BASIC HAZARDOUS WASTE MANAGEMENT - CHAPTER 14 pot

• Understand the causes of underground storage tank and piping failures.. In the Hazardous and Solid Waste Amendments of 1984 HSWA, Congress added a new Subtitle I to the Resource Conser

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Underground Storage Tank Management

OBJECTIVES

At completion of this chapter, the student should:

• Understand the nature and magnitude of the environmental threat of leak-ing underground storage tanks

• Understand the causes of underground storage tank and piping failures

• Be familiar with the theories and practice of internal tank testing and external monitoring for leaks

• Be familiar with remediation measures, tank rehabilitation procedures, and requirements for new tank and piping installations

• Be conversant on the RCRA Subtitle I requirements for underground storage tank management

• Be conversant on the distinctions between migration of subsurface release

of MTBE and releases of other gasoline components and know where to find current information on the problem

INTRODUCTION

Leaking underground fuel storage tanks (USTs) can cause fires or explosions and/or contaminate groundwater More than 50% of the population in the U.S depends upon groundwater for domestic use Petroleum products, including gasoline, are highly mobile as they float on a sloped or flowing groundwater surface Flammable liquids and/or vapors seeping into basements or other subterranean spaces can create explosive conditions, inhalation exposure hazards, or both Thus, leaking USTs have been and are a major threat to the public health and safety and to the environment

In the Hazardous and Solid Waste Amendments of 1984 (HSWA), Congress added a new Subtitle I to the Resource Conservation and Recovery Act (RCRA) to address the problem of leaking underground tanks used for storage of petroleum and hazardous substances The implementing federal regulations are found in 40 CFR 280 and 281 (53 FR 37082) (Tanks used for storing hazardous wastes are regulated by 40 CFR 264 and 265.)

In 1994, the U.S Environmental Protection Agency (EPA) estimated that about 1.2 million tanks at more than 500,000 sites were subject to federal regulation (EPA

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1994d) Tens of thousands of these tanks, including their piping, had leaked or were then leaking The EPA reported that in the 10 years since the Subtitle I regulatory program was authorized, the number of confirmed releases had reached 262,000.1

Moreover, the agency expected the total number of releases to reach 400,000 during the next few years (EPA 1994c) By December 1998, more than 1 million substandard USTs that had been in service in 1988 had been taken out of operation, thereby removing them as sources of leaks Of the 892,000 USTs then in operation, the EPA estimated that approximately 500,000 met the Part 280 and 281 standards (EPA 1998) Typical condition of steel tanks being removed in remediation or replacement activity is shown in Figures 14.1 and 14.2 Many older tanks, and the associated piping, are of unprotected steel construction and can be expected to develop leaks unless they are removed or rehabilitated In this chapter we will overview the nature and causes of the problem, the related technologies, and the regulatory structure

As noted, large numbers of the older USTs are of “bare” steel construction Older tanks, especially those more than 10 years old and/or unprotected from corrosion, are likely to develop leaks A leak from an UST, if undetected or ignored, can cause very large amounts of petroleum product to be lost to the subsurface In a recent case, a tank at a city-owned vehicle maintenance facility lost an estimated half-million gallons of gasoline to a producing aquifer In another case, a major oil company found it necessary to buy and vacate all of the residences on a city block

FIGURE 14.1 Galvanic corrosion of an unprotected steel underground storage tank (From Environmental Technology, Inc., 2541 E University, Phoenix, AZ With permission.)

reported each year (EPA 1998a) The June 2000 Report to Congress, referenced later herein, states that

by September 1999, 400,000 releases had been reported (EPA 2000a, p 5).

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adjacent to a company-owned service station Leaking gasoline had migrated from the underground tanks at the station, and liquid gasoline and vapors entered base-ments on the block Water supply wells adjacent to older service stations are fre-quently contaminated with gasoline or other petroleum products

Underground storage tanks usually release contaminants into the subsurface environment as a result of one or more of four factors: corrosion, faulty installation, piping failure, or spills and overfills Galvanic corrosion, or the breakdown of hard refined steel, is the most common cause of release from bare steel UST systems Because the majority of older UST systems are of bare steel, corrosion is believed

to be the leading cause of releases (EPA 1998a, p IV-2) This may not be true, however, in areas of the arid southwestern U.S

