United States
                    Environmental Protection
                    Agency
 Environmental Monitoring
 Systems Laboratory
 Las Vegas NV 89193
                     Research and Development
EPA/600/S6-87/005 Aug. 1987
AEPA          Project Summary
                    Processes Affecting Subsurface
                    Transport  of  Leaking Underground
                    Tank  Fluids
                    Scott W. Tyler, Michael R. Whitbeck, Marsha W. Kirk, John W. Hess,
                    Lome G. Everett, David K. Kreamer, Barbara H. Wilson, and Jeff van Ee
                      This document  presents the funda-
                    mental theories and an understanding
                    of the processes controlling migration
                    and fate in the subsurface of material
                    released from an underground storage
                    tank.
                      Processes affecting the migration of
                    fluids from a leaking underground stor-
                    age tank and their effects on monitoring
                    methods are reviewed by experts. An
                    understanding of these processes is
                    critical to an understanding of  the
                    methods  that monitor underground
                    storage tanks for material released from
                    the tank in the environment surrounding
                    the tank.
                      Soil heterogeneities and the potential
                    for multiphase flow will lead to high
                    monitoring uncertainties if leak detec-
                    tion systems rely on liquid sampling
                    alone. Vapor transport is also  affected
                    by these properties, although to a lesser
                    degree. More research is needed, how-
                    ever, to better understand the physics
                    of vapor transport.  The processes of
                    adsorption, partitioning, and microbial
                    alteration of fluids in the subsurface
                    may have strong effects on the uncer-
                    tainty of monitoring systems. Fate pro-
                    cesses have received less attention than
                    liquid  and vapor  transport processes
                    and will  require significantly more re-
                    search  before the  effects are fully
                    understood.
                      This Project Summary wag developed
                    by EPA's Environmental Monitoring
                    Systems Laboratory, Las Vegas, NV, to
                    announce key findings ol the research
                    project that  la fully  documented In a
                    separate report ol the same title (tee
                    Project Report ordering Information at
                    back).
Introduction
  Estimates of the number of under-
ground storage tanks in the United States
range from 3 to 5 million. Estimates of
the number of leaking tanks vary,  but
increasingly more incidents of  leaking
tanks  are being reported. These tanks
may contaminate soil and ground water
to the extent that the environment and
human health is adversely impacted.
  The Solid Waste Disposal Act was
amended by the Hazardous and Solid
Waste Amendments of 1984 (HSWA;
Public Law 98-616) to provide  for  the
development and implementation of a
comprehensive regulatory program  for
underground storage tanks (USTs). Tanks
containing hazardous waste are subject
to regulation under  Subtitle C of  the
Resource Conservation Recovery Act of
1976.  Tanks containing petroleum and
hazardous  substances are  subject  to
regulation under  Subtitle  I of the Haz-
ardous and Solid Waste Amendments;
regulations for these will be proposed in
1987  and will become final in 1988.
Regulations  for tanks  containing haz-
ardous waste were promulgated by  the
EPA (40 CFR Part 264) on July 14, 1986.
  Many approaches exist in the preven-
tion, detection, and cleanup of leaked
product from USTs. One approach is to
monitor the environment outside the tank
to determine if product is entering  the
environment from the  tank, piping,  or
surface spills. The Environmental Moni-
toring  Systems Laboratory in Las Vegas
(EMSL-Las Vegas) is conducting research
to evaluate the feasibility of monitoring
outside the tank for leaks from the tank.
  The environment outside a tank is sub-
ject to a number of factors that may

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affect and complicate  detecting a  leak
from  a  tank  system (Figure 1).  These
factors  affect the transport  and fate  of
product from the tank to the external leak
detection system. Studies of these factors,
particularly factors affecting  organic and
petroleum products, have been initiated
in recent  years in response to an in-
creasing number of reported cases where
the environment or humans have been
exposed to material released from USTs.
In addition, recent state and Federal laws
and regulations on ground-water con-
tamination have served to increase the
need of researchers to understand the
processes affecting the subsurface trans-
port and fate of leaking underground tank
fluids.

Approach
   The demand for technical guidance that
has been created by new regulations has
created a need to develop and disseminate
information quickly. Initial steps taken by
EMSL-Las Vegas to evaluate external leak
detection systems have included surveys
of the literature. Federal, state and local
agencies,  industry, and  academia. The
results from these surveys will be made
available  in  a  variety of  reports  and
technical notes. The first effort to develop
information  on the processes  affecting
the subsurface  transport of product from
leaking USTs consisted of several experts
being asked  to summarize  the existing
knowledge on:  liquid flow, vapor flow,
soil surface  and  interfacial effects  of
product in the environment around a
tank, and the implications of subsurface
biological activity  in the monitoring of
 USTs. Four experts in these areas covered
their respective fields, and a team of
hydrogeologists from the Desert Research
Institute coordinated the experts in  their
examination  of the problems posed  by
external  leak  detection  monitoring  of
USTs.
   Each expert was asked to refer to the
 available  literature and to describe in
 layman's terms  the  present  state  of
 knowledge in the subject area. Each ex-
 pert  was also  asked to  address those
 areas where the  understanding of the
 processing affecting subsurface transport
 of leaking undergound tank fluids was
 weak and where  further research was
 required. The conclusions reached by each
 expert were consolidated and summarized
 in the trial section of the full  report where
 the advantages and complications of a
 number of monitoring approaches were
 listed against  four  fate and  transport
 processes. The monitoring  approaches
 were: active and passive liquid monitoring,
                                      2
      Top Soil *

