IMO certified clean fill is very important. One of your neighbours rings the council and you've potentially got lots of problems. I've had alot of dealings with BMX tracks over the last few years and there has been big issues when some clubs have brought in un certified fill. Are you after fill that's free or are you willing to pay? Have a look at some of the dirt merchants in your area, talk to construction/excavation companies/contractors. Alot of times you can get the fill for free as it's cheaper for them to get certify it and give it to you. Also, it's very important the kind of fill you get. There's lots of different stuff you can build out of and surface with. With the clubs, generally how it works is that they will have a member or a contact that's in construction/excavation. They will let them know that they want fill and how much, the company/person will then keep an eye out till they come across some. This is where it's important, it's good if the guy that's getting the fill knows what stuff is good, otherwise you can end up with truck loads of ROCKS with a bit of dirt mixed in. I know of one track that had to wait 6mths-1yr before their guy came across the right stuff. When you get the fill, you need to keep the option open to reject it or inspect it before it gets delivered. This is where paying for it potentially could be a better way to go. Just my 2c
Will the pump track stay dirt? I mean what's your plans for the finish product? will you be maintaining it? gonna get the whole thing tar? tar corners?