1. 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.