NB datapoints

Data and Comments on New Brunswick Issues

What the peer-reviewed science says about shale gas

Last Updat­ed on 2026-04-08

Last Updat­ed on 2026-04-08

Shale gas explo­ration and extrac­tion via hydraulic frac­tur­ing is a con­tro­ver­sial and polar­iz­ing top­ic in New Brunswick. The pub­lic is divid­ed on the issue and, as is often the case these days, social media are being used to ral­ly sup­port­ers to one side or the oth­er. Inflam­ma­to­ry rhetoric and exag­ger­at­ed claims appear to dom­i­nate the dis­cus­sion. That being said, it is far from clear yet whether NB has a suf­fi­cient­ly large and eco­nom­i­cal­ly extractable reserve of gas to cre­ate a sig­nif­i­cant indus­try; it may turn out that shale gas may not exist in suf­fi­cient quan­ti­ties,  or prices may not be suf­fi­cient to jus­ti­fy devel­op­ment at this time.  On the oth­er hand, the gas is a pub­lic asset and so dis­cus­sion of how to devel­op (or not devel­op) and uti­lize the asset is mer­it­ed. The recent com­ments by some of the elect­ed First Nations Chiefs may rep­re­sent an open­ing to devel­op­ment of this resource. For a use­ful out­line of the shale indus­try in New Brunswick, see an arti­cle by A. Park of UNB (16) and an opin­ion piece by var­i­ous UNB researchers.

The devel­op­ment of hydraulic frac­tur­ing tech­nolo­gies over the past 30 years or so has made extrac­tion of shale gas eco­nom­i­cal­ly fea­si­ble and attrac­tive prices have allowed the indus­try to expand rapid­ly. An abun­dance of gas in the mar­ket­place pushed down prices in 2011–2012 and the expan­sion of the indus­try has slowed some­what. Infor­ma­tion in the peer-reviewed sci­en­tif­ic lit­er­a­ture with respect to adverse envi­ron­men­tal and health impacts from shale gas extrac­tion is now begin­ning to appear. A num­ber of these arti­cles are avail­able for free down­load and I would encour­age peo­ple to read them, rather than accept the inter­pre­ta­tions that appear in var­i­ous media (or my inter­pre­ta­tions, for that mat­ter). It is fine to have opin­ions, but much bet­ter to have opin­ions based in ver­i­fi­able data. Then we can have a ratio­nal dis­cus­sion.

The objec­tive of this post is to review what the peer-reviewed sci­en­tif­ic data say about shale gas extrac­tion and its envi­ron­men­tal impacts. I have put togeth­er a list of peer-reviewed sci­ence jour­nal arti­cles relat­ed to shale gas envi­ron­men­tal effects, and have added some com­ments on the results obtained by the researchers (If any­one knows of any that are not list­ed below, please for­ward to me). The num­bers in paren­the­ses below refer to the sci­en­tif­ic cita­tion with the same num­ber. Let’s look at what the sci­ence says with respect to some of the major envi­ron­men­tal issues:

  1. Con­t­a­m­i­na­tion of ground­wa­ter by extract­ed methane.

Methane is the largest com­po­nent of nat­ur­al gas; oth­er hydro­car­bon gas­es, such as ethane and propane, are gen­er­al­ly removed from nat­ur­al gas dur­ing the purifi­ca­tion process. Because it is a potent green­house-gas, methane releas­es into the atmos­phere have long been a con­cern. More recent­ly, methane con­t­a­m­i­na­tion of ground­wa­ter used for drink­ing has become an issue, due to the poten­tial of hydraulic frac­tur­ing tech­nolo­gies that allow methane to escape from deep reserves and poten­tial­ly mix with ground­wa­ter reser­voirs.

