Copper Failure

8/3/2019 Copper Failure

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INVESTIGATIVE REPORT OF COPPERPLUMBING FAILURES UNDERCONCRETE SLABS

Prepared for

National Association of Home Builders1201 15th Street, N.W.Washington,D.C. 20005-2800

by

NAHB Research Center400 Prince Georges BoulevardUpper Marlboro, Maryland 20772

August 1992


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TABLE OF CONTENTS

PAGEINTRODUCTION 1BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1FLORIDA INSTALLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3METALLURGICAL INVESTIGATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3RESULTS 4RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .APPENDIX A

Failure AnalysisAPPENDIX B

Soil Tests


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INTRODUCTIONCopper piping provides a relatively reliable material under most conditions due to the formationof a protective layer of cup rous oxide that protects it in most environments. However, a recentseries of failures of underground copper water supply pipes have been reported near Miami,Florida. All of these failures involve type L copper pipe located under concrete slab-on-gradefoundations in a single sub-division. All of the copp er plumbing under the slab is encased in acontinuous plastic sleeve as required by the state building code. The rationale for the sleeve isto protect the sub-slab copper pipe from aggressive soils, groundwater, and concrete leachate.

One builder last reported failures in 20 homes, some of which incurred multiple failures. Theplumber who installed the copper supp ly pipes indicated that a sec ond builder is facing similarproblems, although these could not be confirmed . This report contains results of a preliminaryinvestigation of failed plumbing m aterials retrieved from two homes.

BACKGROUNDReview s conducted by Waters' and by M yers and Cohen2 suggest the following mechanismscan cause copper corrosion by acting alone or in combination.

Abnormally aggressive soils. This is typically due to the presence of soils with elevatedsulfate or chloride levels and a capacity to retain moisture.

Electrochemical concentration cells created by differences in soil composition. Forexample, backfill soils with a high oxygen content relative to the supporting soil cancause corrosion of the under side of a pipe.

'Waters, D.M.,Internal and External Copper Corrosion in Domestic Water Services," Proceedings of AWWAAnnual Conference, Anaheim, CA, May 1977.2Myers, J.R., and Cohen, A., "Conditions Contributing to Underground Copper Corrosion," Journal A W A ,August 1984.

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Stray electrical currents. One utility companys experience with stray AC currentsresulting from bonding of the electrical system to the plumbing system suggest that thispractice should be stopped in favor of other grounding methods3.

Therm al galvanic effects. This requently results from contact of hot and cold m etal pipescausing corrosion of the hot water pipe.

Galvanic action due to contact of dissimilar metals.

Corrosion fatigue caused by thermal expansion and contraction. This rare type of failureusually occurs with flared joints or where copper passes through a concrete slab.

A review of technical journals and other literature revealed only a few reported incidences ofcopper failures in residential building4,5. Th is may be due to coppers satisfactory performanceunder most conditions.

One study4 conducted for the Washington (DC) S uburban Sanitary Commission indicated anunusual failure mechanism in underground copper pipe. In this situation, one-inch copper pipehad been installed for the water service to hom es. The copper was sleeved at sections where itapp roaches or crosses a sanitary sewer using two-inch or three-inch corrugated plastic drain pipe.An analysis of three failed water supply pipes show ed a series of uniformly spaced cavities. Thespacin gs of the cavities matched that of the corruga tions in the sleeve. The reports author, basedon electron microscope examination results, suggested that a number of corrosion mechanismswere operating. How ever, it was apparent that the primary mechanism involved small vibrationsin the copper pipe that continually destroyed the protective cuprous oxide cover at each point of

3Guerrera,A.A., GroundingofElectric Circuits toWater Services:OneUtilityCompanys Experience,JournalAWWA, February 1980.DeRonja, F.S., Investigation of Failed Copper Water Service Lines, for Washington Suburban SanitaryCommission, April 1990, (unpublished).5Woodside, R.D., Waters,F.O., nd Cornet, I., Corrosion and Other ProbIems in Copper Tubing in SomeSouthern California Housing Tracts, roceedings of the Third InternationalCongress on Metallic Corrosion,Moscow, 1969.