Galvanic Corrosion

The rate and severity of corrosion varies depending upon a number of site-specific factors (e.g., soil moisture, conductivity) that are almost always present when bare steel is placed underground Steel is, by definition, an alloy of iron and carbon, containing other constituents such as manganese, chromium, nickel, molybdenum, copper, tungsten, or cobalt These metals have differing electromotive activities and the more active metals tend to displace the less active Dissimilar metals may be present in the soil surrounding a steel tank Most commonly, part of the tank becomes negatively charged with respect to the surrounding area The negatively charged part

of the UST acts as a negative electrode and begins to corrode at a rate proportional

to the intensity of the current (adapted from EPA 1990, p IV-2) Galvanic corrosion always occurs at a specific point on a tank or pipe where the current exits As the current passes through this point, the hard steel is transformed into soft ore, a small hole forms, and the leak occurs The hole, so formed, is usually small (Figure 14.3),

FIGURE 14.2 Corroded underground storage tank after removal (From Environmental Tech-nology, Inc., 2541 E University, Phoenix, AZ With permission.)

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but large quantities of liquid may be released (see: Cole 1992, Appendix A, for a thorough discussion of the galvanic corrosion of steel underground tanks)

Faulty Installation

Installation failure encompasses a wide variety of problems such as inadequate backfill, allowing movement of the tank, and separation of pipe joints Mishandling

of the tank during installation can cause structural failure of fiberglass reinforced plastic (FRP) tanks or damage to steel tank coatings and cathodic protection Cole lists the causes of failure that are related to backfill:

• Improper, inhomogeneous (sic) backfill material

• Inadequate or improper compaction

• Rocks or debris left in excavation

• Voids left under tank

• Failure to prevent migration of backfill

• Placing a tank directly on a concrete slab or hard native soil

Cole (1992, p 49)

Piping Failures

The underground piping which connects tanks to each other, to delivery pumps, and

to fill drops is even more frequently of unprotected steel (Figure 14.4) EPA studies indicate that piping failure accounts for 50 to 80% of leaks at UST facilities The piping failures are nearly all caused by poor workmanship and/or corrosion Thread-ing of galvanized steel pipe exposes electrically active metal and creates a strong tendency to corrode if not coated and cathodically protected The problem is

com-FIGURE 14.3 Typical pinhole leak caused by galvanic activity (From U.S Environmental Protection Agency.)

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pounded if the fittings and valves used in the system are of dissimilar metals Improper layout of piping runs, incomplete tightening of joints, inadequate cover pad construction, and construction accidents can lead to failure of delivery piping (adapted from Cole 1992, p 2; Munter et al 1995, p 190) Figure 14.5 illustrates

a typical service station tank and piping layout

Spills and Overfills

Spills and overfills, usually caused by human error, contribute to the release problem

at UST facilities In addition to the direct contamination effect, repeated spills of petroleum products or hazardous wastes can intensify the corrosiveness of soils Spills and overfills are almost totally attributable to human error These mistakes can be avoided by following correct tank filling practices and by providing spill and overfill protection The EPA regulations require catchment basins to contain spills and the installation of automatic shutoff devices, overfill alarms, or ball float valves (EPA 1994a; EPA 1998a, p IV-3)

Compatibility of UST and Contents

Another possible cause of tank failure has become of concern in areas of the nation that are experimenting with additives, blends, and alternative (automotive) fuels in the hope of achieving improved air quality The rush to replace steel tanks has enhanced the popularity of fiberglass-reinforced plastic (FRP) tanks and tank liners,

to the end that large numbers of them have been put into service Some FRP tanks

or liners may not be compatible with some methanol-blended (and possibly some ethanol-blended) fuels or with additives such as methyl tertiary butyl ether (MTBE)

FIGURE 14.4 Typical corroded piping at an underground storage tank replacement site Note hole in pipe nipple between elbows (From Environmental Technology, Inc., 2541 E Univer-sity, Phoenix, AZ With permission.)

