Oilfield Production Skim Pits
Earthen pits are used to further separate oil from produced water using gravity-separation. Oil or visible sheens on the surface of pit fluids pose a risk to migratory birds and other wildlife. Birds, including hawks, owls, and songbirds, are attracted to oilfield production skim pits by mistaking them for natural bodies of water. Oil pits also can attract bats, insects, small mammals, and big game. Songbirds and mammals may approach oil-covered pits and ponds to drink, and can fall into the pits, or they can become entrapped if the banks of the pits are oiled. Insects entrapped in the oil can also attract songbirds, bats, and small mammals. Hawks and owls in turn become victims when they are attracted by struggling birds or small mammals. Service personnel have found waterfowl, songbirds, bats, pronghorn, and deer in oil pits and tanks. The sticky nature of oil entraps birds in the pits and they die from exposure and exhaustion. Birds that do manage to escape can die from starvation or the toxic effects of oil ingested during preening. Birds ingesting sublethal doses of oil can experience impaired reproduction.
Visible sheens on the production skim pit fluids are just as deadly to birds. It is critical to avoid the presence of any visible sheens on the surface of evaporation ponds, particularly during the breeding season as female aquatic birds returning to their nests with oil on their feathers can inadvertently apply the oil to the eggs. Microliter amounts of oil applied externally to eggs are extremely toxic to bird embryos.
Oil in the berms of production skim pits can seep onto the pond surface, especially during the summer when warm temperatures can mobilize the oil. Oily bottom sludges and oil-soaked soils along the banks of the ponds contribute sheens and oil onto the pit fluids, especially during hot summer days. Rainfall events or snowmelt will wash oil from the banks back into the pit.