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contact with a corrugation. Th is created a situation where othe r mechanisms, most likelyaggressive water, quickly corroded the copper pipe.

FLORIDA INSTALLATIONSThe plumbing installations were similar in each of the homes under investigation in Florida. Allof the homes are built on concrete slab-on-grade foundations. A polybutylene water service runsfrom the public supply up to the foundation. All of the remaining water supply plumbing iscopper. Sub-slab water supply pipes are type L copper enclosed in a continuous plastic sleeve.There are no joints in the s leeve below the slab. The sleeve terminates just above the floor slab.The joint between the sleeve and copper is typically caulked at some point during constructionwith a comm ercial caulking compound.

Because the fit between the 3/4-inch I.D. leeve and the 1/2-inch copper is tight, the copper isfrequently lubricated prior to sliding it through the sleeve. Dishw ashing liquids and othercommercially available soaps are used as the lubricants, although specific soaps were 'notidentified.

METALLURGICAL INVESTIGATIONResearch Center staff did not have the opportunity to observe any of the failures directly sincethey were repaired as soon as they were detected. None-the-less, two sam ples of failed piperetained by the builder were obtained and analyzed for possible causes of failure.

The first set o f sam ples was forwarded to the C opper Development Association (CDA) inGreenw ich, Connecticut. The second set was analyzed by Forensic Metallurgy Assoc iates(FMA), a private forensics service in Springfield, Virginia. Follow-up tests were conducted byFMA on three soil samples taken from the area near the reported failures: one sample of fillmaterial that is used to su rround the sub-slab plumbing, and two samples of native soil. Resultsof each analysis are included in the Appendix.

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RESULTSResults of the independent laboratory investigations were similar. Both conc luded that thecorrosion was due to contact between the copper pipe and an aggressive solution, possiblycontaining chloride and sulfate ions. Poten tial source s of the water for the solution includegroundwater or surface water that entered the sleeve during construction or condensate thataccumulated after construction.

Soil test results indicated that all three samples had a pH of 8.1 and contained carbonateminerals. The presence of moisture, an alkaline pH, and carbonate minerals will cause corrosionof copper. Sulfate and chloride ions in solution can also cause corrosion of co pper. However,neither of these were present in appreciable amounts in the soil.

RECOMMENDATIONSIt is apparent that the protective sleeve serves as a co llection point for water that combines withaggressive minerals in the soils, leading to corrosion that creates a failure in the copper. Wherelocal experience indicates that a sleeve is necessary with copper pipes, it may be appropriate touse an alternative pipe material or to install the sleeve with the following recommendations:

The sleeve should be one continu ous section. Join ts should be avoided , but if used, theyshould be watertight.

The sleeve should be capped at its ends until the copp er is installed to prevent water fromentering during construction.

Flexible couplings or caulking may be used to close the gap between the copper and thesleeve.

The sleeve and cop per should be fr ee of soil particles and other foreign substances thatcould combine with condensate or moisture from other sources and a ttack the copper.

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Further investigation should be considered to identify the extent of these types of failures and tocollect additional data that could more firmly support these recommendations. Additionalinvestigation should also address whether the benefits of sleeving the copper outweigh thepotential problems the sleeve may cause. For example, in well-drained soils, it may be possibleto install the sub-slab copper directly in the soil.

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APPENDIX AFailure Analysis


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COPPER WATER TUBE/FITTING SPECIMENMULTICON SOUTHEAST, INC.DAVIE, FLORIDABackground

In August 1991, Mr. A.G. Kireta, Regional Manager for the CopperDevelopment Association (CDA) in the eastern states submitted acopper water tube/fitting specimen to the CDA office inGreenwich, Connecticut for laboratory examination. The specimenconsisted of a 29.1-inch length of 0.5-inch diameter (nominalsize) Type L copper water tube with a copper coupling soldered toone end which was, in turn, soldered to a 197.5-inch length ofType L capper water tube. It had been removed from a domesticwater line, under-the-slab, at an unidentified residenceconstructed by Multicon Southeast, Inc., Davie, Florida.According to the information furnished, the specimen wasrepresentative of other, under-the-slab, tubes which haddeveloped leaks in time periods ranging from six months to fouryears. It was also reported that all of the leaking coppertube/fitting sections had been located inside polyethylenetubes/sleeves (i.e., in accordance with state codes).

