United States
Environmental Protection
Agency
Office of
Research and Development
Washington DC 20460
EPA/600/R-92/057
April 1992
vvEPA
Technical Aspects of
Underground Storage
Tank Closure
-------
EPA/600/R-92/057
April 1992
TECHNICAL ASPECTS
OF
UNDERGROUND STORAGE TANK CLOSURE
by
Camp Dresser & McKee, Inc.
Cambridge, Massachusetts 02192-1401
Contract No. 68-03-3409
Project Officer
Anthony N. Tafuri
Superfund Technology Demonstration Division
Risk Reduction Engineering Laboratory
Edison, New Jersey 08837
U.S. Environmental Protection Agency
Region 5, U;;rr,^ (P1 ''
77 V/rciJccks:/
Cliicc&o, IL 6050, c.
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
Printed on Recycled Paper
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DISCLAIMER
The information in this document has been funded, wholly or in part, by the U.S. Environmental
Protection Agency under Contract 68-03-3409 to COM Federal Programs Corp. It has been subjected to
the Agency's peer and administrative review, and it has been approved for publication as an EPA document.
Mention of trade names or commercial products does not constitute endorsement or recommendation for
use.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and practices frequently
carry with them the increased generation of materials that, if improperly dealt with, can threaten both public
health and the environment. The U.S. Environmental Protection Agency (EPA) is charged by Congress with
protecting the Nation's land, air, and water resources. Under a mandate of national environmental laws, the
Agency strives to formulate and implement actions leading to a compatible balance between human
activities and the ability of natural resources to support and nurture life. These laws direct the EPA to
perform research to define our environmental problems, measure the impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning, implementing and managing
research, development, and demonstration programs to provide an authoritative, defensible engineering
basis in support of the policies, programs and regulations of the EPA with respect to drinking water,
wastewater, pesticides, toxic substances, solid and hazardous wastes, and Superfund-related activities. This
publication is one of the products of that research and provides a vital communication link between the
researcher and the user community.
The impacts of underground storage tank (UST) closures on public health and the environment is an
area of major concern. This document provides information on the quantities and characteristics of residuals
found in USTs at closure, the methods used to remove the residuals, and the procedures for cleaning the
tanks. The information generated will aid the regulators and assist those overseeing or implementing closure
activities.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
iii
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ABSTRACT
The overall objective of this study was to develop a deeper understanding of UST residuals at closure:
their quantities, origins, physical/chemical properties, ease of removal by various cleaning methods, and
their environmental mobility and persistence. The investigation covered underground storage tanks
containing: gasoline, diesel oil, and fuel oil. It obtained information in two phases.
Phase I elicited data via telephone contacts with knowledgeable individuals including tank cleaning
companies, from literature cited by these experts, on-site visits and from questionnaires completed by
state representatives.
Phase II monitored selected tank cleaning cases and made quantitative measurements of the amounts
of residuals left in USTs before and after cleaning, characterizing the nature of the residuals and any
rinses generated during the cleaning process. To support the objectives of the study, the following
information was collected for each UST site included in the study: estimates of volumes of tank
residuals and secondary wastes, hazardous characteristics and chemical composition of the residuals
and secondary wastes, detailed descriptions of the cleaning methods used, and background
information on the UST/site that relates to the nature of the residuals.
This report documents the study findings in order to aid regulators and to assist those
implementing/overseeing closure activities. This report covers a period from August 1988 to May 1990, and
work was completed as of May 1990.
IV
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CONTENTS
Page
Foreword iii
Abstract iv
Figures vi
Tables vii
Abbreviations and Symbols viii
Acknowledgments = ix
1. Introduction 1
Phase I: Preliminary Investigation of UST Residuals and UST
Cleaning/Closure Methods 1
Phase II: Field Sampling and Analysis of Residuals at UST
Closure Sites 2
2. Conclusions/Recommendations 3
3. UST Residuals 6
Quantity 6
Origin and Composition of Residuals 10
4. Cleaning and Closure 18
Cleaning Procedures 18
Field Studies of UST Closures 25
Closure 40
5. References 45
Appendices
A. Case by Case Quantities of UST Residuals Estimated by
Phone Survey Respondents 46
B. Summary Steps Recommended by API for Removal of Used
Underground Petroleum Storage Tanks 47
C. Summary of Cleaning Procedures Documented in Phone Survey 48
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FIGURES
Number Page
1 Schematic of UST Tank for Estimate of Residuals Volume 8
2 Quantity of Residuals Found in USTs by One Minnesota
Company 9
3 Schematic of UST Residuals 11
4 Schematic of Standard UST Cleaning Procedure (API
Recommended Practice 1604) 21
5 Potential Treatment Scheme for Secondary Wastes 24
6 Schematic Diagram of Potential Participants in Tank
Closure Operations 41
VI
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TABLES
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Residual Volumes Calculated for Tank Sizes and Liquid Depths
Quantity of Residuals Found in USTs by One Minnesota Company
Benzene, Toluene, Ethylbenzene, Xylene, and Total Hydrocarbons
in UST Bottom Residuals
Calculated Amounts of Internal Corrosion Found in Steel Tanks of Different Sizes . .
Potential Unit Treatment Processes for Secondary Wastes
Specifications of Underground Storage Tanks (USTs) Sampled
Laboratory Parameters and Analytical Methods Used
RCRA Metals and Their Detection Limits
List of Chemicals Targeted for in VOC Analysis
Residual Volume Estimates in USTs Before and After Cleaning
Summary of Typical Analytical Results for Fuel Product in
USTs Before Cleaning
Summary of Analytical Results for Bottom Residuals in USTs
During Cleaning
Summary of TCLP Analyses on UST Bottom Residuals
TCLP Regulatory Levels and Exceedances
Summary of Analytical Results for Aqueous Rinse Samples
Examples of Costs for UST Cleaning and Removal
Cost Estimates for UST Removal and Closure Components
Cost Estimates for UST Removal and Closure Components
Page
7
10
13
16
25
27
29
30
31
33
34
36
37
38
39
42
43
44
vii
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ABBREVIATIONS AND SYMBOLS
ABN Acid/base neutrals
API American Petroleum Institute
BETX Benzene, ethyl benzene, toluene, xylene (combined analysis)
BOD Biochemical oxygen demand
CI' Chloride ion
DOT Department of Transportation
EPA U.S. Environmental Protection Agency
F Fahrenheit
Fe+2 Ferrous ion
FeS Iron sulfide precipitate
Fe2O3 Iron oxide
FRP Fiberglass-reinforced plastic tanks
g Gram
gal Gallon/s
HCO3' Bicarbonate
in Inch/es
kg Kilogram
L Liter
Ib Pound/s (weight)
MDL Minimum Detection Limit
mg Milligram
MTBE Methyl tertiary-butyl ether
Na+ Sodium ion
OUST Office of Underground Storage Tanks
Pb+2 Lead ion
ppm Parts per million
RCRA Resource Conservation and Recovery Act
TCLP Toxicity Characteristic Leaching Procedure
TPH Total petroleum hydrocarbons
TSDs Transportation/storage/disposal facilities (for hazardous waste)
VOC Volatile organic compounds
UST Underground storage tank
viii
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ACKNOWLEDGMENTS
This report originated in conversations with Mr. Ronald Brand and Mr. Thomas Schruben of the Office
of Underground Storage Tanks (OUST), U.S. Environmental Protection Agency, Washington, D.C. The
authors would like to thank them for their contributions of time and information.
The authors would like to express their appreciation to Dr. Warren J. Lyman, Ms. Andrea E. Sewall,
and Ms. Katharine L Sellers of Camp Dresser & McKee, Inc. (Cambridge, MA) for their diligent efforts in
conducting the work presented in this report and in preparing initial versions of this document under EPA
Contract No. 68-03-3409.
The contributions of Jet-Line Services, Inc. (Stoughton, MA), a company that offers a range of
environmental services in the Boston area, including UST cleaning and removal, is acknowledged. Their
participation in the Phase I study as well as in the field studies associated with the Phase II activities is
appreciated.
Finally, the following word processing and editorial contributions should be acknowledged: Katharine
Sellers (Camp Dresser & McKee, Inc.), Michelle DeFort, Marilyn Avery, and Francine Everson (Foster
Wheeler Enviresponse, Inc.), and Debra K. Sager (The Pipkins Group).
IX
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SECTION 1
INTRODUCTION
The overall objective of this study of the Technical Aspects of Underground Storage Tank Closure was
to develop a deeper understanding of underground storage tank (UST) residuals at closure: their quantities,
origins, physical/chemical properties, ease of removal by various cleaning methods, and their hazardous
characteristics. This report documents the study findings in order to aid regulators and to assist those
implementing/overseeing closure activities. The investigation covered underground storage tanks containing
gasoline, diesel oil, and fuel oil. The work progressed in two phases:
PHASE I: Preliminary Investigation of UST Residuals and UST Cleaning/Closure Methods
To obtain preliminary information on UST residuals researchers conducted telephone interviews,
reviewed selected literature, observed actual tank cleaning/removal operations, surveyed state UST program
managers and performed engineering calculations on residual volumes and costs of cleaning/closure.
Telephone Contacts
Telephone contacts were made with groups known to have first-hand knowledge of UST residuals in
16 states plus the District of Columbia. Those contacted included state and local agencies (14); tank
cleaning companies (20); tank removal/disposal companies (10); tank lining companies (5); analytical
service labs (3); petroleum refiners, wholesalers, distributors (8); industry associates (5); environmental
consulting firms (8); and others (2). While those called were almost universally cooperative, they could
contribute little quantitative information on residual volumes and composition. The interviews revealed that
cleaning practices seldom followed formalized procedures. Consequently, most of the information obtained
was qualitative, anecdotal or speculative in nature. Since this limited survey may have overlooked major
regional differences in UST closure practices, a questionnaire targeted a larger group of State
representatives at a National UST Seminar. (See Survey of State Representatives below.)
Literature Review
Based on expert opinion that literature of interest is limited and generally unavailable, no formal search
was undertaken. Instead, telephone surveys of experts elicited citations of published and unpublished data.
(See References.)
Site Visits
Site visits provided an opportunity to observe tank cleaning and removal operations by two companies
at three different sites. Observations continued during a visit to a tank disposal contractor. The cleaning
operations involved pumping out liquids and tank entry for manual removal of residual sludge and scale.
Two sites provided grab samples of the residual sludge for visual inspection.
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Survey of State Representatives
To supplement data from the telephone survey, a supplementary focused survey was conducted during
the November 1988 "Workshop for State Tank Program Managers," in Santa Fe, New Mexico, sponsored
by the U.S. Environmental Protection Agency's Office of Underground Storage Tanks (OUST). A
questionnaire was distributed to elicit information on the following aspects of tank closure:
the number of FY90 tank closings by jurisdiction;
the increase in tank closures from FY89;
the categories and frequency of tank closures by jurisdiction;
authorized procedures and materials for in situ closure (including fill);
the types, frequency, and effectiveness of tank cleaning methods used by jurisdiction;
jurisdictional regulations on tank residues and cleaning by-products;
status of government-sanctioned tank disposal monitoring programs;
tank disposal practices; and
government-sanctioned certification programs for tank removal/closure contractors.
Responses to the questionnaire contributed to this report and are further documented in a separate
report [3]. The data collected cannot be deemed entirely accurate because some respondents indicated
that they had limited data or firsthand knowledge of the underground storage tank programs in their
respective jurisdiction. They had only a limited amount of time to complete the questionnaire during the
session; therefore they could not do any research to complete their responses. While the limited number
of responses can allow a substantial margin for error, the data provided by the carefully targeted
respondents do illuminate some common, jurisdictional, closure practices and indicate which practices are
prevalent.
