1 Soil Sterilants Herbicides

During the initial industrial activities of land clearing, standing vegetation and under storage shrubs need to be removed completely to prohibit any chance of regrowth. To do this, chemical sterilants, commonly used in oil and gas industries, are applied to destroy all forms of living organisms including trees, pests, and pathogens in the soil. The toxicity of sterilants can cause harms to “undesired” organism, as well as the “desired” organism. The high toxicity of these chemicals not only achieves “total kill” of soil organisms, but may cause great harms to human beings as “non-targeted species” (Skelly & Donaldson, 2011).

2 Drilling Fluids and Drilling Fluid Additives

Drilling fluids are mixtures of water with clay, water with silicate, water with polymers, or clay with hydrocarbons, as drilling fluid additives are mixed with fluid to control the fluid characteristics (Dinwoodie, 2017).

Drilling fluid and additives are applied during the well drilling processes. As drill bits lower through the land, high density gel like drilling fluid is injected into the well hole to lubricate and cool the drilling bit, clean the bottom of the hole and carry the left over cuttings to the land surface, and stabilize the hole with control of subsurface pressure (Dinwoodie, 2017). Eventually, drilling fluids, additives, and drilling cuttings are carried to the surface. These all are stored in the open sump that has been dug for holding returned liquid and solid materials from the drilling holes.

3 Salts

Salt contamination is one of the primary issues in oil and gas well sites. During the hydraulic fraction processes, around 2,500,000–4,200,000 gallons (Gruber, 2013) of high-pressured water with selected chemical additives is injected into each well for enhancing water flow and oil and gas production. The water is injected into the well initially, a portion of the water called “ flowback” water returns back the well surface immediately (Earthworks, 2015). The rest of the water that either penetrate into the geological formation or return to the surface after a long time circulation is called “produced water” (Kassotis & Tillitt ect, 2016). Both the flowback and produced water contains variable geological materials such as radioactive materials, heavy metals, hydrocarbons, and primarily naturally occurring salts from shale materials. Due to the dissolution of the geological formation materials, constantly increased the concentration of Cl-, SO42-, CO32-, HCO32-, Na+, K+, Ca2+, Ba2+, Mg2+, Fe2+, and Sr2+ and released of insitu brines are found in both flowback and produced water (Haluszczak & Rose ect, 2013). The Flowback water, which contains the extremely high amount of salts (Pichtel, 2016) is 5 to 10 times concentrated than sea water (Haluszczak & Rose ect, 2013).

4 Petroleum Hydrocarbons

Petroleum hydrocarbons are one of the contaminants that exist in multiple stages of the oil and gas extraction and production processes. During the well drilling process, diesel, common mixtures of petroleum hydrocarbons, is applied as oil based drilling fluid. Some of the lubricating agents applied as drilling additives are also forms of hydrocarbons. Eventually, the drilling fluids and carried cuttings are placed into the onsite sump. As mentioned previously, the resultant water that is brought up to the well surface contains mixtures of environmental hazardous materials inducing significant amounts of hydrocarbons and dissolved gases. As hydrocarbon products are extracted and stored on site, there are potential risks of petroleum hydrocarbons leakages and spills from the knock-out tanks or flare pit.

The challenge comes to the local environment when compounds like BTEX (Benzene toluene, elthylbenene and xylene) and PAHs (polycyclic aromatic hydrocarbons) pollute the surrounding land and water. Small molecule hydrocarbons are most toxic but volatile and short lived (Ver, 2017). For example, a compound like benzene present in 1 L of refined oil can contaminate 1 million L of water (Seddique, 2015). Compared to light weight hydrocarbons, large molecule hydrocarbons are less toxic but much more persistent in the environment.

5 Heavy Metals

The hydraulic fracturing water that is brought to the surface carries not only dissolved salts, but also variable heavy metals from the geological formations. Generally, oilfield produced water contains heavy metals such as mercury and lead, and metalloids such as arsenic (Fakhru’l-Razi & Pendashteh ect, 2009). Other common metals that may be found onsite are Ba, Cd, Cr, Cu, Pb, Hg, Ni, Ag, Zn, Al, B, Fe, Li, Mn, Se, and Sr (Lebas & Shahan, 2013).

Another source of heavy metals getting into the soils are from well site equipment, like rusted well-head. Metals like Fe and Al form oxidized rusts once they are exposed to air and rainwater. With time, these metals are dissolved by the rainwater and contaminate the surface soil. The concentrations of oil field heavy metals vary depending on formation geology and the age of the well.

Heavy metals contaminated water can harm organism if water is the source of supply of drinking and irrigation water.