ResultsExamination of the outside surface of the specimen revealedseveral areas of severe pitting attack (e.g., ee the encircledareas in Figure 1). The corrosion-induced pits contained porousreddish-brown cuprous oxide (Cu2O) hich was typically overlaidwith some green colored copper corrosion products (Figure 2).Stereomicroscopic examination revealed that one of the corrosion-induced pits had propagated through the tube wall (i.e., seeencircled area on the third tube section from the top in Figure1).type perforation had initiated on the outside surface of thetube.Energy dispersive spectroscopy (EDS) and microchemical analysis(MCA) revealed that the green colored copper corrosion productsassociated ith the pitting attack contained major quantities ofcopper, minor amounts of chloride and sulfur (as sulfate), semi-minor quantities of calcium and trace amounts of silicon. Thegreen colored copper corrosion products consisted primarily ofcopper chloride(s) and copper sulfate.

It was clearly evident that the nearly-microscopic pinhole-


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Figure 1 - SECTIONS SHOWING TH E REPRESENTATIVE OUTSIDESURFACE OF THE UNDER-THE-SLAB COPPER WATERTUBE/FITTING SPECIMEN FROM DAVIE, FLORIDASeveral areas of localized pitting attack existedon the outside surface (e. g., see encircledareas).propagated through t he tube wall (i.e ., seetop)

One of these corrosion-induced pits hadencircled area on the third tube section from the

(Magnification: 0.6X)


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Where pitting attack had not taken place on t h e o u t s i d e surface,there was no significant deterioration by the externalenvironment. Basically, the copper in these essentially-unaffected areas was covered with a protective tarnish film ofreddish-brown uprous oxide. At: several locations, the cuprousoxide was overlaid with a thin friable layer of somewhat loosely-adherent green colored copper corrosion products (e.g., see thesecond tube section from the top in Figure 1) which appeared tohave been deposited on the outside surface by the evaporation ofwater which had been transported from pit sites.The total specimen was subsequently sectioned lengthwise in orderto examine the inside surface.Examination of the inside surface revealed no significantdeterioration by the water conveyed. In general, the insidesurfaces of the tubes and fitting were covered with a protectivetarnish film of reddish-brown cuprous oxide.colored copper corrosion products existed on the watersidesurface, no major pitting attack had occurred to the underlyingcopper. It was clearly evident that these longitudinally-oriented corrosion products were soldering flux-related. Forexample, green colored copper corrosion products were observed tobe associated with an 11-inch long sticky petrolatum-basesoldering flux-run which existed at one location on the insidesurface.Where pitting attack had not taken place on the outside surface,micrometer caliper measurements revealed that the tubes on thespecimen still satisfied the wall thickness requirements ofAmerican Society for Testing and Materials (ASTM) StandardSpecification B88 for Seamless Copper Water Tube. The wallthicknesses varied between 0.036 and 0.037-inch which is typicalfor 0.5-inch diameter Type L copper water tube. Similarly, thecoupling still satisfied the wall thickness requirements ofAmerican National Standard ANSI B16.22-1980 for Wrought Copperand Copper Alloy Solder Joint Pressure Fittings.Based upon examination of the specimen submitted for laboratoryinvestigation, it can be concluded that the cause of the pinhole-type perforation through the tube wall was corrosion-inducedpitting attack which had initiated on the outside surface.Although some soldering flux-initiated corrosion had taken place,there was no significant deterioration on the waterside.