Engineering Calculations
Engineering calculations, detailed in Section 2, provided the following estimates:
the volume of residuals likely to be found in USTs;
the amount of water and rust or scale that might be expected in an UST; and
the costs of UST cleaning and closure.
PHASE II: Field Sampling and Analysis of Residuals at UST Closure Sites
Under an agreement with an UST cleaning/removal contractor and with the permission of UST owners,
the Phase II study monitored selected tank cleaning cases and made quantitative measurements of the
amounts of residuals left in USTs before and after cleaning. It characterized the nature of the residuals and
any rinses generated during the cleaning process using sampling and analysis under a proper QA/QC plan.
This field study focused on tanks containing gasoline and No. 2 fuel oil. Time and climatic constraints
limited the field program to three tanks for each product.
To support the objectives of the study, the following information was collected for each UST site
included in the study:
estimates of volumes of tank residuals and secondary wastes;
hazardous characteristics and chemical composition of the residuals and secondary wastes;
detailed descriptions of the cleaning methods used; and
background information on the UST/site that relates to the nature of the residuals.
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SECTION 2
CONCLUSIONS/RECOMMENDATIONS
GENERAL COMMENTS
Gasoline and diesel USTs are found to have significant quantities of residuals in them at closure,
typically tens to a few hundreds of gallons. However, although there is little explicit guidance available, tank
cleaning and removal companies are apparently capable of removing most of these residuals with fairly
simple cleaning techniques. The Phase II field observations, and sampling and analysis program, generally
confirmed the Phase I findings on the effectiveness of relatively simple cleaning operations.
Quantity of Residuals Found at Closure
Gasoline and diesel USTs can usually be emptied by the owner/operator to within 4"-6" of the tank
bottom, and it is this distance which is probably the primary factor regulating residual quantity before
cleaning. For a 10,000-gallon tank, this translates into about 100-200 gallons. Both the Phase I preliminary
investigation and the Phase II field observations (limited to 6 tanks) indicated the median volume of residuals
found in gasoline and diesel USTs before cleaning was slightly below 100 gallons. Some USTs, however,
are found to contain several thousand gallons, consisting mostly either of abandoned fuel and/or water
which has leaked into the UST.
Composition of Residuals
Based on the findings of both Phase I and Phase II, it is estimated that 70-100% of gasoline and diesel
residuals consists of the product itself, probably of somewhat diminished purity. The remaining 0-30%
consists mostly of water (with numerous dissolved constituents); product related residuals (e.g., gum,
sediment, tars); rust and scale (in steel tanks); dirt and other foreign objects; and a small, but
disproportionately-important mass of microorganisms. The importance of the microorganisms comes from
the significant internal corrosion that can be due to the action of sulfate-reducing bacteria.
The Phase II field studies indicated residuals from gasoline tanks would typically be classed a)
hazardous waste because of their ignitability characteristic (flash point below 140°F) and Toxicity
Characteristic Leaching Procedure (TCLP) values for lead and benzene. In addition, USTs containing
gasoline residuals typically will contain vapors in concentrations above the lower explosive limit and above
levels that would impair human health after even short term exposures. Removal of these vapors is
absolutely essential to eliminate any risk from fires, explosions, and the inhalation of toxic vapors. By
contrast, No. 2 fuel oil residuals were not found to be hazardous based on ignitability (flash points were all
above 180°F) or TCLP criteria.
Sludges from both gasoline and No. 2 fuel oil USTs were found to contain significant concentrations
of lead, barium, chromium, cadmium, and arsenic. As expected, both fuel residuals also contained
significant concentrations of benzene, toluene, ethylbenzene and xylene (BTEX). The BTEX fraction
comprised 10-15 percent of the gasoline residuals and 0.1-0.4 percent of the No. 2 fuel oil residuals.
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Aqueous rinse solutions generated from tank cleaning operations were found to contain levels of total
petroleum hydrocarbons (up to 480 ppm) and BTEX (up to 70 ppm) that would likely bar their direct
discharge to sanitary sewers.
While most all of the residuals will reside on the bottom of the tank, the presence of some side-wall
scale and gum is anticipated. The bottom residuals, while containing some gum and grit, are mostly
pumpable liquids and would not properly be considered sludges.
The origins of the various components of the residuals are fairly discernible and this knowledge can
be used to help control the quantity and quality of residuals in future times. The growth of microorganisms,
for example, can be controlled by the use of biocides and/or the elimination of water; this would reduce the
microbiological mass as well as the amount of internal corrosion and rust generation.
Cleaning Procedures
A variety of tank cleaning and removal procedures appear to be in use, although many are variations
of a simple, logical theme. Many of the steps in these procedures are dictated by safety considerations*
and state and local regulations rather than a direct concern for strict tank cleanliness. In one way or
another, most procedures involve an initial pumping of residuals with a suction line and a subsequent rinse
with water with rinse solution removal. The water rinse may involve: (1) filling the tank with water; (2)
rinsing with spray from 'garden' hose [low pressure]; (3) rinsing with high pressure water; (4) steam hosing;
and (5) possible use of a detergent. The American Petroleum Institute's recommended procedures [1] (API
1604) call for filling the tank with water followed by sequential removal of floating product and water.
For USTs with especially viscous residuals, a light fuel oil (e.g., No. 2) is sometimes sprayed into the
tank to assist in cleaning. The suctioned fluid may be filtered and recycled for additional cleaning.
Several tank cleaning companies, after the initial removal of liquid residuals, cut a manhole into the
UST allowing a man to enter and physically remove bottom grit and (with a "squeegee") liquids adhering to
the side walls. Some companies consider this procedure too dangerous, especially for gasoline tanks; the
practice is prohibited in some areas.
With some companies, it is common to put both initially-pumped residuals and aqueous rinse solution
into the same tank truck (for off-site treatment and disposal). Other companies segregate the residuals from
the rinse solution thus facilitating subsequent treatment. Excluding the API 1604 procedure, which calls for
filling the tank with water, the volume of rinse solution generated appears to range from a low of 25 gallons
per tank to about one third of the tank's volume.
The Phase I survey did not uncover any data which provide objective evidence of the degree of
6leanliness achieved by the procedures used. The field observations and measurements carried out in
Phase II (cleaning/closure at three gasoline USTs and three No. 2 fuel oil USTs) did show that a relatively
simple cleaning procedure did a good job of cleaning the tanks. Typically, there was a gallon or less of
residuals (mostly aqueous rinse solution) left in the UST after cleaning.
'Prevention of human exposure to toxic chemicals, fires and explosions and spillage.
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For tanks that are subsequently reused as scrap metal (i.e., crushed or cut up and then remelted), a
modest amount of retained residuals may be environmentally acceptable. Worker protection may be the
more stringent basis for regulation. For tanks that are filled in place or landfilled, the retained residuals are
likely to pose only a small-to-negligible risk of adverse environmental impact. This would be related to the
small volume of retained residuals, limited environmental mobility for most constituents, and limited
lexicological significance for the bulk of the constituents.
Treatment of Secondary Wastes
Little information was obtained on actual methods currently being used to treat and dispose the
secondary wastes generated. It is noted, however, that the treatment and disposal of oil/water wastes is
a common operation and that numerous treatment processes (demonstrated and commercially available)
may be used. Phase separation followed by incineration of the organic phase and a two-step (e.g.,
physicochemical then biological) treatment of the aqueous phase is appropriate.
RECOMMENDATIONS
Guidance on Cleaning Techniques
There is, at present, no guidance available that is directly pertinent to the cleaning of USTs.*
Furthermore, portions of some guidance that is available (e.g., API's Publication 1604) may be providing
inadequate or inappropriate guidance on certain key steps in the cleaning process, specifically the water
wash step and the need (or lack thereof) for a human to enter the tank for removal of sludge and scale.
A short guidance document in the form of a brochure (e.g., 5-10 pages) should be prepared for distribution
to interested parties. If the issues of safety, tank removal and disposal, and treatment and disposal of
secondary wastes were included, the guidance document would be significantly longer.
Treatment and Disposal of Secondary Wastes
This is a problem for a much smaller group of companies who are in the business of hazardous waste
transport, treatment and disposal. There are numerous demonstrated methods available for the proper
treatment of oil/water wastes. Additional research in this area is not necessary. It is probably necessary,
however, to alert tank cleaning companies to the need to pretreat aqueous rinse solutions (for removal of
petroleum hydrocarbons) prior to discharge to a sanitary sewer.
* API's Publication 2015 (reference 2) appears more suited to large, above-ground petroleum storage tanks;
and their Publication 1604 (reference 1) focuses more on the removal and disposal of UST rather than the
cleaning.
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SECTION 3
UST RESIDUALS
Underground tanks storing gasoline and diesel oil have been found to contain significant quantities
of residuals at closure, typically tens to hundreds of gallons. The tanks can usually be emptied by the
owner/operator to within 4-6 in of the tank bottom. This dimension, which determines residual quantity in
an "empty" tank before cleaning, translates into about 100-200 gal for a 10,000-gal tank. Both the Phase
I and Phase II findings indicated that the median volume of residuals found in gasoline and diesel oil USTs
before cleaning was slightly below 100 gal. Some USTs, however, are found to contain several thousand
gallons, consisting of abandoned product and/or water which has leaked into them.
QUANTITY
Field personnel often describe the volume of a tank's contents in terms of inches of residuals on the
bottom of the tank. Table 1 provides a conversion from inches of residuals on the bottom to volume of
residuals for varying sizes of tanks. Figure 1 shows the relationship between the two and the equation used
to calculate the volumes.
By design, the submersible pump systems used to supply product drop down no farther than 4 in
above the tank bottom in steel tanks. This provides 4 in of dead tank space, used to trap sediments and
water in the tank to ensure that they will not be pumped out to the customer. For fiberglass-reinforced
plastic (FRP) tanks, the tube usually ends 6 in above the tank bottom to allow for any settling and
deformation of the FRP tank. These design features leave at least 4 in to 6 in of residuals after a tank has
been "pumped dry" by the tank owner. Based on Table 1, this converts to residuals from 95 to 264 gal for
a 10,000-gal tank - a mid-sized UST.
Gasoline
The volume of residuals found in gasoline tanks at any one site can vary significantly. The majority
of the reporting participants estimated residual quantities up to 1,000 gal. The mean of the values reported
was 160 gal; the median, 75 gal.
Diesel Oil
Most respondents agreed that diesel oil tanks contained more residuals than gasoline tanks, with a
range of up to 200 gal and a mean value of 58 gal. The median estimate was approximately 75 gal.
Fuel Oil
The majority of the respondents agreed that fuel oil tanks produced a greater amount of residuals than
gasoline and oil tanks. The two respondents that provided numbers for this product reported 500 and 1,000
gal, averaging to 750 gal -- significantly higher than gasoline and diesel oil.
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TABLE 1. RESIDUAL VOLUMES CALCULATED FOR TANK SIZES
AND LIQUID DEPTHS
Tank dimensions
Diameter (ft)
Length (ft)
Depth of residuals
remaining in tank
(in)
1
2
3
4
5
6
7
8
9
10
Tank volume (gal)
550
4
6
915
4
10
3
8
15
22
31
41
51
62
73
85
5
13
24
37
52
68
85
103
122
142
5,000
8
13.3
10,000
8
27
10,000
10.5
15.5
20,000
10.5
31
Volume of residuals
(gai)
9
25
46
71
99
130
163
199
237
276
18
52
94
145
202
264
332
404
481
561
12
34
62
95
133
175
219
267
318
372
24
68
124
191
266
349
439
535
637
744
Rinses
The volume of spent rinse solutions generated during the cleaning procedures can vary widely with
the type of cleaning procedure used. Estimates ranged from 100 to 3,300 gal, with an average of 1,200 gal.
