I assume by natural gas, you are asking about any existing utilities on site. The scale of your development (large scale apartment complex or individual singe family housing) will determine the method that you would use to locate any utilities. For multi-level apartment complexes, you would need to contact the county where your development will be located and discuss the matter with them. If it is determine that utilities exist on site, you will need to hire a civil engineering company to coordinate with the utility companies or manage any necessary utility relocation. If your development consist of individual housing structures, simply calling 411 may suffice.
To determine the subsurface soil conditions, you will need a to involve a geotechnical engineering firm. Their level of involvement will also depend on the scale of your project. You could need anything from a borrow pit to determine your near ground soil conditions, or you may need to take borings for subsurface exploration. If you want to estimate the soil type for the area without involving an engineering firm, look up the SC USDA maps for typical soil types in your area. Hope this helps.