Inspection Finds Source of Sewer Odors in a Restaurant

Foul odors from sewer or waste-water pipes can be a serious issue for an restaurant, office or retail space.  These odors can be very difficult to measure and identify, but Hawk Environmental Services, Inc. has the skill and equipment necessary to assist in these types of investigations

Background information on sewer odor issues

The clients have requested indoor air quality testing in an attempt to determine if sewer gases are present and if
the pressure changes created by appliances as it may pertain to drawing foul odors into the building through wall cavities.

• General toxics (to assess potential of sewer gas at 2 locations on the upper level)
  • total VOC’s (in ppm via 10.6 eV PID)
  • Carbon monoxide
  • LEL (lower explosive limits i.e. natural gas)
  • Hydrogen sulfide
  • Oxygen
• Pressure diagnostics
  • After hours scheduling to prevent disruption to business
  • Turn off all exhaust and forced-air appliances
  • Measure baseline pressure to exterior
  • Measure pressure changes when each appliance is activated

Inspection and Testing Summary:

Sewer gases:

• The odors from sewer gases are caused by the byproducts of microbial respiration and the breakdown of organic materials in the waste water. These
  odors are composed of a wide variety of chemicals and gases, but the main component that is testable with data-logging equipment is hydrogen
  sulfide. The odor detection threshold for this gas is 0.05-0.13 parts per million, but the equipment accuracy for measurement is 0.1 part per
  million, this means that the odor may be noticeable by nose but not necessarily detected by testing equipment in all cases.

• Hydrogen sulfide: A clear spike in H2S levels between 11:00 and 11:50 pm on 03/06/2015 was measured within the wall cavity that houses the
  waste-water line behind the kitchen dishwasher. H2S was not detected during the testing period at the other 2 data-collection sites.

• Carbon monoxide: No carbon monoxide was detected in any of the 3 sites at the time of testing.

• Oxygen: No elevated or reduced oxygen levels were detected at any of the testing sites.

• LEL (lower explosive limit): No explosive gases were detected at any of the testing sites.

• Total VOC’s: Total VOC’s measured are consistent with cleaners and fragrances used in a typical commercial space.

Pressure Testing:

• The baseline pressure between the interior and exterior of the restaurant with all exhaust fans and HVAC system deactivated measured an average of
  -5.8 pascals with respect to the exterior.

• The pressure between the interior and exterior of the restaurant with only the HVAC system activated measured an average of -1.7 pascals with
  respect to the exterior.

• The pressure between the interior and exterior of the restaurant with all exhaust fans on low speed measured up to -29.2 pascals with respect to
  the exterior for approximately 45 seconds and then balanced to -5.1 pascals with respect to the exterior once the make-up air system was fully
  activated.

• The pressure between the interior and exterior of the restaurant with all exhaust fans on max speed measured up to -69.2 pascals with respect to
  the exterior for approximately 45 seconds and then balanced to -5.1 pascals with respect to the exterior once the make-up air system was fully
  activated.

• With all exhaust and HVAC systems on a difference in pressure of -5.0 pascals was measured in both the lower level bathrooms, and a difference of
  -15.1 pascals was measured in the mezzanine bathroom (the HVAC supply register in the mezzanine bathroom was closed).

Summary:

• Negative pressure differentials are present under normal baseline conditions in the restaurant. This is likely due to the “stack effect” of warm
  air rising and cold air coming into the space from the lower level. Although high, this is unlikely to be responsible for the odors noted by the
  occupants.

• Significant depressurization of the restaurant occurs for less than 1 minute when the exhaust fans are first activated. This may be a contributing
  factor in drawing odors into the building, but is unlikely to be the ultimate cause.

• The make-up air system appears to be adequately supplying the kitchen exhaust hoods, but is unlikely to provide general ventilation for the
  mezzanine.

How the problem was resolved

After the client received the data from the inspection and testing report, they were able to pinpoint the locations of sewer gas.  Invasive investigation was used by the plumbing contractor and 4 uncapped sewer pipe lines were found.  Once the pipes were capped the odors in the restaurant were mitigated.

If your office, restaurant, or retail space is suffering from unexplained foul odors Hawk Environmental Services, Inc. would be happy to assist with testing and inspection services in Seattle, Tacoma, and the entire Western Washington area.