The development of a statewide rule for water protection was complicated by the many variables that influence the pollution potential throughout the State. The foremost factor undoubtedly is the climate, which not only influences the degree of surface water and ground water pollution, but affects the practices used for oil and gas waste control. In those areas where rainfall is frequent or heavy, greater control of pit design and siting is needed to prevent surface water pollution. In drier climates, where ground water is more commonly the primary water supply, control of percolation from the bottom of pits may be more critical. Climatic extremes are an important consideration in developing practical statewide requirements for surface discharges, pit dewatering, backfilling and landfarming.
Waste Minimization and Pollution Prevention
Regulations regarding oil and gas waste management are becoming increasingly more stringent. Costs for disposal of oil and gas wastes are also increasing, not only in terms of disposal fees, but also in terms of potential liability. The old saying that an ounce of prevention is worth a pound of cure holds true for the oil field. Waste prevention is cheaper in the long-run than disposal.
A smart company will perform detailed internal audits to identify the products it uses, waste-generating processes, wastes generated, classification of the wastes, and waste management practices. This information, along with information concerning environmental conditions of defined areas, will allow the company to develop specific waste management plans to reduce waste generation and manage waste streams from specific operations in an environmentally sound manner.
Waste management choices should be based upon the following hierarchy of preference:
- Source Reduction
The quantity and/or relative toxicity of the waste generated should be reduced. Opportunities for waste volume reduction in exploration and production may be limited for some wastes like produced waters because volumes for some wastes like produced waters are primarily a function of activity level and age or state of depletion of a producing property. Nevertheless, every effort should be made to take advantage of those opportunities that do exist for source reduction.
Products that will result in less toxic waste should be substituted for products that are currently being used. For example, the substitution of less toxic drilling fluid additives will result in less toxic drilling wastes. Biocides, corrosion inhibitors, coagulants, cleaners, dispersants, emulsion breakers, scale inhibitors, viscosifiers, gas sweetening and dehydration agents, weighting agents, and any other products used in exploration and production operations should be selected with potential environmental impacts and disposal needs in mind. Segregation of certain waste streams may increase waste management options. Waste streams that have a higher pollution potential should be segregated from those with a lower pollution potential.
Good housekeeping, such as installing lined sumps to catch leaks or drips from equipment, and equipment maintenance are also two very simple ways to reduce the volumes of waste that are generated at oil and gas facilities.
There are also many opportunities for recycling oil and gas wastes. Drilling wastes generated at one well site should be re-used for plugging or spudding-in of other wells; oil based drilling fluids should be recovered and sent back to the vendor for reprocessing; tank bottoms should be reclaimed; waste lubricating oils and hydraulic fluids should be segregated, collected, and sent to a recycler; non-contaminated metal should be sent to a metal recycler; empty drums should be sent to a drum recycler; and waste antifreeze should be re-distilled.
Techniques should be employed to reduce the volume or the relative toxicity of waste that has been unavoidably generated. A smart company will investigate treatment options to decrease the potential long-term environmental and human health impacts of wastes that are generated. Dewatering, washing, neutralization, and solidification are a few of the treatment options. Landfarming (sometimes called landtreatment or land spreading) is both a treatment and a disposal method.
The choice of a disposal option for a particular waste that has been unavoidably generated should be made after careful consideration of the type of waste, applicable state and federal regulations, the volume of the waste, the disposal environment, short- and long-term impacts to the environment and human health, lease restrictions, and long-term liabilities. If a commercial disposal facility is used, the waste generator should audit the oil and gas waste hauler and the disposal facility for the proper permits, a good compliance history, and environmentally sound waste management practices.
The Commission's Waste Minimization Program provides oil and gas operators with training and technical assistance on source reduction and recycling.
Various disposal options are discussed below.
Waste and Handling Disposal
Oil and gas waste disposal practices vary geographically throughout the State. What might be a common practice in East Texas may not be done at all in West Texas. One of the best examples of this is the disposal of reserve pit fluids. In West Texas, where net evaporation rates are high, pit fluids are usually allowed to evaporate before closing the pit. In East Texas, where annual rainfall commonly exceeds evaporation, reserve pits often do not dry out. Therefore, pits are generally dewatered, and the water disposed of in an authorized well.
