Control de calidad de datos

From start to finish, the extraction of natural gas can affect nearby waterways. During construction for well pads, pipelines, and roads, there is an increase of sediment runoff, which increases the total suspended solids (TSS) in a stream (Olmstead, et al., 2013). The increase in TSS reduces sunlight, raises the water temperature, decreases the dissolved oxygen and clarity, and can cause damage to organisms (Olmstead, et al., 2013).

After construction, the high volumes of flowback water and produced water create a larger issue with stream pollution (Olmstead, et al., 2013; Chapman, et al., 2012). The

wastewater not only contains the chemicals that were added for the hydraulic fracturing process, but other chemicals such as naturally occurring heavy metals and radionuclides were picked up from within the shale (Olmstead, et al., 2013). Flowback water is typically high in total

dissolved solids, salts, toxic metals, and radioactivity (Penn State, 2016; Warner, et al., 2013), but concentrations are lower compared to produced water (Jiang, et al., 2014). Produced water, as time goes on, resembles more and more of the geochemistry of the formation, picking up high concentrations of total dissolved solids, chloride, bromide, and other constituents (Hammer, et al., 2012); Marcellus produced water has been reported as being among the highest in salinity in the U.S. (Weaver, et al., 2016).

Shale wastewater (brine water) is typically high in total dissolved solids (Chapman, et al., 2012; Olmstead, et al., 2013). Typically, freshwater has a concentration of total dissolved solids (TDS) between 100 and 500 mg/L. In comparison, shale gas wastewater can range from 800 to 300,000 mg/L of TDS, which can have major effects on the TDS in a stream (Olmstead, et al., 2013), while the TDS content of seawater is 25,000 mg/L (Vengosh, et al., 2014). There is concern over the capacity of streams in PA to assimilate the high TDS from wastewater

treatment plant effluent in conjunction with previously existing anthropogenic sources, such as AMD and road salt runoff (Olmstead, et al., 2013).

Along with the TDS levels, Marcellus wastewater has elevated chloride, bromide, sodium, calcium, strontium, magnesium, and barium levels, which are most likely from the interaction with the formation (Chapman, et al., 2012; Hayes, 2009; Volz, et al., 2011). The brines (anything with more than 35,000 mg/L TDS, used to describe hydraulic fracturing wastewater) are dominated by sodium, calcium, and chloride (Dressel and Rose, 2010). Brines are also low in sulfate and carbonate (Barbot, et al., 2013). Marcellus produced water has slightly less calcium, much less magnesium, and much more strontium than any other brines, such as conventional brines, found in Pennsylvania (Barbot, et al., 2013).

Chloride is a major component of brine water, with a maximum concentration of 207,000 mg/L in brines (Dressel and Rose, 2010). Chloride is picked up from the rock formations, with the Marcellus having some of the highest levels of chloride (Penn State, 2016). Chloride is also abundant in nature and has several additional sources, including road salt runoff (Katz, et al., 2011). Elevated or fluctuating chloride levels can directly damage aquatic ecosystems by mobilizing heavy metals, phosphates and other chemicals present in sediment (Olmstead, et al., 2013). It is expensive to treat high chloride levels because it is not easily removed through chemical or biological processes, causing an increase in chloride levels downstream (Olmstead, et al., 2013).

Chloride is often compared in ratio with bromide to indicate pollution from brine water and brine water treatment plants. Bromide is often a key indicator for wastewater from oil and gas extraction activities. Bromide occurs in very small concentrations in nature (VanBriesen,

2011; Wilson, 2013). Both conventional and unconventional extraction activities in

Pennsylvania can be sources of high bromide concentrations due to their origins from highly concentrated evaporated seawater (Hladik, et al., 2014; Dressel and Rose, 2010). Deep

formation brines become enriched in bromide as water molecules pass through the layers of clay, which leaves behind bromide ions (Hem, 1985). Chloride is generally 40-8000 times more abundant in nature than bromide, but bromide is slightly more soluble than chloride (Davis, et al., 1998: Katz, et al., 2011). Due to its small natural concentration, relatively small changes in

total mass of bromide will result in large variations in the Br/Cl ratio if chloride stays relatively the same (Davis, et al., 1998). Treatment plants for brine waters are ineffective at removing bromide, so relatively large quantities are discharged in brine treatment plant effluents (Cyprych, et al., 2013 2013). There have been maximum concentrations of around 2,240 mg/L of bromide

reported in natural gas wastewater (Dressel and Rose, 2010); there are no regulations for bromide in effluents or drinking water (Wilson and VanBriesen, 2012). Due to this, streams impacted by natural gas brine water and wastewater from brine treatment plants are expected to have a higher bromide to chloride ratio (Heston, 2015). The increased presence of bromide due to brine water disposed can be an issue for drinking water and human health. During the disinfection process, bromide is oxidized and can reacts with naturally occurring organic matter present in water (VanBriesen, 2011). The result is an increase in trihalomethanes (THM), a carcinogenic and potentially teratogenic disinfection byproduct (Cyprych, et al., 2013 2013;

Wilson, 2013; Chang, et al., 2001). In most freshwater sources, THMs are dominated by chloroform formation, when bromide is not present. As bromide increases, the formation of THMs starts to include brominated species (Handke, 2009). The brominated species of THMs also have more associated human health risk compared to other forms (Wilson and VanBriesen,

2012). This is a major concern with a widespread potential for human exposure due to the many domestic uses of water (Boorman, 1999).

Strontium is a heavy metal that is commonly found in brine waters associated with unconventional wells (Brantley, 2014; Jiang, et al., 2014). Calcium chloride brines are relatively rich in strontium and the concentrations are usually related to the concentration of calcium (Sass and Starinsky, 1979); the Marcellus shale has more strontium than any other brine in Pennsylvania (Barbot, et al., 2013). Strontium levels typically present in flowback and

produced water range between 1000 and 7000 mg/L (Brantley, 2014), with a recorded maximum concentration of 13,100 mg/L (Dressel, 201). There is no published drinking water standard for strontium (Brantley, 2014).

There are no empirical estimates available for the effects of shale gas development on surface water quality. Given the high concentrations of chemicals in wastewater compared to surface water, even small inputs can impact the freshwater quality (Vengosh, et al., 2014). It is critical to protect our water supply, but the task is difficult, as the wastewater requires expensive chemical treatment (Sharp and Pestano, 2013). Controlling pollution from oil and gas

wastewater requires more management to avoid negative effects (Wilson and VanBriesen, 2012).