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KNOWLEDGE COLLECTION Effects of passive ventilation in subslab or crawlspaces to reduce the impact of contaminated vapour on indoor air Environmental project no. 1348 2010

Henrik Husum Nielsen, NIRAS Nanna Muchitsch, NIRAS, now DMR Anders G. Christensen, NIRAS

Follow-up group Ole Kiilerich, The Danish Environmental Protection Agency Susanne Pedersen, Region Zealand Lotte Tombak, Region Zealand Henrik Jannerup, Region Zealand Peder Johansen, The Capital Region Marianna Engberg Pedersen, The Capital Region

NORDROCS 19. September 2012 2

Outline

– Background and objective

– Systems and principles

– Data collection

– Systems in Denmark with passive ventilation under houses

– 38 selected cases with focus on: – Pollution situation

– Construction details

– Preliminary investigations and design basis

– System specifications

– Operation and monitoring

– Achieved effect by passive ventilation

– Economy

– Conclusion and recommendations

3

Background and objective (1 of 2)

Background

– During the last 10 years, passive ventilation has been used as a remediation method to reduce unacceptable transport of contaminated vapours to the indoor air in residential buildings.

NORDROCS 19. September 2012

4

Background and objective (2 of 2)

Objective

– The overall objective of the project is to be able to present a status for the method and its application in Denmark during the period 1999-2009.

– The deployment of the technique, use, effect, and economy is presented, and recommendations for the further activities using the method are outlined.


5

Ventilation drain in capillary-breaking layer connected to a wind-powered cowl on roof with air intake (under existing and new floor)

Ventilation drain in capillary-breaking layer connected to goose necks or similar (primarily under new floor)

Ventilation drain in capillary-breaking layer connected to a wind-powered cowl on roof without air intake (under existing and new floor)

Ventilation of existing crawl space

Systems and principles (1 of 2)

System types Wind-powered cowl

GVS

Capillary-breaking layer Concrete floor

Pollution

Groundwater level

Wind-powered cowl

GVS

Capillary-breaking layer Concrete

floor

Pollution

Groundwater level

GVS

Capillary-breaking layer Concrete floor

Pollution

Groundwater level

GVS

Capillary-breaking layer

Concrete floor

Pollution

Groundwater level

Wind-powered cowl


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Systems and principles (2 of 2)

Principle Spreading of pollution to indoor air by advection and diffusion

Pollution

Groundwater level

Csoil gas Psoil gas

Cindoor climate DIFFUSION

Pindoor climate ADVECTION

DIFFUSION Csoil gas > Cindoor climate

ADVECTION Psoil gas > Pindoor climate

Remediation by reduction of advection (reduction of pressure gradient) and diffusion (reduction of diffusive gradient by lowering concentration under the floor)

Air intake

Wind-operated cowl

Pollution

Groundwater level

Capillary-breaking layer

Vent pipe

Csoil gas Psoil gas

Cindoor climate DIFFUSION, reduced

Pindoor climate ADVECTION, reduced (reduced pressure gradient)


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Data collection


Empirical data collection

Quantitative data – gross list

125 systems

Qualitative data –

site specific from

38 systems

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Systems in Denmark with passive ventilation under buildings (1 of 2)

Gross list 125 systems


74%

5%

2% 19%

VENTILATION OF: Capillary-breaking layer

Crawl space

No data

Other

9

Systems in Denmark with passive ventilation under buildings (2 of 2)

Gross list 125 systems


0

20

40

60

80

100

27

97

1

Num

ber

of

syste

ms

New building

Existingbuilding

Partially

0

20

40

60

8075

44

5 1

Nu

mb

er

of

syste

ms

New floor

Existing floor

New and existingfloor

No data

10

38 selected cases

38 cases primarily selected

– in order to analyze the variation in the existing systems.

– when on basis of the gross list it is assessed (consultant/contractor) that the case presents a good data basis.

– when the passive ventilation has had the intended effect, but also cases with no effect.

– in order that all consultants and contractors are represented.

Must be careful not to conclude anything statistically, but directions / trends are apparent.


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38 selected cases with focus on (1 of 14)

Pollution situation

SOURCE

Dry-cleaner

21

Metal factory

3

Other

2

CONTAMINANT

Landfill gas

4

Hydrocarbons

8

Chlorinated solvents

26


before 1920 11

1920-1970111970-2000

5

after 2000 5

no data6

Contruction year

12


Construction details

Characteristics

– Buildings before 1970 – ground deck directly on ground

– Buildings after 1970 – capillary-breaking layer

– Buildings before 1960 – can be with crawl space


13


Preliminary investigations and design basis

Allways

Pollution investigation and risk assessment

(soil gas and indoor climate measurements. Soil samples in case of new building)

Often

Examination of construction details on-site.

Infrequent

Design related investigations. In certain cases ventilation tests in capillary-breaking layers. Investigation of sinks and pathways.


