Bridges in the USA have been an integral part of the Interstate Highway System growth. Until the mid to late 1970s, all steel bridges were protected from corrosion by paint coatings containing lead and chromate. The majority of the steel bridges in the interstate system were constructed between 1950 and 1980. Most of these structures have paint coatings containing lead and chromate (FHWA-RD-89-127). A large percentage of the existing steel bridges are currently reaching a critical level of deterioration. The expenses for rehabilitation of these bridges are complicated by the presence of lead based paint because of lead toxicity. More than 90,000 bridges - many in need of repairs - in the United States are coated with lead paint (FHWA-RD-91-100). Lead dust and fumes are released into the air whenever lead paint is disturbed during maintenance, reconstruction, and demolition of bridges and other steel structures. Solid paint waste and paint wash-water is also generated onsite.
Because of its toxicity, removing lead paint from bridges and other structures is a major problem facing transportation agencies. While the hazards of lead paint removal from bridges have been identified and enormous advances have been made in the worker protection area, there is still a dire need to identify rapid cost effective methods for lead detection in-situ. Increased levels of expenditure for lead paint removal have resulted over the years.
One major problem that still persists is the presence of lead in paint waste removed from bridges and the lead paint remaining on bridges where 100% removal is not achievable. Residual lead can lead to a non lead based paint (LBP) coating becoming hazardous on subsequent removal. Currently the NYSDOT uses a conservative approach of classifying all bridge paint waste from painted bridges constructed before 1988 as hazardous wastes. This practice stems from the fact that there is no approved reliable, fast, and efficient method for classifying paint waste in situ as non hazardous. This conservative practice impacts NYSDOT bridge painting projects resulting in greater expense with increased regulatory hassles. With the advent of more accurate and sophisticated analytical equipment for in-situ field measurements, state DOTs may benefit from research investigating the reliability of such field equipment.
In-situ measurements of lead using X-Ray Fluorescence (XRF) have become the accepted mode of analysis for many federal and state agencies such as U.S. Department of Housing and Urban Development (USHUD), U.S. Environmental Protection Agency (USEPA), and New York State Department of Environmental Conservation (NYSDEC). Research using field portable XRF meters for lead indicate that the in-situ measurements are extremely accurate and can be used in place of long analytical laboratory analyses. The thermo Scientific NITON XRF- XL3t 700 detector is typically used to conduct non-destructive testing of potential lead-based (along with other metals including RCRA) paint surfaces by USHUD. The Department of Housing and Urban Development Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing describes the standard operating procedure about the use of the Niton XRF meters (FHWA, 1992). Thermo Scientific NITON x-ray fluorescence (XRF) analyzers quickly identify and quantify lead in virtually all sample types: paint, soil, sediment, dust, air, and more. Actual metal values are also displayed; permitting users to more accurately quantify the hazards associated with particular samples.
Similarly field spectrophotometers are now available for measuring lead concentrations in liquid samples. The HACH DR-2800 field spectrophotometer can be used for field measurements of lead in aqueous samples. The method is USEPA approved and can potentially measure lead concentrations in the range of 3-300 mg/L.
The research team will apply the field-portable XRF meters and field spectrophotometers to assess their effectiveness in providing reliable lead concentrations present in bridge paint waste and wash water. These measurements, if reliable, will then be used to classify the waste and/or wastewater as hazardous or non-hazardous. Accuracy of the field measurements will be determined by conducting laboratory analyses using standard inductively coupled plasma mass spectroscopy (ICP-MS) or atomic absorption spectroscopy (AA) for total metals concentration and comparing to the total metals concentration applying laboratory scale XRF. Further tests shall include the U.S. EPA toxicity leaching characteristic procedure (TCLP) for addressing whether the paint waste is classified as hazardous. Field and laboratory results will then be compared and correlated to develop a model that a state DOT can use to determine if lead based hazardous waste will be generated or not for bridge painting projects.
The overall objective of this research is to develop a field approach for assessing bridge paint waste as hazardous or non-hazardous. The technical research objectives of this project are to:
- Conduct literature review to determine existing studies on field and laboratory tests to correlate lead measurements.
- Identify and select NYSDOT bridges for the study.
- Acquire a field XRF meter and a field spectrophotometer.
- Investigate field measurements of the eight RCRA metals along with zinc in bridge paint waste using the in-situ XRF meter at a statistically significant number of bridge sites.
- Analyze the same samples for metal concentrations in the laboratory using EPA Methods, ICP-MS or AA, laboratory-scale XRF, and TCLP.
- Analyze bridge paint wash water for lead using an in-situ field spectrophotometer.
- Collect and analyze total and dissolved metal concentrations in the same wash water samples using laboratory analysis with sensitive analytical instrument such as an ICP-MS or AA.
- Compare and correlate data obtained from the in-situ studies to the laboratory results.
- Develop a reliable statistical model for NYSDOT to determine whether the bridge painting project will generate hazardous waste based on XRF analysis.