These volumes are significantly higher -- in fact an order of magnitude higher -- than the residuals
themselves. API's Recommended Practice 1604 [1] calls for the tank to be filled nearly to the top for
cleaning and/or vapor removal purposes. This practice would generate much greater volumes of spent
rinse residuals than actual product.
A summary of case-by-case estimates obtained during the telephone survey regarding the volume of
residuals and rinse solutions for an average-sized tank is included in Appendix A.
UST Profile
In connection with an UST sediment characterization project for the State of Minnesota, Delta
Environmental Consultants, Inc. examined the files of a tank cleaning and removal company that kept
detailed records on the depth and volume of residuals in each UST it removed [4]. Figure 2 shows the
range of residual volumes the company recorded for gasoline, fuel oil, and waste tanks from 9/1/87 to
8/30/88. Table 2 provides a statistical summary.
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CROSS-SECTIONAL
VIEW
SIDE
VIEW
ED
,Draw pipe
/ Draw pipe
T
D = Tank diameter
L = Tank Length
d = depth of residuals
V= Volume of residuals in UST
Vent
pipe
D
V= O.f
2 arccos
sin
2arccos
Figure 1. Schematic of UST tank for estimate of residuals volume.
-------
Z5
>
tO
LU
O
LU
O
a
LU
O
a=
LU
CD
70-/
60 -
0 20 40 60 80 100 140 180 250 400 600 800 >1000
200 300 1,000
0 20 40 60 80 100 140 180 250 400 600 800 >1000
200 300 1,000
30
20
10
WASTE OIL
|!
0 20 40 60 80 100 140 180 250 400 600 800 >1000
200 300 1,000
(NOTE CHANGES IN SCALE AT 100. 200, 300 AND 1000 93!)
Source: Delta Environmental Consultants (1988)
Figure 2. Quantity of residuals found in USTs by one
Minnesota Company [4]
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TABLE 2. QUANTITY OF RESIDUALS FOUND IN USTs BY
ONE MINNESOTA COMPANY [4]
UST
Number of tanks
Average tank capacity (gal)
Average residuals volume (gal)
Median residual volume (gal)
Gasoline
214
5,800
49
20
Fuel Oil
221
5,900
81
40
Waste Oil
151
3,600
162a
50
a Excluding one tank with 9,375 gal of residuals.
ORIGIN AND COMPOSITION OF RESIDUALS
The basic components of tank residuals, as depicted in Figure 3, usually include the following
components:
residual product;
water;
product-related residuals;
tank rust and scale;
soil, dirt and other foreign objects; and
microorganisms.
Residual product probably constitutes 70-90% of total residuals in an aged tank. The other
components make up the remaining 10-30%, with microorganisms represented in large numbers but a very
small percent of the total weight.
Most residual products and water comprise liquids of relatively low viscosity that can be easily pumped
out of the tank. The remaining materials apparently constitute a relatively small volume of side-wall gum and
scale, and bottom sediment and grit. They possess varying physical properties, ranging from those of
viscous organic sludges to solid inorganic particulates (e.g., the properties of rust flakes and sand). The
ease with which this second group of materials can be removed by standard pumping or cleaning
techniques varies according to the site-specific contents. Generalization is inappropriate.
Residual Product
This component, thought to comprise 70-90% of total residuals, would represent approximately 100
gal in a 10,000-gal tank. The purity of the product must be determined in each case. Resale of gasoline,
for example, might require filtration, dewatering, or further treatment.
In addition to any product that may lie beneath the pump line, additional product residuals can result
from the following reasons:
An owner or operator may have abandoned the tank before pumping it "dry."
A low-level automatic cut-off pump switch might make the tank seem "empty."
10
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UNDERGROUND STORAGE TANK "EMPTIED"
IN PREPARATION FOR CLOSURE
SIDE SCALE,
SCUM
RESIDUAL FUEL
(APPROX. 4 TO 6 INCHES)
SEDIMENT, GRIT, GUM (DIRT, RUST
PARTICLES, OR FUEL SEDIMENT)
THICKNESS OF SLUDGE MAY BE
ENHANCED AT 5- AND 7-O'CLOCK
POSITIONS IN VICINITY OF FILL TUBE.
WATER LAYER
(PROBABLY <; 1 INCH)
Figure 3. Schematic of LIST residuals.
11
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If the tank being removed was abandoned for a long time (months to years), significant changes in
the nature or composition of the residuals might take place due to volatilization, water infiltration, rust
formation or biological action.
Some tank cleaners do not attempt a separate recovery of this residual product to facilitate reuse.
Rather they pump it into the same tank truck used to collect rinses and/or residuals from other product
tanks. They then send the mixed fuel to a treatment facility which separates the product from the water
phase for disposal or incineration.
Product-Related Residuals
Survey respondents discussed the presence of some product-related residuals (e.g., gums, sediment),
but estimated their total amounts to be relatively small. Some interviewees said such materials could be
observed on the insides of tanks as discoloration or thin, sticky film.
Gums and Tars-
Gums and tars (high molecular weight organics left by heavy fuels) are constituents of petroleum
distillates. A small spill of gasoline on an impervious surface (e.g., a car's fender) will, for example, leave
a sticky, viscous film after a few minutes of evaporation. It seems probable that they would build up on the
insides of tanks in the area between the high and low level marks. These wall areas would be alternately
exposed to fuel when the product level was high and then gradually to vapors as the product level fell.
Efforts to obtain quantitative data on the concentration of gums or tars in gasoline and diesel oil from
refiners and wholesalers were abandoned when major companies could not provide such data.
Polymers-
Polymers formed in situ from reactive components of the fuel (e.g., unsaturated hydrocarbons) can
sink to the bottom of the tank. In the study mentioned earlier, Delta Environmental reported analyses of
selected hydrocarbons and total hydrocarbons in composite residuals found at one collection center [4].
Table 3 displays these data.
Sediment-
Sediment present in product upon delivery to an UST would gradually sink to the bottom of the tank.
Refiners and wholesalers were unable to give any data about quantities of sediment in their product. Some
respondents explained that visual clarity was considered a satisfactory check for excess sediment and water,
thus eliminating the'need for quantitative measurements.
Sorbed Components-
Certain fuel components can attach to tank walls or other solid residuals through sorption.
Water
Significant amounts of water lie at the bottom of many, if not most, USTs. The sources of such water
include:
accumulated water present in product upon delivery;
condensation in the tank from infiltrating moisture-laden air;
surface runoff entering fill pipe; and
groundwater leaking into tank or fill pipe.
12
-------
TABLE 3. BENZENE, TOLUENE, ETHYLBENZENE, XYLENE, AND
TOTAL HYDROCARBONS IN UST BOTTOM RESIDUALS8
Sample
number
MDLe
1
2
2d
3
4
4d
5
6
7
r>
8
Parent
material
of sample"
Gasoline
Mixed oil
Mixed oil
Mixed oil
Mixed sludge
Mixed sludge
Mixed sludge
#6 Fuel oil
#2 Fuel oil
#2 Fuel oil
Dried residual
Concentration (mg/kg)
Benzene
0.12
110
5.1
4.9
39
1.9
1.5
190
1.0
3.8
4.0
7.1
Toluene
0.12
270
11
10
100
12
8.4
310
2.4
11
10
160
Ethylbenzene
0.12
30
1.8
1.8
13
6.2
4.4
44
1.0
1.9
1.7
41
Xylene
0.12
140
8.8
8.9
67
19
13
210
6.0
9.4
8.3
210
Total
hydrocarbons
1.0
1700
120
110
800
270
180
2400
86
109
110
1800
a Data from Reference 4.
b Sample descriptions:
1. Sludge at bottom of gasoline storage tank
2. Drying mixed oil residuals in two different tanks
3. Drying mixed oil residuals in two different tanks
4. From mixed sludge drums
5. From mixed sludge drums
6. From drum of #6 fuel oil residuals
7. From drum of #2 fuel oil residuals
8. Composite of dried residual from a number of open tanks
0 MDL Method Detection Limit
d Duplicate analysis
There are many mechanisms by which water can enter an UST. First, small amounts of water are
ubiquitous in nearly all stages of petroleum processing, transport, and storage. It is pumped out of the
ground with crude oil, used as ballast in oil tankers, used as a marker (via inclusion of a slug of water) in
pipeline transport, and trapped in the large storage tanks at so-called "tank farms" of major refiners and
distributors. When approached, such sources did not offer any quantifiable information about the amount
of water conveyed to a retail outlet.
Water can accumulate in a tank dissolved in the product delivered to the site. This water is likely to
be near the solubility limit and, in summer at least, to be warmer than ground temperatures. As the fuel
enters the UST and cools down, the solubility limit falls, causing some water to come out of solution and
13
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form, or add to, a separate aqueous phase. This phase separation process can be especially troublesome
for aviation fuels which, after being put in aircraft fuel tanks, are subjected to very low temperatures at high
altitudes.
The contribution of this phase separation process is estimated to be one gallon of water per tank refill
for gasoline USTs. This is based on the following assumptions:
dissolved water is present at the solubility limit in gasoline (taken as 1 g/L);
the UST is filled with 40,000 L of gasoline;
the solubility limit is reduced by 10% as gasoline cools in the UST, causing 0.1 g/L to separate;
total phase separation = 0.1 g/L x 40,000 L = 4 kg = 4 L (approx. 1 gal).
Water is also suspected to enter USTs via the following means: entry of moist air through the fill tube
when open; runoff of surface water into an open fill tube; and infiltration of runoff or groundwater into the
tank via pipe joints, cracks or corrosion pit holes.
Water residuals in USTs may play a significant role in the internal corrosion of steel tanks. Several
surveys have shown that such corrosion is fairly common, although external corrosion is roughly three times
more important. The presence of water enhances corrosion. Water existing as condensate on tank walls
or as a layer on the bottom can cause internal corrosion.
Water present in an UST can exist partly as a separate phase and partly in solution with the fuel.
Water present as a separate phase may remain in colloidal suspension throughout the volume of fuel or -
if given time to settle - lie as a separate layer below the fuel.* The solubility limits for water in gasoline and
in diesel oil are not known precisely but are judged on the order of 1,000 mg/L and 100 mg/L, respectively.
Significantly larger amounts may be present in solution with fuels containing hydrophilic additives such as
ethanol or methyl tertiary-butyl ether (MTBE).
It is a common practice for owners of USTs in service to check for the presence of water (and
sediment) with a dip stick prior to refilling the tank. The end of the dip stick is coated with a special paste
that changes color upon contact with water.
The "rule of thumb" used by some gas stations prescribes limiting the depth of water to 1 in. They
pump out any excess over this limit prior to refilling the tank. As shown in Table 1,1 in of liquid in a 10,000-
gal tank represents about 12-18 gal. In places where water input rates are high or in tanks where water is
not periodically monitored/removed, the volume of water could clearly be much higher.
Water found in USTs prior to cleaning generally would contain a significant amount of dissolved
hydrocarbons (-100-300 mg/L), dissolved salts (e.g., Na+, CI", Fe+2, HCO3", Pb+2) and other soluble
components or additives in the fuels (e.g., ethanol, MTBE, detergents).
Pure water has a density of about 1.0 g/ml and seawater about 1.028 g/ml. Automotive gasoline and No. 2 fuel oil are lighter,
with respective densities of 0.71-0.75 g/ml and 0.87-0.90 g/ml.
