Petroleum Products Overview

Storing liquid petroleum products, such asmotor fuel and heating fuel, above ground orunderground presents a potential threat to pub-lic health and the environment. Nearly one outof every four underground storage tanks in theUnited States may now be leaking, accordingto the U.S. Environmental Protection Agency.If an underground petroleum tank is more than20 years old, and especially if it is not protect-ed against corrosion, the potential for leakingincreases dramatically. Newer tanks and pipingcan leak, too, especially if they were notinstalled properly.

Even a small gasoline leak of one drop persecond can result in the release of about 400gallons of gasoline per year. A few quarts ofgasoline in the ground water may be enough toseverely pollute drinking water. At low levelsof contamination, fuel contaminants in watercannot be detected by smell or taste, yet seem-ingly pure water may be contaminated to thepoint of affecting human health.

Preventing tank spills and leaks is especiallyimportant because gasoline, diesel and fuel oilcan move rapidly through surface layers andinto ground water. Also, vapors from an under-ground leak that collect in basements, sumpsor other underground structures have thepotential to explode.

Petroleum fuels contain a number of poten-tially toxic compounds, including common sol-vents such as benzene, toluene and xylene, aswell as additives such as ethylene dibromide(EDB) and organic lead compounds. EDB is acarcinogen, a cancer-causing agent, in laborato-ry animals, and benzene is considered a humancarcinogen.

This publication focuses on safe storage ofgasoline, diesel, kerosene and liquid heatingfuels. It does not apply to liquid propane (LP)gas, since such leaks vaporize quickly and donot threaten ground water. A glossary at theback of this publication explains the terminolo-gy used. The following areas are covered:

1) Storage tank location2) Tank design and installation3) Monitoring tanks4) Tank closure5) Evaluation table

Storage Tank Location

From a water quality standpoint, one of themost important aspects of your liquid petrole-um storage tank location is how close it is toyour water well. State well regulations requirethat petroleum storage tanks be at least 100feet from a water well. Minimum separationdistances regulate only new well installation.Existing wells are required by law only to meetseparation requirements in effect at the time ofwell construction. However, making everyeffort to meet current regulations wheneverpossible will further reduce the risk of contam-ination.

Every site has unique geologic and hydrolog-ic conditions that affect ground water move-ment. The time it takes petroleum products toreach ground water also will depend upon localsoils. The more porous the soil (sands and grav-els, for example), the faster the rate of down-ward movement to ground water. You maychoose to locate a new tank more than 100 feetaway from a well to provide reasonable assur-ance that subsurface flow or seepage of conta-minated ground water will not reach the well.If possible, the tank should be located down-slope from the well. Figure 1 illustrates petrole-um product seepage into soils.

If you have an above-ground tank, followexisting regulations for underground storagetanks as a guide. To protect against explosionand fire, do not locate tanks (especially above-ground tanks) closer than 25 feet to existingbuildings. Previous regulations for siting above-ground storage tanks were concerned morewith the danger of explosion than with thedanger of ground water pollution. State agen-cies have revised above-ground storage tankregulations to better protect ground water.However, always keep in mind the potential forvapors to accumulate in or under nearby stor-age buildings. These vapors can directly affecthuman health and are a fire hazard.

Along with maintaining adequate distancefrom your drinking water well, choose a loca-tion for a new tank based on the following con-siderations:

★ Soil characteristics. Highly corrosiveclays, wet soils and acidic (low pH) soilscan significantly increase the rate of corro-sion of underground metal tanks and pip-ing. Use clean backfill during installation

to decrease the negative effects of sur-rounding soils.

★ Soil stability. Assess the suitability of theunderlying soil to support both under-ground and above-ground tanks. At specialtank locations, such as hillsides, be sure toproperly anchor and hold tanks in place.Regardless of soil conditions, locate above-ground tanks over an impermeable linermade of concrete or one of the newer syn-thetic fabrics and build a collection basinfor spills.

★ Damage control. Be sure that pipes can-not twist or break if the tank is bumpedor disturbed.

★ Current and previous land use. Sitesthat contain abandoned pipes and tanks,agricultural drainage tiles or waste materi-als pose special installation problems. Anymetal already in the ground at your cho-sen site will increase corrosion rates forthe new tank.

★ Traffic. Assess traffic patterns around thetank. Determine whether the location ofthe tank or dispenser will block move-ment of vehicles during refueling or causespecial problems if any work needs to bedone on the tank. Protect piping from col-lisions with vehicles.

★ Depth to ground water. Floodways orareas where the water table is close to thesurface are poor locations for storagetanks. Tanks placed in such areas require

special installation. To reduce pollutionpotential, an above-ground tank may bepreferable to an underground tank insome situations.

