Michigan Department of Transportation - MoDOT

MatesApril 1991

————ADVANCES IN BRIDGE BLAST CLEANING TECHNOLOGY This system was effective but proved t% be-- toitly-’’aiia”––

introduced some new environmental problems in trvin~Since the publication of Bob Nordlund’s article on the

management of hazardous waste generated by the blastcleaning of Michigan% steel bridges (MATES Issue No. 50,1991), a new set of requirements has been developed bythe Departments involved. This article provides a briefgeneral background and describes the improved environ-mental protection techniques now specified for contractbridge painting. For information on the toxicity testingand disposal requirements of blasting residue, please referto the earlier article.

Prior to 1975, it was common practice to coat thestructural steel in bridges with lead-based paints. Sincethen lead-based paints have been banned due to the adverseeffects of lead on human health and on the environment.A problem of considerable magnitude arose during the1980s involvimg the safe removal of these lead-based paintsduring the maintenance repainting of bridges.

Maintenance repainting starts with an abrasive blastcleaning process that generates a large amount of dustand a waste material that includes the paint chips, abrasiveparticles, dust, and debris removed from the bridge. Thedust generated by blasting and the residual material istoxic to both humans and the environment because of thehigh lead content of the paint being removed. Typically,the total lead content of the waste material will rangefrom 3,000 to 5,000 parts per million (ppm). With someof the more advanced removal techniques involving therecycling of steel grit the amount of waste materialgenerated is greatly reduced but the total lead contentof the waste material can be in excess of 50,000 ppm. Anywaste with a total lead content in excess of 500 ppm isconsidered to be toxic to humans.

Joint Task Force Develops Specification

In the fall of 1986 a ioint task force was formed withmembers from the Michigan Departments of Transportation,Natural Resources, and Public Health to devise a systemfor removing lead-based paints from bridges that wouldmitigate the problems of human exposure and environmentalpollution. At that time the technology available to theindustry did not offer a good system for total containment,so the philosophy of ‘lBest Available Control Technologyrl(BACT) was adopted. This resulted in a specification thatallowed some dust and other waste material to escapefrom the work area when no human exposure would beanticipated adjacent to the structure (a limit ofapproximately 200 ft). The specification for these bridgesrequired ground cloths (or a barge in the case of a bridgeover a waterway) to be placed under the work area to collectthe waste materials. Tarpaulins were draped around thework area to limit the amount of dust that would escape.When residential, recreational, or other occupied propertiesexisted within the 200 ft limit, total enclosure of the workarea was required. Because of the lead level in the dustgenerated by blast cleaning within a total enclosure, air-fedblasting hoods were not adequate to protect the workers.Thus, a two-step procedure was developed for the blastcleaning. The first step involved a water-abrasive blastwhich removed the paint without generating dust. Thiswas then followed by a dry abrasive blast after the steelhad adequately dried (usually requiring two to three days).

to contain the water used in wet-blast_ing and rinsing “th;structure,

Environmental Concerns Intensified.—__—.. _——_—. _.... __ .—— ——_— ——-—________

During the 1990 construction season all problemsassociated with the approved 1987 BACT system cameto a head when the Department received citations fromthe Michigan Department of Natural Resources (MDNR)for alleged violations on seven different bridge paintingprojects. In addition to citing several alleged violationsof the hazardous waste management laws, the MDNR wasno longer willing to accept the release of dust and theother waste material to the environment, regardless ofthe proximity of humans to the bridge. Public Act 64prohibits such releases to the lands and waterways of theState without a permit and the MDNR is not willing toissue such a permit for bridge blast cleaning. This resultedin reconvening the joint task force to develop a newcontainment approach acceptable to all parties.

,—The joint task force did a thorough review of the problems

associated with the 1987 BACT system as well as thetechnological advances made by the blast cleaning andcontainment industries. The task force concluded thatthe state-of-the-art had advanced to the point where totalcontainment was now available at reasonable cost. Totalcontainment would afford complete protection to theenvironment and would eliminate the potential for humanexposure in proximity to the bridge. A new specificationwas issued by the Department in February 1991 requiringthe use of this new technology.