Although some green


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Figure 2 - HIGHER MAGNIFICATION VIEW SHOWING REPRESENTATIVECORROSION-INDUCED PIT SITES ON THE OUTSIDE SURFACEOF THE SLEEVED SPECIMEN FROM DAVIE, FLORIDAThe corrosion-induced pits on the outside surfacecontained porous reddish-brown cuprous oxide whichwas typically overlaid with some green coloredcopper corrosion products.

(Magnification: 2X)


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ConclusionsThe only viable explanation for the external corrosion waslocalized areas of moisture/water w h i c h had collected andconcentrated inside the polyethylene tube/sleeve. The source ofthe water was possibly groundwater which had seeped. into the non-metallic tube. Alternatively, the polyethylene tube may havecollected water during construction of the residence. Regardlessof the source of the water, aggressive chloride and sulfate ionsin the aqueous environment initiated and supported the pittingattack. The source of the chloride ions could have been thegroundwater. Alternatively, their source could have been theconcrete used to form the slab. Most likely, the source of thesulfate ions was the groundwater.

RecommendationsWhen non-metallic sleeves/tubes must be placed around copper (orother metallic) tubes/fittings, the installation practice mustpreclude the ingress of moisture/water. For example, the ends oftubes must be appropriately sealed. The tubes/sleeves must alsobe free of moisture/water when the copper tubes/fittings areinserted.Preferably, copper water tubes/fittings should be placed inunderground environments without tubes/sleeves because the use ofthese shielding devices precludes the use of cathodicprotection for corrosion mitigation in those very-rare instanceswhere the soil/groundwater is aggressive to copper.Additional information on the underground corrosion of copper andthe cathodic protection technique for mitigating thisdeterioration is presented in the paper "Conditions Contributingto Underground Copper Corrosion." A copy of this paper isincluded 'in the Appendix.September 18, 1991JRM/AC/jm157/1


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FORENSICASSOClATESMETALLURGY7503Maritime Lane Springfield,p-A 22153 (703)455-4446

INVESTIGATION OF AFAILED COPPER WATER SUPPLY LINE

Prepared forNAHB National Research Center400 Prince George's BoulevardUpper Marlboro, MD 20772-8731

byFrank S. DeRonja

April 30, 1992

FMA File No. 203251


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Backaround:A copper water supply line under a residential foundation in Davie, Florida, failedas a result of perforation of the copper tube wall after about three years of service. Th e

copper line had been installed within a protective plastic tube sleeve that passedthrough and underneath the concrete foundation slab.

Sections from the failed supply line and a sample of the type of sleeve materialused in the installation were furnished to Forensic Metallurgy Associates to identify thepossible cause(s) of the copper tube failure. Figure 1 shows a general view of thesamples that were received for study.

Specimens Examined:

Q1: Section of failed copper water supply line containing a perforatedwall.Q2: Section of failed copper water supply line exhibiting corrosion

damage.K1: Sample of plastic tube sleeve.

Examination Results and Observations:

Measurements of Specimens Q1 and Q2 revealed that the copper tube satisfiesthe wall thickness requirements of the American Society for Testing and Materials(ASTM) Standard Specification B88 for 1/2-inch diameter, Type L, seamless copperwater tube. Compositional analysis by energy-dispersive x-ray spectrometry (EDS)disclosed that the tube composition is consistent with that set forth inthe B88Standard.

Microscopic examinations of Specimens Q1 and Q2 revealed that the externalsurface lacks a continuous film of protective cuprous oxide (Cu2O) and displays areasof pitting corrosion. One of the corrosion pits on specimen Q1 had completelypenetrated the tube wall and formed a pinhole. The inside surface of the specimensis covered with protective cuprous oxide andshows nosignificant deterioration from theinternal environment. Figures 2and 3 show views of the corrosion-damaged externalsurface. The location and pattern of the corrosion attack indicate that portions of thecopper supply line had been incontact with a liquid. Aqueous solutions containing highcontents of oxidizing acids, aerated non-oxidizing acids, ammonia compounds fromfertilizer, or oxidizing salts are most destructive to copper because they prevent theformation of or dissolve the protective cuprous oxide film. Pitting is the usual form of

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corrosive attack of copper when the protective cuprous oxide film has not completelyformed or has been dissolved or has been exposed to extraneous surface deposits ofdirt or other foreign substances.