In two wide­ly-report­ed stud­ies (11, 15), researchers at Duke University’s Nicholas School of the Envi­ron­ment found high lev­els of gas from ther­mo­genic (i.e. like­ly from deep gas reserves) sources in a num­ber of drink­ing water wells that were locat­ed less than 1 km from gas well sites, main­ly locat­ed in Penn­syl­va­nia. Ground­wa­ter sam­ples tak­en fur­ther way from gas wells has sig­nif­i­cant­ly low­er lev­els of methane, and the methane in those lat­ter sites was a mix of ther­mo­genic and bio­genic (i.e. like­ly from shal­low gas reserves adja­cent to ground­wa­ter) methane. How­ev­er, the authors report­ed that methane was found in 85% (15) and 82% (11), respec­tive­ly, of all water sam­ples tak­en from  hous­es in the research areas. In oth­er words, the research took place in an area where bio­genic and like­ly ther­mo­genic methane already were com­mon con­t­a­m­i­nants, and the near­by pres­ence of gas wells increased  methane con­cen­tra­tion in the water sup­plies of hous­es close to those wells. Methane is known to be nat­u­ral­ly present in drink­ing water in dif­fer­ent loca­tions in North Amer­i­ca, includ­ing NB. Those are the regions that would seem to be the most like­ly to see increased methane lev­els in drink­ing water, when the gas wells are close by. In oth­er areas, the like­li­hood of gas leak­ing into ground­wa­ter may be relat­ed to the geol­o­gy of the region. Hous­es less than 1 km from gas wells also had  propane and ethane con­t­a­m­i­nants, pre­sum­ably from the same nat­ur­al deep under­ground sources that pro­vid­ed the high­er lev­els of methane.

These two stud­ies sug­gest that if gas wells are locat­ed 1 km or more from the house, the chances increased con­t­a­m­i­na­tion by methane are fair­ly low. The authors of the 2013 study (11) con­clud­ed  that the source of the high­er lev­els of methane, propane and ethane was prob­a­bly faulty well cas­ing con­struc­tion that result­ed in gas leaks into water. In oth­er words, the prob­lem was not the hydraulic frac­tur­ing process itself, but poor well con­struc­tion. Davies (4), Saba and Orze­chows­ki (18) and Schon (19) crit­i­cized Osborn (15) for char­ac­ter­iz­ing the addi­tion­al methane as result­ing from hydrofrac­tur­ing  and empha­sized that the most like­ly cause, faulty well-cas­ing, was not inher­ent­ly relat­ed to hydraulic frac­tur­ing tech­nol­o­gy. If cor­rect, that sounds like a fix­able prob­lem, pro­vid­ed there is suf­fi­cient mon­i­tor­ing to detect the leaks.

Final­ly, I’d note that the Jack­son (11) arti­cle report­ed that the Penn­syl­va­nia Depart­ment of Envi­ron­men­tal Pro­tec­tion issued 90 vio­la­tions in 2010 and 119 vio­la­tions in 2011 for faulty cas­ing and cement­ing of gas wells. That points out the need for care­ful and vig­or­ous mon­i­tor­ing of gas wells by inde­pen­dent agen­cies, although, to keep things in per­spec­tive, it is worth not­ing that by 2011 there were over 8000 gas wells in Penn­syl­va­nia. Jack­son (11) also rec­om­mend­ed exten­sive pre-drilling data col­lec­tion on ground­wa­ter qual­i­ty and pub­lic dis­clo­sure of same. It fol­lows that pub­lic agen­cies would need to have the resources to over­see or car­ry out those tasks.

