Sewers as a Preferential VI Pathway Dynamic Measurements ... · The test site in the Region of...

Battelle Chlorinated Conference, 2018

®

Per Loll R&D Manager, Ph.D.

Sewers as a Preferential VI

Pathway – Dynamic

Measurements and

Quantitative Risk

Assessments

Poul Larsen and Claus Larsen, DMRHanne Nielsen, Kristian Raun, Kim Thygesen and Klaus Mortensen, Region of Southern Denmark

®

2Per LollBattelle Chlorinated Conference, 2018

Preferential pathways

• A preferential pathway serves as a high permeability and capacity pathway of VOC vapors from a source area to and into a building.

• We distinguish between external and internal preferential pathways.

– External: Sewers, land drains, utility tunnels, …

– Internal: Cavity walls, elevator shafts, stairwells, attic spaces, …

®


Some questions about sewers at any given site

• What can be expected from the sewers at a given site?

– Size of differential pressure and concentrations?

– Temporal variation in differential pressure and concentrations?

– Size of sewer air exchange (design of tracer gas studies)?

– What is the effect of mechanical ventilation (fan)?

– What is the effect of a hole in the sewer?

– How to deal with 2-4 OOM temporal variability?

– How can we make sure that we collect samples at the “right” time for a robust risk assessment?

• Standard Danish practice in relation to risk assess-ment is 10 L samples of sewer air on Dräger B carbon tubes for lab. analysis (could be Summa).

• What to expect? Tools and thoughts on application.

®


• We looked at 2

The test site in the Region of Southern Denmark

• A three-level building from 1900.

• Apartments on the 2nd and 3rd floor.

• Various activities on 1st floor through time

– Plumber

– Electronics Repairs

– Foot Clinic

• Site investigations and remediation attempts 2000-15.

• Building was condemned and was purchased for tests.

– Dry Cleaner (PCE)

1st floor 2nd floor

3rd floor

• 6 toilets in all.

®


• Logging of proxy and secondary parameters + automated sampling for chemical analysis (via valves and pumps):

We created an automatic sampling unit (prototype)

PID-sensor– 2 PID-sensors (10,6 eV; 1 ppb-40 ppm & 0,1-6000 ppm)

– 2 differential pressure (dP) sensors

– 1 barometric pressure sensor

– 1 temperature sensor

PID-sensor (room)PID-sensor (sewer)

dP sensor (sewer)

dP sensor (floor/outer wall)

2 x carbon tubes for sample collection

LED Display

– Option of collecting 2 samples on carbon tubes

– Display, on-line data logging & remote controllable

®


Sampling toilet (for equipment protection)

• We constructed a sampling toilet which allows for regular use while logging (shown for the 1st floor toilet):

– Constructed using standard plumbing components.

• The actual toilet was leak tested (no leaks).

• So was the sampling toilet (no leaks).

• 5% H2 / 95% N2

®


Differential pressure – 1st floor toilet

• 1 month of logging 4 times per minute.

Door closed, toilet not in use

Toilet

FloorToilet vs. floor

Average 1,5 Pa

Min -5,3 Pa

Maks 7,9 Pa

Percent > 0 Pa 98 %

Percent >+1 Pa 82 %

Percent >+2 Pa 11 %

Average 0,31 Pa

Min -2,3 Pa

Maks 3,1 Pa

Percent > 0 Pa 91 %

Percent >+0,5 Pa 21 %

Percent >+1 Pa 0,12 %

®


Average 0,08 Pa

Min -19 Pa

Maks 16 Pa

Percent > 0 Pa 65 %



Average 0,77 Pa

Min -19 Pa

Maks 17 Pa

Percent > 0 Pa 85 %



Differential pressure – 2nd floor toilet

• 1 month of logging 4 times per minute.

Door closed, toilet not in use

Toilet

Outer wallToilet vs. outer wall

®



• Significance of absolute barometric pressure?

