Page 231 - Environmental Control in Petroleum Engineering

Remediation of Contaminated Sites 217

before remediation begins. A site assessment is the first step in
determining what remediation method is to be used, if any.
Site assessments are normally conducted in stages (American Petrol-
eum Institute, 1989). The first stage is to gather all relevant back-
ground information about the site. This includes reviewing available
records and reports and may include interviewing site personnel. From
this information, the magnitude and composition of the release is
estimated. The next stage is to characterize the site. The purpose of
site characterization is to determine the exact locations, contaminant
concentrations, and extent of the contaminated zone and to evaluate
the potential for the contaminants to migrate from the site. Depending
on the magnitude of the release and its potential for adverse environ-
mental impact, a risk assessment study may be needed. A risk assess-
ment study would quantify the potential environmental impact of the
various remediation processes being considered, and the results could
be used when negotiating the specific details of a site remediation
project with applicable regulatory agencies.
An important part of site assessment is to develop a detailed
sampling and sample analysis plan that clearly identifies the objectives
of the analysis and how those objectives are to be met. This plan must
also address quality assurance and control to ensure that the data
obtained accurately reflect the actual concentrations being measured
(Keith et al., 1983). This plan determines the number of samples to
be obtained and their locations. Normally, a network of sampling
points is selected around the site. Geological and hydrological factors
must be considered in selecting each point, including any local ground-
water flow, the hydraulic conductivity (permeability) of the soil,
geological heterogeneities that can affect fluid flow, and geochemical
processes, such as ion exchange, that can cause contamination to
migrate at a rate different from the physical flow of groundwater.
Additional sampling sites may be added if a statistical analysis of the
initial samples indicates that the confidence limits are unacceptably
low (Wojtanowicz et al., 1989).
Two types of samples are generally obtained: core samples and fluid
samples. Core samples provide information about liquids trapped with
the solids by capillary pressure, while fluid samples provide informa-
tion about mobile liquids. The type of samples required depends on
the type of contaminant and may be specified by applicable regulatory
agencies. Other types of measurements, such as electromagnetic