Install new line to cistern wall, worried about loose dirt flow back into cistern

Hello, I have a 25 foot cistern/well, which I am replacing the line to my pump to. I am going to have to dig up around the side of the wall of the well to get to the pipe, I am concerned that when I back fill the dirt will be loose and will flow into the limestone lined well. Is there anything outside of getting a compactor, that maybe I should lay up against the wall of the well and then back fill? I thought of plastic but dont like that idea as I believe it will deteriorate and wind up in the well also. Thanks.

Place gravel against the well as you fill

It probably isn't approved by the local and state regulators however the best way to seal around a hole in a cistern wall is to place at least 1 bag of "Bentonite Hole Plug" around the hole and cistern. When it is wetted and covered over it will swell and seal keeping water, dirt, trash and contaminates from entering. Go to the following site for an explaination of Bentonite http://www.tundrasales.com/product/34. Any well supplier or your local well driller in your area will have the 3/8" Hole Plug. It's not expensive and it will do the job. Bentonite is the same clay that assisted in plugging the recent oil blowout in the Gulf.

I interpeted that as a stone lined "well" that was designed to let water in all around. What is a "limestone" lined well? mortared rock? then he could just use mortar, no? Must leak anyway.