METALS SCREENING IN PAINTED CONCRETE INFORMING DECISIONS AROUND ONSITE REUSE VERSUS OFFSITE DISPOSAL

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1 METALS SCREENING IN PAINTED CONCRETE INFORMING DECISIONS AROUND ONSITE REUSE VERSUS OFFSITE DISPOSAL Introduction Alex Davies-Colley & Joanne Ferry, Tonkin & Taylor Ltd 9 Clifton Road, Hamilton The Church of Jesus Christ of Latter-Day Saints Trust Board is in the process of large scale redevelopment of the former Church College of New Zealand campus. Most of the buildings located on the former campus were built in the 1950s. Many of the buildings are constructed of concrete blocks which have been painted. Given the age of the buildings, some were likely to have been painted with lead-based paint which was commonly used in New Zealand prior to the 1980s as a pigment, to speed up drying, and to increase the paint lifespan (MfE, 1997). As part of the redevelopment of the former Church College campus, many of the buildings are proposed to be removed. This will result in the generation of a large amount of waste concrete. Tonkin & Taylor Ltd (T&T) were engaged to assess the suitability of waste concrete (once crushed) for reuse as cleanfill in defined areas around the site as an alternative to landfill disposal. Concrete is identified by the Waikato Regional Council (WRC), and Ministry for the Environment (MfE) as cleanfill material. However, crushed concrete which includes leadbased paint may not meet other cleanfill criteria, which specifically excludes materials with leachable components and hazardous substances. MfE identifies materials painted with lead-based paint as an unacceptable cleanfill material (MfE, 2002). The reuse of crushed concrete which contains lead-based paint may affect human health or the wider environment if it is not placed appropriately. Other less commonly considered potentially toxic metals (particularly zinc) are also known to be present in older house paints (Hall& Tinklenberg, 2003). To assess the presence of lead and other metals, in situ testing of more than 60 concrete block buildings was conducted using a portable XRF (X-ray fluorescence) instrument. A 1

2 portable XRF is a field screening tool that is capable of detecting the relative concentrations of a wide range of metals. It is able to provide real time information on the concentrations of metals for a large number of samples. The portable XRF produces a concentrated beam of x- rays which excites the constituents of a sample at the sub-atomic level and results in an emission (fluorescence) of x-rays from individual atoms. Each element has a characteristic spectrum which is detected by the XRF and used to calculate a relative concentration for that particular metal (Kalnickya& Singhvi, 2001). Portable XRF units have various uses including mining and exploration, scrap metal sorting, and environmental remediation. Sample substrates can include in situ soils, thin films and particulates, and paint (Kalnickya& Singhvi, 2001). XRF analysis has been successfully used as a portable screening tool for the presence of lead-containing paint in real-world field situations (Ashley et al., 1998) for over 25 years (Afshari, Nagarkar, & Squillante, 1997). XRF analysis has also been used to non-destructively assess relative concentrations of other metals (including zinc and titanium; used more recently as substitutes for lead) in house paints (Hall& Tinklenberg, 2003). Depth of x-ray penetration is variable depending on type and composition of the sample and is likely to be between a few hundred µm and more than 1 cm (USEPA, 2004; Block et al., 2006). Laboratory analysis of ground concrete samples was used to correlate the XRF results and to develop assessment criteria. We formulated a robust methodology to enable the in situ assessment of anticipated waste concrete building materials prior to demolition to determine whether or not they meet the WRC cleanfill definition. This paper shows that portable XRF testing can be used to assess painted concrete for cleanfill suitability. Methodology Approach In this investigation we first used laboratory analysis to confirm that the paint (rather than the underlying concrete) was the main source of lead. We then trialled the use of a paint shop test kit to assess for the presence of lead and when that proved unsuccessful a portable XRF was trialled. Laboratory analysis was then undertaken on a limited number of painted concrete samples to calibrate field testing (portable XRF) results. The investigation involved a quality assurance programme incorporating: (1) portable XRF depth testing to 2