Tank Design and Installation

Whenever you install a fuel storage tank,carefully follow the manufacturer’s recom-mended installation practices. Proper installa-tion is one sure way to minimize leaks fromthe tank or connected piping. Scratches in ametal tank caused by careless installation canincrease corrosion and tank deterioration.

Underground Tanks

All new underground petroleum storagetanks and related piping must be constructedof non-metallic materials, such as fiberglass, orhave corrosion protection. Methods of corro-sion protection include using interior liners andsacrificial anodes which are connected to thetank.

A sacrificial anode is a special material witha greater tendency to corrode than the tankmaterial. The anode will typically protect thetank for up to 30 years. Interior liners aremade of non-corrosive synthetic materials andalso can be effective in protecting metal tanks.

Texas regulations require that all new under-ground tanks (other than heating oil tanks foron-site use) have spill and overfill protection.Spill protection typically consists of a catchbasin for collecting spills when the tank is

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Slow Seepage into

Permeable Soil

High Volume Seepage into

Permeable Soil

Seepage into Stratified Soil with

Varying Permeability

Land Surface

Figure 1. Petroleum product seepage into soils. Source: Underground Tank Corrective ActionTechnologies, EPA/625/6-87-015, January 1987.

filled. Overfill protection is either a warningdevice, such as, a buzzer or a prevention devicesuch as an automatic shutoff. Spill and overfillprotection are important because they can pre-vent pollution from a number of small releasesover a long period of time.

Above-ground Tanks

State regulations for above-ground tankinstallation seek to reduce the potential forboth pollution and fire. Requirements includethe following:

1) enclosing the tank within a secure 6-footfence or well-ventilated building constructedof non-combustible material; and

2) constructing a fire wall between the fuel dis-pensing area and the tank.

To decrease pollution potential, place tankswithin a secondary containment structure con-sisting of a dike and a pad. All piping shouldbe above ground within the dike or may goover the dike wall. However, if it goes over thedike wall, it must be placed below the groundand within 10 feet of the dike wall. Above-ground piping must be made of steel and coat-ed to prevent corrosion. Any below-ground pip-ing may be either steel or fiberglass, but thesteel piping must be coated and cathodicallyprotected.

Monitoring Tanks

Regulations for new underground tanksrequire that they have a method of detectingleaks. Select the tank location carefully toensure that installation is easy and leak detec-tion methods reliable. Test the tank periodicallyfor leaks, and measure the tank inventory on amonthly (or more frequent) basis to help detectleaks before major problems develop.

Since cleanup of gasoline leaks is alwayscostly and often not totally effective, it isimportant to constantly monitor undergroundtanks containing petroleum products. If youalready have a petroleum storage tank, be espe-cially aware of the age of your tank as well asthe need to establish a leak-detecting program.Figure 2 shows how ground water can be con-taminated by underground tanks.

Since most older tanks are bare steel, theyare likely to corrode and leak. If your tank ismore than 20 years old or if you do not knowits age, make a special effort immediately todetermine whether there are leaks.

Even when a tank has been tested andproven tight, existing regulations and goodpractice require that you have a method forregularly detecting leaks. Some good methodsinclude the following:

★ Installing internal or external devices tomonitor ground water and vapor, or toautomatically gauge tanks.

★ Measuring tank inventories regularly.Leakage is apparent when there is anydecrease in level over time, without anywithdrawal of fuel, or when there is anincrease in water in the tank. Whileinventory measurement will not detectvery small leaks, it will at least provide awarning that further investigation may benecessary.

★ Using a measuring stick to measure tankliquid level. This method is acceptable,but be sure that the stick does not punc-ture or damage the bottom of the tank.

The closer the tank is to a water well, themore important it is to have an adequate leakdetection system in place.

Tank Closure

Tanks no longer in use can cause problemsfor owners and operators many years later.They will continue to corrode and, if they stillcontain gas or oil, will likely contaminateground water.

Try to determine the location of any unusedtanks on your property. Also, try to find outwhether the tanks still hold product or haveholes. These tanks must be pulled from theground and disposed of in a landfill or at ascrap dealer.

State law requires that only certified individ-uals can legally pull a tank. Always notify yourlocal fire department at least 1 month beforeyou have the tank pulled so that they can takeprecautions to prevent an explosion or otherproblem. Deaths have occurred because ofimproper closure.

