geochemical characterization of acidic sand used as …
TRANSCRIPT
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GEOCHEMICAL CHARACTERIZATIONOF ACIDIC SAND USED ASURBAN CONSTRUCTION
FILL MATERIAL
J.H. Rule
Department of Ocean, Earth & Atmospheric SciencesOld Dominion University
Norfolk, VA 23529
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INTRODUCTION
Sand from a Hampton Roads, VA, borrowpit was used to provide backfill for a street extension through a section of anold landfill.
Aluminum storm drain was then emplaced within the sand fill.
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INTRODUCTION
Three months later there was significantpipe corrosion and in localized areascomplete pipe faliure.
According to the pipe manufacturer the lifetime of this material should have been in excess of 15 years.
A detailed study was conducted to determine the cause of this corrosion.
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ROAD FILL SITERoad fill site with one section of damaged drain pipe removed
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ROAD FILL SITEAppearance of new drain pipe
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DAMAGED DRAIN PIPE WITH MILD
CORROSION
Groundwater/leachate discharge from storm drain. Note discoloration of pipe interior and of water.
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ROAD FILL SITE
Road fill (partially excavated) beside landfill (LF). Note iron stain from acid sand reactions in water.
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ROAD FILL SITECloser view of groundwater with mixture of leachate acid reaction products and. Note LF debris and stain on pipe.
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ROAD FILL SITECorrosion of pipe is evident
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ROAD FILL SITEClose-up view of severe pipe corrosion
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SCHEMATIC OF ROAD FILL SITE
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Note dark colored layer at surface in the background, Fe-stains at the base and white-colored crust on the sand pile.
SAND PIT
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Note organic-rich layer at top of the sequence in the background and iron-stained sand in foreground.
SAND PIT
Organic-rich layer
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Acid water with Fe-oxide precipitates; Note acid-tolerant algae in the foreground and well-leached sand in the background.
SAND PIT
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Acidic water with Fe-oxide precipitation
SAND PIT
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Sands layered with organic-rich reduced muds.
SAND PIT
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Reduced layer containing well-preserved organic matter.
SAND PIT
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SCHEMATIC OF SAND PIT
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MECHANISM OF SULFIDE ACCUMULATION
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Leaching column for determinationfor lime requirement of acid sand inLowery Road. Data are for the firstfew column volumes of water leachedthrough the column.
Migration of lime downwardwas much too slow for surface application of lime to be an acceptable remedial action.
DETERMINATION OF LIME REQUIREMENT
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Sample pH Eh (mv)Lowery Road 1 2.8 +376Lowery Road 2 2.7 +406Sand Pit 1 2.5 +386Sand Pit 2 2.5 +386
SEDIMENT (SAND) pH and Eh
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Sample pH Eh (mv)Land Fill 1 6.8 -309Land Fill 2 6.8 -314Land Fill 3 6.8 -309Land Fill 4 6.8 -314Lowery Rd Drain 4.0 +176
WATER SAMPLE pH AND Eh AT THE LOWERY ROAD SITE
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• Corrosion tests of the Al storm drain material predicted a corrosion rate of 0.98 mm inthree months.
• In some cases corrosion of 1.5 mm of materialoccurred in the fill site.
• Corrosion tests predicted that severe pipefailure would occur within one year.
• All Al storm drain was removed and replacedwithin one year of the study.
CORROSION TEST RESULTS
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• Sand from the borrow pit caused pipedeterioration.
• Groundwater from the adjacent landfillwas a source of neutralization of the acidity from the sand fill, but had nooverall impact on corrosion rates.
• The source of the acidity was organic-rich muds from an overlying Pleistoceneswamp deposit.
SUMMARY & CONCLUSIONS
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• Sulfide reserves in this type of sand aresufficient to generate acid productionover a several month period.
• Fill sands from these types of depositionalenvironments should be tested prior toemplacement.
• Corrosion rates of reactive material canbe successfully predicted from laboratory test results.
SUMMARY & CONCLUSIONS