3 determine that the portable XRF is assessing the full thickness of the paint, (2) portable XRF quality assurance testing to assess reproducibility, and (3) lab replicate analysis to assess the variability of the samples. Results of the quality assurance programme showed that XRF testing was reproducible, with the results suitable for interpretation, and that sample variability was not considered to affect the outcomes of the investigation. Portable XRF testing identified elevated concentrations of several metals including titanium and zirconium. Although not discussed here, titanium and zirconium are considered unlikely to have a significant adverse effect on the environment. Details of the quality assurance programme, and consideration of titanium and zirconium, are provided in full in the T&T investigation report (T&T, 2013). Portable XRF testing For this investigation a Niton XL3t portable XRF analyser was used. The portable XRF analyses concentrations of 24 metals. The results were logged electronically by the instrument for subsequent data download. At each testing location, the lens of the portable XRF was held flat against a relatively smooth painted concrete block section. XRF analysis was conducted until the on-screen lead concentration had stabilised, or for the full length of the testing cycle (approximately 30 seconds). The testing location was recorded on a plan of the site. In situ XRF testing was undertaken across more than 60 concrete block buildings and other concrete structures which are to be removed. Testing was conducted at several locations (both inside and outside) at each building. Over 700 individual XRF tests were undertaken across the site. Laboratory analyses Seven representative samples of painted concrete blocks were collected which exhibited a range of portable XRF lead concentrations (between 32 and 8,204 mg/kg). The samples comprised a portion of a concrete block with paint on one side only, and typically represented half of the total wall thickness. The samples are considered to be representative of typical painted concrete blocks found on site, and the ratio of paint to concrete is likely to be consistent with the proposed crushed material. Samples were shipped to Hill Laboratories, Hamilton, under chain of custody documentation. 3

4 The entire concrete sample was crushed with a rock grinder at the laboratory to replicate the concrete crushing process, and then sieved through a 2mm sieve. In reality, the crushed material used as cleanfill will contain fragments much greater than 2mm. Therefore, the laboratory methodology is likely to be conservative with regards to metals mobilisation as it would result in a greater relative surface area than would occur onsite when reused as cleanfill. A subsample from the ground and sieved sample was then analysed as follows: Total metals analysis for arsenic, lead, and zinc (elements which portable XRF results indicated may be elevated in the paint) to allow direct comparison against the adopted cleanfill criteria; and Synthetic precipitation leaching procedure (SPLP) analysis for arsenic, lead, and zinc to mimic the effect of environmental conditions (slightly acidic rainfall) that the crushed concrete would be exposed to onsite as cleanfill and estimate the leachability of the metals by rainfall. These results can then be compared against guidelines for the protection of freshwater ecosystems to assess the potential environmental effect. Cleanfill acceptance criteria WRC do not define thresholds for contaminants in cleanfill. Therefore, guidelines for sensitive land uses and potential receptors have been adopted as discussed below. Adopted cleanfill criteria have been developed using soil guidelines for standard residential land use from New Zealand (MfE, 2012), Australia (NEPC, 2013), and the United States (USEPA, 2013) to assess the potential risk to human health. To assess the potential effect of leachate from the material on ecological receptors, water quality guidelines (ANZECC, 2000) for the protection of aquatic species have been used. A direct comparison of leachate quality to the water quality guidelines is conservative, as we have made no assumptions on dilution or attenuation of these contaminants in ground or surface water prior to discharging to surface water bodies. Site specific guidelines have been developed for lead and zinc in accordance with the ANZECC (2000) methodology based on the hardness of the resulting leachate. 4