14
-------
Tank Rust or Scale
The survey and information cited by respondents indicated that steel tanks are likely, over time, to
shed rust particles (iron oxide, Fe203), and iron scale. This internal corrosion may be caused by galvanic
action* or bacterial action. (See Microorganisms below.)
Concentrated internal corrosion often occurs directly under the fill tube where the gauge stick strikes
the bottom of the LIST. The use of a strike plate, thicker steel under the fill tube, or limitation of "sticking"
measurement can easily prevent tank failure due to corrosion in this location.
As noted above, surveys of UST removals have clearly demonstrated the importance of internal
corrosion to UST failures. In one review of 1,900 failures, for example, 29% had holes due to internal
corrosion, 90% due to external corrosion [5]. Other surveys have indicated that internal corrosion
constituted only 5% of corrosion incidents in tanks [6]. A study in Suffolk County, NY, indicated that a 20-
year-old steel tank had about a 3% probability of failing due to internal corrosion [7].
Some rust and scale may remain on tank walls, while portions will drop and accumulate on the bottom.
The total volume of side and bottom scale is thought to be relatively small, perhaps no more than one liter.
Table 4 presents one set of speculative estimates on the amount of rust generated in old steel tanks.
It assumes that 0.1 % of the mass of the steel tank is converted from Fe to Fes03. The 0.1% value is arbitrary
but perhaps not unreasonable, given that corrosion usually occurs in concentrated spots (pits), and that any
larger average loss would probably imply leakage through corrosion holes. These calculations forecast
about 10 Ib of rust generation in a 10,000 gal tank.
Soil. Dirt and Other Foreign Objects
The Phase I survey and field trips provided evidence of the following foreign objects in USTs: soil, dirt,
rubber hoses, soft drink cans, and similar trash. Although this material probably entered via the fill tube,
some may have been discarded in the tank prior to its initial use. There is also potential for the entry of
foreign objects at other times (e.g., repairs).
Microorganisms"
Like water, microorganisms appear to be fairly ubiquitous in petroleum storage and distribution
systems. They can reside in the tank before it is used, and enter from the outer environment via an open
fill tube or cracks. While they may appear to be present in large numbers (102 to 103 organisms/L), their
combined mass is small. At times, however, large floes can form, clogging fuel lines and filters.
Microorganisms need water to thrive and, in storage tanks, are usually found at the fuel-water interface.
The mix of hydrocarbons, water, oxygen (low for anaerobes), nutrients, and a compatible pH all contribute
to their growth. They apparently thrive better in fuel oil than in gasoline.
* Galvanic action occurs when dissimilar metal surfaces at different places in the tank are linked electrically by water.
"Much information in this subsection is drawn from Reference 8.
15
-------
TABLE 4. CALCULATED AMOUNTS OF INTERNAL CORROSION
FOUND IN STEEL TANKS OF DIFFERENT SIZES3
Capacity
(gai)
300
550
1,000
2,000
4,000
6,000
8,000
10,000
12,000
20,000
30,000
Diameter
(in)
38
48
48
64
64
72
96
96
96
126
126
Length
(in)
60
72
128
144
288
341
256
324
384
372
558
Wall
thickness
(in)
.1046
.1793
.1793
.1793
.1793
.25
.25
.25
.25
.3125
.375
Calculated
weight
(Ib)
280
736
1,165
1,800
3,270
6,050
6,500
7,950
9,240
15,300
24,200
Weight of
corrosion
product if
0.1% loss"
(Ib)
0.40
1.05
1.66
2.57
4.67
8.64
9.29
11.36
13.20
21.86
34.57
a Calculations are rough estimates of what might be found inside a steel tank after many years of service, assumption of 0.1 % weight
loss due to internal corrosion.
b Corrosion products assumed to be in form of iron oxide (Fe203).
The microorganisms in USTs include several varieties of bacteria and fungi. One especially important
class (sulfate-reducing bacteria) can cause significant iron and steel corrosion. They perform anaerobic
respiration by oxidizing certain organic compounds or H2, and reducing sulfate -- and often other reduced
sulfur compounds -- to hydrogen sulfide. The sulfide can then react with iron to form an iron sulfide (FeS)
precipitate that may expand the solid portion of UST residuals. During the course of hydrocarbon
metabolism, other microorganisms can produce organic acids, such as acetic acid, which can also
contribute to corrosion.
Corrosion is usually evidenced as pits below microbial mats. There are numerous unproven theories
about the biochemical and chemical basis for this corrosion. No data were available on the rates of
microbial corrosion to be expected in USTs.
16
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Tank/Site Factors Affecting Residual Quantity and Composition
It is possible to identify a number of tank and site factors that control the nature, quantity, and
composition of UST residuals. Some of these factors include tank design, use, cleaning procedures, repair
practices, age, total volume throughput, site factors, hydrogeology, meteorology, product type, and product
composition. For example, the distance from the bottom of the suction line (or submersible pump intake)
to the tank bottom is a key aspect of tank design. It defines the minimum volume the owner/operator can
leave at closure. The location of pipes and pumps, materials of construction, corrosion protection, and tank
tilt all will affect residuals throughout the tank's useful life and at closure.
Age and volume throughput are related to the accumulation of rust, sediment, and gum, etc. However,
a large volume throughput might tend to flush out some residuals, since they are stirred up (and dispersed
throughout the product) every time the tank is filled. The hydrogeological and chemical profiles of the site
will affect residual composition, as will the rainfall, humidity, and temperature in the area. Finally, the
product itself, its additives, the residuals present at delivery, and the suitability of the material for microbial
growth will increase or lessen the accumulation of non-product residuals.
These factors also suggest ways to reduce the volume -- and/or control the composition -- of UST
residuals. For example:
lowering the suction tube deeper into the tank increases the maximum pumpable by the
owner/operator, and therefore lowers the volume of remaining product;
frequent testing for water, with removal as necessary, can prevent the buildup of a water layer;
corrosion prevention measures (e.g., cathodic protection, protective coatings, and use of biocides
in the product) will reduce amounts of rust and scale generated; and
use of biocides and/or elimination of tank water will control growth of microorganisms.
The origins of the various components of the residuals are fairly discernible. This knowledge and
information on relevant site/tank factors can help to control the future quantity and quality of residuals. For
example, the use of biocides and elimination of water can control the growth of microorganisms. This would
lessen corrosion and rust generation in addition to reducing residual mass. New tank design could reduce
infiltration of foreign objects found in bottom residuals.
17
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SECTION 4
CLEANING AND CLOSURE
CLEANING PROCEDURES
A variety of tank cleaning and removal procedures appear to be in use; many are variations on a
simple, logical theme. Many steps are dictated by safety considerations and state and local regulations
rather than concern for tank cleanliness. The guiding set of objectives in emptying/cleaning USTs should
entail minimization of the following:
environmental/health hazards presented by the tank and its residuals;
explosion hazard of removing the LIST;
volume of secondary waste generated; and
cost of UST closure.
Tanks in Use
Although USTs are emptied or cleaned for decommissioning and removal or for closure in place, tanks
still in use are cleaned for reasons such as the following:
to adhere to a regular maintenance program;
to clean up contents of a tank that has become contaminated; or
to ready a tank for storage of a different product.
General Procedures
Rinses-
In one way or another, most procedures begin by pumping residuals with a suction line, then rinsing
the tank with water, and finally removing the used rinse solution. The American Petroleum Institute's
recommended procedures (API 1604) [1] call for filling the tank with water followed by sequential removal
of floating product and water.
The "rinse cycle" may involve the following steps or a combination of some of them:
filling the tank with water;
rinsing the tank with spray from a low-pressure hose;
rinsing the tank with high pressure water;
steam hosing;
addition of a detergent.
18
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For USTs with especially viscous residuals, a light fuel oil (e.g., No. 2), sprayed into the tank, may
assist in the cleaning. This fluid, when suctioned out of the tank, may then be filtered and recycled for
additional cleaning cycles.
Manholes-
Several tank cleaning companies, after the initial pumping of liquid residuals, cut a manhole into the
UST so that a workman can enter, and then manually remove bottom grit and, with a "squeegee," wipe
liquids adhering to the side walls.
Cutting manholes in tanks is a dangerous procedure. Several contractors stated that they do not cut
open tanks because of the explosive potential, and at least one regulatory agency (Sacramento County, CA)
requires that no tank be cut open on-site because of the risk of explosion. This risk is significant, particularly
for tanks which have not been properly purged. However, benefits gained from the increased cleaning
efficiencies and closer inspection of the tank may sometimes outweigh the hazards.
Disposal of Residuals-
Some companies put both initially-pumped residuals and used aqueous rinses in the same tank truck
for off-site treatment and disposal. Other companies segregate the residuals from the rinses, thus facilitating
subsequent treatment.
Disposal of Tanks-
For tanks that will be crushed/cut and remelted, a modest amount of retained residuals may be
environmentally acceptable. Worker protection may be the more stringent basis for regulation. For tanks
that are filled in place or landfilled, the retained residuals are likely to pose only a small-to-negligible risk of
adverse environmental impact due to the small volume of retained residuals, limited environmental mobility
for most constituents, and limited lexicological significance for the bulk of the constituents.
Most often, disposal facilities use a hydraulic press to crush the tank. Steel tanks are then sold as
scrap iron, while FRP tanks (after shredding) are landfilled. Occasionally, steel tanks are cut into pieces
using saws or torches, before being sold as scrap iron, although this method seems to present more
hazards than the press.
American Petroleum Institute Recommendations
The basis of most UST cleaning methods identified through the survey is API's Publication 1604,
"Removal and Disposal of Used Underground Petroleum Storage Tanks" [1] and API's Publication 2015
"Cleaning Petroleum Storage Tanks" [2]. Publication 1604 does not address cleaning methods explicitly,
but it does describe the removal process. A summary of the steps recommended in API's Recommended
Practice 1604 is illustrated in Figure 4 and presented in Appendix B.
Publication 2015 describes a recommended cleaning process in the format given below:
1. Completing preliminary preparations
externally inspecting the tank
surveying the immediate area
training/indoctrinating the crew
inspecting equipment
2. Determining that the dike area is free of flammable or toxic materials before personnel are
permitted to enter the tank
19
-------
3. Controlling sources of ignition in, around, and on the tank
4. Emptying the tank by pumping out residual liquid and floating it with water
[This is probably the most commonly used procedure, but other methods may be
employed.]
5. Blinding off the tank and de-energizing electrical circuits after as much of the contents as
possible have been removed
6. Vapor-freeing the tank [Mechanical, steam, and natural ventilation are alternatives.]
7. Testing the tank for oxygen, hydrocarbon vapors, and toxic gases.
8. Opening the tank for entry
removing sludge
sending sludge for appropriate disposal
The UST is then transported to a licensed UST disposal facility for ultimate disposal.
Additional Practices Reported
The Phase I survey of tank cleaning and tank removal contractors provided a variety of cleaning
procedures in addition to that described above. Appendix C lists the various cleaning procedures identified
through the survey. Some interesting variations suggest the following:
Cleaning residuals from the tank while it is still in the ground by spraying rinse through fill or vent
pipes and then pumping the rinse out. This was presented as an alternative to the use of a
manhole.
Using a degreaser or detergent as the rinse agent (e.g., Citrikleen or Slix).
Circulating filtered fuel from the UST back to the tank, possibly for several cycles, rather than
introducing additional volumes of wash water.
Rinsing with a caustic (high pH) detergent solution that acts as an emulsifier (e.g., Mark Clean 55).