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Compatibility for tanks means that the fuel components would not change the physical or mechanical properties of the tank Compatibility for liners requires that the fuel components not cause blistering, underfilm corrosion, or internal stress or cracking Owners/operators of FRP-constructed or lined tanks should consult the appropriate standards of the American Petroleum Institute (API) (adapted from Leiter

1989, p 55)

Mobility of Leaked Hydrocarbon Fuels

Motor fuels, when leaked, are acted upon by gravitational forces which act to draw the fluid downward Other forces act to retain the fuel, which is either adsorbed

to soil particles or trapped in soil pores The amount of fuel retained in the soil is

of primary importance, as it will determine both the degree of contamination and the likelihood of subsequent contaminant transport to groundwater (Bauman 1989,

p 3) Upon reaching the saturated zone, some of the lighter components may dissolve in water, but large quantities can float on the water surface, sliding downgradient over great distances This mobility frequently causes remediation of leaking UST sites to be costly, involving many recovery wells and large-scale separation of pumped water and recovered product MTBE, a gasoline additive (see box), is water soluble, does not partition with the gasoline, and is transported with the groundwater flow

FIGURE 14.5 Typical service station tank and piping layout (From U.S Environmental Protection Agency.)

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Methyl tertiary butyl ether (MTBE), a synthetic chemical oxygenate, is blended with gasoline to improve combustion and reduce carbon monoxide and ozone emissions from automobile exhaust systems MTBE may comprise up to 10%,

by volume, of gasoline (Robinson et al 1993).This additive chemical does not behave in the manner of gasoline, or other additives, when released to the subsurface In a recent well-reasoned paper, a developer/marketer of bioreme-dation products2 summarized the factors contributing to the complexity of reme-diating properties contaminated with fuels containing the chemical:

• MTBE degrades very slowly under aerobic conditions

• MTBE is not recognized as an anaerobically degradable compound

• Unlike BTEX, MTBE is highly soluble and does not retard on the aquifer matrix The compound is therefore capable of rapid and pervasive disper-sion in groundwater

• The toxicity and carcinogenicity of MTBE have not been established

• Taste and odor thresholds for MTBE are very low

• Although MTBE is extremely volatile, when dissolved in water, it is dif-ficult to strip which complicates sparging and pumping options In the latter case, pumped water may have to be treated in bioreactors (Regenesis 1999) The Regenesis paper, which reports on experiments with oxygen release com-pounds (ORC®) in wells, suggests that it may be possible to achieve some deg-radation of MTBE in groundwater by enhancing conditions for aerobic activity The paper can be accessed at <http://www.regenesis.com/ORCtech/Tb2231.htm> The impacts and issues generated by the use and release of MTBE are many faceted and conflicting An EPA publication reports that experiments with lab-oratory microcosms constructed with material from an MTBE-contaminated aquifer indicate that significant reductions in MTBE were achieved under meth-anogenic conditions (EPA 2000) A study by the Lawrence Livermore National Laboratory concluded that MTBE is a “frequent and widespread contaminant”

in groundwater throughout California and does not degrade significantly once

it is there The study estimates that MTBE has contaminated groundwater at over 10,000 shallow monitoring stations in California The California Depart-ment of Health Services (DHS) adopted a primary (health-based) drinking water standard of 5 ppb in April 2000 (ACWA 2000)

The EPA issued an Advance Notice of Proposed Rulemaking (ANPRM) to issue a rule under the Toxic Substances Control Act (TSCA)(40 CFR 755) to Control MTBE in Gasoline The ANPRM states that the outcome of the rule-making could be a total ban on the use of MTBE as an additive or several lesser limitations (65 FR 16093, March 24, 2000) On July 12, 2000, the EPA issued

a Notice of Proposed Rulemaking (40 CFR 80), which adjusted the Clean Air Act regulations to “… increase the flexibility available to refiners to formulate

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RFG3 without MTBE while still realizing ozone benefits that are similar to those

… (existing)” (65 FR 42920) On August 4, 2000, the EPA issued a Notice of Proposed Rulemaking (40 CFR 80 and 86) to “… develop a framework to construct a national mobile source air toxics program … and make a commit-ment to revisit the issue of mobile source air toxics controls in a 2004 rulemak-ing.” The action creates a list of 21 Mobile Source Air Toxics (MSATs), which includes MTBE; however, the only MSAT for which immediate action is pro-posed is benzene (65 FR 48057)

