If you're worried about which environmental groups the Waltons support (which has developed overnight for some news outlets), a comprehensive list is here.
"But what is a bit surprising is how much of a player in conservation Walton has become, rising along the same trajectory as Walmart's growing emphasis on sustainability. Many environmentalists have pointed out the dissonance here, and Walmart's CEO recently acknowledged that Walmart's carbon emissions are actually higher now than they were in 2005, given the chain's expansion. But the Walton Family Foundation’s impact on conservation is undeniable, especially when it comes to a few of its favorite green groups. The Waltons’ two favorite environmental groups—Environmental Defense Fund and Conservation International—combined took home almost 40 percent of the foundation’s $93 million in environmental giving last year. Extend that count to its top five grantees you get 53 percent of its green grants from 2013." -- Tate Williams, Inside Philanthropy