The selection of such variations may depend on factors such as the type of residuals, the future use
or disposal of the tank, the tank's size and design, and the availability of water.
Secondary Wastes
Secondary waste streams from UST cleaning operations consist of the tank residuals and rinses.
Spent rinses are generated when water, steam, detergent, or some other agent is used to clean the tank.
The rinse volumes may vary depending on the nature and volume of residuals found in the USTs. As noted
above, survey respondents reported rinse volumes ranging from 100 gal/tank to one third of the tank
volume.
20
-------
VENT
1. Prepare workers and area for operators 2. Drain product piping into tank 3. Remove liquids and residues from tank
DRY ICE
4.& 5. Excavate to top of tank and remove
piping, pumps, and other fixtures
6. Purge tank of flammable vapors
Figure 4. Schematic of standard UST cleaning procedure (API Recommended Practice 1604,
Refer to Appendix B for description of steps).
-------
7. Fill tank with water
N>
ro
DRY ICE
8. Pump out water
9. Test tank atmosphere for vapors
10.& 11. Plug all holes, excavate, and remove tank
Figure 4 (Continued). Schematic of standard UST cleaning procedure (API Recommended
Practice 1604, Refer to Appendix B for description of steps).
-------
Treatment-
Little information was found on methods used to treat and dispose of the secondary wastes generated.
However, the treatment and disposal of oil/water wastes is successfully accomplished by numerous
demonstrated and commercially available processes, such as phase separation followed by incineration of
the organic phase and a two-step (e.g., physical/chemical and biological) treatment of the aqueous phase.
Quantity and Composition-
Secondary wastes from UST cleaning operations fall into three groups:
"Pure" residuals removed from the UST (and stored separately) before cleaning begins [70-90%
product, e.g., gasoline or diesel oil];
Spent rinse solution ~ usually a simple water wash sprayed into the UST, with detergents sometimes
added; and
Combined wastes - produced when some cleaning companies pump the raw residuals and rinse/s
into the same tank truck at the UST site.
No reliable data were received on the composition of the secondary wastes. A "combined waste," for
example, might be a mixture of fuel, water, detergent, side scale, gum, and bottom sediment. Depending
on the cleaning method, some of these components might not be transferred from the UST to the secondary
wastes. All waste groups are likely to have emulsion characteristics, i.e., small droplets of one phase
dispersed throughout the other phase. The use of detergents would increase the degree of emulsification.
Available Treatment Techniques-
Very little information has been obtained on actual treatment of UST secondary wastes. However, an
initial separation of hydrocarbon liquids from aqueous phases (in a large settling tank) is a potential solution.
The aqueous phase, after varying degrees of pretreatment, may be acceptable to a sanitary sewer leading
to a municipal biological treatment plant. The hydrocarbon phase could be treated as a waste oil (i.e.,
shipped to an oil re-refiner), incinerated, or drummed and sent for proper disposal.
Based upon industry's long experience with oil/water wastes, there are numerous treatment techniques
available for secondary waste streams from UST cleaning. Some of the more important treatment categories
and schemes are listed in Figure 5, while Table 5 lists potential treatments for each residual phase. Nearly
all of these unit operations have been demonstrated in full scale operations and many can be purchased
in standard sizes and designs from vendors of pollution control equipment. There is, at present, limited
capacity for the incineration of hazardous wastes in the United States (approximately 300,000,000 gal. per
year [10]); the total volume of UST residuals that might be removed in the next five years, perhaps
10,000,000 gal, would not significantly stress this capacity.
Effectiveness of Cleaning Procedures
The Phase I survey revealed no contractor contacted knew just how clean a tank their procedure/s
could achieve. Most contractors believe that if they follow the company's standard cleaning procedures,
then the tank will be "clean." Visual inspections of "clean" are also common. When UST closure procedures
preclude the use of a manhole in the UST, visual inspection of "clean" is quite difficult. At present, no
standard measure of the cleaning effectiveness seems to have been set. Phase II attempted to resolve this
question by actually visiting tank cleaning/removal operations and characterizing the residuals before and
after cleaning.
23
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PHETREATMENT
TREATMENT FINAL TREATMEhJT OR DISPOSAL
SECONDAHY
WASTES
LIQUID-ORGANICS
FIITRATON
LIQUID AQUEOUS
SOLID/SLUDGE
DISTILLATION
INCINERATION
BIOLOGICAL
PHYSICAL
CHEMICAL
REUSEASFUEL
SEWER. POTW
LANDFILL
REUSE FOR WASH
M LAND TREATMENT
SURFACE WATER
LANDFILL
LANDFILL
Figure 5. Potential treatment scheme for secondary wastes.
-------
FIELD STUDIES OF UST CLOSURES
As previously indicated, the Phase I assessment of closure activities found that the tank cleaning
methods currently in use appear to be able to satisfactorily clean most gasoline and light oil tanks. This
assessment was made on the basis of interviews and limited observations; no data indicated just how clean
the tanks actually were. Furthermore, the survey found that there was no generally accepted method of tank
cleaning, nor were there any generally accepted criteria for assessing tank cleanliness. Accordingly, Phase
II was formulated to collect information at actual UST closure sites to determine:
Background information on USTs/sites that relates to the nature of the residuals;
Detailed descriptions of cleaning methods used;
Estimates of volumes of tank residuals and secondary wastes;
Hazardous characteristics and chemical composition of the residuals and secondary wastes;
Costs of cleaning and closure.
TABLE 5. POTENTIAL UNIT TREATMENT PROCESSES
FOR SECONDARY WASTES
Phase separators
Physical
Chemical
Gravity oil/water (e.g., API separator)
Dissolved air flotation
Induced air flotation
Fabric filtration
Ultrafiltration
pH adjustment
Emulsion breakers
Solvent extraction
Aqueous phase treatment
Physical
Chemical
Biological
Adsorption on carbon (or other sorbent)
Filtration (fabric or granular media)
Air stripping
Flocculation
Coagulation
Oxidation
Activated sludge
Trickling filtration
Lagoons
Organic phase treatment/use
Incineration
Reuse as fuel
Use of asphalt manufacture
Sludge/solids phase treatment
Incineration (ash to landfill)
Landfill
Solidification/encapsulation (product to landfill)
25
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Field case studies were conducted in concert with a company that offers a range of environmental
services, including UST cleaning and removal. The company agreed to compile a list of representative UST
closure jobs that would meet the objectives of the field study. If the UST and proposed cleaning technique
at a particular job were of interest to the study, the study group requested permission from the site
owner/operator to monitor the job and perform sampling during the normal course of the closure.
Monitoring and sampling activities followed the requirements of a Quality Assurance Program Plan (QAPP).
Cleaning techniques were not modified for the study; however, normal variations in procedures were made
in response to site-specific conditions, including the nature and amount of residuals found within the tank.
The field study focused on tanks containing gasoline and No. 2 fuel oil. Time and climatic constraints
limited the field program to three tanks for each product. Where available, the following background
information was recorded for each of the six USTs:
Product content
Dimensions
Capacity
Material of construction
Details about installation
Age
Condition upon removal
Depth in ground
Water table depth
Much of the background information associated with the six tanks is similar, especially the material
of construction, condition, and product. Table 6 presents a summary of this data.
UST Removal and Cleaning Procedures Observed
Observers noted the following common steps in cleaning procedures:
1. Residual product (No. 2 fuel oil or gasoline) vacuumed from UST to tank truck.
2. For gasoline tanks, dry ice added to displace oxygen with carbon dioxide.
3. Overlying soil excavated (some tanks pulled from excavation pit at this point).
4. Manhole cut into top or side of tank to allow worker entry.
5. Tank interior scraped (manually) to remove residual sludge. (Saw dust added in one case to
absorb residual sludge.)
6. Tank interior rinsed with tap water and rinsed water vacuumed into tank truck. After rinse,
UST pulled from excavation pit.
7. Tank exterior scraped clean before transport to tank yard.
Details of the actual procedures used at each tank were recorded. Visual estimates of the cleaning
effectiveness were also recorded.
26
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TABLES. SPECIFICATIONS OF UNDERGROUND STORAGE TANKS (USTs) SAMPLED
She
No.
1
2
3
4
5
6
Size
(gai)
±4,000
1,000
10,000
±1,000
±500
±2,000
Fuel
type
No. 2
No. 2
No. 2
Gasoline
Gasoline
Gasoline
Material
type
Steel
Steel
Steel
Steel
Steel
Steel
Condition
Very good, No rust
Fairly rusted
Good, some rust
at ends
Rusty, but intact
Rusty, but intact
Very good, no rust
Age
(yrs)
15
15
20
11 +
20+
11 +
Depth to
groundwater
(«)
Unknown
Unknown
Unknown
±20
4
4
Depth to
tank (ft)
20
4
±3
±4
±2
±3-4
Product
volume in
tank (gal)
4,400
800
94
±90
±2
±55
-------
Sampling and Analysis Procedures Employed in Characterizing Residuals
Residual Volume-
Estimates of the volumes of residuals in the UST before and after cleaning (and of secondary waste
generated) were calculated using dip sticks, simple volume levels observed, pumping rates and durations,
or visual proportions. (Inch measurements in cylindrical tanks can be converted to fluid volumes by
standard trigonometric functions as described in Section 2.) Where possible, volume estimates were
obtained for the following:
Liquid organic phase: before and after cleaning
Aqueous phase: before and after cleaning
Rinse solutions: amount used for cleaning
Samples Collected-
In general, three (3) types of samples were collected from each UST for laboratory analysis:
Original fuel product (if present)
Bottom residuals
Aqueous rinse
Sampling Points and Tools-
Original fuel product remaining in the UST was sampled prior to removal using a clear, plexiglass
bailer. Once the fuel product was removed via pumping, bottom residuals were sampled with plastic
buckets. Once these sludge-like materials were completely removed, rinse water was added to the UST and
a workman entered the tank to scrub the inside walls. The rinse water containing the residuals from the
walls was pumped out of the tank and sampled. For this study, a final rinse was performed on each of the
six "cleaned" USTs to evaluate cleaning effectiveness. This "final rinse," with tap or bottled water, was not
part of the regular cleaning procedure. In addition, measurements of vapor concentrations inside the UST
were made at various stages in the cleaning/closure procedure.
Laboratory Parameters and Analytical Methods-
The residual product, bottom residuals, and used rinses were analyzed for a series of chemical
parameters. Table 7 outlines these parameters and the respective analytical methods used. Table 8 lists
the specific RCRA metals and the reported detection limits for which the tests were run. Table 9 shows the
specific VOCs targeted in the analyses. Generally, detection limits for VOC water blanks were in the range
of 0.005-0.010 ppm. However, when 100- or 200-fold dilution of fuel samples (or TCLP extracts) was
required, VOC detection limits ranged from 500-1000 ppm.
28
-------
TABLE 7. LABORATORY PARAMETERS AND ANALYTICAL METHODS USED
Parameters
Total Petroleum Hydrocarbons
Oil and Grease
Flash Point
5-day Biochemical Oxygen Demand
Total Organic Carbon
PH
Metals
Volatile Organic Compounds
TCLP Extraction:
Metals
Volatile Organic Compounds
Semivolatile Organic Compounds
Fuel
Product
X
X
X
X
Sludge
X
X
X
X
X
X
X
Aqueous
Rinse
X
X
X
X
X
X
X
EPA
Method No.
