Sinkholes, Springs and the HPS Mine
Nearly all of Florida sits atop the Floridan aquifer, a vast limestone and dolostone formation that stores enormous quantities of groundwater. Karst, quite simply, is what happens when slightly acidic rainfall seeps into that formation and, over many thousands of years, causes fissures and pockets to form. This process, called dissolution, over time results in caves, springs, sinkholes, closed depressions, sinking springs, and other geologic features broadly known as “karst landforms” or “karstic features.” Sometimes these features can actually connect the surface to the Floridan aquifer far below, which can impact groundwater quality in the aquifer. In an area where karst landforms are known to exist, therefore, care must be taken to ensure that surface activities will not cause water quality impacts to the Floridan aquifer. Such care has been taken here.
The Suwannee River Water Management District region, in which the proposed HPS mine is situated, is known to have karstic features. Consequently the HPS team conducted a robust study of karstic features in the area of the mine. This study included review of regional geologic and geotechnical data, aerial photography, and databases and field reconnaissance to verify any possible karstic feature identified in the vicinity of the project. No karstic features were found on the HPS property, and the entire project lies outside of the District’s designated Karst Sensitive Area. The HPS project is also not located within any springshed.
Besides the lack of karstic features on the site, there are several features of the HPS mine project that will prevent HPS mine operations from impacting the Floridan aquifer. Importantly, the majority of the HPS mine is situated over an area where the Floridan aquifer is covered by a layer of thick clay with low permeability. This clay barrier helps prevent rainwater that percolates from the surface from breaking down the underlying rock formation. Mining will not occur in or affect this clay layer; the phosphate matrix lies above the clay barrier, and the planned depth of mining will not reach it. Furthermore, no mining is proposed in areas where materials overlying the limestone layer have completely eroded away over time, such as near the New River. And the HPS team will conduct comprehensive water well monitoring before, during and after mining, pursuant to a state-approved monitoring plan, to assure that groundwater quality is not being affected by mining.
Finally, prior to and during mining, the proposed mine area and its perimeter will be inspected daily by a mining engineer or geologist. In the very unlikely event karst development occurs, the features will be identified, clearly marked, and reported to the appropriate state agencies. If needed, mining will be temporarily halted in the area, and appropriate remedial measures, approved by the Florida Department of Environmental Protection, undertaken.