Evaluation Table

The following table can be used to help agri-cultural producers and rural homeownersdetermine the risk that drinking water on agiven property will be contaminated because ofthe management practices being used. Foreach category on the left that is appropriate,

read across to the right and circle the state-ment that best describes conditions on yourland. Allows 15 to 30 minutes to complete thetable, and skip any categories that do notapply. Note any high risk ratings and takeappropriate actions to remedy them. Strive forall low or low-moderate risk ratings.

Fuel tank�leakage through tank wall

Contamination of groundwater due to improper fuel storage and transfer

spillage during fuel

transfer

spillage during tank filling

contaminatedaquifer

Figure 2. Contamination of groundwater due to improper fuel storage and transfer. Source: Handling and Underground Storage ofFuels, Cooperative Extension Service, Michigan State University, Extension Publication WQ0l, Reprinted, February 1986.

Petroleum Product Storage: Assessing Drinking Water Contamination Risk

Low Risk Low-Moderate Risk Moderate-High Risk High Risk

Location (all tanks)

Position of tank in Tank downslope more Tank at grade or up- Tank downslope more Tank at grade orrelation to drinking than 100 feet from slope more than 100 than 100 feet from upslope less thanwater well well in medium- or feet from well in well in coarse-tex- 100 feet from well

fine-textured soils medium- or fine-tex- tured soil (sands, in coarse-textured(silt loam, loam, clay tured soils (silt loam, sandy loam) with soil (sand, sandyloams, silty clay) with loam, clay loams, high permeability.* loams) with highlow permeability.* silty clay) with low permeability.*

permeability.*

Tank location and Well-drained soils. Moderately well- Located more than 50 Located less thanlocal land use Water table always drained soils. Only feet from buildings. 50 feet from build-(leakage potential) beneath tank. Above occasionally high Medium- or fine-tex- ings and in areas

ground tank more water table. tured soils (silt loams, with fine-texturedthan 50 feet from loam, clay loams, silty soils (clay loams,buildings. clay) saturated silty clay, clay) often

seasonally. saturated.

Design and Installation Table (all tanks)

Type and age of Synthetic tank or tank Steel tank less than Coated steel tank 15 Bare steel tank 15tank/corrosion with cathodic corro- 15 years old, coated or more years old. or more years old.protection sion protection. with paint or asphalt. Bare steel tank less

than 15 years old.

Spill and tank over- Impermeable catch Impermeable catch Impermeable catch No protection.fill protection basin plus automatic basin plus overfill basin or concrete

shutoff. alarm. catch pad.

Piping Piping protected from Piping galvanized but Pipe galvanized, not Piping and tankrust and corrosion by not isolated from tank. isolated or bare. Pip- isolated and of dis-cathodic protection. Pipe drains back to ing sloped back to similar materials.Piping isolated from tank. Check valve at tank, but check valve Uninsulated pipetank and sloped back pump. is located at tank bare, cannot drainto tank. Check valve (foot valve). freely to the tank.at pump (not at tank). All pressure pipe

systems.

Tank installation Installed by state Installed according to No information on Installed withoutcertified installer. recommendations installation. backfill, setback,

provided with new secondary contain-tank by seller. ment, anchors and

other protection,OR by untrained individual.

Design and Installation (above-ground tanks only)

Tank enclosure Tank surrounded by Tank surrounded by Tank surrounded by No enclosure.6-foot-tall non-com- low fence with lock. low fence. No lock.bustible building or Firewall in place if No firewall.fence with lock. Build- setbacks do not con-ing well-ventilated. form to code.Firewall in place if setbacks do not con-form to code.

*See Glossary.

Glossary

Cathodic protection: One of several tech-niques to prevent corrosion of a metal sur-face by reversing the electric current thatcauses corrosion. A tank system can beprotected by sacrificial anodes or impressedcurrent (See sacrificial anodes andimpressed current.).

Certified installer: A person certified by thestate to install and repair petroleum storagetanks.

Corrosion: Deterioration of a metallic materialdue to a reaction with its environment.Damage to tanks by corrosion is causedwhen a metal underground tank and itsunderground surroundings act like a bat-tery. Part of the tank can become negative-ly charged and another part positivelycharged. Moisture in the soil provides theconnecting link that finally turns on thesetank batteries. Then, the negatively chargedpart of the underground tank system wherethe current exits from the tank or its pipingbegins to deteriorate. As electric currentpasses through this part, the hard metalbegins to turn soft, holes form and leaksbegin.

Corrosion protection: One method of corro-sion protection is cathodic protection. Steeltanks can be protected by coating themwith a corrosion-resistant material com-bined with “cathodic” protection. Steelunderground tanks also can be protectedfrom corrosion if they are bonded to athick layer of noncorrosive material, suchas fiberglass-reinforced plastic. Also, thecorrosion problem can be entirely avoidedby using tanks and piping made completelyof noncorrosive material, such as fiberglass.