Specimens Q1 and Q2 were washed with distilled water to remove superficialsurface deposits and then examined with a scanning electron microscope (SEM).Figure 4 shows views of the pinhole failure and a nearby pit on Specimen Q1.

Compositional analyses by EDS revealed the pitted areas on both specimenscontain chlorine and elements consistent with the presence of sulfate and clayconstituents. This indicates that the copper water supply tube was in contact withground water/soil that had entered the plastic tube protection sleeve. Wet soils andwater with high concentrations of chloride and sulfate ions can be extremely corrosiveto copper metal, particularly where the water is entrapped and stagnated.

Typical EDS analysis spectra for the compositions of the surface deposits on thespecimens are shown in Figures 5 through 7.

The microstructure of Specimen Q1 was examined in the pitted area near thepinhole. Figure 8 shows where the metallographic sample was removed from thespecimen and Figure 9 shows views of the microstructure. The examination revealedthat the corrosion pitting was not related to deficiency in the copper metal material orto stress corrosion cracking of the copper.

Examination of the K1 3/4" plastic sleeve revealed that it is an olefin plastic andas such contains no reactive chemical constituents that could be detrimental to copperin physical contact with it.

Conclusions:Based on the above results and observations, the copper water supply line failed

prematurely because of external pitting corrosion. The pittingwas caused by exposureof the copper tube to highly corrosive water/silt that had entered the plastic tubeprotection sleeve.

Any soap-type lubricant that may have been used to facilitate insertion of thecopper tube into the sleeve was probably not a factor in the pitting corrosion. Withrespect to other types of substances or liquids that may have been used as a "lubricant"or that may have been applied during termite or rodent control, a knowledge of specificingredients in the substance is necessary to determine if that substance could havebeen a contributing factor to the pitting corrosion.

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Recommendations for Eliminating the Corrosion Problem:Based on the examination results, corrosive water/silt was present within the

plastic sleeve and provided th e environment for corrosion of the copper tube within thesleeve. Therefore, it appears that the corrosion problem can be eliminated by takingprecautions that will prevent the entry of liquids and solids into the plastic tubeprotection sleeve. The following precautions are recommended:

1) Use a larger diameter sleeving tube so as to eliminate or minimize the needfor a lubricant during insertion of the copper tube into the sleeve. This will ensure thata lubricating substance that might affect the corrosion behavior of the copper tube ormight be detrimental to the plastic sleeve is not introduced into the system.

2) Protect the sleeve from accidental entry of soil during installation by cappingthe sleeve ends.

3) If sleeve sections must be joined, make the connection with watertightcouplings.4) Keep the sleeve ends capped until the copper tube is inserted into the sleeve.5) After insertion of the copper tube into the sleeve, seal the sleeve at each end

with a Fernco-type flexible coupling to prevent entry of ground water, rain water ormoisture, If lexible couplings are not available, seal the ends with an adequate amountof elastic caulking sealant.

6) During replacement of any failed water supply lines, ensure that the sleeveis watertight and that no water is present within the sleeve before insertion of the newreplacement copper tube.

Recommendations for Additional Technical Investigation:The conclusions and recommendations derived from the above study should only

be considered tentative since the study was based on limited availability of informationand samples relating to one water supply line failure. It would be desirable to studyanother similar type of copper tube failure in the Davie, Florida region to ensure that alllogical corrosion variables have been adequately considered. Such a study shouldbegin before repairs are made to the failed supply line and should include the following:

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Figure 1. General view of samples, as received condition.


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Figure 2. Close-up views of Specimen Q1 . Bottom photoshows pitting corrosion and the pinhole failure (arrow).

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Figure 4. SEM views of Specimen Q1. The top photo showsthe pinhole as viewed from the external surface; thebottom photo shows a corrosion pit near the pinhole.

