Fill on top of leaching feild

Before buying the house, I had the former owner replace the stone leaching feild for the septic. It was dug out and new clean stone was put in, however, the old stone was left on top and poorly graded. Basically can't mow it. Besides raking out the surface stone and regrading, can I put fill (topsoil) on top and all around the system? If so, what's the recommended max. depth of fill so I don't harm the underneath? Also, there were vent pipes installed on the four corners, can I cut them down low and plant bushes to hide them? Thank you for your input.

 

[CarlB]

You should contact the local authority/agency having jurisdition, they should be hepful and have handouts with typical design information. Could also contact a local engineer practicing septic system design, they could probably direct you. In my experience the stone only needs to extend a few inches above the drain pipe, probably no more than 6 inches. Top of drain pipe shoule be at least 18 inches deep, deeper in colder climates. Above the stone should be a geotextile (filter fabric) to prevent finer soils from getting into the stone. Above that you can place nearly any type of soil including topsoil. Also not a good idea to have stone to the surface as then runoff can esaily penetrate the drainfield. Local codes will also tell you that standpipes and cleanots should extend above the ground, probably one foot minimum. You could stick a tape measure down a standpipe and may find how deep your drainfield pipe is.