  1. Con­t­a­m­i­na­tion by flu­ids used in hydraulic frac­tur­ing

In the 2011 study referred to above, Osborn (15) did not detect drink­ing water con­t­a­m­i­na­tion by hydraulic frac­tur­ing flu­ids. Data show­ing con­t­a­m­i­na­tion of drink­ing water from frack­ing flu­ids are hard to find in the peer-reviewed sci­en­tif­ic lit­er­a­ture. The Unit­ed States EPA, in 2011, report­ed con­t­a­m­i­na­tion of ground­wa­ter in Wyoming by such flu­ids. The EPA test wells were drilled near domes­tic water wells where res­i­dents had com­plained about water qual­i­ty for sev­er­al years and those wells were with­in a few hun­dred metres of gas wells. The EPA has tried with­out appar­ent suc­cess to devel­op a peer-review eval­u­a­tion of the meth­ods and data used in that study.  The area in ques­tion has had inten­sive gas drilling for decades, using both con­ven­tion­al and hydraulic frac­tur­ing tech­niques, and the report­ed con­t­a­m­i­na­tion may or may not be due to the lat­ter tech­nol­o­gy. Waste pits from oil and gas drilling activ­i­ties and con­tain­ing var­i­ous con­t­a­m­i­nants are found in the area. It sounds like some errors were made in site selec­tion and those errors result­ed in data that can­not be con­clu­sive­ly linked to hydraulic frac­tur­ing.

Some have mis­char­ac­ter­ized the EPA results and claimed that the EPA could not repro­duce the results show­ing con­t­a­m­i­na­tion. In fact, repeat­ed sam­pling has shown detectable lev­els of con­t­a­m­i­na­tion, and those con­t­a­m­i­nants might indeed be the cause of the odour, taste and pos­si­ble health effects report­ed by res­i­dents at the Wyoming site. The prob­lem encoun­tered by the EPA in con­nect­ing their results to hydraulic frac­tur­ing seems to be site selec­tion. The EPA chose sites where ground­wa­ter con­t­a­m­i­na­tion may have occurred from caus­es oth­er than hydraulic frac­tur­ing, and con­se­quent­ly the EPA can­not prop­er­ly test the hypoth­e­sis that flu­ids used in frac­tur­ing are respon­si­ble for the con­t­a­m­i­nants found in ground water. It is impor­tant that sites select­ed for study of con­t­a­m­i­na­tion be areas where tra­di­tion­al oil and gas explo­ration and drilling have not been done, in order to sep­a­rate the effects of past prac­tices from new prac­tices. Addi­tion­al­ly, you would pre­fer a site where base­line data are avail­able, in order to sep­a­rate out nat­u­ral­ly-occur­ring prob­lems or oth­er ‘human-induced’ prob­lems from those caused by gas devel­op­ment.

It is clear from the Wyoming exam­ple that the oil and gas indus­try does not exact­ly have a stel­lar track record with respect to envi­ron­men­tal stew­ard­ship, and that prop­er reg­u­la­tion and mon­i­tor­ing are required to reduce risk.  How­ev­er, the Wyoming case does not help much either way with respect to the impact of hydraulic frac­tur­ing on ground­wa­ter con­t­a­m­i­na­tion.

The data pre­sent­ed in these two stud­ies from Duke Uni­ver­si­ty on the oth­er hand sug­gest that water wells 1 km or more from gas well sites are not like­ly to become con­t­a­m­i­nat­ed with methane and that flu­id con­t­a­m­i­na­tion from hydraulic frac­tur­ing is unlike­ly. Prop­er­ly con­struct­ed and mon­i­tored gas wells might reduce that dis­tance even fur­ther, but dif­fer­ing geolo­gies might affect gas migra­tion.

  1. Sur­face water con­t­a­m­i­na­tion

Olm­stead (14) found high­er lev­els of con­t­a­m­i­nants (they used chlo­ride as a ‘mark­er’ for con­t­a­m­i­nants and found increas­es of approx 10% per treat­ment facil­i­ty) in sur­face water (rivers, streams) sam­ples col­lect­ed down­stream from frack­ing flu­id water treat­ment facil­i­ties, com­pared to sam­ples from con­trol loca­tions. The pres­ence of gas wells upstream increased (5% per 18 addi­tion­al well pads) the amount of total dis­solved solids down­stream, but this appeared to be relat­ed to land-clear­ing or oth­er actions relat­ed to con­struc­tion of the gas wells rather than frack­ing flu­id con­t­a­m­i­na­tion per se.

