$StartingPath = "I:\"
$Right = "FullControl"
$Principal = "<domain>\<group>"

$Rule = New-Object System.Security.AccessControl.FileSystemAccessRule($Principal,$Right,"ContainerInherit, ObjectInherit", "None","Allow")

foreach ($Folder in $(Get-ChildItem -Directory $StartingPath -Recurse)) {

$Acl=Get-Acl $Folder.FullName
Write-Host $Folder.FullName
$Acl.SetAccessRule($Rule)
Set-Acl $folder.Fullname $Acl
}