Safe Environments

Remediation of Black Water Intrusions into Residential Structures: Guidelines

The following is a check list for remediation of black water into residential structures. This checklist should be followed in such conditions as, sewer backups and river floods. It is not a cookbook, as each situation requires modification in the procedures for remediation.

Emergency Response: 
Worker Protection/Health and Safety

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Emergency Response Procedures:

  1. Shut down the ventilation system. Seal all registers and cold air returns with plastic. If the duct system has had black water intrusion, then the ducts will have to be replaced.
  2. Pump out all liquids and solids.
  3. Dispose of all black water damaged carpets, pads, underlayment and saturated fabrics.
  4. Put down a disinfectant. Avoid mixing ammonia with bleach. Set up refrigerant dehumidification if the structure is to be remediated quickly. Do not use air movers. If the remediation is to be delayed, dry the structure quickly using desiccant dehumidification in exhaust mode.
  5. Make sure workers do not track contaminants throughout the structure. Lay out plastic on the floor for access to and from the contaminated site.

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Remediation

  1. Test the structure for moisture using a non penetrating and penetrating moisture meter. The use of a penetrating moisture meter is especially important in detecting wet insulation and moisture in exterior wall cavities.
  2. Pack out contents. Irreplaceable papers items that were in direct contact with sewage should be salvaged by using recommended restoration decon- tamination procedures involving gently rinsing with cold water and freeze drying. Other irreplacable porous materials that cannot be disposed of will require special handling.
  3. Isolate the contaminated area from the rest of the structure with critical barriers using negative air units. The containment area should be at least
    0.02 inchs of water, negative in pressure as compared to the adjoining interiors.
  4. All black water saturated porous materials, i.e. sheetrock, plaster, baseboard, warped hardwood floors, plywood subfloors, wall coverings and insulation should be disposed of. Cut at least a foot out from any elevated moisture. All contaminated wood paneling will have to be removed, sanitized and sealed. Non-porous materials can be cleaned, consider the psychological issues of cleaning and returning items that were sewage contaminated to the owners vs. disposal of these items, as it relates to cost value. HEPA vacuum all debris left from the demolition.
  5. The entire area should now be free of contents and surfaces should be relatively free of debris. If some large contents have to remain in place then they must be completely dry and wrapped in plastic.
  6. Remove toilets and if necessary, bathtubs, if water got underneath them. Seal any open toilet drains with a plumbers pipe cap to avoid sewer gases from coming out. Cap off all other drain lines. If the traps will not be used for more then a few weeks remember to prevent the traps from becoming dry.
  7. Open up all kick plates on vanities that came in contact with sewage.
  8. If water has gotten behind vanities then they will have to be removed, to access hidden sheetrock.
  9. Pressure wash using low pressure, with an off the shelf chlorox (sodium hypochlorite) detergent solution the interior wall cavities. Follow with a 2nd treatment of chlorox. (Follow label instructions). Lemon scented tends to have less odors. Let stand 20 minutes and extract the solution. Pay special attention to cracks and sill plate floor junctions by re spraying these areas. Iodine solution can be used on structural materials, instead of chlorox. Also, iodine solution should be used to wash down cement slabs. Both chlorox and iodine should not be applied to any surface that can be stained or bleached.
  10. As an alternative biocide, consider using Chlorine Dioxide 5% (Oxine).  It has advantages in that it does not leave a residue or lingering odor. Follow all OSHA regulations regarding its use.
  11. Rinse and extract the water. Then use dehumidification and air movers to dry the structure down quickly to avoid further contamination. Make sure all air movers are disinfected afterwards. Moisture test all areas for any residual moisture. Pay attention to hard to reach areas. Use both non penetrating and penetrating moisture meters. Make sure that the amount of water in the air is calculated to determine if the structure has been dried down sufficiently.
  12. HEPA vacuum all surfaces. All surfaces must be free of particulates if environmental testing is required.
  13. Have the structure tested if there are individuals that are high risk occupying the space. Also, conduct testing if the project is high profile or liability issues are a concern.
  14. If this is first time having testing performed for a black water loss do not be surprised that some areas will remain contaminated. Be ready to do more cleaning.