– High (>1020 mbar)

– Low (<1005 mbar)

Baro vs. outer wall

Baro vs. toilet

Toilet

Outer wall

Barometric pressure

®


R² = 0,0424

-2

-1

0

1

2

-2 -1 0 1 2

dBaro/dt vs. WC (timemidling)

R² = 0,0424

R² = 3E-05

R² = 0,0675

-2

-1

0

1

2

-2 -1 0 1 2

dBaro/dt vs. WC (timemidling)

R² = 0,008

-2

-1

0

1

2

-2 -1 0 1 2

dBaro/dt vs. Ydermur (timemidling)

R² = 0,008

R² = 0,0023

R² = 0,0123

-2

-1

0

1

2

-2 -1 0 1 2

dBaro/dt vs. Ydermur (timemidling)

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

01-11 03-11 05-11 07-11 09-11 11-11 13-11 15-11 17-11 19-11 21-11 23-11 25-11 27-11 29-11 01-12

Æn

dri

ng

i bar

om

ete

rtry

k (m

bar

/t)

Trykstigning

Trykfald

Stabilt tryk

Rising

Falling

Stable

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

01-11 03-11 05-11 07-11 09-11 11-11 13-11 15-11 17-11 19-11 21-11 23-11 25-11 27-11 29-11 01-12

Æn

dri

ng

i bar

om

ete

rtry

k (m

bar

/t)

Trykstigning (29%)

Trykfald (27%)

Stabilt tryk (44%)


• Significance of barometric pressure changes?

– Rising

– Falling

– Stable

• Analysis of hourly avg. data

>0,5 mbar/hr

<-0,5 mbar/hr

[-0,5;+0,5] mbar/hr

dBaro/dt vs. toilet

dBaro/dt vs. outer wall

Rising (29%)

Falling (27%)

Stable (44%)

Toilet Outer wall

Barometric pressure

®


-7

-5

-3

-1

1

3

5

13:30 14:00 14:30 15:00

dP

(P

a)

Door open

Fan on (door closed)

Effect of mechanical ventilation (1st floor toilet)

Ventilation fan on(closed door):

5-6 Pa negative dP in room

6-8 Pa positive dP across sewer

4-5 Pa positive dP across floor-3

-1

1

3

5

7

9

13:30 14:00 14:30 15:00

dP

(P

a) Baseline (dør åben) In-line ventilator / Strip på dør

dP faldstammedP over gulv

Baseline in agreement with long term data:

1-2 Pa positive dP across sewer

0-1 Pa positive dP across floor

• In-line ventilation fan (~51 m3/hr; ACH= 8,6 hr-1)

– Differential pressure (room) door closed

Sewer

Floor

Fan on (door closed)Baseline (door open)

Ventilation fan adds about 4-6 Pa of extra pressure gradient

®


0

100

200

300

400

500

600

700

800

900

10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00

PID

(p

pb

)

Car

bo

n tu

be

sam

pli

ng

(10L

)

+hole

Op

en

to in

stal

l PID

se

nso

r

Car

bo

n tu

be

sam

pli

ng

(10L

)

Car

bo

n tu

be

sam

pli

ng

(10L

)

-3

-1

1

3

5

7

9

14:00 15:00 16:00 17:00 18:00 19:00

dP

(P

a)

Sewer

Floor

Door open

Fan on (door closed)

-15

-10

-5

0

5

10

14:00 15:00 16:00 17:00 18:00 19:00

dP

(P

a)

+5 mm hole

Fan on

(door closed)

Door open for

+2 mm hole

Effect of a hole in the sewer (1st floor toilet)

Ventilation fan +2/5 mm hole leads to < 5,5 L/min flow out of the sewer (<1% of the combined flow/ACH).

10 L sampling leads to a temporary drop in PID (700->300 ppb).

Addition of a hole leads to a ‘permanent’ drop in PID (->200 ppb).