New Total Containment Technology

The new specification requires that all bridge blastcleaning be performed within a total containment enclosureof the work area regardless of paint type on the steel.The actual design of the enclosure is left to the contractorwith the stipulation that it must prevent the release ofany dust or waste material to the air, ground, or waterway.Within the enclosure all waste materials must be collectedand cleaned up and stored daily.

To protect the blasting operators within the enclosure,the contractor must install air moving equipment capableof creating a Ifnegative pressure condition.ll The air flowwithin the work enclosure must be adequate to sufficientlypurge the air of dust in order to provide good visibilityand a safe working environment for the blasting operators,who must still wear air-fed hoods for protection. Thisnegative pressure (or relative vacuum) within the enclosurealso prevents the escape of dust or waste materials tothe outside environment. All air exhausted from the workarea must be filtered by means of a portable filtering systemor bag house. This filtering system affords completecollection of all the dust and waste materials containinglead that previously may have escaped to the environment.

This negative pressure enclosure approach to the problemhas been under development since 1987 by several Michiganpainting contractors. The feasibility and cost effectivenessof the system have been well demonstrated by the -

Materials and Technology Engineering and Sciencepublished by MDOT’S Materials and Technology division

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.___—.-——_ —______ ._..>.._ _______contractors who have used this system in lieu of the two-step expll’clt about the contractor’s responsibilities in conforming -wet blast/dry blast system specified in the 1987 BACTsystem. The equipment involved is now readily availableto all contractors who wish to develop the capability ofdoing negative pressure containment work. The Depart-ment is now actively letting bridge painting contractsspecifying this method, regardless of coating type on thestructure. It is anticipated that the bid prices for the blastcleaning of the steel will increase between 30 to 40 percentfor this system. This cost increase is well justified bythe environmental protection achieved. The alternativeis to not paint steel bridges but schedule their replacementafter corrosion reduces the bridges’ steel members to thepoint of obsolescence. This option is unacceptable in mostcases and the costs associated with such a program wouldultimately be prohibitive.

Waste Management Developments

Due to the presence of lead and zinc in the paints usedon steel bridges, all waste materials generated by the blastcleaning process have the potential of being classifiedas a hazardous waste. A waste is defined as hazardousby an acid leaching test, not to be confused with the toxicnature of the waste. All waste materials must be testedby the Department in accordance with the U. S.Environmental Protection Agency’s “Toxicity CharacteristicLeachate Procedure” (TCLP). This test simulates the amountof lead, zinc, or other toxic materials that could be leachedffom the waste if exposed to an acidic environment suchas acid rain percolating through a non-sealed landfill. Thestrength of the acid solution in the leaching test is equivalentto that in a typical Type II (sanitary) landfill. If the TCLPtest reports leachable lead equal to or greater than 5.0ppm, the spent material is classified as a hazardous wasteand must be handled, stored, transported, and disposedof at a licensed hazardous waste facility in accordancewith the very complex requirements of Public Act 64. Thishas been a source for citation of alledged violations inthe past and the Department’s new specifications are very.—

TECHADVISORIES

The brief information items that follow here are intended to aid MDOT technologists by advising or clarifying, for them,current technical developments, changes or other activities that may affect their technical duties or responsibilities.

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to State and Federal waste management laws. The contrac~ Ispecifications hold the contractor fully responsible forcompliance.