[11,12,13]
418.1
413.2
1010
405.1
415.1
150.1
6010
700
7471
624
8240
Method Description
Freon extraction/I R
Extraction/I R
Pensky-Martins Closed Cup
Combustion
Electrometric
ICP
AA
CV
Purge and trap
GC/MS
ZHE
-------
TABLE 8. RCRA METALS AND THEIR DETECTION LIMITS
Metal
Arsenic
Barium
Cadmium
Chromium
Lead
Mercury
Selenium
Silver
Detection Limit (ppm)
Aqueous and
TCLP Blanks
0.02
0.02
0.10
0.25
0.25
0.0005
0.02
0.10
Fuel Blanks
Base oil<"
(Site 1)
0.50
2.0
1.25
3.125
6.25
0.5
0.1
0.3
Kerosene'2'
(Sites 2-6)
0.1
0.25
0.5
1.0
1.0
0.05
0.10
1.0
Sludge Blanks
Soil
(Site 1)
0.02
2.0
0.1
0.25
0.5
0.5
0.01
0.03
Solid
(Sites 2-6)
0.4
2.0
1.0
2.5
2.5
0.2
0.4
1.0
(1> Base oil is the oil used to dissolve the metals.
(2> Kerosene is the petroleum base used to dissolve the metals for analytical purposes.
-------
TABLE 9. LIST OF CHEMICALS TARGETED FOR IN VOC ANALYSIS
CAS Number
74-87-3
74-83-9
75-01-4
75-00-3
75-09-2
75-69-4
67-66-3
107-06-2
71-55-6
56-23-5
79-01-6
124-48-1
79-00-5
71-43-2
10061-01-5
110-75-8
75-35-4
75-35-3
156-60-5
75-27-4
79-34-5
78-87-5
10061-02-6
75-25-2
127-18-4
108-88-3
108-90-7
100-41-4
1330-20-7
95-50-1
541-73-1
106-46-7
Compound
Chloromethane
Bromomethane
Vinyl chloride
Chloroethane
Methylene chloride
Trichlorofluoromethane
Chloroform
1,2-Dichloroethane
1,1,1 -Trichloroethane
Carbon tetrachloride
Trichloroethene
Dibromochloromethane
1 ,1 ,2-Trichloroethane
Benzene
cis-1 ,3-Dichloropropene
2-Chloroethyl vinyl ether
1,1-Dichloroethene
1,1 -Di chloroethane
trans-1 ,2-Dichloroethene
Bromodichloromethane
1 ,1 ,2,2-Tetrachloroethane
1 ,2-Dichloropropane
trans-1 ,3-Dichloropropene
Bromoform
Tetrachloroethene
Toluene
Chlorobenzene
Ethyl benzene
Total xylenes
1,2-Dichlorobenzene
1 ,3-Dichlorobenzene
1 ,4-Dichlorobenzene
Hazardous Characteristics and Chemical Composition-
Various UST residuals were sampled and analyzed for both hazardous characteristics (e.g., ignitability
and corrosivity) and chemical composition. The analyses specifically included the following:
Characteristics
Ignitability
Corrosivity
Toxicity Characteristic
Leaching Procedure
(TCLP)
Composition
Volatile Organic Analysis (VOA)
Total Petroleum Hydrocarbons (TPH)
Oil and Grease
Biochemical Oxygen Demand (BOD)
Total Organic Carbon (TOG)
pH
RCRA Metals (As, Ba, Cd, Cr, Pb, Hg, Ag, and Se)
31
-------
Modifications to this sampling and analysis program were made on a case-by-case basis after
considering site-specific conditions. For example, in some cases there was no material present to sample
(e.g., no aqueous phase present before cleaning, or no aqueous rinse generated).
Field Study Results
The results of the preliminary tank cleaning survey are based on three types of measurements: (1)
the volume of residual sludge and aqueous rinse associated with the USTs after cleaning; (2) the
concentration of chemical constituents found in these residuals; and (3) the organic vapor concentrations
found inside the USTs after cleaning.
Because chemical constituents in the residuals may originate from scaling and rusting of the tank
body, it is important to note that the six tanks analyzed in this survey were all of steel construction, that their
ages ranged from 11 to 20+ years and that they all contained petroleum distillates, either No. 2 fuel or
gasoline (Table 6). Therefore, it may be inferred that the type and quantity of tank-related contamination
in the UST residuals sampled in this survey should be similar.
Volume of Residuals Remaining in USTs After Cleaning-
The first direct indication of effective UST cleaning is the visual examination of residual organic liquid,
sludge, or aqueous rinse remaining in the UST after it was cleaned. As indicated in Table 10, the residual
volume estimates of either organic liquid, sludge or rinse vary between negligible amounts and 3 gallons
of residual. These residual volumes are less than 1% of the total tank volumes. (Tank volumes were
indicated in Table 6.) In addition, the volume of residual appears to be independent of the tank volume.
Any variation in volumes of residuals is probably dependent upon the daily variations in field conditions and
operating procedures followed at a given site.
Analyses of UST Residuals-
Trie second measure of effective UST cleaning is the concentration of chemical constituents found in
the residuals remaining in the USTs after cleaning. There were three types of samples collected and
analyzed from the USTs in this survey: (1) fuel product remaining in the tank before removal and cleaning;
(2) sludge remaining in the tank after the fuel product was pumped out of the tank; and (3) aqueous rinse
used to clean the tank after the sludge was removed.
Product-
Laboratory analyses of the two types of fuel products removed from the USTs in this survey (i.e.,
gasoline and No. 2 fuel oil) did not yield any unusual results (Table 11). VOCs, metals, TPH, and flash point
measurements were all within ranges that are consistent with those for No. 2 fuel or gasoline. As expected,
the BTEX concentrations for gasoline were higher than those in No. 2 fuel. Metal concentrations were either
below the detection limit or exhibited some lead. The fact that the reported TPH measurements on the fuel
products did not match 100% TPH (1,000,000 ppm) does not necessarily reflect non-TPH contamination in
the fuel, since the specified analytical procedure used a synthetic non-fuel standard for instrument
calibration.
The flash point measurements indicate that the gasoline would be considered a hazardous waste
because of its ignitability characteristics (flash point below 140°F). The fuel oil would not be considered
hazardous by this characteristic.
32
-------
TABLE 10. RESIDUAL VOLUME ESTIMATES IN USTs BEFORE AND AFTER CLEANING
Site
No.
1
2
3
4
5
6
Volume of Residual Before Cleaning (gal)
Organic
Liquid
4,400
800
94
90
5
55
Aqueous
Liquid
17
None
None
10
5
5
Sludge
<1
1
70
7
1
None
Amount of
Rinse Used
in Cleaning
(gai)
25
None*
49
28
10
25
Volume of Residuals After Cleaning (gal)
Organic
Liquid
1
None
None
«1
None
None
Sludge
None
1
None
«1
None
None
Rinse
1-2
None*
None
3
1
<1
' Sawdust used instead of water.
-------
TABLE 11. SUMMARY OF TYPICAL ANALYTICAL RESULTS FOR FUEL PRODUCT
IN USTs BEFORE CLEANING
Site
No.
1
2
3
4
5
6
Fuel Type
No. 2
No. 2
No. 2d
Gasoline
Gasoline
Gasoline
TPH
(ppm)
788,000
702,000C
518,000C
485,000C
634,000s
Flash
Point
(°F)
>200
185
25
21
23
Metals
Detected*
(ppm)
BDLb
BDL
Lead 5.3
Lead 1,370
BDL
VOCs Detected*
(ppm)
Toluene 743°
Ethyl benzene 222°
Total xylenes 2,81 Oc
Benzene 37
Toluene 220
Ethyl benzene 150
Total xylenes 977
Benzene 12,000
Toluene 30,800
Ethylbenzene 53,700
Benzene 17,700°
Toluene 39,400°
Ethylbenzene 13,900°
Total xylenes 78,600°
Benzene 13,000°
Toluene 37,000°
Ethylbenzene 14,500°
Total xylenes 75,500°
a See Tables 8 and 9 for list of chemicals analyzed.
b BDL - below detection limit.
c Average of two values.
d No analyses performed.
-------
Bottom Residuals-
These materials were probably a combination of settled petroleum products, tank scale, and
accidentally introduced soil. The results of laboratory analyses performed on this material (Table 12) were
consistent with its sources. TPH and VOC concentrations were slightly lower than the fuel products, flash
points were roughly similar to fuel products, and metals concentrations were higher than the fuel product.
Higher concentrations of arsenic, barium, cadmium, chromium, lead and silver were found. The origin of
the metals could either be from settled impurities or additives in the gasoline (such as tetraethyl lead),
impurities in the tank steel, or constituents of soil that was accidentally introduced into the tank. According
to the removal company, high barium concentrations are often seen in analyses of petroleum products.
In addition to the routine TPH, metals, and VOC measurements, the bottom residuals were also
subjected to a TCLP extraction to assess what concentration of metals, VOCs, and ABNs (Acid/Base
Neutrals) could potentially become mobile in the presence of an acidic leachate. TCLP results (Table 13)
indicated that only a fraction of the metals and VOCs present were potentially mobile as aqueous solutes.
Based upon these TCLP results and the recently revised TCLP criteria (Federal Register, Vol. 55, No. 61,
March 29, 1990), bottom residuals from two of the gasoline tanks would be considered hazardous waste
sludges by the EPA. The regulatory levels and exceedances are shown in Table 14. The only unexplained
TCLP result is the presence of methylene chloride at site No. 1; the chemical may have been introduced
during the laboratory analysis.
Aqueous Rinse-
The rinse analyzed in this survey was intended to simulate the rinse water used during the final rinse
of the fuel tanks. As indicated in Table 15, the TPH concentrations ranged from 4 to 379 ppm, and metals
concentrations were either below the detection limit or a fraction of the concentrations found in the bottom
residuals. For example, at Site No. 4 the concentration of lead in the rinse was 12.6 ppm whereas the
concentration of lead in the bottom residuals was 2230 ppm. VOC concentrations in the aqueous rinse
reflected the VOC concentrations in the fuel product stored in the tank. Tanks that stored gasoline had
higher VOC concentrations than those that contained No. 2 fuel. The presence of low levels of
trihalomethanes such as chloroform and bromodichloromethane in some of the aqueous rinse samples
probably reflects the presence of trihalomethanes in the public drinking water used to clean the tanks in
Sites 1, 2, and 3.
Additional tests of the aqueous rinse compared its quality with the guidelines for discharge of industrial
waters containing the following materials to sewers serving POTWs (Publicly Owned Treatment Works): oil
and grease, 5-day BOD, TOG, and pH. The oil and grease measurements reflect the presence of high
molecular weight organics in the fuel. BOD (Biochemical Oxygen Demand) is used as a measure of the
amount of degradable organic material present in the waste, and TOC (Total Organic Carbon) is a surrogate
measure of organic carbon present. The pH range of the samples collected, 4.7-6.6, is consistent with the
range in natural waters. The tanks at sites 5 and 6 were washed with non-municipal groundwater, which
may account for the lower pH measurements (4.7 and 5.4, respectively).
Organic Vapor Concentrations
The low concentration of organic vapors found inside the tanks after cleaning indicates the
effectiveness of the cleaning as well as the potential explosion hazard that the tank may present. The
concentration of organic vapors was measured in three of the tanks following the procedures using an HNu
organics analyzer equipped with a photo-ionization detector. The organic vapor concentrations in the tanks
ranged from 26 ppm to 250 ppm. These concentrations are well below the lower flammable limits for
gasoline (> 1.2% by volume).
35
-------
TABLE 12. SUMMARY OF ANALYTICAL RESULTS FOR BOTTOM RESIDUALS
IN USTs DURING CLEANING
Site
No.
