Practical case study of design and operations of a subslab depressurization system in a large commercial building. Poster presented at AEHS 23rd International Conference, San Diego 2013

1. Full Building System
System Summary
A total of 61 extraction points spaced approximately 120 feet
apart along the building’s existing structural steel
A total of 91 sub-slab monitoring points throughout the facility
System components include:
• Four 150 horsepower
blowers
• Moisture separator
• Condensate storage
tank
• Heat exchanger
• Chilled water system
• Two 10,000 pound
carbon vessels
• Emergency generator
• Fully integrated System Control Center
Summary of System Performance
The system meets or exceeds all design objectives.
• Sub-slab pressure differentials of -0.004 or greater – often by an order of
magnitude
• Discharge concentrations are below the detection limit of the analytical
method
• Carbon usage rates of 10 pounds per day
• Reliable and trouble-free operations from system components since being
placed into service
Design and Operations of Sub-slab Depressurization Systems
in a One Million Square Foot Commercial Multi-tenant Building
Chris Engler, Rachel Saari, Nadine Weinberg and Chris Lutes (ARCADIS)
Stewardship and Monitoring
SSDS System Operations and Stewardship
• Quarterly indoor air sampling
• Continuous pressure communications monitoring to confirm the extent of
the vacuum under the slab also known as the ROI
• Continuous monitoring of operational parameters (i.e., flow and pressure)
at each extraction point. Data are
recorded and alarm set points will
notify system operators of
changes in operation
• Quarterly reporting of system
operation to the State
Timeline and Overview
2006: State releases guidance for indoor and sub-slab vapor concentrations
2007: Indoor air/sub-slab sampling begins
A. March 2007: 19 sub-slab soil gas, 27 indoor air samples
B. October 2007: four sub-slab soil gas samples
C. December 2007: 25 sub-slab soil gas, 33 indoor air samples
2008: Localized eastern SSDS installed
D. January 2008: 13 indoor air samples
E. March 2008: 42 sub-slab soil gas and 13 indoor air samples
F. September – November 2008: 52 sub-slab soil gas and 24 indoor air
samples
2009: Localized central SSDS installed
2009: Site-wide SSDS design alternatives evaluated
G. January 2009: 46 sub-slab soil gas, 38 indoor air samples
H. March 2009: 22 sub-slab soil gas, 28 indoor air samples
I. December 2009 – January 2010: 85 sub-slab soil vapor, 89 indoor air
samples
2010: Final approval of Conceptual SSDS design by the State
2010: Western SSDS installation in main building began
J. March 2010: 12 sub-slab soil vapor, 18 indoor air samples
2011: Eastern SSDS installation in main building began
K. March 2011: 68 sub-slab soil vapor, 68 indoor air samples
2012: Construction began for equipment/control building
L. February – March 2012: 76 sub-slab soil vapor, 95 indoor air samples
2013: SSDS construction complete; System Operational
M. February – March 2013: 79 sub-slab soil vapor, 98 indoor air samples
Year
Installed
Time to
Design/Install
Coverage
(ft2)
Horsepower
Horsepower
per ft2
Localized Eastern System 2008 5 months 24,000 2.5 1/10,000
Localized Central System 2009 1 months 50,000 5 1/10,000
Full Building Permanent
System
2013 3 years 1,000,000 225* 2.25/10,000
* The system has the capacity to run at 450 horsepower, it is currently operating at 225 horsepower
Localized Eastern System
• Covers approximately 24,000 ft2
• 2.5 horsepower blower
Localized/Mobile Central
System
• Covers approximately 50,000 ft2
• 5 horsepower blower
Interim and newly expanded sub-slab vacuum system.
Extracts vapors from beneath the entire building and
pipes them to the garage where they are treated. Clean
air is released.
Preparation for Installation
Installation
Typical Roof Top Pipe System
Underground Pipe Installation
Construction of Equipment Building
SSDS Risers & Enclosures
SSDS Extraction and Monitoring Points SSDS Sub Slab Pressure Contours during
Startup
2007 2008 20112010 20122009
A B C D E F G H I J K
2013
L M
Sealing expansion
joints up to 2" wide
provided
considerable
improvement in SSD
performance
Continuous Monitoring
Point Detail
Notes:
1. The goal of the sub-slab depressurization system is to maintain a minimum
of -0.004 inches water column (in.w.c.) differential pressure in the target
area.
2. Differential pressure refers to the difference in air pressure recorded across
the building’s concrete floor slab. Measurements above the concrete floor
slab are taken within one foot above the finished floor of the building. A
positive differential pressure value indicates that air pressure under the floor
slab is higher than air pressure above the floor slab; a negative differential
pressure indicates that the air pressure under the floor slab is lower than the
air pressure above the floor slab. Differential pressure measurements are
collected using continuous logging micro-manometers that continuously
record the “high” and “low” differential pressure across the floor slab during
a 24-hour monitoring period.