Water Quality Management of Leachates From
Power Station Coal Ashes
DENNIS W. WEETER, Assistant Professor
Department of Civil Engineering
University of Pittsburgh,
Pittsburgh, Pennsylvania 15261
JAMES E. NIECE, Project Engineer
ANTHONY M. DIGIOIA, JR., President
General Analytics, Inc.
Monroeville, Pennsylvania 15146
INTRODUCTION
In the United States the demand for electrical energy is increasing at a rate that doubles
total power consumption every ten years. Coal burning, in 1971, accounted for 44.3 percent
of the total electrical power demand (1). Projections for the future indicate that the
percentage of coal used in electric power generation may decrease somewhat, but with
demand increasing, the tonnage of coal consumed will also increase.
With this increasing use of coal, the subsequent environmental problems associated
with coal fired power stations becomes more widespread and, in some cases, more severe.
Not only will the problems with gaseous emissions increase, but the problems associated
with disposal of residual noncombustible coal ashes will also become more of a problem.
The coal ashes include bottom ash, which is removed from the bottom of the furnace, and
fly ash, which is collected from the flue gas by air pollution control devices. In 1971, for
example, 27.8 million tons of fly ash was generated in the United States. The bottom ash
generated in 1971, was 10.1 million tons (2).
The history of the disposal of coal ashes has included several phases. In the early
history, coal ashes were simply dumped for permanent disposal. However, approximately a
decade ago, attempts were made to identify secondary recycled uses for the coal ashes. For
example, fly ash is used as an asphalt concrete filler, an additive for concrete building blocks
and structural concrete, as a fill material, and as an alkali for farms, lawns, and gardens. Fly
ash has even been proposed to be used as a water pollution control chemical for various
chemical treatment systems. For example, fly ash has been proposed as an adsorbent for
removal of phsophate and, also, as a conditioner for thickening wastewater sludges (3).
However, for secondary uses, only 11.7 percent of fly ash and 16.0 percent of bottom
ash was being utilized in 1971 (2). The remainder must be placed in permanent disposal.
Therefore, the major problem continues to be not one of looking for other secondary uses,
but one of facing the challenging problem of disposal of these coal ashes. The problem of
disposal will not be one without environmental confrontations (4).
DiGioia, et al (4) have discussed the comprehensive environmental dangers that may
be encountered by the disposal of coal ashes. With regard to these environmental problems,
this study will discuss aspects of the water pollution problem associated with coal ash
disposal.
WATER POLLUTION POTENTIAL
At the ash disposal site, water quality degradation can result from two common
situations. If the site is not constructed properly, ground water may pass through the fill
either constantly or during periods of high ground water. Secondly, if surface drainage and
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