Andale_Draft Pressure Monitoring to measure Performance-OCR

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Appendix I
Pressure Monitoring to Measure Performance of Sub-Slab
Venting/Depressurization Systems
In some circumstances it may be possible to use pressure monitoring and data logging to
measure the performance of sub-slab venting or depressurization systems. With these systems, it
is necessary to create a pressure differential between sub-slab air and indoor air adequate to
interrupt the vapor intrusion pathway. If pressure is continuously and adequately lower in the
sub-slab area than in the occupied area of the building, then air movement -always from higher
pressure to lower pressure -will be from the occupied space to the sub-slab region, which is
opposite the direction necessary for vapor intrusion to occur.
In most vapor mitigation systems, the pressure differential is created by mechanical exhaust
ventilation of the sub-slab vented area (sub-slab depressurization). In some circumstances it may
be possible to pressurize the occupied area of a building using HV AC equipment. Although this
option is generally much more expensive to operate than a sub-slab depressurization system, it
may be preferred by building operators where continuous building pressurization is part of
normal building operation. Dedicated manometers with data loggers may be used to measure
these pressure differentials to verify adequate performance of sub-slab venting/depressurization
systems.
The following are recommendation for performance monitoring of sub-slab depressurization
systems:
• Install at least one dedicated micromanometer per 500 square feet of vented floor area. A
single manometer should be used to measure the sub-slab/indoor pressure differential.
Manometers should be sensitive to plus/minus 0.1 Pascal (Pa.).
• A minimum of a 2 Pa pressure difference between the sub-slab venting space and the
indoor space directly above that point (lower pressure in the sub-slab) is considered
significant for the purpose of interrupting the vapor intrusion pathway. In general an
adequate pressure differential should be demonstrated for 95% of the monitoring period.
This percentage may be adjusted depending on the concentration of contaminants in the
sub-slab, the sensitivity of the population exposed or other factors.
• Pressure monitoring data should be captured at 10 second intervals or less. Ten second
data may be averaged, and 1 to 5 minute averages should be recorded. Pressure
differentials should be presented graphically for each monitoring period.
• Monitoring should be conducted for three discreet monitoring periods, or for a seven
month continuous monitoring period.
References
o For three discreet monitoring periods, the first monitoring period will be for 30
consecutive days with at least 15 of those days in July. The second period will be
for 30 consecutive days with at least 15 days in April or October. The third
monitoring period will be for 30 days with at least 10 days in January. The three
monitoring periods may be conducted in any order. Monitoring data should be
reported at the end of each monitoring period.
o Alternatively monitoring may be done continuously for a seven month period that
includes all of July and January. Data should be reported at the end of each 60
day monitoring period.
1. ASTM Designation: E 2121-03. Standard Practice for Installing Radon Mitigation
Systems in Existin~ Low-Rise Residential Buildings. 2003.
2. Bill Brodhead: li Annual International Radon Symposium in Reno, NV. Designing
Commercial Sub-Slab Depressurization Systems. 2002.
3. USEPA. EPA/600/R-08-115. Engineering Issue: Indoor Air Vapor Intrusion Mitigation
Approaches. 2008.
4. ITRC Technical and Regulatory Guidance. Vapor Intrusion Pathway: A Practical
Guideline. 2007.
5. USEPA. EPA/625/R-92/016. Radon Prevention in the Design and Construction of
Schools and other Large Buildings. 1994.
6. Massachusetts DEP. Guidelines for the Design, Installation and Operation of Sub-Slab
Depressurization Systems. 1995.
7. DJ Folkes and DW Kurz. Proceedings: Indoor Air 2002. Efficacy of Sub-Slab
Depressurization for Mitigation of Vapor Intrusion of Chlorinated Organic Compounds.
2002.
8. Jim DiLorenzo. NARPM Presentation July 2002. Ending the Vapor Intrusion Confusion:
Practical Points for Remediation. 2002.
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September, 2011
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