   Vadose Zone -+
Capillary Fringe *
   Water Table
                                                           Sampling Points

                                                                \
                                                              Pea Gravel
                                                                          - Aquifer

                                                                          *- Clay
                                                                          - Drinking
                                                                            Water
                                                                            Aquifer


                                                                          Spill
Figure  1.
              The hydrogeologic  environment  around underground storage  tanks  can be
              complicated even under idealized circumstances.
  Tab/* 1.    Parameters Affecting the Transport and Fate of Organics in the Soil and
            Ground Water
              Soil
                                     Contaminant
                                                             Environmental
  Multiphase permeability
  Residual saturation
  Pore size distribution
  Fracture density
  Wettability
  Soil texture
  Porosity
  Variability of soil properties
  Porosity
  Water content
  Soil structure & variability
  Permeability to air
  Moisture content
  Organic content
  Clay content
  Soil surface area
  Pore water chemistry
  Soil gas diffusion
  Colonization potential
  Oxygen concentration
  Methane concentration
  Contaminant velocity
                             Fluid Transport Parameters

                           Density
                           Viscosity
                           Solubility
                           Surface tension
                             Vapor Transport Parameters

                           Volatility
                           Vapor diffusivity
                           Distribution coefficients
Temperature
Precipitation
Depth to water table
Biological activity
Recharge
Temperature
Barometric changes
Water table fluctuations
                           Surface Chemistry Parameters

                           Solubility                    Temperature
                           Concentration                Pressure
                             Microbiological Parameters

                           Nutrient loading
                           Toxicity
                           Solubility
                           pH
Temperature
Recharge & groundwater
transport

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  active and passive vapor monitoring, and
  surface and borehole geophysics.

  Conclusions
    The monitoring of leaks from outside
  the tank is complicated by a number of
  factors (Table 1), and no one monitoring
  approach will be applicable for all ap-
  plications.  The  assessment  of  those
  factors in evaluating the'performance of
  external leak detection monitoring sys-
  tems  is not easy. Uncertainty in flow
  directions because of variations in con-
  ductivity, water content, texture, etc. is a
  major problem  in obtaining predictable
  performance from an external leak detec-
  tion sensing system. Since an increase in
  the distance from the leak to the sensor
  also increases  the number of hetero-
  geneities encountered and, hence, in-
  creases the uncertainty in flow direction,
  it is important to locate the sensor close
  to the leak source. Tank installations may
  be  engineered  to reduce  further the
  heterogeneity near the  tank, and  this
  would make the sensor location  less
  sensitive.
    Active  samplers,  i.e., samplers  that
  pump the environment, appear to be less
  affected  by  transient spills;  however,
  further research  is needed to develop
  sensor criteria.
    The  present  state  of  knowledge is
  limited in the transport and fate processes
  affecting leaked organic products from
  USTs.  Further  research  is needed to
  understand those processes.
                    Scoff W. Tyler,  Michael R. Whitbeck, Marsha W. Kirk, and John W. Hess are
                      with the Desert Research Institute, Reno, NV 89506; Lome G. Everett is
                      with Kaman  Tempo, Santa Barbara, CA 93102; David K.  Krearner is with
                      Arizona State University,  Tempe, AZ 85287; Barbara H. Wilson is with the
                      University of Oklahoma, Ada, OK 74820; and the EPA author Jeff van Ee
                      (also the EPA  Project Officer, see below) is with the Environmental Monitoring
                      Systems Laboratory, Las Vegas, NV 89193-3478.
                    The complete report entitled "Processes Affecting Subsurface  Transport of
                      Leaking Underground Tank Fluids," (Order No. PB 87-201  521/AS; Cost:
                       $13.95, subject to change) will be available only from:

                            National Technical Information Service
                            5285 Port Royal Road
                            Springfield, VA 22161
                            Telephone: 703-487-4650

                    The EPA Project Officer can be contacted at'
                            Environmental Monitoring Systems Laboratory
                            U.S. Environmental Protection Agency
                            P.O. Box  93478
                            Las Vegas, NV 89193-3478
United States
Environmental Protection
Agency
           Center for Environmental Research
           Information
           Cincinnati OH 45268
Official Business
Penalty for Private Use $300

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