1
2
3
4
5
6C
Fuel Type
No. 2
No. 2d
No. 2
Gasoline
Gasoline
Gasoline
TPH
(ppm)
237,000
355,000
114,000
Flash
Point
(°F)
181
205
45
Metals Detected*
(ppm)
Arsenic 0.83b
Barium 5.7b
Lead 20.9b
Arsenic 2.7b
Barium 157b
Cadmium 2.3b
Chromium 12.7b
Lead 59.2b
Arsenic 25.8
Barium 23.9
Cadmium 19.8
Chromium 51.3
Lead 2,230
Silver 2.2
Arsenic 8.4b
Barium 22.8
Cadmium 13.5b
Chromium 50.4b
Lead 232b
Silver 264b
VOCs Detected*
(ppm)
Toluene 110
Ethylbenzene 196
Total xylenes 993
Benzene 1 7
Toluene 133
Ethylbenzene 138
Total xylenes 640
Benzene 5.2
Toluene 370
Ethylbenzene 774
Total xylenes 334
Benzene 624
Toluene 639
Ethylbenzene 284
Total xylenes 765
* See Tables 8 and 9 for list of chemicals analyzed.
b Average of two values.
c No bottom residuals in tank.
d No analyses performed.
-------
TABLE 13. SUMMARY OF TCLP ANALYSES ON UST BOTTOM RESIDUALS
Site
No.
1
2
3
4
5
6C
Fuel
Type
No. 2
No. 2d
No. 2
Gasoline
Gasoline
Gasoline
Metals Detected*
(ppm)
Barium 3.23
Cadmium 0.019
Chromium 0.005
Lead 0.047
Barium 10.5
Lead 0.83
Arsenic 0.031
Barium 3.58
Cadmium 0.19
Lead 23.2
Barium 2.6b
Lead 0.34b
VOCs Detected*
(ppm)
Methylene chloride 0.24
Acetone 20
Benzene 0.23
Tetrachloroethane 0.49
Toluene 0.69
Ethyl benzene 0.15
Total xylenes 0.82
Benzene 0.1 5b
Toluene 0.40b
Ethylbenzene 0.158b
Total xylenes 0.87b
Benzene 29.7
Toluene 23.6
Ethylbenzene 2.3
Total xylenes 14.3
Benzene 23.1
Toluene 32.1
Ethylbenzene 4.8
Total xylenes 23.2
Seml-VOCs Detected
(ppm)
Naphthalene 0.10
2-Methylnaphthalene 0.41
Acenaphthylene 0.002
Diethylphthalate 0.033
Di-n-butylphthalate 0.044
Bis(2-ethylhexyl) 0.044
phthalate
Naphthalene 0.170
Phenol 0.14
2-Methylphenol 1.12
2,4-Dimethylphenol 0.39
Naphthalene 0.22
2-Methylnapthalene 0.83
Phenol 0.51
Benzyl alcohol 0.024
2-Methylphenol 0.63
4-Methylphenol 0.81
2,4-Dimethylphenol 0.26
Naphthalene 0.20
2-Methylnaphthalene 0.028
u>
" See Tables 8 and 9 for list of chemicals analyzed.
b Average of two values.
c No bottom residuals in tank.
d No analyses performed.
-------
TABLE 14. TCLP REGULATORY LEVELS AND EXCEEDANCES
EPA/TCLP
Chemical
Arsenic
Barium
Cadmium
Lead
Benzene
Benzene
Criterion (ppm)
5
100
1.0
5.0
0.5
0.5
Exceedances
Tank
4
4
5
Cone, (ppm)
None
None
None
23.2
29.7
23.1
Hazardous Composition of Residuals
The Phase II field studies indicated that residuals from gasoline tanks would typically be classed as
hazardous waste because of their ignitability characteristic (flash point below 140°F) and Toxicity
Characteristic Leaching Procedure (TCLP) values for lead and benzene. In addition, USTs containing
gasoline residuals typically present vapors in concentrations above the lower explosive limit and above levels
that would impair human health after even short-term exposures. Removal of these vapors is absolutely
essential to eliminate risk from fires, explosions, and the inhalation of toxic vapors. By contrast, No. 2 fuel
oil residuals were not found to be hazardous based on ignitability (flash points above 180°F) or TCLP criteria.
Bottom residuals from both gasoline and No. 2 fuel oil USTs contained significant concentrations of
lead, barium, chromium, cadmium, and arsenic. As expected, product residuals from both also contained
significant concentrations of benzene, toluene, ethyl benzene and xylene (BTEX). The BTEX fraction
comprised 10-15 percent of the gasoline residuals and 0.1-0.4 percent of the No. 2 fuel oil residuals.
The aqueous rinses resulting from tank cleaning operations contained levels of total petroleum
hydrocarbons (up to 480 ppm) and BTEX (up to 70 ppm) that would likely bar their direct discharge to
sanitary sewers.
While most of the residuals lie on the bottom of the tank, some scale and gum may adhere to the side
walls. The bottom residuals, although containing some gum and grit, consist mostly of pumpable liquids
and therefore would not properly be considered sludge.
Despite the limits of explicit guidance available, tank cleaning and removal companies are apparently
capable of removing most UST residuals with fairly simple cleaning techniques. The Phase II field
observations, and sampling and analysis program, generally confirmed the Phase I findings on the
effectiveness of relatively simple cleaning operations.
38
-------
TABLE 15. SUMMARY OF ANALYTICAL RESULTS FOR AQUEOUS RINSE SAMPLES
Site
No.
E1C
2
3
4
5
6
Fuel
Type
No. 2
No. 2
No. 2
Gasoline
Gasoline
Gasoline
TPH
(ppm)
156b
379b
20.3b
4.4b
74.3
5-day
BOD
(ppm)
210
330
240
2,165
35.0
TOC
(ppm)
109
646
150
1,168
33.7
OII&
Grease
(ppm)
405b
23.9b
12.5b
83.1
pH
6.6
6.1
6.0
5.4
4.7
Metals Detected*
(ppm)
BDMd
BDM
Arsenic 0.047
Chromium 0.27
Mead 12.6
Cadmium 0.17
Chromium 0.33
Mead 4.2
BDM
VOCs Detected*
(ppm)
Chloroform 0.016
Bromodichloromethane 0.009
Benzene 0.009
Toluene 0.082
Ethylbenzene 0.087
Total xylenes 0.332
Chloroform 0.009b
Benzene 0.01 5b
Toluene 0.54b
Ethylbenzene 0.039b
Total xylenes 0.395b
Benzene 4.98
Toluene 12.0
Ethylbenzene 3.57
Total xylenes 14.0
Benzene 11.5
Toluene 28.1
Ethylbenzene 7.32
Total xylenes 24.0
Benzene 0.848
Toluene 31.4
Ethylbenzene 1.28
Total xylenes 3.89
a See Tables 8 and 9 for list of chemicals analyzed.
b Average of two values.
c No sample collected.
d Below detection limit.
-------
CLOSURE
Participants in Tank Closure Operation
Like many construction or demolition jobs, the closure of an UST can involve several participants
employed by a variety of private and public institutions. Figure 6 provides a schematic diagram of the
potential participants in a tank closure operation. Certain entities shown as separate in this Figure (e.g., the
waste hauler, TSD operator and dirt contractor) may in common practice be employees of the UST removal
contractor or the subcontractors. The use of a single contractor prevents logistical and safety problems in
collecting such a large number of individuals with minimal risk of harm to workers or the public from fires,
explosions or toxic chemical vapors. A principal contractor can better institute and enforce a comprehensive
health and safety plan (including proper communications and personnel protective equipment), while
operating an efficient closure operation.
Wisconsin Survey-
In May 1988, the editors of Underground Tank Technology Update (UTTU) sent out about 130 tank
closure questionnaires to state agencies. The results of this survey were published in August 1988 [9]. They
indicated that some inappropriate UST closures and residuals disposal were suspected to have taken place
in the past. The respondents at that time estimated that the number of USTs being abandoned in place
equalled those being removed. By contrast, PEI's more recent survey of state UST officials showed tank
removals to be far more common than closure in place by about a 10 to 1 ratio [3].
UST Cleaning and Closure Costs
The costs of cleaning and closing (by removal) USTs are highly variable, ranging from under $1,000
to over $10,000 for individual tanks in the 1,000-10,000 gal range. The range of costs per unit tank size is
a little narrower, $0.3-1.0/gal of tank capacity in most cases. Table 16 lists examples of actual costs paid,
according to results of surveys done by the University of Wisconsin [9] and COM in 1988. As noted in this
table, extreme values of up to $36,700/tank and $8/gal of capacity were reported.
The cost variability represents the fact that the time and equipment requirements for tank cleaning and
closure are very specific to the site and the situation. Key variables include the nature and depth of covering
material (concrete, asphalt, soil), proximity to structures and underground utilities, amount of residuals
remaining in the tank, level of worker protection required, equipment availability, inspection logistics and
sample collection requirements. The type of cleaning method does not appear to play a significant role in
the total cost.
Tables 17 and 18 present information on the total costs of cleaning and removal. Table 17 provides
a compilation of price estimates for seven components in a tank closure sequence. Again, respondents
reported costs with wide variability.
Table 18 provides estimates for labor, equipment and materials costs for three major steps in tank
cleaning and removal. The total estimated cost ($10,920), which is at the high end of the range of actual
1988 costs (Table 17), indicates either a more complete coverage of all costs (e.g., some Table 17 costs
may have excluded backfill or tank disposal, etc.) or an overly conservative approach. In this hypothetical
example, labor accounts for 33% of the costs, equipment charges are 61%, and materials are 6%.
40
-------
FEDERAL, STATE, and LOCAL
AGENCIES & DEPARTMENTS
(Approves plans; inspects site)
PARENT CO./
FRANCHISER
OWNER/
OPERATOR
UST REMOVAL
CONTRACTOR
CONSULTING ENGINEER
or GENERAL
CONTRACTOR
KJv" J»l":^AMvJC«to« iiofJJ^-? MM :
-------
TABLE 16. EXAMPLES OF COSTS FOR UST CLEANING AND REMOVAL8
Tank capacity (gal)
1,000
<2,000
10,000
Unknown or mixed sizes
Cleaning and removal cost
$ per tank
1,200-1,600
5,000
8,000
805
1,400
625
3,000
5,100
8,000
3,500-5,000
2,500-4,000
2,000-4,000
36,700
3,000-3,500
1,000-1,500
6,500
5,000
6,500
$/gal of capacity
1.2-1.6
5.0
8.0
0.8
0.7
0.3
0.3
0.51
0.8
0.35-0.5
0.25-0.4
0.2-0.4
3.7
1.0-1.5
0.54
0.29
1.0
8 Data are a combination of survey results from contacts made by COM in December 1988, and by the University of Wisconsin
in mid-1988 [9]. Individual data points represent from one to six tanks.
42
-------
TABLE 17. COST ESTIMATES FOR UST REMOVAL
AND CLOSURE COMPONENTS"
Hem/component
Cost estimate
Excavation
400-500
650
2,000-2,500"
Tank cleaning and removal
Empty/purge/rinse/removal
Empty/inert/squeeze/removal
fil
2,500-3,000"
3,000
5,500-6,000
Disposal of liquids and sludges
Gasoline tank
Diesel tank
($/g«n
1.25
1.49
1.75
1-3
0.50
0.50
Tank hauling
Tank cut up
(S/tank)
600
350e
1,200
600
3,000
Waste hauling (drums)
($ for <40 drums for <100 miles)
150
Tank disposal in landfill
($/gal)
0.04
0.05
0.06
$250/tank
Soil testing (TPH Analysis)
(S/sample)
100
90
50
50
40
a Price estimates in December 1988 survey of tank cleaning and disposal companies (supplemented by CDM estimates)
and analytical service laboratories. Each entry represents a price estimate from a different company.
b For a typical 10,000 gal gasoline tank.