These data sug­gest that water treat­ment facil­i­ties may be releas­ing con­t­a­m­i­nants into water­sheds. Con­t­a­m­i­nants are also released into water­sheds by domes­tic water treat­ment facil­i­ties, but prop­er reg­u­la­tion and mon­i­tor­ing can be used to main­tain drink­ing water stan­dards.  There have also been reports in the media of spills of flu­ids caus­ing sur­face water con­t­a­m­i­na­tion. Rozell (17) used a risk analy­sis pro­ce­dure to deter­mine that leaks and spills dur­ing waste­water dis­pos­al posed a large threat to drink­ing water sup­plies. It sounds rea­son­able, there­fore, to require inde­pen­dent and trans­par­ent mon­i­tor­ing of sur­face waters near water treat­ment facil­i­ties, and that con­t­a­m­i­na­tion lev­els in treat­ed water be reg­u­lat­ed to meet at least drink­ing water stan­dards. It is also impor­tant to note that water dis­charged from munic­i­pal sewage treat­ment plants is not free of con­t­a­m­i­nants; there is a dif­fer­ence between a water source that is free of con­t­a­m­i­nants and one that meets water drink­ing stan­dards.

  1. Methane leaks into atmos­phere

Methane is a potent green­house gas and increased methane emis­sions into the atmos­phere will cer­tain­ly con­tribute to glob­al warm­ing. There is a great deal of con­cern about release of methane from thaw­ing Arc­tic per­mafrost for that very rea­son.

When used as a fuel in pow­er gen­er­a­tion, nat­ur­al gas (NG) releas­es few­er CO2 emis­sions than coal or oil. Low prices for NG, fol­low­ing the expan­sion in sup­ply result­ing from hydraulic frac­tur­ing, have led to replace­ment of coal by NG in pow­er gen­er­a­tion in some parts of the US. Green­house-gas emis­sions have fall­en slight­ly in the US and that decline might be a con­se­quence of the switch from coal and oil to NG. That would seem to sug­gest ben­e­fits where shale gas replaces ‘dirt­i­er’ fuels such as coal or oil for pow­er gen­er­a­tion.

A report by Howarth (9) caused alarm as it sug­gest­ed that large amounts of methane might be escap­ing from nat­ur­al gas wells. They cal­cu­lat­ed that, large­ly because of these methane emis­sions, the GHG ‘foot­print’ of shale gas might be greater than that of coal. Howarth et al’s cal­cu­la­tions were based large­ly on an EPA report. How­ev­er, the EPA has now issued a revised report that sig­nif­i­cant­ly reduces the amounts of methane they expect to be released from shale gas wells [EPA (2011a) Inven­to­ry of U.S. Green­house Gas Emis­sions and Sinks: 1990–2009. April 14, 2011. U.S. Envi­ron­men­tal Pro­tec­tion Agency, Wash­ing­ton DC]. Jiang (12) also cal­cu­lat­ed GHG emis­sions relat­ed to shale gas extrac­tion (methane leak­age, flaring/venting of gas from wells dur­ing flow test­ing, and CO2 emis­sions relat­ed to oper­a­tion of diesel equip­ment at well sites). They con­clud­ed, in con­trast to Howarth (9), that shale gas had a low­er GHG foot­print than coal, when used for elec­tric­i­ty gen­er­a­tion.

