Impact of Oil-Contaminated Floodwater on Building Materials
At Tuskegee University (TU), where my colleagues and I teach and do research in the College of Engineering, we’ve learned a lot about how building materials respond to water damage and how to remediate that damage. But what about building materials exposed to contaminated water? It’s rare that floodwater contains just water.
The initial flood damage resistance work performed at TU focused on the ability of common construction materials to withstand the impacts of wetting and drying associated with exposure to flooding (see “After the Flood—There’s Hope,” HE Sept/Oct ’04, p. 18, and “Flood Testing Gets a Reality Check,” HE July/Aug ’06, p. 18). The work at TU provided a scientific basis for updating FEMA’s Technical Bulletin No. 2 (TB-2) and was used to substantiate changes to the 2015 International Residential Code (IRC) concerning construction below the base flood elevation (BFE).
Gypsum Interior Wall
Gypsum Exterior Wall
Table 1. Bioremediation Product Effectiveness
However, experience from actual floods has shown that materials that “pass” by withstanding wetting and drying can “fail” when other factors, such as exposure to polluted floodwater or residual mold development, are considered.
In 2010–12, as part of a project sponsored by the Southeast Region Research Initiative, we, along with colleagues at Mississippi State University, examined the interaction of engine oil (SAE 10W-30) in water with concrete blocks, oriented strand board (OSB) sheathing, sawn lumber in the form of 2 x 4 studs, gypsum wallboard used for both interior and exterior walls, and fiberglass batt insulation. We completed additional follow-up studies on concrete block in late 2013.
One of our goals was to identify the extent and location of chemical pollutants (represented by engine oil) found in floods in selected building materials and systems. Another goal was to evaluate the effectiveness of various potential remediation strategies on contaminated materials.
Understanding the impact of contaminants on the performance of building materials is critical, because materials that can withstand the wetting and drying cycle (for example, concrete block) can become a potential health hazard when contaminated by petroleum products. Therefore they become an unacceptable material unless a satisfactory remediation strategy is found.
Our work was done in laboratory tests that simulated flooding conditions. For all the materials tested, oil-contaminated floodwater was initially simulated using 0.5% engine oil by volume in a filtered tap water mixture. Follow-up tests with the concrete blocks used higher percentages (2%, 10%, and 100%) of oil, in order to study the effect of oil concentration on the absorption mechanism. The results discussed here are for the 2% oil/water mixtures.
We placed samples of each material in 5-gallon holding tanks that contained the appropriate amount of engine oil. Samples were tied down, when necessary, to prevent floating.
The samples remained in the tanks for three days. The oil-water mixture was then removed via transfer tubes. Wall sections were monitored for oil before disassembling. Exposed surfaces were visually inspected after draining and were monitored throughout the drying period. After another five days, samples were cut from the wall sections for analysis. These samples were labeled “wet.” Another set of samples was taken after five weeks’ drying time. This period of time was chosen to simulate the wait time that may occur after flooding before a structure is available for reentry. These samples were labeled “dry.”
Before we placed the concrete blocks in the holding tanks, we applied two coats of latex paint to all of them. We painted some on all four sides and others only on the two narrow sides. This was done because exposed concrete block in houses can be either painted or unpainted. After painting, the blocks were placed in the 5-gallon holding tanks and tested in the same way as the wall sections.
After testing the samples in oil-contaminated water, we measured the total petroleum hydrocarbon (TPH) and water content for each sample. EPA Method 8015B was used to determine the TPH concentration (see “TPH Testing”). Water content was measured using an oven-drying method.
Concrete blocks. Samples were taken by drilling ½ inch deep into several locations on front and back sections above and below the waterline. Paint was removed using an electric sanding machine prior to drilling. The collected samples were approximately the size of sand particles.
OSB sheathing. OSB was cut just above the waterline and then sliced longitudinally to provide equal sections for front and back above and below the waterline.
Sawn-lumber studs. Very small samples were cut from the 2 x 4 studs just above the waterline, where the oil stain can be clearly seen.
Gypsum wallboard. The same cutting and sampling procedures used for OSB were used for the gypsum wallboard samples.