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EG&G O r t e c System 5000Spectrum P lot t ing ProgramP r in t p lo t V O Z . 0 5

Sample ID: Copper line w i t h pin h o le , i n holeEnergy Range: 0 - 20 keV 1 0 eV/ch H i ResP r e s e t : L i v e Time 100 SecondsReal T i m e : 309.52 Sec. L i v e Time: 100.00 Sec.60% Deadtime 30307 Counts/Second

Acquisition d a t e : 09-Apr-91 Acquisition ti e 09:30:00


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EG&G O r t e c S ystem 5000S p e c t ru m P l o t t i n g P ro gr amPrintplot V02.05

Sample IC: Copper line w i t h pin ho l e , blocky solidEnergy Range: 0 - 20 keV 10 eV/ch Hi ResPreset: Live T i m e 100 SecondsReal T i m e : 1041.06 Sec. Live Time: 100.00 Sec.

81% Deadtime 40794 Counts/SecondAcquisition da t e : 04-Apr-91 Acquisition time: 09:45:18


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EG&G Ortec System 5000Printplot V O Z . 0 5Spectrum Plotting Program

Sample ID: Copper line no hole, pre-hole a r e aEnergy Range: 0 - 20 kev 10 eV/ch Hi ResPreset: L i v e Time 100 SecondsHeal T i m e : 325.70 Sec. Live Time: 100.00 Sec.69% Deadtime 27955 Counts/Second

A c q u i s i t i o n d a t e : 09-Apr-91 Acquisition time: 11:02:50


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Figure 8. Views of Specimen Q1 after removal of themetallographic sample. The arrows designate t h epinhole failure.


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APPENDIX BSoil Tests


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FORENSICMETALLURGYASSOCIATES7503 Maritime Lane Springfield, VA 22753 (703)455-4446

INVESTIGATION OF AFAILED COPPER WATER SUPPLY LINE

Prepared forNAHB National Research Center400 Prince Georges BoulevardUpper Marlboro, MD 207 72-8 731

byFrank S. DeRonja

July 22, 1992

FMA File No. 203251


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Backaround:A water supply line under a residential foundation in Davie, Florida, failed shortly

after installation as a result of perforation of the copper tube wall. The failed line hadbeen sleeved with a protective plastic tube that passed through and underneath theconcrete foundation slab. Forensic Metallurgy Associates conducted laboratoryexaminations and tests on samples of the failed line and reported those findings in apreviously submitted report dated April 30,1992.

The technical investigation was subsequently expanded to include analyses oftypical soils in the construction area. This report summarizes the results of the soilanalyses.

Specimens Analyzed:K2: Sample of soil, labeled "#1 Fill"K3 : Sample of soil, labeled "#2Native"K4: Sample of soil, labeled "#3 Native,

Hawke's Bluff, Lot 2, Block 13"

Examination Results and Observations:

The K 2 through K 4 soil samples were evaluated to determine their potential forcausing corrosion of copper water pipe. Measurements were made of the conductanceof a water extract of each soil (a measure of the amount of soluble salts present in thesoil), the pH of the water extract, and the neutralization equivalent relative to pH 7.0.Water extracts of the soils were also analyzed for the presence of chloride and sulfateions.

All three soil samples were found to have a pH of 8.1. This pH was well bufferedin the presence of excess soil; it fell rapidly to 7 when the soil was removed from theliquid by filtration. The presence of carbonate minerals in the soils was confirmed bythe generation of carbon dioxide gas when the samples were treated with acid. Noappreciable amounts of either chloride or sulfate were found in any of the three extracts.The results of electrical conductance measurements and the neutralization equivalentdeterminations are presented in Table 1.

The combination of an alkaline pH and carbonate minerals in moist soil will causecorrosion of copper metal in contact with the soil. Copper metal etches slowly in an1


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Specimen Conductivity

K 2 (fill) 108 mmoh

K3 (native) 118mmohsK4 (native) 114 mmohs

Neutralization Equivalent(total alkalinity to pH 7.0)732.3 mg CaC03 per kg soil

1077.51007.5

Copper Failure

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