Why random fill is harmful. Why it pollutes soil and groundwater.

Abstract

Altering The Landscape - Random Fill And Effects On Recharge And Creation Of Contaminated Groundwater In Piedmont Saprolites and Partially

Weathered Rocks.

Donald Privett, STAR Environmental, 1 Circle St. Great Falls, SC 29055 Areas of large random fill (such as broken concrete, mixed with foreign saprolite and soil etc.) permit rapid infiltration and little run-off. Most random fill consists of sequences of different materials and/or material of different sizes, where fill is used to raise an area too low for construction (an old railroad cut) or extend and enlarge a sloping area to construction grade. Interfaces between different “beds” of various sizes and different degrees of compaction may act as a base to impede or enhance flow to the water table.

Seepage flow paths through random fill and into saprolite are quite different, because primary and secondary structures, textures and geometry, surface and “soil” properties are very different. Water movement is determined by gravity, external pressure and internal resistance to flow (viscosity), the onset and extent of runoff depends on infiltration rates at specific locations. The volume of surface or overland flow and infiltration determines groundwater recharge in any catchment area.

Preferred flow-paths through extremely heterogeneous material may permit rapid infiltration through the unsaturated zone to the base of the fill or gravitational runoff with little groundwater recharge. The volume of water within preferential paths is much larger and it may move to the base or to the edge of the fill.

Dual porosity transport (determination of water movement through naturally fractured rocks) is valid for most partly compacted fill materials where movement is along continuous fractures and along contacts of larger particles i.e. connected porosity and much slower to stagnant through the surrounding finer grained but porous matrix. Water moves through both the matrix of finer material and more rapidly at and along large slabs and between coarse fragments. Flow through macro voids produces an even more complex flow patterns. Slumping or gravitational flow of surface material over earlier dumped layers may form yet another semi-graded unit with still different transport properties.

Pollutants deposited intentionally or unintentionally may migrate rapidly by advection, diffusion, dispersion, sorption and degradation towards the groundwater table. Fractures, fissures, voids and cracks direct preferential rapid flow and transport. Infiltration through and recharge from any contaminates greatly reduces the quality of groundwater.

Poster presented at the 11th Annual David S. Snipes/Clemson Hydrogeology Symposium April, 2003, Abstracts p.20-21.