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Offshore Environmental Risks - Surface Storage or Disposal Pits

If surface pits or ponds are used for wastewater storage or for interim disposal during operations, the pits should be constructed outside environmentally sensitive locations.

  1. Installation of a liner so that the bottom and sides of the pit have a coefficient of permeability no greater than 1 x 10-7 centimeters per second (cm/sec). Liners should be compatible with the material to be contained and of sufficient strength and thickness to maintain the integrity of the pit. Typical liners may include synthetic materials, cement/clay type or natural clays, although the hydraulic conductivity of natural liners should be tested to ensure integrity
  2. Construction to a depth of typically 5 m above the seasonal high water table
  3. Installation of measures (e.g., careful siting, berms) to prevent natural surface drainage from entering the pit or breaching during heavy storms
  4. Installation of a perimeter fence around the pit or installation of a screen to prevent access by people, livestock and wildlife (including birds)
  5. Regular removal and recovery of free hydrocarbons from the pit contents surface
  6. Removal of pit contents upon completion of operations and disposal in accordance with the waste management plan
  7. Reinstatement of the pit area following completion of operations


Workover and completion wastes

Workover and completion wastes result from operations where an oil well’s head is partially open to the atmosphere and is filled with a water based fluid that maintains pressure on the formation to prevent blowout. Workover fluid is injected into a well while the well’s interior tubing string, valves, packer gaskets, or other components are undergoing maintenance. When maintenance is complete, the workover fluid is removed from the well before starting routine operation. Completion fluids are typically used in a well when the well casing is perforated just before starting production. Both fluids become contaminated with oil and formation brine.


Proppants/frac sand

Proppants (also called “frac sand”) refers to the aluminum silicate beads of varying sizes injected into wells to hold formation fractures open, thus increasing subsurface oil flow to the wells. When these materials are transported back to facilities with crude oil from the wells, the beads settle out, along with formation sand, to form a semi-solid sludge in the bottoms of vessels.


Bottom wastes

Tank bottom wastes are a type of sediment that accumulates in oil field vessels and pipelines when fluid turbulence is low. These dense sludges are composed of crude oil, paraffin, asphaltics, reservoir material, drilling mud, and radioactive material (called NORM) in addition to the frac sand/proppant discussed above.


Dehydration and sweetening wastes

Polyols and glycols are used in the oil and gas industry as antifreeze additives and to remove traces of water from natural gas streams in the production of fuel gas. Waste dehydration polyols and glycols sometimes emit traces of benzene.

H2S, a corrosive gas more toxic than hydrogen cyanide, is emitted by sulfate-reducing bacteria growing in subsurface formations and oil field surface equipment.


Oily debris and filter media

Oily debris saturated with crude oil comes from oil spill cleanups (minor and major) and can include oily soil and gravel. Similarly, filter media which filter crude oil may become saturated with oil.


Hydrocarbon wastes

Oil and gas fields generate waste hydrocarbons such as “dirty diesel” fuel contaminated from pressure testing pipelines.



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