I would expect that due to the possibilities of bacterial infection that 
your health/safety authorities might insist on mud being removed by 
specialist contracters and the cistern being infilled by concrete.

paul courtney
leicester
UK

Ron May wrote:

>Susan,
> 
>Since the cistern is deeper than four feet, you will need to work with  
>California OSHA for safety planning. They may require wearing a safety harness  and 
>having some sort of crane on hand to pluck you out if the sides cave-in.  
>They may also require Hazardous Material training, breathing apparatus, steel  
>toe shoes, and possibly shoring. These things can get complicated, but better  
>that than a fatal accident.
> 
>The U.S. Navy required me to retain a civil engineer to design a safe  
>excavation that went below four feet. We had shoring, sump pumps, and wore hard  
>hats, but CAL OSHA never inspected that site because it was on federal  property.
> 
>Ron May
>Legacy 106, Inc.
>
>  
>