In his new series, ProPublica's Abrahm Lustgarten has been investigating injection wells — disposal sites thousands of feet beneath the earth's surface — where industries ranging from agriculture to pharmaceuticals to gas drilling have been dumping their trillions of gallons of toxic waste.

Federal officials and geologists have long insisted that injection wells pose a minimal risk, but Abrahm's review of well records and case histories have found that structural problems are common and the EPA's oversight lax. He joins the podcast this week to explain why injection wells are a much bigger issue than fracking, the problems he faced with the EPA while reporting, as well as possible solutions to this growing problem.

You can read more about injection wells on our series page. And make sure to subscribe to all of ProPublica's podcasts on iTunes.