Aye, you need a group of 3+ people I think, and someone who counts down for the first person to start digging. Then the rest joins in as soon as they see that person dig. It might take half an hour or longer before you've got everyone to complete that quest (unless you are the only one ofcourse), but it's a great way to meet people.
I'll be playing/looking after my kid so not very nice for him if I log in now, otherwise I could have help you. Try asking in Global chat for help.
Eon, you definitely need help from other players. Ask in global chat if anyone else is trying to complete the quest and see if you can recruit a team to work together. I completed this one a couple of nights ago with help from just one other player, but then it turned out that he didn't manage to finish before the timer ran out! So we tried again with 3 players total, and he finished the quest within 3 dirt piles. In glitch, more help is almost always better. Kajuu is a great place to find dirt piles--other regions, not so much.
There are 2 quests that sometimes get confused with each other because they're both digging challenges--the other one is called Peter Out Peat and I think that the general rule with that one is that you can complete it with 5 people total, but it works best with 6. That's the one that you'll need to be able to find a full bog for.