58    CHARACTERIZATION AND TREATMENT OF SPENT
HYDROSTATIC TEST WATER IN THE NATURAL GAS
INDUSTRY
Forrest R. Sprester, County Public Health Engineer
City of El Paso
El Paso, Texas 79936
Fernando Cadena, Associate Professor
Civil Engineering Department
New Mexico State University
Las Cruces, New Mexico 88003
Donald J. Fingleton, Project Manager
Energy and Environmental Systems Division
Argonne National Laboratory
Argonne, Illinois 60439
INTRODUCTION
Meyer [1] estimates that over one million miles of collection and distribution pipelines are presently
in use by the natural gas industry in the United States. These lines are used to transport natural gas
from the production fields to the consumer. The Institute of Gas Technology [2] reports that gas
pipelines are periodically tested for physical integrity using any one of the following procedures:
acoustic, hydrostatic, isotopic, radiographic, and ultrasonic techniques.
Hydrostatic testing of natural gas pipelines is one of the most popular means for leak detection
since it offers the additional advantage of removing obstructions in the pipeline. The main intent of
such testing is to identify weaknesses in the pipeline by hydrostatically pressurizing a segment of
pipeline. Minimum test pressures have been established by industry associations and the U. S. Department of Transportation for various operating pressures. Water used in hydrostatic tests is often
disposed without treatment into temporary infiltration (percolation) pits or into any nearby ditch or
body of water. Land disposal of these wastes is usually followed by site recovery using a soil layer to
cover the remaining sludge. Natural gas pipelines have been recently recognized as sources of contamination to groundwater [3]. Some preliminary guidelines to minimize the environmental impact of
wastes generated by the natural gas industry during hydrostatic testing of transmission pipelines are
presented in this document.
HYDROSTATIC TEST DESCRIPTION
Description of hydrostatic test procedures for natural gas pipelines have been reported in the
literature beginning in the late 1950's and early 1960's by Brooks [4,5], Heineman [6], and Gray [7]. A
more recent review of operational procedures is presented by the Institute of Gas Technology [2].
During a hydrostatic test, a pipeline is divided into a test section, or sections, ranging in lengths of
up to 15 miles. The length of these sections depends upon the position of existing valves, availability
of water, and differences in elevation along the pipeline. In order to minimize the amount of air in the
pipeline, water is injected into the line behind a foam or rubber "pig" in the shape of a ball or bullet, as
shown in Figure I. Following the filling of the line, the pressure in the line is increased to the pre-
established test pressure using a positive displacement pump. Once test pressure is successfully
reached, the pressure is maintained for a minimum of eight hours before discharging the water from
the pipeline. In order to squeegee out as much water as possible, the Institute of Gas Technology [2]
recommends discharge velocities greater than 3 to 5 miles per hour. Alcohol is oftentimes run between
two pigs after test completion [2). This additive removes any remaining water from the line and
prevents valve "freeze-ups" and hydrate formation.
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