Now.....I really don't want to be a prophet of doom .....but......we had a lawn layed/laid (never sure which is right) - beautiful lush green turf - then, like you, the worm casts started coming until our lawn was a total sea of mud which sadly never recovered, the grass all sort of disappeared! Had yet another load of turf put down and then called in one of those lawn care companies and told them their remit was to keep it looking just like it was then!! So far so good - just had the spring treatment done and in spite of all the rain this winter the worms seem to have stayed where they belong!