Cath­les (2, 3) also con­clud­ed that shale gas would pro­vide marked reduc­tions in GHG emis­sions if it replaced coal and oil as an ener­gy source. Cath­les (2) stress that, while methane is a potent GHG, it per­sists in the atmos­phere for about 20 years, while CO2 emis­sions from coal and oil con­sump­tion per­sist for hun­dreds of years. Even with leak­age from gas wells, they con­clud­ed that the use of gas is vast­ly less dam­ag­ing in terms of glob­al warm­ing than coal and oil. Howarth (10) respond­ed in 2012 with a defense of their posi­tion. The dif­fer­ent con­clu­sions appear to be based large­ly on whether one believes we should look at the impacts of emis­sions over a decadal or 100 year time scale. Both groups of authors agree that more inde­pen­dent data on methane emis­sions are need­ed.

Inter­est­ing­ly, the Cath­les group and the Howarth group are both based at Cor­nell Uni­ver­si­ty in upstate New York – I can imag­ine the ‘angry words’ dur­ing cof­fee breaks! For a com­men­tary on this dis­pute, see here.

If a com­pa­ny is in the busi­ness of sell­ing methane (i.e. nat­ur­al gas), you’d think they would try to reduce any leak­age as much as pos­si­ble. After all, loss of gas by vent­ing into the atmos­phere is a poten­tial loss of prof­it – they have already invest­ed in the well, so would they tol­er­ate such a loss? Of course, the high­er the val­ue of the gas, the greater will be their inter­est in cap­tur­ing as much of it as pos­si­ble. By con­trast, when gas is cheap, the cost of cap­ture might be greater than the val­ue of the gas. It’s true that the oil indus­try may at times vent off large amounts of gas in order to secure the more valu­able oil from under­ground reserves, but the shale gas indus­try is in the gas busi­ness. Accord­ing to the EPA,  the indus­try has made sig­nif­i­cant strides in reduc­ing emis­sions of methane from wells. That, plus the reduc­tion in GHG emis­sions in the US referred to above, would sug­gest Howarth’s cal­cu­la­tions are off the mark.  Lu (20) found that CO2 emis­sions fell between 2008 and 2009 in the US and attrib­uted that decline to a switch in the use of gas for coal in pow­er gen­er­a­tion. Indeed, oth­er sci­en­tif­ic pub­li­ca­tions (2, 3, 12) have claimed that the methane emis­sions from shale gas wells, and their impacts, are small enough that the use of this gas results in a net reduc­tion in GHG emis­sions, where the shale gas replaces coal or oil in pow­er gen­er­a­tion. The weight of the evi­dence appears to sup­port the use of nat­ur­al gas as a tran­si­tion fuel.

  1. Seis­mic events

It has been claimed that earth­quakes may be trig­gered by hydraulic frac­tur­ing tech­nolo­gies. The word ‘earth­quake’ tends to con­jure up visions of mas­sive seis­mic events result­ing in large amounts of destruc­tion and loss of life. It’s help­ful to con­sid­er that most earth­quakes are minor seis­mic events and cause no dis­cernible dam­age. While most earth­quakes are nat­ur­al events, minor man-made events can occur as a result of blast­ing (road con­struc­tion, min­ing). The force or mag­ni­tude of an earth­quake is mea­sured on a log­a­rith­mic scale: those below a mag­ni­tude of 5 rarely cause dam­age; those below a mag­ni­tude of 3 (i.e. 100 times less intense) are rarely felt, although they will be record­ed on the seis­mo­graphs used to record earth­quake events.

Earth­quakes Cana­da pro­vides data on earth­quakes occur­ring in Cana­da and New Brunswick earth­quake infor­ma­tion can be found here also. For exam­ple, in 2012 there were 91 earth­quakes record­ed in the New Brunswick region (because regions are defined by lon­gi­tude and lat­i­tude, the NB region also includes parts of Maine, PEI and Nova Sco­tia. You can adjust the set­tings pro­vid­ed by Earth­quakes Cana­da to expand or reduce the area to be report­ed on.).  Of the 91, 89 had a mag­ni­tude of 2 or less. Only 31 of the 91 were report­ed by mem­bers of the pub­lic.  Many of these were from the earth­quake ‘swarm’ that occurred in the Macadam area. In 2013, 19 events were record­ed from Jan­u­ary through June. Sev­en­teen of those were mag­ni­tude 2 or less.  So earth­quakes are not uncom­mon, but very few earth­quakes in New Brunswick cause dam­age. If you check the Earth­quakes Cana­da site you can see for your­self whether or not seis­mic test­ing for shale gas over the past cou­ple of years has result­ed in an increase in the num­ber of record­ed quakes in New Brunswick.