A myriad of operational situations exists from field to field that presents varying degrees of hazard to fresh water resources. These may involve the use of the types of pits listed in the definition section of Rule 8, or may result from the use of other special use pits that are not specifically described by definition or in the context of the rule.
While the use of any pit offers some degree of hazard to water resources, the availability of a pit can mitigate the harm to fresh water. There are situations when, if no pit were available to collect salt water overflows, considerable water pollution or land damage would result. For example, use of an emergency salt water storage pit to collect water during failure of disposal well equipment will certainly be a better alternative than allowing the water to overflow onto crop land and into the Colorado River. Also, in circumstances where pumpers do not make daily rounds or where severe weather conditions make lease roads impassable, emergency pits can prevent extensive pollution.
The need for workover pits varies widely from field to field. Generally, old wells in old fields require more frequent workovers. Wells in sour crude fields or that produce paraffinic crude are worked over more frequently. Each time a pit is used, even though the use is justified, a pollution factor exists. The volume of waste in the pit during any one operation might be less than 100 barrels, but each time the pit is used, a few barrels may seep from the bottom and sides. Over a period of time significant pollution may occur. As described below, a few barrels of concentrated salt water can cause considerable damage. When workover pits remain open, accumulation of rainfall and rainfall runoff can provide a fluid head to accelerate the downward movement of waste fluids that have permeated strata beneath the pit. These are reasons for requiring the dewatering and backfilling of workover pits.
Type and Volume of Wastes
Two factors that have a considerable impact on the pollution potential are the type of waste and the volume of waste. These factors were given considerable consideration in the drafting of Statewide Rule 8. Often these factors must be considered in combination. Additionally, the volume of waste must be viewed as the total quantity for the entire period that the pit will be in use, or the disposal or storage operation will be performed and not viewed as the quantity in the pit at any one time. This rationale supports restricting the use of emergency salt water storage pits and requiring that they be dewatered within a specified period. In comparison, the volume of fluid with, for example, 6000 milligrams per liter chloride, in a two acre reserve pit would be large compared to a 10 x 20 x 4 foot emergency storage pit for produced water. The reserve pit, however, contains fluid with a lower potential for pollution and may remain full for one year.
To illustrate what effects a small volume of waste may have, suppose that ten barrels of salt water with 100,000 mg/l chloride seep from the 10 x 20 x 4-foot pit, reach an aquifer that contains water with a native quality of 100 mg/l chloride, and mix uniformly to the extent that the chloride content in the aquifer increases to 500 mg/l. How much ground water would have been polluted to the extent that it tastes too salty to many people? 104,454 gallons would have been polluted, which is more water than the average family of four uses in one year. Yet, the ten barrels that seeped from a 10 x 20 x 4-foot pit would represent only seven percent of the pit capacity. When a salt water of lesser chloride concentration, for example 1,000 mg/l chloride, is placed in the pit described above, the pollution would be one hundred times less, not considering the density difference effect on seepage rates. Nevertheless, if fluid is retained in the pit for two years instead of a week, the effect on ground water quality is practically the same.
The type and volume of waste were evaluated when considering authorized disposal of drilling fluid. Studies have shown that low chloride drilling fluid has very little detrimental impact on the soil, and, in fact, may be beneficial to some soil types. When drilling fluid has a high chloride content (i.e. greater than 3,000 milligrams per liter chloride), however, the leaching of salt from the mud may not only effect the re-establishment of vegetation, but may also impact ground water.
Low chloride drilling fluids in large volumes may impact the environment. Such might be the case when drilling muds are disposed of at a central location among several leases or when drilling mud disposal is a commercial venture. Large volumes of drilling muds may present a pollution threat to surface waters because of overflow from pits or improper landfarming.
Rule 8 limits the types of wastes to be disposed of into each category of pit authorized by rule. The purpose is to prohibit the indiscriminate storage or disposal of wastes and to prevent the mixing of wastes that have a high pollution potential with rather innocuous waste. For example, if a small volume of high chloride completion fluids is placed in a pit with low chloride drilling fluid, the resulting mixture might be so high in chloride that land farming the waste would not be permissible.