Fiberglass batt insulation. A few grams of insulation was removed for analysis above and below the waterline.
Test Results: Visual
Photo 2 shows the two-sides-painted concrete blocks after flood testing. The block on the left was submerged for three days in water only; this block served as a control. The middle block, designated “wet,” remained in the tank for five days after the oil-water was drained and was then sent for TPH analysis. The block on the right, marked “dry,” was left to dry for approximately five weeks after the oil-water was drained. As you can see, the oil in the floodwater has left permanent discoloration on the concrete blocks below the waterline. There is also evidence of wicking of about 1 inch, characterized by the discoloration above the waterline. The “dry” block has noticeably faded and is discolored on its surface. This can be attributed to off-gassing of the adsorbed oil on the surface of the blocks. This occurs on the surface only, and the subsurface absorbed oil is still trapped inside.
For the concrete blocks painted on all sides, we sent a 1-inch slice of the “wet” sample for TPH analysis five days after testing. Particlulate samples were taken at the lab from this slice for testing. The “dry” sample was sent for analysis about five weeks after testing. Visual observation indicated little noticeable discoloration and suggested very little diffusion of oil into these blocks. Interestingly, subsequent TPH analysis did not support this observation.
Photo 3 shows “wet” and “dry” gypsum wallboard samples. The front of the gypsum wallboard has obvious oil discoloration below the waterline in both samples.
Photo 4 shows the back of the gypsum wallboard, with discoloration below the waterline similar to the discoloration on the front. Wicking and discoloration was seen at the edge of the samples that were adjacent to the studs. Wicking on the “wet” sample is about 5 inches above the waterline, while wicking on the “dry” sample is about 3 inches above the waterline. Drying appears to have reduced the extent of wicking.
We also analyzed the “wet” and “dry” OSB samples. There was clear discoloration below the waterline due to the oil contamination. The discoloration of the “dry” sample was slightly lighter than that of the “wet” sample. The back of the OSB also showed discoloration below the waterline. However, there was no significant visual difference between the “wet” and “dry” samples.
A polar substance has molecules that have an uneven distribution of electrons—that is, one region has mostly positive charges while another region has mostly negative charges. Polar substances include water, ethanol, vinegar, and glass. Fiberglass tends to be polar and therefore will not attract to the nonpolar oil.
Test Results: TPH Analysis
The TPH analysis provided a more definitive understanding of the “wet” and “dry” samples after exposure to oil contamination. The results for the concrete blocks are shown in Figure 1. Although the visual observations indicated significantly more oil in the samples painted on two sides, the TPH measurements show that the two-sides-painted and all-sides-painted samples absorbed somewhat similar amounts of oil. The sample with two sides painted showed a proportionally slightly larger reduction in oil content upon drying than did the sample with all sides painted.
Figure 2 shows the TPH measurements for gypsum wallboard used as an interior wall (no insulation and no sheathing). “Adjacent” means the portion of the sample near the stud, and “away” means the portion of the sample midway between the studs. The “adjacent” sample absorbed significantly more oil; it also showed a proportionally larger reduction in oil content upon drying. These TPH measurements are consistent with the visual observations.
The TPH measurements for gypsum wallboard used as an exterior wall (with insulation and sheathing) are shown in Figure 3. This wallboard absorbed significantly more oil near the stud than did the gypsum wallboard used as an interior wall. Away from the stud, the interior wallboard absorbed more oil than the exterior wallboard. This may be because of the insulation in the exterior wall cavity. The gypsum wallboard used as an exterior wall lost significantly more oil upon drying than the interior wallboard.
The OSB sheathing absorbed significant amounts of oil both near and away from the stud (see Figure 4). Interestingly, there was no significant loss of oil from this material away from the stud and even a small gain in the amount of oil for the sheathing near the stud. This suggests that the oil is attracted to the sheathing due to the fibrous nature of the sheathing. Batt insulation did not absorb a significant amount of oil, and much of this oil off-gassed its lighter hydrocarbon content upon drying (see Figure 5). We believe that this observation reflects the polar structure of the fiberglass insulation, which gives it no affinity for attracting the nonpolar oil (see “Polar Substances”).
