Sewers as a Preferential VI Pathway Dynamic Measurements and Quantitative Risk Assessments

Transcription

1 Sewers as a Preferential VI Pathway Dynamic Measurements and Quantitative Risk Assessments R&D Manager, Ph.D. Poul Larsen and Claus Larsen, DMR Hanne Nielsen, Kristian Raun, Kim Thygesen and Klaus Mortensen, Region of Southern Denmark

2 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, 2

3 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? Standard Danish practice in relation to risk assessment is 10 L samples of sewer air on Dräger B carbon tubes for lab. analysis (could be Summa). 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? What to expect? Tools and thoughts on application. 3

4 The test site in the Region of Southern Denmark A three-level building from Apartments on the 2 nd and 3 rd floor. Various activities on 1 st floor through time Plumber Electronics Repairs Foot Clinic Dry Cleaner (PCE) Site investigations and remediation attempts Building was condemned and was purchased for tests. 6 toilets in all. We looked at 2 1 st floor 2 nd floor 3 rd floor 4

5 We created an automatic sampling unit (prototype) Logging of proxy and secondary parameters + automated sampling for chemical analysis (via valves and pumps): 2 PID-sensors (10,6 ev; 1 ppb-40 ppm & 0, ppm) 2 differential pressure (dp) sensors 1 barometric pressure sensor 1 temperature sensor Option of collecting 2 samples on carbon tubes Display, on-line data logging & remote controllable PID-sensor PID-sensor (room) PID-sensor (sewer) dp sensor (sewer) LED Display 5 dp sensor (floor/outer wall) 2 x carbon tubes for sample collection

6 Sampling toilet (for equipment protection) We constructed a sampling toilet which allows for regular use while logging (shown for the 1 st floor toilet): Constructed using standard plumbing components. The actual toilet was leak tested (no leaks). So was the sampling toilet (no leaks). 5% H 2 / 95% N 2 6

7 Differential pressure 1 st floor toilet 1 month of logging 4 times per minute. Toilet Average 1,5 Pa Min -5,3 Pa Maks 7,9 Pa Percent > 0 Pa 98 % Percent >+1 Pa 82 % Percent >+2 Pa 11 % Door closed, toilet not in use Floor Toilet vs. floor 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 % 7

8 Differential pressure 2 nd floor toilet 1 month of logging 4 times per minute. Toilet Average 0,77 Pa Min -19 Pa Maks 17 Pa Percent > 0 Pa 85 % Percent >+2 Pa 2,4 % Percent >+5 Pa 0,05 % Door closed, toilet not in use Outer wall Toilet vs. outer wall Average 0,08 Pa Min -19 Pa Maks 16 Pa Percent > 0 Pa 65 % Percent >+2 Pa 0,9 % Percent >+5 Pa 0,04 % 8

9 Differential pressure 2 nd floor toilet Toilet Significance of absolute barometric pressure? High (>1020 mbar) Low (<1005 mbar) Barometric pressure Baro vs. toilet Baro vs. outer wall Outer wall 9

10 Ændring i i barometertryk (mbar/t) Differential pressure 2 nd floor toilet 2,0 Trykstigning (29%) 1,5 Trykstigning Rising 1,0 0,5 0,0 Stabilt tryk (44%) Rising (29%) Stable (44%) Barometric pressure -0,5-1,0 Trykfald Falling -1,5 Trykfald Falling (27%) (27%) -2, Significance of barometric pressure changes? Rising Falling Stable vs. WC (timemidling) dbaro/dt vs. toilet R² = 0,0675 >0,5 mbar/hr <-0,5 mbar/hr [-0,5;+0,5] mbar/hr Analysis of hourly avg. data R² = 0,0424 R² = 3E vs. Ydermur (timemidling) dbaro/dt vs. outer wall Toilet Outer wall R² = 0,0123 R² = 0,008 R² = 0,

