62    LEACHING POTENTIAL OF TWO INDUSTRIAL SLUDGES:
AN EVALUATION OF TOXICITY CHARACTERISTIC
LEACHING POTENTIAL (TCLP) TEST
Somnath Basu, Engineer
Camp Dresser & McKee
Boston, Massachusetts 02108
Irvine W. Wei, Associate Professor
Civil Engineering Department
Paul H. King, Dean
College of Engineering
Northeastern University
Boston, Massachusetts 02115
INTRODUCTION
Proper disposal of sludges generated from the treatment of industrial wastewater has been a
difficult problem to rapidly developing society. Typically many such sludges find their way into a
landfill system. Solid wastes placed in a landfill undergo a number of physical, chemical, and biological changes, such as, anaerobic biodegradation of high molecular weight organic compounds to
simple compounds, typically methane and organic acids; percolation of rainwater, stormwater, agricultural runoff, and other liquids through the sludge mass; dissolution and leaching of organic and
inorganic materials and movement of leachate through the fill in the direction of hydraulic gradient;
and transport and escape of gases through and out of the fill. Generation and containment of the
leachate has been a major concern during the past two decades because of the potential of these
leachates ultimately finding their way into the nearby groundwater table and polluting the groundwater with chemical species in dissolved or suspended form.1,2 Some of these chemicals, for example,
metals and refractory organics, such as pesticides or PCBs are extremely hazardous to human health.
From this perspective, unless proper care is taken, every landfill is a potential hazardous waste site.
HISTORICAL DEVELOPMENT
As authorized by the Resource Conservation and Recovery Act (RCRA), passed by the Congress in
19763, the U.S. EPA tried to establish a national framework for monitoring the generation, transportation, and disposal of solid wastes. One of the major steps taken by EPA to achieve this goal was
establishment of a set of criteria in order to evaluate a waste to decide if it is hazardous and should be
managed as such. One such criterion is the Extraction Potential (EP) Toxicity Test,1,4 published by
EPA on May 2, 1980, designed to identify wastes that have the potential of leaching of selected
chemical species, believed to be hazardous, above designated levels of concentration. In essence, this
test is a laboratory scale, short time simulation of what happens in reality over a long period of time to
a solid waste when it is land impounded. Relevant sections of this test will be referred to in a later
section. Table I outlines the chemical species and their maximum permitted levels in the EP Tox Test
extract for a waste being identified as nonhazardous. These numbers are basically 100 times the
corresponding numbers for the drinking water standards.
It was recognized by the early '80s that there existed many more hazardous substances, especially
organics, not included in list of Table I, that can emerge with leachates from land impoundments.
Accordingly, in 1984 EPA amended RCRA, establishing what is known as Hazardous and Solid
Waste Amendment (HSWA), which prohibited the land disposal of toxic wastes. All these measures
resulted in the development of a second generation test called the Toxicity Characteristic Leaching
Potential (TCLP) procedure on November 7, 1986. TCLP encompasses a long list of organic chemicals along with respective permitted levels, as detailed in the Federal Register5.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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