0 For a typical 10,000 gal tank.
43
-------
TABLE 18. COST ESTIMATES FOR UST REMOVAL
AND CLOSURE COMPONENTS"
Component
1
2
3
Cost Kam
Preparation and excavation
Labor
1 Foreman
1 Operator
1 Operator
2 Laborers
I
Equipment
Backhoe
Loader
Compressor
Jackhammer
Tank removal and shipping
Labor (same as #1)
Equipment
Cascade
Respirators
Tractor trailer truck
Explosion meter
Vacuum tanker
Materials
Dry ice
Oil absorbent pads
Drums
Cleaning and Backfill
Labor (two times #1)
Equipment (two times #1)
Bobcat
Compactor
Materials
(miscellaneous)
Hours
4
Cost ($)
200
340
140
220
Subtotal 900
200
1,100
195
55
Subtotal 1 ,550
Component 1 total: $2,450
4
900
500
40
250
70
340
Subtotal 2,100
200
150
150
Subtotal 500
Component 2 total: $2,600
8
1,800
3,100
470
300
200
Component 3 total: $5,870
a Costs based on conversations with CDM engineers and tank cleaning/removal companies in December 1988.
44
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SECTION 4
REFERENCES
1. Removal and Disposal of Used Underground Petroleum Storage Tanks. API Recommended Practice
1604, second edition. American Petroleum Institute, Washington, D.C., 1987.
2. Cleaning Petroleum Storage Tanks. API Publication 2015, third edition. American Petroleum Institute,
Washington, D.C., September 1985.
3. PEI Associates, Inc. Background Report on Current UST Practices: Results from the National
Workshop for State UST Program Managers. Draft report under EPA Contract No. 68-03-3409, Work
Assignment 16, Washington, D.C., January 1989.
4. Delta Environmental Consultants. Tank Sediment Characterization and Disposal Reports. Report to
Minnesota Pollution Control Agency. St. Paul, MM, November 1988.
5. Rogers, Warren, Leaks Induced by Internal Corrosion in Steel Tanks. Warren Rogers Associates, Inc.,
Newport, Rl.
6. Donovan, Brian, The Search for Reliable Underground Storage." Pollution Engineering, pp. 39-43,
December 1986.
7. Donovan, Brian, "Internal Corrosion: STI's Solution to a 3% Problem." Tank Talk. The Steel Tank
Institute, Northbrook, IL, Vol. 3, No. 1, January 1988.
8. Petroleum Microbiology. R.N. Atlas (ed.). MacMillan Publishing Co., New York, 1984.
9. Underground Tank Technology Update. Department of Engineering Professional Development,
University of Wisconsin - Madison, College of Engineering, Vol. 2, No. 4, August 1988.
10. Hazardous Waste: Future Availability of and Need for Treatment Capacity are Uncertain. Report to
Congressional Requesters. GAO/RCED-88-95. U.S. General Accounting Office, April 1988.
11. USEPA. Methods for Chemical Analysis of Water and Waste. EPA/600/4-79-020. U.S. Environmental
Protection Agency/EMSL. Cincinnati, OH, 1983.
12. USEPA. Test Methods for Evaluation Solid Waste: Physical Chemical Methods. U.S. Environmental
Protection Agency, Office of Solid Waste and Emergency Response, SW-846, November 1986.
13. Federal Register. Vol. 51, No. 216, November 7, 1986.
45
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APPENDIX A
CASE BY CASE QUANTITIES OF UST RESIDUALS
ESTIMATED BY PHONE SURVEY RESPONDENTS
Gasoline: Tank cleaning/removal contractor
Approx. 1" of rusty water sitting on top of 1" of solids; nothing clinging to sides or bottom.
About 10% of tank size.
About 75 gallons for 20 yr old 10,000 gallon tank.
More than 15-20 gallons/10,000 gallon tank of sludge that cannot be pumped out.
About 2% of tank volume.
Usually no residuals.
Less than 75-100 gallons.
4" to 5" remaining in tank.
75 gal for 20 yr old 10,000 gallon tank; 0 gal for 5 yr old 10,000 gallon tank.
100-200 gallon for a 10,000 gallon tank.
Gasoline: Petroleum industry organization
Little to no sludge; water removed throughout life of tank as operating procedure.
Diesel: Tank cleaning/removal contractor
Approx. 55 gallons for 20 yr old 10,000 gallon tank; almost always <100 gallons.
More than 15-20 gallons/10,000 gallon tank of sludge that cannot be pumped out.
Typically no heavy sludges.
Approx. 75 gallons for 10,000 gallon, 20 yr old tank.
Approx. 2% of tank volume.
Little sludge
Fuel Oil: Tank cleaning/removal contractor
No. 2 and No. 6 fuel oil produce more sludges than gasoline.
Tanks containing No. 4 and No. 6 have approx. 500 gallons of sludge.
No. 6 fuel oil in a 10,000 gallon 20 yr old tank will have 1-2 feet of sludge.
Most sludge found in No. 4 and No. 6 fuel tanks.
Spent Rinse Solutions: Tank cleaning/removal contractor
200 gal for 10,000 gallon tank.
100 gal for 10,000 gallon tank.
1 /3 total of tank volume.
46
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APPENDIX B
SUMMARY STEPS RECOMMENDED BY API FOR REMOVAL
OF USED UNDERGROUND PETROLEUM STORAGE TANKS*'"
1. Prepare workers and area for safety operations:
- Instruct/train workers
- Eliminate sources of ignition
- Prevent accumulation of vapors at ground level
- Check for hazardous vapor concentrations
2. Drain product piping into tank:
- Also cap or remove product piping.
3. Remove liquids and residues from tank:
- Use explosion proof or air-driven pumps with proper bonding to tank or grounding
- Monitor and evaluate all vapor emissions during process
4. Excavate to top of tank
5. Remove tank piping, pumps and other fixtures:
- Cap or remove all non-product lines
- Leave vent line connected; plug other tank openings
6. Purge tank of flammable vapors:
- Can purge with inert gas (e.g., N2), or carbon dioxide from dry ice; or
- Can ventilate tank with air; or
- Can fill tank with water.
7. Fill tank with water until floating product nears the fill opening:
- Remove floating product
8. Pump out water
9. Test tank atmosphere for flammable or combustible vapor concentrations
- Purge again, if necessary
10. Plug or cap all accessible holes except 1/8" vent hole
11. Excavate and remove tank
* Source: Reference 1 (Note: Several details relating to safety and regulatory compliance have been
omitted for brevity).
b See Figure 4 for Illustration of Steps.
47
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APPENDIX C
SUMMARY OF CLEANING PROCEDURES DOCUMENTED IN PHONE SURVEY
Source*
Comment
A,B, C
API 1604b
1. Empty tank as much as possible.
2. Triple rinse, with high pressure water (gasoline tank) or
detergent (diesel tank).
3. Inert tank with N2 or CO2.
4. If necessary, enter tank and physically remove sludge.
5. Punch 6 holes, each 1 ft2, to render tank useless.
6. Remove tank from ground.
1. Empty tank as much as possible.
2. Purge tank.
3. Cut opening(s) in tank.
4. Rinse, pump out rinse solution.
5. Remove tank from ground.
Proprietary process involving pumping fuel out of tank, filtering
through vacuum, spraying fuel back into tank through nozzle,
pumping, filtering, etc. May take numerous cycles to clean tank.
Warm water and detergent used as rinse agent; high-pressure not
used because of safety hazard.
H
1. Empty tank as much as possible.
2. Inert with C02.
3. Cut opening in tank.
4. Worker enters tank, physically removes any sludge or scum.
5. Remove tank from ground.
1. Empty tank as much as possible.
2. Purge tank.
3. Cut 2-fr2 opening in tank.
4. Worker enters tank: squeegees sides and bottoms; scrapes
sides and bottoms; washes with water.
5. Rinse solution is pumped out.
6. Tank is removed from the ground.
48
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Source*
J
K
L
M
Comment
1.
2.
3.
4.
5.
1.
2.
3.
4.
5.
6.
1.
2.
3.
4.
1.
2.
3.
4.
Empty tank as much as possible.
Purge tank.
If tank has a manhole: rinse with caustic (high pH) detergent.
Pump out residuals and rinse solution.
Remove from ground, lay on its side.
Empty tank as much as possible.
Inert with CO2.
Cut opening in tank.
Physically clean residuals.
Inert tank.
Remove from ground.
Empty tank as much as possible.
Triple rinse with high pressure steam.
Inert with CO2.
Remove from ground.
Empty tank as much as possible.
Remove tank from ground.
Cut manhole in tank.
Worker physically removes residuals.
a Most of the sources are tank cleaning and removal companies who are describing their own standard
procedures. In two instances, the procedures are those specified by a county agency.
b "Removal and Disposal of Used Underground Petroleum Storage Tanks," API Recommended Practice
1604, Second Edition, December 1987 (American Petroleum Institute, Washington, D.C.).
49
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TECHNICAL REPORT DATA
II icate read instructions on the reverse before completincl
];PA/(>Ol)/K-'.)2/Or>7
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Technical Aspects of Underground Storage Tank Closure
5. REPORT DATE
7 AUTHORS)
Anthony N. Tafuri
.--
0. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
CDM Federal Programs Corporation
]'3135 Lee Jackson Memorial Highway - Suite 200
Fairfax, Virginia 22033
12. SPONSORING AGENCY NAME AND ADDRESS ~ '
Risk Reduction Engineering Laboratory-Cincinnati, Oil
Office of Research and Development
U.S. EPA
Cincinnati, Oil 45260
PB92-161199
1992
10. PROGRAM ELEMENT NO.
CBIIU1A
11. CONTRACT/GRANT NO.
68-03-3409
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: Anthony N. Tafuri
(900) 321-6604; PI'S: 340-6604
16. ABSTRAC
Tho overall objective of this study was to develop a deeper understanding of UST residuals at
closure: their quantities, origins, physical/chemical properties, ease of removal by various cleaning
methods, and their environmental mobility and persistence. The investigation covered underground
storage tanks containing: gasoline, dlesel oil, and fuel oil. It obtained Information In two phases.
« Phase I elicited data via telephone contacts with knowledgeable Individuals including tank
cleaning companies, from literature cited by these experts, on-sile visits and from
questionnaires completed by state representatives.
o Phase II monitored selected tank cleaning cases and made quantitative n asuremenls of the
amounts of residuals left In USTs before and after cleaning, characterizing the nature of the
residuals and any rinses generated during the cleaning process. To support the objectives of
the study, the following Information was collected for each UST site included in the study:
estimates of volumes of tank residuals and secondary wastes, hazardous characteristics and
chemical composition of the residuals and secondary wastes, detailed descriptions of the
cleaning methods used, and background informallon on the UST/site that relates to the nature
of the residuals.
This report documents trie study findings in order to aid regulators and to assist those
implementing/overseeing closure activities.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
UST Residuals
Tank Closure
UST Clean Up Methods
UST Physical/Chemical Properties
3. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report/
UNCLASSIFIED
21. NO. OF PAGES
59
20. SECURITY CLASS (1 his page/
UNCLASSIFIED
EPA Form 2220-1 (9-73)
22. PRICE
&U.S. GOVERNMENT PRINTING OFFICE- I-W2 - 64«-003/41X10
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