5 Results and discussion Portable XRF testing results An initial screening assessment of the data was undertaken by comparing all individual XRF results directly with residential guidelines for soil. The results of the initial field screening identified that, while some elevated concentrations of metals were recorded, most of the buildings recorded relatively low and consistent concentrations of metals. Of the 24 metals analysed for by the portable XRF, three of the analytes (lead, arsenic, and zinc) recorded a significant number of exceedences of the residential guidelines. Lead concentrations present the most exceedences of the guideline and were variable in the paint across the site. The results show that 70 % of the lead concentrations are below 100 mg/kg, with higher concentrations typically clustered in particular areas. Less than 22 % of the data exceeded the residential criteria of 210 mg/kg, with a maximum lead value of 220,800 mg/kg recorded. 81 % of the arsenic concentrations were below the analytical detection limit (approx. 9 mg/kg), with only 12 % of the data exceeding the residential soil criteria of 20 mg/kg. Elevated arsenic concentrations are typically associated with elevated lead concentrations. Zinc concentrations show more variability. The majority of the data ranges from 500 to 3,000 mg/kg, with less than 11 % of results exceeding the residential criteria of 7,400 mg/kg. The elevated zinc concentrations are not typically associated with elevated lead concentrations. Laboratory analysis results Laboratory results are summarised in Table 1 together with respective portable XRF results. Comparison of laboratory results against the adopted cleanfill acceptance criteria shows that the leachability of the material is the controlling factor in determining compliance with the criteria. Total metals concentrations, as recorded at the laboratory, are well within the adopted cleanfill acceptance criteria. The results of laboratory testing for arsenic show very low leachability potential and low total arsenic concentrations; therefore arsenic concentrations are unlikely to affect the overall suitability for reuse as cleanfill. 5

6 Table 1 Summary of laboratory analysis results Sample No. Lead Arsenic Zinc XRF Total metal SPLP extract (g/m 3 ) XRF Total metal SPLP extract (g/m 3 ) XRF Total metal B1 8, < LOD - - 4, B2 4, < LOD - - 2, SPLP extract (g/m 3 ) B < < , < B < < < B , B < LOD B < LOD , B7r < LOD , Adopted acceptance criteria , Laboratory concentrations reported are average concentrations from two duplicate samples. 2. Average total metal concentrations included in data analysis. Shaded cells indicate an exceedence of the adopted acceptance criteria. LOD refers to XRF limit of detection. The results show a positive correlation between portable XRF and laboratory concentrations of both lead and zinc. Graphs 1 and 2 below show that the portable XRF consistently over estimates the concentration of lead and zinc in the samples. This is Lead expected as the paint represents only a very small proportion of the total sample that was analysed in the laboratory. Samples B7 and B7r (a primary and duplicate sample pair) recorded consistent Zinc XRF and total metal concentrations; however, the relationship between the two parameters for zinc is inconsistent with the other results (as shown in Graph 2). Graphs 1 and 2 Portable XRF concentrations vs. total concentration in ground, sieved samples. 6

7 While higher total lead concentrations in the laboratory do correlate with higher SPLP lead concentrations, the relationship between the parameters is inconsistent as shown in Graphs 3 and 4. All results Low range results Low range results (Graph 4) Graphs 3 and 4 Laboratory lead concentrations vs. SPLP lead concentrations This may be a result of the paint containing different forms (therefore different leachability characteristics) of lead. Despite the inconsistent relationship, the data shows that all samples with total lead concentrations of less than 15 mg/kg (lab), recorded SPLP lead concentrations below the adopted acceptance criteria of g/m 3. Therefore, using this conservative relationship between total metal concentrations and SPLP concentrations, a regression analysis has been completed to calculate the maximum acceptable portable XRF concentration. Using a laboratory lead concentration of 15 mg/kg, the maximum acceptable portable XRF lead concentration is calculated to be 300 mg/kg. The relationship between total zinc concentrations and SPLP concentrations is more consistent as shown in Graph 5. Results for both B7 and B7r are included (values on right hand side of graph) which demonstrates the potential variability within the method. To assess the impact of this variability, a regression analysis has been undertaken to calculate the acceptable portable XRF concentration using the result from B7, then repeated using the result from B7r, as shown in Table 2. Graph 5 Laboratory zinc concentrations vs. SPLP zinc concentrations Table 2 provides values used in the calculation of the portable XRF acceptance criteria. 7

