A method and apparatus for converting spent water-based drilling mud into fertile indigenous top soil at a well site or location. The fertile indigenous top soil is produced by the steps of: admixing, at a well site, effective amounts of spent water-based drilling mud, mature compost, organic fertilizer, and top soil from the well site to provide a mixture containing spent water-based drilling mud, from about 30 to about 150 volume percent mature compost, from about 5 to 20 volume percent organic fertilizer, and from about 5 to 20 volume percent top soil from the well site wherein each of the volume percents is based on the volume of the spent water-based drilling mud present in the mixture; stirring the mixture for a period of time effective to form a substantially homogenous mixture; and drying the substantially homogenous mixture so as to provide fertile indigenous top soil possessing similar microbial and enzyme characteristics as the top soil at the well site.