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Nationwide Insurance, - Center for Radiation Oncology, 7315 Green Slope Drive, Zephyrhills, FL Lab No. 190442 Page 13 cost of grouting is based upon a recent review of the unit costs supplied by qualified specialty contractors who perform this work. This estimate may vary from actual bid costs due to material cost changes, labor costs and mobilization costs that have changed since our review. Our estimate of costs for the soil stabilization program recommended (deep grouting program) is between $106,000 and $138,000. Additional to these costs will be our fees to monitor the grouting program and to provide a final report and a certification of the work performed. Our fees are estimated at $7,000 to $9,000. Sinkhole Parameters Exactly what is a sinkhole? What causes it? What defines sinkhole damage to a structure? These are all important and valid questions. The American Heritage Dictionary defines a sinkhole as a natural depression in a land surface communicating with a subterranean passage, generally occurring in limestone regions and formed by solution or by collapse of a cavern roof. The word karst is a term that is associated with sinkholes. Karst landscape is formed from the dissolution of carbonate bedrock. Karst terrain is characterized by the presence of sinkholes, springs and caves. It is typically drained internally where drainage moves rapidly into the ground through a network of fractures, pores and voids in the bedrock. Sinkholes occur naturally due to the dissolution of the soluble carbonate bedrock. The beginnings of sinkhole development or karstic erosion begins as slightly acidic groundwater flows through interconnected pores and fractures in the carbonate bedrock (limestone or dolostone). The groundwater becomes slightly acidic as the rainwater passes over decaying plant matter that gives off carbon dioxide. This carbonic acid attacks the carbonate rock and increases the size of the pores and fractures through which it flows. The more the size of the fractures and pores increases, the more the rate of dissolution increases due to the increased volume of flow. Different types of sinkholes can form depending upon the depth at which the bedrock occurs, what the overburden soils consist of and how thick they are. Where there is very little or no soil cover above the limestone bedrock, dissolution sinkholes can form. This is a very slow developing type of sinkhole and presents no hazard in the lifetime of a person. The dissolution of the limestone may take hundreds or thousands of years for a single foot. The ones that have formed are seen surficially as broad, saucer shaped landforms. The second type of sinkhole forms where there is a collapse in the bedrock and is called a cavern collapse or a bedrock collapse sinkhole. These are the type of large catastrophic sinkholes that are occasionally seen in news headlines. These form when the roof over a large void or cavern in the bedrock collapses and the overlying ground surfaces collapses to fill the void that has been created. These are rare and only a very small percentage of the sinkholes that develop in Florida are of this type. Central Florida Testing laboratories, Inc. 12625 - 40th Street North, Clearwater, FL 33762