Understanding the impact of contaminants on the performance of building materials is critical because they can become a health hazard.
While the original goal of the project was to examine a variety of pollutants, we eventually decided to examine engine oil alone. Since the chemical pollutants that we might otherwise have examined are typically organic materials with polarities similar to those of engine oil, we expected that the level of attraction of these pollutants would be analogous to that of engine oil. The absorption of engine oil, a nonpolar substance, by the various building materials followed a logical progression based on the nature (polar or nonpolar) of the various materials.
The oil appeared to have significantly impregnated the OSB sheathing, gypsum wallboard, and concrete blocks. The 2 x 4s and the fiberglass batt insulation showed a much lower level of impregnation. Interestingly, we found that painting concrete blocks with latex paint reduced the visual appearance of oil contamination, but did not significantly affect the TPH measurements, which remained similar for the blocks that were painted on all sides and the blocks that were painted only on two sides.
Because FEMA does not consider paper-faced gypsum wallboard, OSB sheathing, and fiberglass insulation acceptable for use where flooding can occur, and because the wallboard and sheathing showed significant potential for contamination from oil, we chose to focus our remediation efforts on concrete block. FEMA considers this material acceptable for use where flooding can occur, and it also showed significant potential for contamination from oil. We did not study the 2 x 4 studs in depth because this material is accepted by FEMA and showed only a slight potential for contamination from oil.
Remediation Strategies for Oil-Contaminated Materials
We developed alternative remediation strategies that we believed might improve the effectiveness or lower the cost of treatment on the contaminated test samples. Our focus was on oil-contaminated concrete blocks, studs, and OSB sheathing.
We initially chose three cleaning agents: Dawn Ultra Concentrated, an anionic surfactant containing no phosphates; WD-40, a mixture of more than 90% hydrocarbon materials and less than 10% inert materials; and Pour-N-Restore, a mixture of proprietary materials labeled as surfactants, chelating agents, particulates, and emulsifiers with less than 4% terpene hydrocarbons. We chose WD-40 because it has solvent characteristics that we thought might dissolve the embedded oil and make it easier to remove. Subsequently, we investigated two additional cleaning agents: ACT Terra Firma and BioWorld Hydrocarbon Treatment, (BHTP) both proprietary bioremediation products.
Our initial TPH testing used gas chromatography (EPA Method 8015B) to determine hydrocarbon content with a boiling point up to 430˚C. Gas chromatography is a technique that can analytically determine the content of a sample containing substances that do not decompose upon vaporization. It relies on the sample containing substances of different boiling points that will vaporize at different times and thus allow for their separation.
In our subsequent testing of bioremediation products, we used sandlike particles from our sampling and mixed them with the solvent. An ultrasonic bath was used to help extract the oil from these particles. Part of the oil-filled solvent was used in the gas chromatography (GC). The remainder was heated or left at room temperature to vaporize the light solvent, leaving an oily residue at the bottom of the glass tube. The residue was then weighed on a sensitive balance. The GC method gave one value, and the weight method gave another value, of the amount of oil in a specific weight of concrete. The two values do not have to be the same because the GC gives selective peaks for individual components of the oil, whereas the weight method gives a total difference in oil content. The GC technique can be used to compare individual components before and after cleaning.
In my opinion, the weight method is more conclusive than the GC method, and more representative of actual values. A nondestructive test could be conducted in the field based on the weight method. After a concrete wall or slab is cleaned, a very small chip of concrete could be taken and tested. The chip would be so small that it would not affect the integrity of the wall, and the chipped spot could easily be filled with cement paste if needed. The weight method is less than 10% of the cost of the GC method, based on labor and necessary equipment.
Initially, we performed three cleaning procedures.
Surfactant. The surfactant was sprayed over the oil-contaminated area and allowed to stand for one hour. The sample was then sprayed with hot water to remove the surfactant and was wiped with a towel.
WD-40. The WD-40 was sprayed over, and allowed to soak into, the oil-contaminated area. After one hour, this area was sprayed with hot water until no further change was noted. It was then wiped with a towel.
Pour-N-Restore. The oil-contaminated area was covered with Pour-N-Restore and allowed to stand until the Pour-N-Restore had dried to a powder. This can take up to eight hours, depending on the drying conditions. The resulting powder was removed by brushing.