Can hydraulic frac­tur­ing cause earth­quakes? The sci­en­tif­ic evi­dence sug­gests that either frac­tur­ing itself or waste­water injec­tion may induce small earth­quakes, but there does not seem to be evi­dence that these are nor­mal­ly dam­ag­ing to infra­struc­ture or the envi­ron­ment (13). For exam­ple, Hol­land (7) con­clud­ed that hydraulic frac­tur­ing of an oil well in Okla­homa trig­gered earth­quakes. A series of 116 earth­quakes result­ed. These occurred from 17–23 Jan­u­ary 2011 with no oth­er sim­i­lar earth­quakes iden­ti­fied at oth­er times pri­or to or post-hydraulic frac­tur­ing. In oth­er words, the earth­quakes end­ed when the frack­ing stopped. The iden­ti­fied earth­quakes ranged in mag­ni­tude from 0.6 to 2.9, with only 16 of 116 earth­quakes of mag­ni­tude 2 or greater.  Very minor earth­quakes  such as these would not be expect­ed to cause dam­age and none was report­ed.

Brod­sky and Lajoie (1) found a good cor­re­la­tion between the vol­ume of frac­tur­ing flu­ids inject­ed or extract­ed from a well and seis­mic activ­i­ty in Cal­i­for­nia. In this case, the objec­tive of frac­tur­ing was not to obtain shale gas but to devel­op geot­her­mal ener­gy sources. As the frac­tur­ing con­tin­ued over a series of decades, the num­ber of earth­quakes per amount of frac­tur­ing activ­i­ty appeared to decline. That might sug­gest a lim­it in earth­quake activ­i­ty in response to frac­tur­ing, but, again, that might depend upon the geol­o­gy of the region. Ellsworth (5) not­ed that earth­quakes induced by frac­tur­ing appear to be main­ly minor events, but cau­tioned that deep injec­tion of waste­water might result in larg­er earth­quakes. He not­ed that waste­water injec­tion was the like­ly cause of major quakes in the U.S. in 2011 and 2012, in par­tic­u­lar the 5.6 Mag­ni­tude quake that struck Okla­homa and destroyed sev­er­al homes. Hor­ton (8) found sim­i­lar swarms of seis­mic events in Kansas that were appar­ent­ly asso­ci­at­ed with waste­water injec­tion. It is pos­si­ble there­fore that waste­water injec­tion, as opposed to frac­tur­ing itself, might pose a par­tic­u­lar haz­ard. Ellsworth sug­gest­ed increased mon­i­tor­ing, espe­cial­ly near waste­water injec­tion sites. Van der Elst (6) reached sim­i­lar con­clu­sions, not­ing that frac­tur­ing seis­mic activ­i­ty in a region increased the like­li­hood that the region might be hit by larg­er earth­quakes orig­i­nat­ing at remote loca­tions. Again, that might be depen­dent upon local geol­o­gy; increased mon­i­tor­ing at well-injec­tion sites was rec­om­mend­ed.

Over­all, there does seem to be a rela­tion­ship between the deep injec­tion of waste­water and seis­mic activ­i­ty. For the most part, that activ­i­ty does not appear to be dan­ger­ous, but there are some reports sug­gest­ing that these minor events might make a region more sus­cep­ti­ble to quakes that orig­i­nate else­where. That pos­si­bil­i­ty needs fur­ther inves­ti­ga­tion and, again, under­lies the need for trans­par­ent and pub­lic mon­i­tor­ing.