• In-line ventilation fan (~51 m3/hr; ACH= 8,6 hr-1) + drilled hole

®


PCE 780 840 780

TCE 39 43 39

TVOC 2300 2000 1100

(µg/m3)

PID/concentration in sewer (1st floor toilet)

PCE 780 840 780

TCE 39 43 39

(µg/m3)

-Hole +Hole

70-80% of TVOCs are C6-C10

0

100

200

300

400

500

600

700

800

900

10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00

PID

(p

pb

)

Car

bo

n tu

be

sam

pli

ng

(10L

)

+hole

Op

en

to in

stal

l PID

se

nso

r

Car

bo

n tu

be

sam

pli

ng

(10L

)

Car

bo

n tu

be

sam

pli

ng

(10L

)

• Automated sampling from sewer

– 2 x without a hole (@ PID = 720) and 1 x with a drilled hole

– In-line ventilation fan on (ACH = 8,6 hr-1)

TVOCs have never been investigated at the site before

®


-10

-8

-6

-4

-2

0

2

4

6

8

10

0

1

2

3

4

5

6

7

8

9

10

16-11 18-11 20-11 22-11 24-11 26-11 28-11 30-11

Dif

fere

nst

ryk

(P

a)

PID

(pp

m)

Faldstamme

dP faldstamme

Alm. prøvetagning

Alm. prøvetagning

PID/concentration in the sewer (long term)

PCE 75 700 630

TCE 1,2 4,4 35

(µg/m3)

Sewer samples

(10L on carbon tubes)

PCE 75 700 630

TCE 1,2 4,4 35

TVOC 820 6000 < 1000

(µg/m3)

>75% of TVOCs are C6-C10

Red = maximum value

• Automated sampling (1st floor toilet, the least dynamic):

– PID ≥ 5 ppm and dP ≥ 1 Pa (pressure gradient toward room).

Manual

sample

Manual

sample

PID sewer

dP sewer

Automated

sample

®


PID/concentration in the sewer (long term)

-10

-8

-6

-4

-2

0

2

4

6

8

10

985

990

995

1000

1005

1010

1015

1020

1025

16-11 18-11 20-11 22-11 24-11 26-11 28-11 30-11

Dif

fere

nst

ryk

(Pa

)

Atm

osf

ære

tryk

(mb

ar)

Atm.tryk

dP faldstamme

Intelligentprøvetagning

Alm. prøvetagning

PCE 410 480 590

TCE 16 15 26

TVOC 1100 3500 1200

(µg/m3)

Sewer (10L on carbon tubes)

Red = maximum value

• Automated sampling (2nd floor toilet, PID yielded only noise):

– Pressure drop > 1 mbar/hr and dP ≥ 1 Pa (pressure gradient toward room).

Automated

sampleManual

sample

Barometric pressure

dP sewer

®


Air exchange in the sewer (method & results)?

0

50

100

150

200

250

300

350

400

450

500

16:00 16:30 17:00 17:30 18:00

PID

(pp

m)

WC 1.sal

+100 ppm

+1000 ppm

100 ppm test

y = -4,94x + 3,52

1000 ppm testy = -5,75x + 5,73

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35

Ln(P

ID)

Tid (timer)

Natural air exchange: Ls= 5-6 hr-1

A previous study [Loll et al. 2015]: Ls= 160 hr-1

Take home message: Hard to guess; but it’s easy to measure.

• Addition of isobutylene (100 and 1000 ppm) and PID decay.

2nd floor toilet

®


Summary

• We have developed and applied an automated sampling unit that allows us to analyze temporal variability and collect samples at desired times (various sensors can be attached).

100 ppm testy = -4,94x + 3,52

1000 ppm testy = -5,75x + 5,73

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

0,000,05

0,100,15

0,200,25

0,300,35

Ln(P

ID)

Tid (timer)

• We also tested:– A sampling toilet that allows for long-term monitoring in normal use.

– A metod for estimating air exchange in sewers (use in tracer studies).

• Such tools allow us to account for high temporal variability in our risk assessments.

– And we found a low level ppb sensor (10,6 eV & 0,5 ppb-4 ppm):

®


How to apply in quantitative risk assessment?

• Until we know sewer dynamics better we might need to measure and analyze every time – establish normal and critical behavior.

• Collect samples for lab analysis at critical times + documentation.

– What’s the concentration and how (much) does it vary?

• Determine sewer ACH for design of tracer studies (PFT tracers)

– Then we can determine a quantitative sewer contribution to indoor air.

– I have previously tried designing by guessing at ACH – unsuccessfully.

PID sewer

dP sewer

Date post:	13-Jun-2020
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

Sewers as a Preferential VI Pathway Dynamic Measurements ... · The test site in the Region of...

Documents