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System specifications. Choice of materials

Capillary-breaking layer:

Coarse gravel, pebbles, leca and gravel in layer thickness 80-400 mm

Ventilation pipes under ground:

PE or PVC ø50-110 mm (drain and pipes)

Coarse gravel 32-64 mm Pebbles 16-32 mm Leca 8-22 mm

Course Region Syddanmark, AAB, Grontmij | Carl Bro


15



Difusion reducing membrane (used on approx. ¼ of the 38 selected cases):

R.A.C. membrane

Generally no investigations of the tightness of the membrane performed after

installation.

Tightness examined in 2 cases with PID-gauge of type ppbRAE and by

thermography and blower door.

ppbRAE: Some leakages in corners

Termografi: Many leakages at clamping rails and in corners NORDROCS 19. September 2012

16



Piping above ground: Wind operated cowl:

ø70-80 mm galvanized pipes SupaVent 10’

Source Region Syddanmark, Rambøll


17


Operation and monitoring

Indoor air measurements performed:


Yes 26

No 12

- Landfill gas (4)

- Oil Pullution (6)

- Not established as indoor climate protection (1)

- System established in existing dry-cleaning establishment (1)

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Operation and monitoring Monitoring of airflow and air sampling of discharge air

(system with wind-operated cowl):

– In connection with measurements of airflow, point measurements and continuous

measurements over several weeks have been performed.

– Performing point measurements gives an ”up-to-the-minute account” of the airflow under the actual wind conditions.

– Continuous measurements allow the possibility of obtaining a picture of the average airflow, including periods with reduced airflow, corresponding to periods with weak wind action.

Airflow

Datalogger box

air velocity Air sample

Source Region Syddanmark, LIDL, Grontmij | Carl Bro


19



Monitoring of airflow and air sampling of discharge air

(system with goose necks or similar):

– Airflow not measured

– Air sample often taken out from goosenecks or similar


20



Monitoring of concentrations in the air in capillary-breaking layer:

(established on approx. 1/3 of the 38 selected cases)

Ex. ø6 mm copper pipes installed under floor and let up along the wall and fitted with a ball valve in a monitoring box.


21



Monitoring frequency

(typically 2 monitoring campaigns)

(each year or several times per year)

(each 2 year or less)

Monitoring period


22



Supplementary investigations

Supplementary investigations at sites with inadequate effect have included:

– Monitoring of groundwater level in surficial aquifers

– Mapping of pollution in the unsaturated zone with Gore-Sorber

– Identification of pathways using a VOC sensing instrument

– Identification of pathways using tracer gas measurements

– Identification of pathways by thermographi and blower door

– Air flow measurements and measurements of wind velocity

– Tracer test for control of ventilation in capillary-breaking layer

– Atmosphere, wind, and barometer (weather conditions)


23


Achieved effect of passive ventilation under buildings

Effective: Concentrations in the indoor air reduced to a level below the indoor air criteria

Partly effective: Concentrations in the indoor air reduced, but not below the indoor air criteria

ex. other pathways

Not effective: Concentrations in the indoor air not reduced to a level below the indoor air criteria

Uncertain: ? Effect difficult to assess

ex. excavation of pollution in connection with establishment, active ventilation in combination with passive ventilation, natural degradation of oil

15

?

10

9

4

SITE SPECIFIC FORMS


24


Economy € excl. VAT

CONSTRUCTION COSTS

No data

15

>130.000

3

65.000- 130.000

6

15.000- 65.000

10

<15.000 4

ANNUAL OPERATION AND MONITORING COSTS

2.500-5.500 15

5.500-8.000 4

>8.000 3

No data 15

<2.500 1


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Conclusion and recommendations for further activities (1 of 4)

Conclusion

– Despite the simple principle, it is difficult to achieve the effect desired

(only approximately 40% reaches the goal – under indoor air criteria)

– The varying success could be related to a limited design basis

– Often, the systems are solely based on risk assessments made in the investigation phase

– Insufficient focus on the documentation of the ”tightness” of the selected method.


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Conclusion

– In the monitoring phase, the function of the systems is documented by

– In the monitoring phase, a series of supplementary investigations were carried out where the established passive ventilation under buildings did not have the desired effect.

Pollution

Groundwater level

Wind-powered

cowl

Soil gas measurements under floor

Measurements of airflow (point and continuous)

: systems with goosenecks or similar

Contaminants in discharge air

Indoor climate measurements ( oil pollution)


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Recommendations for further activities It is assessed that the certainty of effect can be substantially increased by future

investments in improved design/basis before construction of the systems.

It is recommended

– That a conceptual model for evaluation and understanding of possible pathways are always made.

– Based on the conceptual model, it is possible to carry out supplementary investigations. Investigations which were earlier performed in the operation and monitoring phase, ex. tracer gas measurements and thermography, and new types ex. radon measurements for clarification of i.a. attenuation factor above floor constructions.

– By mapping the pathways, it is investigated whether passive ventilation should be selected in combination with other methods of remediation or be left out of consideration.


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Recommendations for further activities

It is recommended that a catalogue of methods be assembled.

The catalogue should contain instructions and descriptions of practical tools that can be used in the dimensioning, design, and control of systems with passive ventilation.

The catalogue will be linked to the conceptual model in connection with the identification of pathways.

Catalogue of Methods

Conceptual model


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