Non-hazardous Waste Measures

A revolutionary development is occurring in the methodused to remove lead-based paint by blast cleaning and theresulting waste material. It has been discovered by industrythat if steel grit is usedin the blasting process, the resultingwaste material reliably tests non-hazardous by the TCLPtest. Evidently, the leachable lead in the waste combineschemically with the steel. This favorable result is achievedby using either steel grit in total, usually with a recyclingprocess, or by the addition of at least eight percent byweight of steel grit to the mineral abrasives used for blastcleaning. The non-hazardous waste materials are stilltoxic to humans if exposure occurs, but the storage anddisposal costs are much lower. The non-hazardous wastesrequire disposal at a Type II (sanitary) landfill. And asnoted previously, though considered non-hazardous, thiswaste is still toxic to humans so no other method of disposalis allowed by law.

With the adoption of the total containment systemthe problems of human health and environmental pollutioncaused by the removal of lead-based paint appear to havebeen mitigated. Industry will undoubtedly continue todevise more efficient ways of performing the blast cleaningwithin a total containment enclosure. Further developmentof steel grit usage to eliminate the hazardous wasteclassification for the resulting waste material will greatlyreduce the waste management costs and remove a significantload from hazardous waste disposal facilities, which arerapidly approaching the point of overload. The Departmenthas once again advanced to the implementation of thel~Best Available Control Technology” for its contract bridgepainting program.

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PERSONNEL NOTES--r=o_.-. _

f the Sofid’ Bi~u~~ou~~– Three new emDlovees

Because of the length of the lead articles in the last fewissues, we have been unable to recognize our retirees andnew employees. Retirement claimed three employeesrecently; in order of seniority, Tom Green, Darrell Hall,and Bob Johnson. Tom Green was the Division’s ‘seniorcitizen’ in terms of time in grade, with 42 years. Tomwas the supervisor of concrete products control, and ourscale certification program, after serving in a numberof other positions in the Division. Darrell was the Engineerof Specifications, and was recognized throughout the Depart-ment for his care and expertise in this crucial phase ofour work. Darrell came to us from the Design Division,and had a total of 35 years with the Department. Bobwas an engineering technician in the Testing LaboratorySection, whose duties involved the testing of aggregateand metals. He had a total of 31 years with the Depart-ment. These three. valued friends and workers thus hada total of 108 years serving the Department and the peopleof the State of Michigan. Those years of experience cannotbe replaced, and their expertise will be missed. ,.

have joined the Testing Laboratory Section: Bfl Redmond –as a Technician in the Aggregates and Metals Unit; JohrsStaton, Structural Testing Engineer; and, Roger Till asthe new Structural Services Supervising Engineer. TheGeophysical-Geoenvironmental Section welcomes threenew members: Scott Thayer, Environmental Engineer; BarbVetort, Geologist; and, James Woodruff, EnvironmentalQuality Specialist, all in the Geoenvironmental Unit. Welook forward to working with these new staff members,and the new perspectives they will bring to their jobs.

NEW MATERIALS ACTION

The New Materials Committee recently:Approved

Bold Eagle Barrel HarnessTensar Bituminous Pavement ReinforcementConspec 100 Non Shrink GroutPolyject 1257Super Cushion RR crossing

.Turning to new employees, we would like to welcome the ‘“ Approved for Trial Installation

following new faces to the Division. In the Research Labora- Exact Tact Tackifiertory, Mike Lsola has joined us as an Engineer in the Struc-tures Research Unit; Steve Shaughnesay is a new Labora- It should be noted that some products may have restrictions

tory Scientist in the Chemistry and Photometry Unit; and, regarding use. For details please contact chairperson of-.

Dave Smiley is the newly appointed Supervising Engineer New Materials Committee at (517) 322-1632.

This document is disseminated as an element of MDOT’S technical transfer Technology Transfer Unit

program. It is intended primarily as a means for timely transfer of technical Materials and Technology Division

information to those MDOT technologists engaged in transportation design, Michigan DOT

construction, maintenance, operation, and program development. Suggestions P.O. Box 30049

or questions from district or central office technologists concerning MATES Lansing, Michigan 48909

subjects are invited and should be directed to M&T’s Technology Transfer Unit. Telephone (51 7) 322-1637