Made ground, how much to excavate?

[eandg]

Hi, our site is on a couple of metres of made ground which a WAC report advises contains stable non hazardous waste. Our site investigation recommends putting a capping layer of 600mm soil on any ground used to grow etc. Currently confirming levels with setting out engineer who'll calculate excavation and disposal needed. Any thoughts on whether I should dispose and cap below decking and artificial turf? My landscaping guy says made ground is fine for the latter and will be better for him to work from than fresh soil. Cheers. 

[Declan52]

Below decking it should be fine covered over with black polythene but you will need a hardcore base for artificial grass. I put near 250/300mm of well compacted stone under mine then a screed layer of quarry dust for the grass to sit on.

[eandg]

18 minutes ago, Declan52 said:

Below decking it should be fine covered over with black polythene but you will need a hardcore base for artificial grass. I put near 250/300mm of well compacted stone under mine then a screed layer of quarry dust for the grass to sit on.

Thanks - to confirm, in general there's no need for a capping layer prior to hardcore base for the turf? 

[Declan52]

If you have polythene spare it won't do any harm. What exactly did they find??

[eandg]

4 minutes ago, Declan52 said:

If you have polythene spare it won't do any harm. What exactly did they find??

That's fine if it won't need more brought in. From memory it was a bit of all your bad sounding stuff but not in particularly concerning concentrations.