8 To allow for the variability between portable XRF, total metal and SPLP concentrations, and the small number of data points, more conservative portable XRF concentrations have been adopted for both lead and zinc as acceptance criteria for cleanfill. A factor of safety of three has been applied to the calculated acceptance criteria for both lead and zinc. Table 2 Adopted portable XRF acceptance criteria Lead Zinc Acceptance criteria (ANZECC) g/m g/m 3 Corresponding maximum total metal (lab) 15 mg/kg Calculated maximum acceptable XRF concentration 300 mg/kg 17,750 23,400 mg/kg 1 Adopted portable XRF acceptance criteria 100 mg/kg 6,000 mg/kg 1 - Range represents variability within the data set (use of B7 and B7r) Based on comparison of portable XRF data against the adopted portable XRF acceptance criteria, approximately 48 out of 67 of buildings assessed are considered likely to be suitable for cleanfill. The proportion of waste concrete that these buildings represent is estimated to be slightly higher, (around 75 % of the total volume) based on building size. Conclusion Concentrations of toxic metals (particularly lead, zinc, and arsenic) are present in painted concrete at the former Church College campus. This could preclude the classification of this material as cleanfill. This investigation has involved the development of a methodology by which painted concrete can be quickly and easily assessed in situ to determine whether or not it is likely to meet cleanfill criteria. Adopted portable XRF acceptance criteria have been developed for lead and zinc using a degree of conservativeness to account for variability and investigation uncertainty. Approximately 48 out of 67 of the buildings assessed in this investigation were found likely to be suitable for cleanfill. This material may have otherwise required disposal to landfill or required pre-treatment prior to reuse. The outcome, that painted concrete block can meet cleanfill criteria, will result in significant cost savings for the redevelopment project, as well as reducing waste disposal volumes to landfill while generating a useful resource resulting in a more sustainable development. Acknowledgements We would like to thank Paul Coward and Don White from The Church of Jesus Christ of the Later-Day Saints Trust Board and Chris Dawson from Bloxam Burnett and Olliver for the opportunity to be involved in this project. 8

9 Bibliography Afshari, S., Nagarkar, V., and Squillante, M. R.; 1997; Quantitative measurement of lead in paint by XRF analysis without manual substrate correction, Applied Radiation and Isotopes; 48, 10-12, Ashley, K., Hunter, M., Tait, L. H., Dovier, J., Seaman, J. L., and Berry, P. F.; 1998; Field investigation of on-site techniques for the measurement of lead in paint, Field Analytical Chemistry & Technology; 2, 1, Australian and New Zealand Environment and Conservation Council (ANZECC); 2000; Australian and New Zealand guidelines for fresh and marine water quality, New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ). Block, C. N., Shibata, T., Solo-Gabriele, H. M., and Townsend, T. G.; 2007; Use of handheld X- ray fluorescence spectrometer units for identification of arsenic in treated wood, Environmental Pollution; 148, 2, Hall, G. S. and Tinklenberg, J.; 2003; Determination of Ti, Zn, and Pb in lead-based house paints by EDXRF, Journal of Analytical Atomic Spectrometry; 18, Kalnicky, D. J. and Singhvi, R.; 2001; Field portable XRF analysis of environmental samples, Journal of Hazardous Materials; 83, 1-2, Ministry for the Environment (MfE); 1997; State of New Zealand's Environment 1997,Ministry for the Environment. Ministry for the Environment (MfE); 2002; A guide to managing cleanfill, Ministry for the Environment. Ministry for the Environment (MfE); 2012; Users Guide- National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health. Ministry for the Environment. National Environmental Protection Council (NEPC); 1999 (updated 2013); National Environment Protection (Assessment of Site Contamination) Measure 1999, National Environmental Protection Council Service Corporation. Tonkin & Taylor Ltd (T&T); 2013; Church College Redevelopment Project Assessment of concrete building materials for reuse. United States Environmental Protection Agency (USEPA); 2004 (updated 2013), Regional Screening Levels (RSL) for Chemical Contaminants at Superfund Sites, United States Environmental Protection Agency. United States Environmental Protection Agency (USEPA); 2004, X-ray fluorescence (XRF) instruments frequently asked questions (FAQ), United States Environmental Protection Agency. 9