielding a significant amount of water to a well or spring.

Any material or substance which flows or moves, whether semisolid, liquid, sludge, gas or any other form or state.

Any body of consolidated or unconsolidated rock characterized by a degree of homogeneity in its physical properties which is commonly, but not necessarily, tabular that can be mapped on the earth's surface or traced in the subsurface.

Ground Water
When water seeps into the ground, it moves downward due to gravity through the pore spaces found between soil particles and cracks in rock. Eventually, the water reaches a depth where the soil and rock are saturated with water. Water which is found in the saturated part of the ground underneath the land surface is called, "ground water."

Injection Well
A bored, drilled, or driven shaft, or dug hole, whose depth is greater than the largest surface dimension.

Underground Source of Drinking Water
An Underground Source of Drinking Water (USDW) as defined in Title 40, Code of Federal Regulations (40 CFR), Section 144.3 is an aquifer or part of an aquifer which:

  • supplies any public water system, or contains a sufficient quantity of ground water to supply a public water system and currently supplies drinking water for human consumption or contains fewer than 10,000 milligrams/liter of Total Dissolved Solids (TDS)


  • is not an exempted aquifer.

An "exempted aquifer" is part or all of an aquifer which meets the definition of a USDW but which has been exempted according to the criteria found in 40 CFR Section 146.04, which specifies that it does not currently serve as a source of drinking water, and it cannot now and will not in the future serve as a source of drinking water for one of the following reasons:

  • It is mineral, hydrocarbon or geothermal energy producing, or can be demonstrated by a permit applicant as part of a permit application for a Class II or III operation to contain minerals or hydrocarbons that considering their quantity and location are expected to be commercially producible
  • It is situated at a depth or location which makes recovery of water for drinking water purposes economically or technologically impractical
  • It is so contaminated that it would be economically or technologically impractical to render that water fit for human consumption
  • It is located over a Class III well mining area subject to subsidence or catastrophic collapse; or The total dissolved solids content of the ground water is more than 3,000 and less than 10,000 milligrams/liter and it is not reasonably expected to supply a public water system

Well Injection
The subsurface emplacement of fluids, into the ground through a well.