I am having an inground pool demolished. To do that I need about 140 cu yds of fill and all of it has to be brought in by crossing my drain field.
The contractor says just have lighter loads on bigger trucks (more tires) but It sounds like from these discussions as if there is no way I can avoid destroying the drain field if I proceed. Any way to protect it? Is there a maximum load I can stay below and reduce my chances of collapse? Or just take the damage and repair it afterwards?
Any suggestions?

Any way to protect it? Is there a maximum load I can stay below and reduce my chances of collapse? Or just take the damage and repair it afterwards?For openers I'd get a statement from the Demo company accepting liability for any damage done to my property. I would then may out a route over the drainfield and locate the different branches. Would it be possible to place planks over the pipes to distribute the weight of the tires? That's about all I can come up with. Your thoughts? Tom

Thanks

In the road building arena, a fully compacted earth mound is placed over culverts to prevent damage to the culvert pipe when contractors need to cross those pipes with very heavy equipment, before the higher fill is placed.
But that is not appropriate over soil which may be saturated or otherwise unstable and building the protective fill and removing it would require heavy equip. working over the drainfield too, not too mention extra soil for protection while hauling the fill material in and expense of getting rid of the now unneeded extra fill.
Timber mats are used by heavy const. contractors to support large cranes on swampy ground. Similar to Tom's suggestion with planks but the timbers are interlocked into one large mat distributing the load over a large area.
Tom is headed in the right direction I think.
The contractor doing the work should give you his plan and unless it is totally unacceptable to you, let him do it and get in writing who is responsible for what.
Get copies of his insurance policies and check directly with his insurer to verify that the policy(s) is paid and current. If you specify the method of protection of the lines, unless you get his written approval of YOUR plan, you will have a share of the responsibility.
Maybe both could agree on a plan and agree to split the cost of any repairs if necessary-- might be some middle ground. Even if professionally surveyed and tested it is not a guarantee.
More wheels doesn't necessarily cause less weight per sf. Depends on the tare weight of the truck. A 10 whl truck that weighs 20,000 lbs puts down 2,000 lbs per sf empty, while a small dump at 8,000 lbs tare and 6 wheels is about 1,330 lbs per wheel. The old concrete is probably about 2 tons per cy and the dirt coming in about 1.5 tons per CY depending on soil type and moisture content, so load lower in the truck coming out than the truck coming in.
You will be hauling the concrete out and soil in so you have a fair number of crossings.
Is there absolutely no other way in and out? Maybe across a neighbor's property or something but I know that can get sticky too, with more agreements and hassle.