Galvanized: The result of coating an iron orsteel structure with zinc. Galvanized mate-rials do not meet corrosion protectionrequirements.

Impressed current: This protection systemintroduces an electric current into theground through a series of anodes that arenot attached to the underground tank.Because the electric current flowing fromthese anodes to the tank system is greaterthan the corrosive current attempting toflow from it, the underground tank is pro-tected from corrosion.

Interior liner: A liner for petroleum storagetanks made of noncorrosive synthetic mate-rials that can be effective in protectingmetal tanks.

Petroleum Product Storage: Assessing Drinking Water Contamination Risk

Low Risk Low-Moderate Risk Moderate-High Risk High Risk

Design and Installation (above-ground tanks only) (continued)

Secondary Tank placed within Tank placed within Tank placed on pad. No secondarycontainment concrete or synthetic dike and pad made containment.

dike with pad able to of low permeabilityhold 125% of tank soils*, able to holdcapacity. 125% of tank

capacity.

Monitoring (all tanks)

Tank integrity Regular (monthly) Daily inventory con- Occasional inventory No inventory con-testing and leak leak monitoring. trol and annual tank control and annual trol, testing or moni-detection tightness testing. tank tightness testing. toring.monitoring

Tank Closure (underground tanks)

Unused tank Tank removed from Tank filled with inert Tank removed or filled Tank left in groundground. Excavation material and excava- with inert material. (illegal after 12checked for evidence tion checked for Excavation not check- months).of contamination. evidence of leaking. ed for contamination.

*See Glossary.

Inventory control: Measuring and comparingthe volume of tank contents regularly withproduct delivery and withdrawal records tohelp detect leaks before major problemsdevelop.

Sacrificial anodes: Pieces of metal attacheddirectly to an underground tank that aremore electrically active than the steel tank.Because the anodes are more active, elec-tric current runs from the anodes ratherthan from the tank. The tank becomes thecathode (positive electrode) and is protectedfrom corrosion. The attached anode (nega-tive electrode) is “sacrificed” or consumedin the corrosion process.

Secondary containment: A system such as asealed basin and dike that will catch andhold the contents of a tank if it leaks orruptures.

Soil permeability: The quality that enablessoil to transmit water, air or other fluids.Slowly permeable soils have fine-texturedmaterials, such as clays, that permit onlyslow fluid movement. Moderately or highlypermeable soils have coarse-textured mate-rials, such as sands, that permit rapid fluidmovement.

Spill and overfill protection: Spill protectionusually consists of a catch basin for collect-ing spills when the tank is filled. Overfillprotection is a warning device such as abuzzer or a prevention device such as anautomatic shutoff. These precautions canprevent a number of small releases overtime from polluting ground water.

Tank tightness testing: A procedure for test-ing a tank’s ability to prevent the leaking ofany stored substance into the environment,and to prevent ground water from seepinginto the tank.

Contacts and References

For additional information contact:

★ The Texas Natural Resource ConservationCommission at (512) 239-1000,

★ Texas Agricultural Extension Service WaterQuality unit (409) 845-0887,

★ Texas State Soil and Water ConservationBoard, (817) 773-2250.

Internet address: TEX*A*Syst bulletins andlinks to other water quality sites are containedin a homepage located on the World Wide Webat: http://waterhome.tamu.edu.

TEX*A*Syst is a series of publications to help rural residents assess the risk of ground water pollution, and to describeBest Management Practices (BMPs) that can help protect ground water. The TEX*A*Syst documents were developedfrom the national Farm*A*Syst ground water protection program. The TEX*A*Syst system is designed to help the userlearn more about the environment, existing environmental policies and regulations, and recommended managementpractices. Thus, the user can voluntarily reduce the pollution risks associated with water wells.

TEX*A* Syst materials were edited by Anna Schuster Kantor, and reviewed by M.C. Dozier and the personnel of theUSDA-Natural Resources Conservation Service, U.S. Environmental Protection Agency, Texas Department ofAgriculture, Texas Natural Resource Conservation Commission, Texas Water Development Board, Texas State Soil andWater Conservation Board, Texas Water Resources Institute, and Texas Farm Bureau. Editorial and formatting assis-tance were provided by the Department of Agricultural Communications, The Texas A&M University System.

The TEX*A*Syst program is sponsored by the U.S. EnvironmentalProtection Agency under Section 319(h) of the Clean Water Act.Funds for this program are administered by the Texas State Soil andWater Conservation Board’s Agricultural/Silvicultural NonpointSource Management Program.