Lots of potential environmental harm, up to and including, poisoning of the aquifers.

It's potentially dangerous if companies cut corners on their well design or completion, and don't case and cement off surface water tables successfully.

Vertical fracking has been done for years. Horizontal fracking is relatively new. Plus several horizontal lines can radiate from one well head. Large numbers of fracking accidents and pollution have been covered up. See the ads promoting safe and clean fracking? Don't just look at the showcase wells used for PR purposes. Lease holders claim the anti-fracking groups are stealing their mineral rights, but the opposite is the fact. Drilling under my property, without my permission, is stealing my mineral rights. A few "land men" have outright lied to me to get my signature on a lease. If you have to use subterfuge, something is definitely wrong. Also, note that landowners in PA are getting bills instead of royalty payments in some cases. Sounds like a deal to me.

At least its spread is fairly new.

In many states, mineral rights are severable from surface rights.

The problem is that a lot of claims about the dangers of fracking are strictly hyperbole. A lot of claims that fracking is safe rely on nitpicking, on hairsplitting. Just as you can't rely on the showcase examples of "good, clean" fracking you also can't rely on showcase examples of "bad, dirty" fracking. A few examples either way aren't reliable information, they're nifty anecdotes to tell around the water cooler to convince the no-information listener with low-information speech. The best you get out of that is a low-information voter convinced he's the Stephen Hawking of the hydrofracturing world.

A lot of the anti-fracking furor has precious little to do with aquifers and land-rights. It has to do with fossil fuel use and global warming. The zealots fighting anthropogenic climate change aren't very careful with the facts because they have a goal they've vested with importance to defend. Just as those engaging in fracking have a goal they've vested with importance--profits. The morality of distorting the truth doesn't depend on the purpose in this case. The truth should be fully adequate.

Then there's the earthquake terror unleashed on parts of the country. There's a 2.5 quake and people are terrified. Why? No clue. Perhaps some think if there's a 2.5 there could be an 8.2. Structural geology, not a long suit for most people. Others are convinced that every quake must be the actual fracturing during fracking, which is also a bit loony. Or that a quake 4000 feet below and 5 miles away from a fracking zone must be causally connected. Even if they've been happening for decades. Scared and ignorant makes for bad policy whether it's the day after 911 and you're scared of Islamist terra or it's 2/14 and you're scared of corporatism.

A few inches of concrete won't keep poison out of my water well. All well casings will fail over time. We live on a fault line. That's one of the reasons they want to frack in my neighborhood. This was told to me by a gas company employee when they wanted to do seismic tests on our property. We've had enough personal contact with people who have been harmed by fracking in PA. Settlements with landowners have non-disclosure agreements. That gives the gas companies double protection. Shut up the victims and exclaim that there's no documented problems. Believe the PR if you wish, but the fracking is dangerous. These companies are taking shortcuts underground and above ground. Also, the job promotion is BS. They like to multiply the number of wells by the number of people needed per well. So I guess if 10 guys drill a well and then go drill another well, that's 20 jobs created? That's the kind of nonsense going on. Once the gas companies are done, the mess will be on the hands of the tax payers. I grew up in NEPA and lived through the cleanup of the hard coal mining mess left by the owners who were long gone. Also people should know, each well is a separate corporation. So if necessary, they can go bankrupt, leaving a hole and some pipe and the landowners are liable for damages.

the bat and then others break down after. I can get in my car and drive 20 mins south from the city and landowners there have to have their drinking/ bathing water trucked in because their wells are toast. If I drive in the other direction NW for about 50 mins I can meet, and have, spoke to ranchers whose cattle are losing their hair, sores on their bodies etc. But of course we all know this is hyperbole.

this is off the top of my head... why it is different from what you will hear people say "we've been doing this for 40 years".

high volume - as much as 5 million gallons of water mixed with maybe 40000 gallons of various chemicals and sand to prop open fractures, per well

Slick water - the chemical additives include friction reducers so that the water can be pumped at high pressure (10,000 psi) down the well bore. other chemicals used may be for anticorrosion, anti-foaming, breakers, biocides, gelling agents.

Some portion of this Frack Fluid, 30-90%, comes back out of the well as Flowback, contaminated by salts, heavy metals and naturally occuring radioactive material from the shale layer and has to be disposed of.

there is a lot more to learn... if you want

ponds ( I think that's what they're called) have been fraught with environmental nightmares here in Alberta and are seldom reported on.