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Remediation of crawlspaces

  1. Pump out all standing water.
  2. Remove all contaminated ducts and insulation. Seal all wiring runs and plumbing chases to the interior building envelope. Seal all registers.
  3. Set up a negative pressure in the crawlspace. Make sure the negative pressure does not overwhelm combustion gas exhaust ventilation in the building interior. Analysis of pressures should be done using a micro- manometer.
  4. Reflood or pressure wash 80 to 120 psi the soil with a non foaming surfactant solution to break the surface layer. Pump out the remaining water. Start drying the crawlspace. Make sure the crawlspace remains under negative pressure.
  5. Rake out the remaining solids and a few inches of soil. Rototill the soil to aerate.
  6. Consider the following options:
    1. Put lime down in the crawlspace either straight or mixed with dry soil. Drawbacks, can be come aerosolized when dry and is caustic. Any workers entering the crawlspace in the future will have to be notified and wear proper protection. Negative pressure can not be applied under plastic in this case.
    2. Put down fresh sterile potting soil over the ground.
    3. Cover the ground with plastic. Make sure the plastic goes up above the pier blocks and is taped and staked.
  7. If lime is not used, set a permanent negative pressure of 5 pascals in the crawlspace and exhaust the air above the roof. Put the negative pressure under the plastic or above. Putting negative pressure under the plastic will require less exhaust air to be effective. Negative pressure will effectively eliminate the entrainment of volatile organic compounds from sewage into the building envelope. Make sure the negative pressure does not overwhelm the combustion gas ventilation in the building interior.
  8. Maintain negative pressures under the plastic for at least 2 years.
  9. If the subfloor needs to be opened up to perform the above tasks,the room will have to be under negative containment.
  10. All return ducts will have to be routed through the attic. Consider removing the air handler to outside of the crawlspace. If the air handler has to remain in the crawlspace all seams and joints will have to be sealed with tape and water soluble mastic.

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Other considerations

  1. When opening up drywall, use a sheetrock knife or jig saw to minimize dust.
  2. If you find extensive mold growth behind sheetrock walls or other locations, then mold remediation issues go into effect, i.e.. the size of the contamination, the type of mold found, etc.
  3. Test the ducts to make sure they have not gotten blackwater into them.
  4. If any non metal plenums or acoustic sound insulation in the plenum has been contaminated, then the plenums will have to be rebuilt and the acoustic removed. All metal plenums and rigid ducts can be cleaned and sanitized.
  5. All negative air units, air scrubbers and HEPA vacuums need to be tested using a laser counter to see if they are working properly.

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Resources
Berry, M.A, Bishop, J., Blackburn, C., Cole, E., Ewald, W., Smith, T., Suazo, N., Swan, S., (1994) "Suggested Guidelines for Remediation of Damage from Sewage Backflow into Buildings" J. of Environmental Health. 57(3) : 9-15
De Serres G, et al., (1995) "The need for vaccination of sewer workers against leptospirosis and hepatitis A" Occup Environ Med 52: 505 - 507
Institute of Inspection Cleaning and Restoration Certification. (1994), Standard and Reference Guide for Professional Water Damage Restoration. S500-94, Institute of Inspection Cleaning and Restoration Certification, Vancouver, Washington.
McCunney, R.J., (1986) "Health Effects of Work at Waste Water Treatment
Plants: A Review if the Literature With Guideline for Medical Surveillance"American Journal of Industrial Medicine 9: 271-279
Mumma, et al., (1984) "National Survey of Elements and Other Constituents in Municipal Sewage Sludges" Arch. of Envir. Contamination and Toxicology 13: 75-83.
Zuskin, et al., (1993) "Respiratory Function in Sewage Workers"American Journal of Industrial Medicine 23: 751-761

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