It is unclear what, if any, perturbations the MTBE concerns hold for prac-titioners; however, it is clear that UST-related program managers, consultants, technicians, contractors, manufacturers, financial interests, and insurers must take steps to remain informed and focused on the subject

As noted, leaked or spilled gasoline percolates to the groundwater surface, then floats on that surface, traveling downgradient at rates determined largely by the physical characteristics of the geologic materials, which make up that portion of the vadose zone and by the slope of the water table The highly soluble and miscible MTBE readily mixes with a moving groundwater plume and may move ahead of the gasoline plume (Weaver et al.1999; see also: Swain 2000; EPA 2000; Cater et

al 2000)

Galvanic corrosion is the most common cause of corrosion and subsequent release from bare steel UST systems Steel tanks and piping can be protected from corrosion

by coating them with a corrosion-resistant coating and by using “cathodic” protec-tion Cathodic protection reverses the electric current that causes corrosion and can

be applied in the form of sacrificial anodes or as an impressed current

Protection by Sacrificial Anode

Sacrificial anodes are pieces of metal that are more electrically active than steel in the UST to which they are attached Because the anodes are more active, the electric current will exit from them rather than from the steel tank Thus the tank becomes the cathode and is protected from corrosion while the attached anode is sacrificed Depleted anodes must be replaced in order to achieve continuous protection of the UST (EPA 1998b)

Protection by Impressed Current

An impressed current protection system uses a rectifier to convert alternating current

to direct current The current is sent through an insulated wire to the anodes, which are metal bars buried in the soil near the UST The current flows through the soil

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to the UST system and returns to the rectifier through an insulated wire attached to the UST Since the electric current flowing from these anodes to the tank system is greater than the corrosive current attempting to flow from it, the UST is protected from corrosion (EPA 1998b; see also: Cole 1992, Appendix A)

Protection by Cladding or Dielectric Coating

Steel-fiberglass-reinforced-plastic composite tanks are adequately protected from corrosion by the thick outside layer (or cladding) of FRP (Figure 14.6) Cathodic protection is not needed with this method of protection (40 CFR 280.20) New steel tanks for petroleum storage must be coated with a dielectric coating (asphalt or paint) and cathodically protected (40 CFR 280.20) Care must be taken during installation to protect the coating from damage Any separation (“holiday”) of the coating from the tank tends to focus the galvanic forces, accelerates corrosion, and may cause a release (Leiter 1989, p 22)

Protection of Piping

The UST regulations require that piping in contact with the ground be constructed entirely of fiberglass-reinforced plastic or if of steel be cathodically protected by:

• Coating with suitable dielectric material

• Field-installed cathodic protection system designed by a corrosion expert

• Impressed current system

• Cathodic protection conforming with listed codes and standards (40 CFR 280.20)

FIGURE 14.6 Composite steel-fiberglass reinforced plastic tanks.

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Seven general methods of leak detection are used for underground storage tanks Some of the methods have many variations Practitioners and tank testing companies vigorously argue the merits of particular methods and the supporting technologies The Subtitle I regulations allow owners or operators of UST facilities to choose between leak detection methods and impose specific requirements on the use of each method The student should refer to Figure 14.7 as the methods are briefly described

1 Automatic Tank Gauging This method uses probes which are permanently installed in the tank and an external control device to monitor product level and temperature These systems automatically calculate the changes

in product volume that can indicate a leaking tank (EPA 1998a; see also:

Leiter 1989, p 174; Wilcox 1990, pp 119ff)

2 Groundwater Monitoring. This method is used to detect the presence of gasoline or other liquid product floating on the groundwater Monitoring wells are placed at strategic locations in the ground near the tank and piping runs The wells may be sampled periodically by hand or continu-ously with permanently installed equipment The method is effective only

at sites where groundwater is within 20 ft of the surface (EPA 1998a)

3 Soil Vapor Monitoring Leaked petroleum product releases vapors into the soil surrounding the UST Vapor monitoring around the tank and piping senses the presence of vapors from leaked product The method requires that tanks be backfilled with porous soils and that monitoring locations

be carefully planned Vapor monitoring can be performed manually, on a prescribed frequency, or continuously, using permanently installed equip-ment (EPA 1998a)

FIGURE 14.7 Underground storage tank leak detection alternatives (From U.S Environ-mental Protection Agency.)

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