Stray natural gas is common in northeast Pennsylvania. It existed before hydraulic fracturing for gas began in the area. The Marcellus Shale is the main rock formation from which natural gas is being extracted, but all the formations above the Marcellus also have natural gas. The Lockhaven and Catskill are the main drinking water formations that people in the area drill into for water supply and are located several thousand feet above the Marcellus Shale. There is plenty of water monitoring data showing natural gas already existed in the water supply formations before hydrofracturing occurred in the area. But between 2009 and 2011, the Pennsylvania Department of Environmental Protection investigated somewhere around 90 complaints of stray gas in domestic water wells. Obviously something new was happening.
When I envision stray gas, I always get this picture in my head of stray cats. You leave the door open one day and your cat slips out. It becomes a stray, living in the woods, killing songbirds for food, trespassing into people’s backyards, and generally making a nuisance of itself. Stray natural gas is really the same thing, you don’t do such a good job cementing your casing and you leave the door open for natural gas to come up the sides of the casing, it enters into groundwater rock formations and sometimes travels through natural fractures in the rock, it slips into people’s water wells and sometimes their basements, it can cause groundwater in the well to become discolored and turbid as iron and other minerals precipitate out of the water, and it generally makes a nuisance of itself because after all natural gas can explode.
The Environmental Protection Agency selected Northeast Pennsylvania for one of their five “Retrospective Studies.” The selections were made based on complaints of water well contamination in areas that were undergoing hydraulic fracturing for oil and gas. The study being “retrospective” was designed to determine through various chemical tests whether the Environmental Protection Agency could determine if the gas in people’s water wells in northeast Pennsylvania came from hydrofracturing activities in the area.
Based on the Environmental Protection Agency’s research, two main water types are being used for water supply in the study area. There is a nice calcium bicarbonate water in the upland areas and in the river valleys a sodium chloride or sodium bicarbonate type water. Geologists in the area have proposed that rivers followed weaker naturally fractured rock to form the valleys. The geologists further theorize that brines from lower rock formations moved upward through these highly fractured rocks underneath the valleys into the shallower drinking water formations, hence the chloride and sodium. Methane is common in the valley groundwater both in wells and in springs but is uncommon in the upland wells.
The main line of evidence that hydraulic fracturing in the area is the cause of stray gas in water wells comes from stable isotope work conducted by the Environmental Protection Agency and others. In a previous post I mentioned that stable isotopes have a signature. Remember from high school or college science: atoms have electrons, neutrons, and protons. So let’s take carbon as an example, it has 6 neutrons and 6 protons. That is called carbon 12. Get it, six and six is twelve. Okay, about one percent of carbon has 7 neutrons and 6 protons. It is called carbon 13. Since it has one less neutron, carbon 12 is lighter and reacts a little quicker in chemical bonding than its heavy brother. So various compounds that contain carbon have different amounts of carbon 13 to 12 based on their origin. These ratios are expressed in parts per thousand and give a signature that can be used in this case to determine the origin of methane.
Methane, a component of natural gas, is a compound of carbon and hydrogen. Hydrogen also has a stable isotope signature. Methane can be produced by bacteria in surface water. Methane in natural gas and methane produced by bacteria have two different carbon and hydrogen signatures. Methane is just one component of natural gas. Other components include ethane, propane and butane which are also compounds of carbon and hydrogen. And guess what? Each component of natural gas has a very specific ratio of carbon isotopes in relation to the other components for most of the oil and gas deposits around the world. Except in gas shales like the Marcellus where the ratio is reversed. If you got this reversal of the methane and ethane isotopic signatures in water wells, you would know immediately from where the gases originated. The problem is that there is usually not enough ethane found in water wells to analyze.
Okay enough for our background science. The Environmental Protection Agency tested 36 drinking water wells over a one and a half year period. They did three rounds of sampling and analysis. All wells sampled were within a mile of a hydraulic fracturing site. In addition to stable isotopes, the drinking water was tested for chemicals used in hydrofracturing fluid. The good news is that no drinking water wells tested were found to have hydrofracturing chemicals in them.
Some of the 36 drinking water wells the Environmental Protection Agency tested had natural gas that originated in deep rock formations. Three wells had isotopic signatures of natural gases from rock formations above the Marcellus and five had isotopic signatures of possibly the Marcellus or other deep rock formations. What is the cause of the movement of the stray gas? The Environmental Protection Agency cites a 2012 report by the Groundwater Protection Council that blames inadequate cementing of the casing that allowed gas to move from depth into shallower formations. However, the Environmental Protection Agency says that without having been able to sample the water wells before the hydraulic fracturing occurred in the area, it is difficult to determine exactly what the impacts have been to drinking water in the area.
It sounds to me like there is a strong need for groundwater assessment and sampling before hydraulic fracturing is conducted in an area instead of having to ferret out environmental impacts after the fact. The Environmental Protection Agency cites a study in Northeast Pennsylvania done by an oil and gas company prior to fracturing a well 800 feet from a drinking water well. Multiple rounds of sampling were conducted before and after the hydrofracturing occurred. Data showed a 7 fold increase in methane and a 1000 fold increase in ethane in the drinking water well after the hydraulic fracturing took place. Isotopic testing showed the gas entering the drinking water well came from deep gas bearing rocks but not the Marcellus itself. Little consolation to the homeowner I suspect who probably didn’t care where the gas came from, just that it hadn’t been there prior to hydrofracturing.