Remediation of salt affected soils

Water separated from oil and gas during production contains dissolved solids, including salts. Produced water with sufficient salt concentrations can damage plants and soils, if improperly handled. Remediation of salt-affected sites can be performed for a number of reasons. The driving forces behind the need to assess and restore a site affected by a saltwater release can include landowner claims, lease agreements, federal, state, and local regulations, reduction in long-term liabilities, company policies, and/or protection of useable land and water resources

Remediation goals

Severe sheet and rill erosion on highly erodible soils in northwest Iowa after heavy rains. The spring rains fell on soils that had no protection against soil erosion.(Photo: Lynn Betts 1999)

Setting reasonable objectives for the remediation effort is critical to developing a viable remediation plan. In some cases, the objectives may be established by legal, regulatory, or lease constraints. In other situations, the objectives may be based on more flexible criteria. It is advisable to, at a minimum, review the following factors prior to initiating any remediation effort:

• Lease requirements
• Regulatory constraints
• Corporate policies
• Environmental conditions

Landowner and lease requirements

Consulting the landowner and lease requirements is crucial before any remediation process starts. Landowners will often have opinions on various remediation options. Cooperation with landowners should be a high priority due to the fact that a dissatisfied landowner may be in a position to complicate a resolution.

Regulatory constraints

Federal, state, and local regulations may pertain to various aspects of remediation of produced water spills, including spill response, vegetation, vadose zone, groundwater or surface water impacts, and possibly air emissions. Regulations may influence the choice of remediation technology and the associated costs. A technology which may be suitable for certain conditions in one state may not be well received in an adjoining state.

Corporate policies

Corporate polices may include certain specific or general protocols and criteria for addressing a spill.

Environmental conditions

The successful remediation of a saltwater spill on land depends on several environmental factors including the soil, climate, and water.

Soil

Remediation efforts require a basic knowledge of soil’s physical components, texture, layers, slope and erosion characteristics, drainage, and chemistry. Soil has four physical components: inorganic solids, organic matter, water, and air. The texture is the different characteristics of the particle size ranging from sand, silt, and clay. The layer is a typical vertical section of soil to about a 6-ft depth; these layers are called horizons. Soils have different vulnerabilities to erosion related to slope grade and length, plant cover, rainfall, and the texture with the combined stability of the soil. Soil drainage is very important, particularly with regard to salt remediation. Chemical reactivity in a soil can be usually linked with particle size.

Climate

Generally climate determines the type of soil in a specific location. Climate dictates the frequency, duration, and quantity of precipitation and evaporation, as well as extremes and duration of temperature and wind.

Water

A basic understanding of water is an essential to understand how salts are transported within the soil. Understanding applied surface water, groundwater, and soil-pore water are the most important to successful salt mobility and remediation.

Land use

Class II wells inject fluids associated with oil and natural gas production. (EPA 2012)

Even without a spill, some soils would have substantial land use limitations due to natural factors.

Land capability classifications

Land capability classifications were developed by the USDA-NRCS to show the ways in which a soil could be acceptably used, and to alert landowners about uses which were impractical due to soil limitations. R1 Climate, erosion potential, slope, and drainage are important factors in land use classifications. Land capability classification is a system of grouping soils primarily on the basis of their capability to produce common cultivated crops and pasture plants without deteriorating over a long period. Land capability classification is subdivided into capability class and capability subclass nationally. R4

Capability class 

The broadest category in the system. Class codes I to VIII indicate progressively greater limitations and narrower choices for agriculture. The numbers are used to represent both irrigated and nonirrigated land capability.

Capability subclass 

The second category in the system. Class codes e (erosion problems), w (wetness problems), s (root zone limitations), and c (climatic limitations) are used for land capability subclasses. 

The eight land use capability classifications are:

Suitable for Cultivation

1. Required good soil management practices only.
2. Moderate conservation practices necessary.
3. Intensive conservation practices necessary.
4. Perennial vegetation - infrequent cultivation.
5. No restrictions in use.
6. Moderate restrictions in use.
7. Severe restrictions in use.
8. Best suited for wildlife and recreation.

