CSM-2014 Vapor Intrusion Mitigation for Complex Buildings - Revised KL - pdf

2014 – Contaminated Site Management (CSM-2014) Sustainable Remediation & Management of Soil, Sediment and Water


INNOVATIVE VAPOR INTRUSION

MITIGATION DESIGN FOR COMPLEX

BUILDING FOUNDATIONS

http://source4interiors.com/blog/wp-content/uploads/2009/10/white-sheer-curtains-blowing-in-wind-barbra-barry2.jpg


PRESENTATION OUTLINE

Vapor Intrusion

How to Mitigate

What is SSDS?

SSDS versus SVE

Components of a SSDS Design

SSDS Design Challenges

Case Study – Manhattan, New York

Case Study – Wayne, New Jersey

Lessons To Be Learned


VAPOR INTRUSION Migration of volatile chemicals from contaminated groundwater or

soil into buildings above

Indoor Air Quality

Chronic and acute health/safety hazards


HOW TO MITIGATE

Passive Venting Systems

Impermeable Membrane Liners

Sub-Slab Depressurization Systems

HVAC/Ventilation System Modifications

http://www.nj.gov/dep/srp/guidance/vaporintrusion/subsurface.htm




WHAT IS A SSDS?

Active venting system consisting of:

Fan/Blower

Well Network

Vacuum/Air Flow Rate Instrumentation

Control Panel

Telemetry System

Emission Controls


SSDS VERSUS SVE

Differences: Purpose

MITIGATION versus REMEDIATION

Capture versus Extraction

Similarities: Principals

Active Pneumatic Systems

Dependent on intrinsic permeability


Mitigation vs. Remediation

Depressurization System SVE System

Objective:

Create a differential pressure barrier between

subsurface and buildings

Design Basis:

Vacuum Gradient = 0.004 – 0.025 IWC

Objective:

Remove contaminants from the vadose zone

Design Basis:

Pore Volume (PV) Exchanges

Sands = 500 PV/year

Silts = 1,500 PV/year

Silty Clays/Clays = 2,500 PV/year


DESIGN COMPONENTS OF A SSDS DESIGN

Pilot Testing

Modeling

Design Criteria

Air Flow Rate

Vacuum

ROI


SSDS DESIGN CHALLENGES

Equipment Limitations

Vacuum Limitations:

• Industrial fan: 3 to 4 IWC

• Compact radial blower: 10 to 14 IWC

• Regenerative blower: 90 IWC (6.5” Hg)

• PDB: 220 IWC (16” Hg)

• LRP: 350 IWC (28” Hg)

Site Challenges

Slab-on-grade

Low permeability sub-slab material

Shallow water table

Subsurface heterogeneity

Below-grade structures

Non-confining leaky surface layer

Space limitations

Varying partial pressures/Henry’s Law constants

of complex soil gas mixtures


CASE STUDY – MANHATTAN, NEW YORK


SITE BACKGROUND

Operated until June 2013 as an active dry cleaning facility

Residential dwellings located on floors two through five.

Indoor air assessment - PCE and TCE in exceedance of NYSDOH

Vapor Intrusion Guidance Matrix.


SITE CONSTRAINTS

2 - 6 inch thick concrete slab with granite bedrock beneath

Limited space for implementation/Manual drilling required

Possible demolition of building during application period


PILOT TESTING

5 Vapor Recovery Wells (VP)

3 Shallow Vapor Probes (SVP)

Understand the site-specific sub-surface parameters

(i.e., permeability) to design the full-scale SSDS.


Outputs:

Ki , ROI, FD, PV

exchanges

Benefits:

More cost-effective design

Valuable tool for SVE and VI Mitigation systems

Helps to ensure efficient and effective vapor mitigation

PNEUMATIC MODELING MDFIT – Computer Pneumatic Modeling Program


Existing Vapor Recovery Well Network

Process Equipment:

• Blower

• AMS

• Control panel/Instrumentation and auto-dialer

• VGAC

SYSTEM DESIGN

DESIGN AIR FLOW RATE = 200 SCFM AT 80 IWC WELLHEAD VACUUM


FULL-SCALE RESULTS SSDS was meeting the required minimum sub-slab vacuum of 0.004

inches of water column (as recommended by USEPA)

SVE and SSDS can be implemented efficiently and cost effectively, even at complex sites, if we understand and consider the constraints of the site when designing the system. Importance of pilot testing and pneumatic modeling when designing/installing a SVE / SSDS at complex sites

SVE Mass Removal Rate =

1.25 lbs VOC / day


CASE STUDY – WAYNE, NEW JERSEY


SYSTEM IMPLEMENTATION – MARCH 2013

Design air flow rate = 500 scfm

Design wellhead vacuum = 35 IWC

Remote telemetry system

Operational sub-slab vacuums >> 0.004 IWC

Initial VOC mass removal rate = 0.25 lbs./day

Design and Operational Key Features:


STRATEGY BENEFITS

Effective Vapor Intrusion Mitigation

Source Mass Removal

Cost Savings

Reduced Remedial Timeframes

Design and Operational Key Features:


LESSONS LEARNED Importance of pilot testing and pneumatic modeling when designing/installing an

SVE/SSDS at complex sites

If designed correctly, SVE and SSDS can be implemented efficiently and cost effectively,

even at complex sites.

Integrated SVE and VM Approach – Effective Optimization Strategy

Effective Vapor Intrusion Mitigation

Source Mass Removal

Benefits:

Cost Savings

Reduced Remedial Timeframes


QUESTIONS?

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CSM-2014 Vapor Intrusion Mitigation for Complex Buildings - Revised KL - pdf

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