Control de calidad de los datos

In the United States the use of roadway deicing agents is a common practice. Applying road salt helps to make winter roads safer for vehicles to travel. Eventually, the salt dissolves and washes off the roads and into the streams or soil and is forgotten (Jackson and

Jobbagy,2005). As the population grows, there is an increase in impervious surfaces and roadways to which salt is applied. The increase in chloride concentrations that eventually washes into the streams from road salt is threatening the availability of freshwater in the Northeastern United States (Kaushal, et al., 2005).

The practice of using road salt began in the 1940s (Kelly, et al., 2008). Its application increased rapidly until the 1970s, when it plateaued due to an increased environmental

awareness, but began to increase again after the 1990s (Bubeck,et al., 1971; Jackson and Jobbagy, 2005). Prior to 1941, the common practice was to apply chloride treated sand only to hills, curves and intersections, but by the late 1940s, the use of chloride salts become common (Bubeck,et al., 1971). Sodium chloride (NaCl) is the most common deicing agent used in North America (Kelly, et al., 2008). The use of rock salt (NaCl) on U.S. roads has skyrocketed in the last 65 years. In 1940, the sale of rock salt for highways in the U.S. was only 149,000 metric tons compared to today’s estimate at 18 million metric tons, which is over 100 times greater (Jackson and Jobbagy, 2005). Increases in urbanization increased impervious surfaces, road density, and human population density, which are linked to an increase in the use of road salt (Rhodes, et al., 2001; Heisig, 2000; Smith, et al., 1987; Kelly, et al., 2008). The increased urban development each year increases the surfaces to which winter deicing agents are applied (Corsi, 2010). It is estimated that more than 22 million tons of salt are scattered on the roads in the U.S.

annually (Stromberg, 2014).

There are significant consequences to the widespread and increasing use of rock salt.

Road salt runoff poses an increasing threat to aquatic ecosystems, particularly those in urban land and transportation corridors, but dramatic impacts have been observed on the local,

regional, and national scales (Corsi, 2010). After salt dissolves, it becomes sodium and chloride ions, which are carried away as runoff. These ions can be deposited in soil, surface water, or groundwater (Stromberg, 2014; Panno, et al., 2006).

There is a great problem with salination of freshwater throughout the Northeastern region, as chloride and total dissolved solid (TDS) concentrations have been observed at up to 25% the level of saltwater (Kaushal, et al., 2005); for many freshwater organisms, this exceeds their tolerance. Chronic concentrations of chloride as low as 250 mg/L have been recognized to have harmful effects on freshwater life and are not potable for human consumption. Increase in concentration up to 1000 mg/L can have lethal and sublethal effects on aquatic life (Kaushal, et al., 2005). High levels interfere with how animals regulate their uptake of salt into their bodies and can negatively impact the survival of crustaceans, amphibians, fish, plants, and other organisms (Stromberg, 2014).

The major solutes associated with road salt are chloride, sodium, and calcium;

magnesium may also be introduced where magnesium chloride salt is used. Typically, chloride is the best indicator of road salt pollution because it is the primary component of deicing

compounds and is chemically unreactive in most environments (Heisig, 2000). Chloride levels are also a big concern because it is transported more easily than sodium. An estimated 40% of US urban streams have chloride levels that can exceed tolerance for freshwater life (Stromberg, 2014, Kelly, et al., 2008). In one study (Kelly, et al., 2008), road salt on roadways contributed nearly 83% of chloride and sodium in a stream, while parking lots contributed nearly 8%.

Sewage and water softeners contributed 7% and only 2% was from atmospheric deposition and rock weathering. This signifies that 98% of the chloride contribution was from anthropogenic sources (Kelly, et al., 2008). Chloride is also a concern because it can enter a stream through many pollution sources, not just road salt, which can combine to greatly increase the chloride concentration in a stream (Thomas, 2000). Chloride can also be added through domestic wastewater, sewage, agricultural runoff, AMD, natural salt deposits, rock weathering, and wastewater from the extraction of natural gas (Kelly, et al., 2008; Nimiroski, 2002; Boutt, 2001;

Peters, 1981; Sherwood, 1989).

Many streams are seeing significant annual increases in chloride and total dissolved solids and road salt is a major component. The highest levels of chloride occur in winter and after snow melt (Stromberg, 2014). Although road salt is usually only applied in the winter months, there have been increases in summer months as well (Kelly, et al., 2008). In 2005, concentrations of chloride and sodium were three times the levels of 1986 and the increase occurred both in summer and winter. Chloride can be retained in the soil and groundwater, which can create a lag effect for chloride entering a stream (Kelly, et al., 2008; Jackson and Jobbagy, 2005). Even in summer, chloride concentrations in streams near roads have been measured to remain at levels up to 100 times greater than non-impacted forest streams (Kaushal, et al., 2005). Even rural streams have been shown to exceed baseline levels in summer (Jackson

and Jobbagy, 2005). This suggests that there still may be increases in concentrations of chloride in surface water for decades to come (Kelly, et al., 2008). Studies show that if the salinity in streams were to continue at its current rate, many surface waters in the northeastern U.S. would not be potable for human consumption and would be toxic to freshwater life within the next century (Kaushal, et al., 2005). Studies also show that even if salt input decreases or ceases all

together, concentrations in surface water may continue to increase, possibly for decades (Kelly, et al.2008).

In Pennsylvania, road salt is a common practice. Many counties in the Allegheny drainage basin apply large amounts of road salt in the winter (Table 2-1,Figure 2- 4). To help reduce the problem, many places are employing new strategies to reduce the road salt use and runoff into streams. Pre-treatment rather than post-treatment is used for storms. Salt is also often mixed with water allowing it to spread more, requiring less (Stromberg, 2014). Blending the salt with sand or gravel is a strategy that also reduces the salt use, sticks more easily to the road, and improves the traction for cars. There is also continued to work to find alternatives (Stromberg, 2014).

Table 2-1: Pennsylvania Counties in the Allegheny Drainage Basin that utilize road salt and the amount applied to roads in the winter of 2012-2013 (PennDOT, 2013).

County Tons of Road Salt applied

Gallons of Salt Brine applied (Salt and water mix produced by PennDOT)

Counties with a majority of area in the Allegheny Watershed

Warren 6,500 871,710

McKean 9,895 8,200

Venango 12,973 69,000

Forest 2,014 583,319

Elk 5,822 0

Clarion 13,872 117,901

Jefferson 19,260 85,963

Indiana 21,186 249,548

Armstrong 16,758 125,133

Westmoreland 36,008 208,796

Cambria 27,143 151,066

Counties with a portion of area in the Allegheny Watershed

Somerset 27,634 91,608

Potter 6,554 353,990

Butler 22,781 316,317

Allegheny 44,255 194,669

Crawford 14,627 878,130

Clearfield 18,588 368,275

Figure 2- 4: Map of Pennsylvania Counties within the Allegheny River Watershed.

2.5 Current Pollution Problems- Natural Gas Extraction