Remediation types

Natural

Natural remediation is unenhanced and/or passive. This process is usually recommended with the salts effects are minor. The natural process requires little to no intervention. Natural remediation should be considered when reviewing any remediation effort.

Chemical

In Situ chemical remediation are used to remove salts from the root zone. Chemical remediation is somewhat more expensive than natural remediation and could possibly be the hardest of the three technics.

There are a variety of chemical amendments can be used to remobilize salts including:

Neutral soils

• Gypsum (CaSO₄:2H₂O) – Used for neutral soils
• Calcium Chloride (SaCl₂:2H²O)
• Limestone (CaCO₃)
• Dolomite (CaCO₃:MgCO₃)
• Calcium Oxide (CaO)
• Calcium Hydroxide [Ca(OH)₂]

Alkaline soils PH>8.5

• Sulfur
• Sulfuric acid (H₂SO₄)
• Aluminum sulfate [Al₂(SO₄)₃:18H₂O]
• Iron Sulfate (FeSO₄:7H₂O)

Other

• Polymers
• Propriertary chemicals
• Diammonium phosphate [(NH₄)₂(HPO₄)]

Mechanical

Mechanical remediation involves mechanically moving the soil such as tilling or excavating. There are two basic types of mechanical treatment.

Dilution by land spreading effected soils into unaffected areas to reduce concentrations to an acceptable level or enhance other treatment options. Care must be taken so that land spreading does not create a larger area of contamination.

Disposal is usually the most expensive of treatments and is usually only considered as a last resort. 

Salt concentration

Salt concentrations of produced water from E&P operations vary from low salt concentrations to brackish water. Total dissolved solids (TDS) can range from less than 4,000 parts per million (ppm), to brines with salt concentrations greater than 100,000 ppm.

Saltwater release

Total salt and total sodium concentration in a saltwater release can cause the soil to become saline and sodic. Produced water with high concentrations of total salts (salinity) and sodium (sodicity) can have a detrimental effect on terrestrial and freshwater environments. Excessive salts can create adverse chemical and physical conditions in soils and damage or kill vegetation.

Surface spills of produced water can occur as a result of:

• Equipment failure
• Pipeline corrosion
• Weather
• Human error

Disposal

An aerial view of the evaporation ponds to the south of the Dead Sea operated by the Dead Sea Works (NASA 1989)

Disposal of most inland produced waters is by injection into enhanced oil recovery or produced water disposal wells. Some inland facilities may use evaporation pits to dispose of produced water.

Injection well

An Injection well is a device that places fluid deep underground into porous rock formations, such as sandstone or limestone, or into or below the shallow soil layer. These fluids may be water, wastewater, brine (salt water), or water mixed with chemicals.

The EPA breaks injection wells into six classes; Class II wells are associated with oil and natural gas production. Most of the injected fluid is salt water (brine), which is brought to the surface in the process of producing (extracting) oil and gas.

Evaporation pit

There are several types of pits traditionally associated with oil and gas production. Following are three types of salt-related pits:

• Production pit - Used for saltwater storage, oil and water separation, and solids settling.
• Reserve pits - Used for solids separation during drilling and workover operations and for holding waste drilling muds and cuttings.
• Produced water storage (emergency) pits - Also known as Produced water storage are constructed to contain produced waters temporarily in the event of equipment malfunction.

Remediation monitoring

Completed remediation projects require an observation period of at least two years and in some case longer. In some instances follow-up tests and treatments are necessary if initial remediation is not returning expected results.

Noteworthy papers in OnePetro

Carty, D. J., Priebe, W. F., Swetish, S. M., & Crawley, W. W. 1997. An Organized Approach Toward Remediation of Salt-Affected Soils at E & P Sites. Society of Petroleum Engineers. http://dx.doi.org/10.2118/37421-MS

Deuel, L. E., & Holliday, G. H. 2003. Remediation of Salt-Impacted Soil and Waste. Society of Petroleum Engineers. http://dx.doi.org/10.2118/80947-MS

External links

Managing Soil Salinity

A guide for remediation of salt/hydrocarbon impacted soil.

Unites States Department of Agriculture

See also

Environment

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