Lit­er­a­ture cit­ed:

  1. Brod­sky, E. and Lajoie, L. 2013. Anthro­pogenic Seis­mic­i­ty Rates and Oper­a­tional Para­me­ters at the Salton Sea Geot­her­mal Field. Sci­ence 1239213 (Pub­lished online 11 July 2013) [DOI:10.1126/science.1239213]
  2. Cath­les, L., Brown, L., Taam, M., and Hunter, A.2012. A com­men­tary on ‘The green­house-gas foot­print of nat­ur­al gas in shale for­ma­tions’ by R.W. Howarth, R. San­toro, and Antho­ny Ingraf­fea,” Cli­mat­ic Change 113, no. 2: 525–535.
  3. Cath­les, L. M. 2012. Assess­ing the green­house impact of nat­ur­al gas. Geo­chem­istry, Geo­physics, Geosys­tems 13: 1525–2027 doi 10.1029/2012GC004032
  4. Davies, R. 2011. Methane con­t­a­m­i­na­tion of drink­ing water caused by hydraulic frac­tur­ing remains unproven. Pro­ceed­ings of the Nation­al Acad­e­my of Sci­ences 108, no. 37: E871.
  5. Ellsworth, W.L. 2013. Injec­tion-Induced Earth­quakes. Sci­ence (July 12) Vol.341 (6142) doi: 10.1126/science.1225942
  6. van der Elst, NJ; Sav­age, HM; Ker­a­nen, KM,; Abers, GA.2013. Enhanced remote earth­quake trig­ger­ing at flu­id-injec­tion sites in the mid­west­ern Unit­ed States. Sci­ence (Jul 12) 341(6142):164–167. doi:10.1126/science.1238948.
  7. Hol­land, A. 2013. Earth­quakes trig­gered by hydraulic frac­tur­ing in south-cen­tral Okla­homa. Bul­letin of the Seis­mo­log­i­cal Soci­ety of Amer­i­ca 103(3):1784–1792
  8. Hor­ton, S. 2012. Dis­pos­al of Hydrofrack­ing Waste Flu­id by Injec­tion into Sub­sur­face Aquifers Trig­gers Earth­quake Swarm in Cen­tral Arkansas with Poten­tial for Dam­ag­ing Earth­quake. Seis­mo­log­i­cal Research Let­ters, March/April 2012, v. 83, p. 250–260, doi:10.1785/gssrl.83.2.250.
  9. Howarth, RW., San­toro, R., and Ingraf­fea, A. 2011. Methane and the green­house-gas foot­print of nat­ur­al gas from shale for­ma­tions. Cli­mat­ic Change 106, no. 4 : 679–690
  10. Howarth, RW., San­toro, R., and Ingraf­fea, A. 2012. Vent­ing and leak­ing of methane from shale gas devel­op­ment: response to Cath­les et al. Cli­mat­ic Change 113, no. 2 : 537–549
  11. Jack­son, R., Ven­gosh, A., Dar­rah, T., Warn­er, N., Down, A., Pore­da, R., Osborn, S., Zhao, K., and Karr, J. 2013. Increased stray gas abun­dance in a sub­set of drink­ing water wells near Mar­cel­lus shale gas extrac­tion. Pro­ceed­ings of the Nation­al Acad­e­my of Sci­ences 110, no. 28: 11250–11255.
  12. Jiang, M., Grif­fin, WM., Hendrickson,C., Jaramil­lo, P., Van­Briesen, J., and Venkatesh, A.  2011. Life cycle green­house gas emis­sions of Mar­cel­lus shale gas, Envi­ron­men­tal Research Let­ters 6, no. 3. 034014.
  13. Nation­al Research Coun­cil. Induced Seis­mic­i­ty Poten­tial in Ener­gy Tech­nolo­gies . Wash­ing­ton, DC: The Nation­al Acad­e­mies Press, 2012.
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