Geology Reference
In-Depth Information
EXERCISE
15
Groundwater and Surface
Water Contamination
from Resource Extraction
than 25 mg/L. Sea water is less salty than the brines,
with a chlorinity of 19,000 mg/L, which makes up 55
percent of the total salt content of sea water.
Once the oil wells and pits are closed, the chemical
quality of the groundwater tends to improve, usually
very slowly, as the concentrated solutions migrate to
areas of discharge such as springs, streams, or wells. The
natural flushing of the groundwater system depends on
the hydraulic conductivity of the rocks, the hydraulic
gradient, the effective porosity, and the amount and rate
of infiltration of rain and snowmelt. It may require
decades for the groundwater system to return to its nat-
ural chemical state. The rate of flushing and the amount
of time that the groundwater reservoir remains contami-
nated are of profound interest in legal cases.
The brines sterilize the soil, kill vegetation, and
create an undesirable taste in drinking water. The con-
centration at which a brine becomes harmful to vege-
tation depends on the type of plant, the depth of the
root system, the season, and the depth of the water
table, to mention only a few factors. Dead trees and
other vegetation, however, commonly mark areas
where brine-contaminated groundwater discharges
into streams or where it flows from springs. The
USEPA recommends that drinking water contain no
more than 250 mg/L of chloride, since higher concen-
trations cause a salty taste. Higher concentrations are
not likely to cause illness in humans because the water
is too salty for consumption.
Most of the problems developed prior to 1980;
however, research on the fate of contaminant plumes
continues to the present.
INTRODUCTION
G
ROUNDWATER AND SURFACE WATER MAY BE CONTAMI-
NATED BY ACCIDENT OR BY IMPROPER STORAGE OR DISPOSAL
OF WASTES AT THE SURFACE.
I
MPROPER STORAGE OR DIS-
POSAL HAS OCCURRED IN MANY AREAS DUE TO OUR IGNO-
RANCE ABOUT GROUNDWATER FLOW AND POTENTIAL HEALTH
EFFECTS, THE LACK OF CONCERN FOR WATER SUPPLIES, AND A
SHORT-TERM VIEW OF THE BEHAVIOR OF GROUNDWATER AND
OUR FUTURE NEEDS FOR WATER.
I
N THIS EXERCISE WE LOOK AT CASES IN WHICH PITS
AND HOLDING PONDS WERE USED TO DISPOSE OF OR STORE
LIQUID WASTES.
I
N THE PAST IT WAS EXPEDIENT TO CREATE
WASTE PONDS, WHERE THE WASTES DECREASED IN VOLUME
THROUGH EVAPORATION OR INFILTRATION.
I
N THIS EXERCISE WE
EXPLORE THE CAUSE AND EXTENT OF CONTAMINATION FROM
OIL FIELD BRINES AND RUNOFF FROM A LEAD MINE.
PART A. GROUND WATER CONTAMINATION
FROM OIL FIELD BRINES IN CENTRAL OHIO
In many oil-producing areas, severe problems of
groundwater contamination were common. These
were caused primarily by the infiltration of saltwater
into the ground. Saltwater, or brine, is produced with
the oil and, since the brine often is a by-product of lit-
tle or no economic value, when unregulated it was
commonly disposed of in the most economical manner
possible. In most areas this is done by reinjection into
the oil-producing zone by means of a well. In others it
is accomplished by pumping the brine into holding
ponds or pits, where a small percentage evaporates
but most of it infiltrates. Infiltration can lead to severe
groundwater pollution since the chloride concentra-
tions of the brines may exceed 35,000 mg/L. In con-
trast many areas have groundwater with background
or naturally occurring chloride concentrations of less
Groundwater Contamination
near Delaware, Ohio
In this part of the exercise we study the extent, move-
ment, and changes in concentration of oil field brines
that contaminated a site on the nearly flat floodplain of
the Olentangy River in Ohio. Three oil wells were
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