11 dp (Pa) dp (Pa) Effect of mechanical ventilation (1 st floor toilet) In-line ventilation fan (~51 m 3 /hr; ACH= 8,6 hr -1 ) Differential pressure (room) door closed Door open -1-3 Fan on (door closed) :30 14:00 14:30 15: Sewer dp faldstamme dp over gulv Floor 5 3 Baseline (dør (door åben) open) Fan In-line on ventilator (door closed) / Strip på dør :30 14:00 14:30 15:00 Baseline in agreement with long term data: 1-2 Pa positive dp across sewer 0-1 Pa positive dp across floor 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 Ventilation fan adds about 4-6 Pa of extra pressure gradient 11

12 PID (ppb) Open to install PID sensor Carbon tube sampling (10L) Carbon tube sampling (10L) Carbon tube sampling (10L) dp (Pa) dp (Pa) Effect of a hole in the sewer (1 st floor toilet) In-line ventilation fan (~51 m 3 /hr; ACH= 8,6 hr -1 ) + drilled hole Door open for +2 mm hole +5 mm hole 7 5 Fan on (door closed) Door open -10 Fan on (door closed) :00 15:00 16:00 17:00 18:00 19:00-1 Sewer Floor -3 14:00 15:00 16:00 17:00 18:00 19: hole :00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 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). 12

13 PID (ppb) Open to install PID sensor Carbon tube sampling (10L) Carbon tube sampling (10L) Carbon tube sampling (10L) PID/concentration in sewer (1 st floor toilet) 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 ) hole :00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 (µg/m 3 ) PCE TCE TVOC Hole +Hole 70-80% of TVOCs are C 6 -C 10 TVOCs have never been investigated at the site before 13

14 PID (ppm) Differenstryk (Pa) PID/concentration in the sewer (long term) Automated sampling (1 st floor toilet, the least dynamic): PID 5 ppm and dp 1 Pa (pressure gradient toward room) Manual Alm. prøvetagning sample Automated sample PID Faldstamme sewer dp sewer dp faldstamme Alm. Manual prøvetagning sample Sewer samples (10L on carbon tubes) (µg/m 3 ) PCE TCE 1,2 4,4 35 TVOC < 1000 Red = maximum value >75% of TVOCs are C 6 -C 10 14

15 Atmosfæretryk (mbar) Differenstryk (Pa) PID/concentration in the sewer (long term) Automated sampling (2 nd floor toilet, PID yielded only noise): Pressure drop > 1 mbar/hr and dp 1 Pa (pressure gradient toward room) Barometric Atm.tryk pressure dp sewerdp faldstamme Intelligent Alm. Manual Automated prøvetagning prøvetagning sample sample Sewer (10L on carbon tubes) (µg/m 3 ) PCE TCE TVOC Red = maximum value 15

16 PID (ppm) Ln(PID) Air exchange in the sewer (method & results)? Addition of isobutylene (100 and 1000 ppm) and PID decay ppm WC 1.sal 2 nd floor toilet 7,0 6,0 5, ppm test y = -5,75x + 5, ppm :00 16:30 17:00 17:30 18:00 4,0 3,0 2,0 1,0 100 ppm test y = -4,94x + 3,52 0,0 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 Tid (timer) Natural air exchange: L s = 5-6 hr -1 A previous study [Loll et al. 2015]: L s = 160 hr -1 Take home message: Hard to guess; but it s easy to measure. 16

17 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). 7,0 6,0 5,0 Ln(PID) 4,0 3, ppm test y = -5,75x + 5,73 2,0 1,0 100 ppm test y = -4,94x + 3,52 0,0 We also tested: 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 Tid (timer) A sampling toilet that allows for long-term monitoring in normal use. A metod for estimating air exchange in sewers (use in tracer studies). And we found a low level ppb sensor (10,6 ev & 0,5 ppb-4 ppm): Such tools allow us to account for high temporal variability in our risk assessments. 17

18 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. PID sewer dp sewer 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. 18