Finally, the Type 6 feature does not necessarily include a karst-related structure but rather represents intact bedding or undisturbed section. A moderate to thick overburden overlies a deeper limestone surface that may not be within the imageable area of the HRSP, in which case depth to limestone is estimated from other methods, such as gamma profiles of well logs. This type of stratigraphy may occur over the entire survey area if there is a thick overburden, or as fill within karst features. Communication between the surface and groundwaters may be minimal in these areas.

All of the lakes surveyed that have legible seismic profiles show at least one of the features noted in the summary reflections but usually there are multiple features present. Where these features have been identified in the profiles, their corresponding number has been annotated on the index map for each individual lake. The extent of the coverage, along with correlation from other sensing techniques such as gamma logs, and general knowledge of Florida geology, has allowed for some inference as to the type of material associated with the acoustic return. Parallel reflections or “transparent” return infer a stratigraphy of sand and clays. A jagged or noisy return indicates the limestone surface is near the lake bottom. As mentioned earlier, the type of feature present is probably a function of type and amount of overburden, proximity of karst surface to the lake bottom and maturity of karst development. Each of the identified features influence leakage between surface waters and the Floridan aquifer. Studies using seepage meters are being conducted to quantify variations in leakage related to a particular subsurface feature (Hirsch, 1998).