We subsequently performed experiments to compare cleaning with WD-40 to cleaning with two commercially available bioremediation agents (ACT Terra Firma and BioWorld BHTP). Each cleaning agent, including the WD-40, was applied to one surface of the concrete blocks vertically. The WD-40 was cleaned in a short period of time, due to the fact that it dissolves the oil immediately and needs to be washed off within a short period of time. The bioremediation agents, on the other hand, were left for 14 days to give the microbes a chance to work. We then conducted an initial analysis. This analysis indicated that ~60–65% of the oil had been removed. The treatment was then reapplied and left for another 14 days before the final oil analysis was conducted.
ACT Terra Firma. The ACT Terra Firma powder was sprinkled and brushed evenly on one surface of the concrete. The treatment was then completed as described above.
BioWorld BHTP. To form the cleaning solution, ½ lb of BHTP powder was rehydrated in 1 gallon of 38ºC water for 20 minutes followed by filtering to remove any undissolved particulates. An enhancer liquid (provided by the manufacturer) was first sprayed on the vertical surface of the concrete samples. The filtered BHTP solution was then sprayed over the concrete while it was still wet with the enhancer.
Analysis of Cleaning Effectiveness
Testing was conducted as described in the sidebar “TPH Testing.” Samples to be tested were taken as described below.
Surfactant, WD-40, and Pour-N-Restore. Samples were taken by drilling about ½ inch deep into several locations on the front and back sections of the concrete block, above, below, and at the waterline, using a ¼-inch carbide bit. The particles that resulted from the drilling were collected for oil analysis. Samples from each section were thoroughly homogenized for analytical analysis. Samples from above the waterline from each concrete block were considered as control.
ACT Terra Firma and BioWorld BHTP. Samples were taken using the same procedure given above for the surfactant, WD-40 and Pour-N-Restore.
The uncontaminated (control) concrete blocks did not contain any measurable level of TPH. The concrete blocks cleaned with WD-40 showed a significantly higher concentration of TPH than any of the other samples from the blocks where other cleaning agents were used, both above and below the waterline. WD-40 is a petroleum-based cleaning solvent, and adsorption of hydrocarbons by the “cleaned” concrete would explain this finding. There was no significant difference in TPH values for blocks cleaned with surfactant and Pour-N-Restore, either above or below the waterline.
Overall, the results indicate that surfactant and Pour-N-Restore, as tested, cleaned concrete block better than WD-40. However none of them was as effective as the bioremediation products tested.
The bioremediation products (ACT Terra Firma and BioWorld BHTP) were about equally effective at removing oil from concrete particles for the 2% oil-water test. Both performed as advertised, removing approximately 90% of the oil contamination after a second treatment. The WD-40 added hydrocarbon content to the concrete (see Table 1).
The results for the nonbioremediation cleaning agents indicate that WD-40 can add TPH to the samples, while surfactant and Pour-N-Restore reduced TPH but not as effectively as the bioremediation agents. The bioremediation agents, ACT Terra Firma and BioWorld BHTP, were compared with WD-40. The ACT and BioWorld products were about equally effective at removing oil from concrete for the 2% oil-water test. Both performed as advertised, removing approximately 90% of the oil contamination after a second treatment (Table 1).
Our results from the bioremediation of oil-contaminated concrete show promise. In addition, the ACT and BioWorld websites also claim their own impressive results for their bioremediation materials when applied to contaminated soil. Both companies sell products designed for use on concrete walks and drives, but these are horizontal surfaces rather than concrete walls, and the companies do not provide measured results for these products.
Contact the author at firstname.lastname@example.org.
The Bottom Line
Can remediation of oil-contaminated building materials reduce TPH contamination below the levels that are considered a long-term health risk to building occupants? The jury is still out on that question. This is partly because there are no definitive guidelines for determining the health effects of exposure to the broad range of potential chemical pollutants, including TPH, found in floodwater. Additional work is also needed to overcome the experimental challenges, such as sampling techniques and large variences in data induced by the inherent diversity in building materials that we experienced in conducting our research.
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