AEHS 14th Annual West Coast Conference, March 2004 EPA Vapor Intrusion Workshop Case Study of TCE Attenuation from Groundwater to Indoor Air and the Effects of Ventilation on Entry Routes Presented by: Alborz Wozniak, PE March 15, 2004 1
CONSIDER THIS! HVAC Commercial Building (TYP) Paved surface 14 (no seasonal fluctuations) sand/gravel low permeability alluvial deposits sand/gravel sand/gravel Vadose Zone TCE ~ 100 μg/l Unconfined Aquifer 2
QUESTIONS? Are vapors entering the building? If so, at what levels? And, If so, what can be done to minimize vapor intrusion? 3
Findings Our Study shows that: Vapor Intrusion (VI) is real. VI can easily be measured along floor cracks. Without building pressurization: there is a two-order of magnitude attenuation in TCE concentrations from the floor to the breathing zone. Building pressurization can effectively minimize VI. WE WILL NOT DISCUSS : What level of TCE vapors in the breathing zone poses an unacceptable risk? 4
TCE Regulatory Standards and Risk-Based Criteria OSHA PEL TWA 1,000,000.0 100,000.0 537,000 269,000 135,000 ACGIH TLV CalOSHA PEL TWA ATSDR MRL-A 10,000.0 10,740 ATSDR MRL-I EPA's Provisional PRG - 10-4 Cancer Risk 1,000.0 537 RWQCB ESL -Commercial Indoor Air TCE Limit (ug/m 3 ) 100.0 10.0 1.0 0.1 4.8 2 0.19 0.048 EPA's Provisional PRG - 10-6 Cancer Risk Avg. Lab Reporting Limit EPA Region IX Protective Risk Range base d on provisional conservative new TCE toxicity value 0.0 5
Presentation Content CASE STUDY Site Background / Conditions Study Objectives Study Approach/Methods Data Evaluation Conclusions 6
Site Background Superfund Site (US EPA lead agency) Manufacturing processes released solvents to the subsurface Soil cleanup completed in 1985 GW cleanup under way since 1986 using extraction and treatment Two aquifers (A- and B-Zones) are impacted with TCE In 2002 began an evaluation of potential for GW to indoor air vapor intrusion and associated risk to building tenants This Study was a subset of a larger investigation. 7
Site-Wide Groundwater TCE Iso-Concentration Contour Site Slurry Walls Commercial business area 8
TCE Iso-conc. contour (ppb) Section 2 Section 1 Indoor breathing zone sample Indoor pathway sample Outdoor HVAC intake sample AIR SAMPLING LOCATIONS 9
Site Conditions Building Condition Commercial building: single story, constructed in 1965 Slab-on-grade concrete with perimeter foundation Sub-slab material = unknown Utilities (e.g. sewer) exist beneath building foundation Two separated sections of building, Section 1 - vacant office space, Section 2 - occupied and used to manufacture batteries Two separate HVAC systems Building Section 2 is typically occupied M-F, 7AM - 5PM No indoor sources of VOCs were identified 10
View from the Front Groundwater Treatment System View from the Back 11
Site Conditions Site Condition TCE Plume beneath the building, ~100 ppb avg conc. Depth to water = 14 ft, <1 ft of seasonal variation Groundwater cleanup using pump-and-treat, 2 nearest extraction wells 20 ft from edge of building Groundwater treatment involves GAC No known outdoor sources of TCE within one mile of the site (e.g. no operating air strippers) 12
Study Objectives Answer these questions: Are cracks along concrete floor a pathway for subsurface TCE vapors? What is the TCE vapor attenuation between the concrete floor and breathing zone? What is the effect of ventilation/pressurization on vapor intrusion through floor cracks? 13
Study Approach Phase 1 Baseline Sampling (spring) Data Evaluation Phase 2 HVAC Repairs/Improvements Bldg. Pressure and Air Flow Testing Phase 3 Confirmation Sampling (summer/winter) 14
Field Events Phase 1 Phase 2 Phase 3 Date Activity May 6, 2003 Baseline Sampling Event 1 May 13, 2003 Baseline Sampling Event 2 June 2003 Baseline Data Evaluation July-August 2003 HVAC Repairs/Testing September4, 2003 Confirmation Sampling Event 1 September 11, 2003 Confirmation Sampling Event 2 November 2003 Confirmation Data Evaluation December 23, 2003 Confirmation Sampling Event 3 15
CONCEPTUAL MODEL HVAC Commercial Building (TYP) C IR = C OP = C BKG = 14 (no seasonal fluctuations) EW sand/gravel C IP = C ss? low permeability alluvial deposits C sg? sand/gravel Paved surface Vadose Zone sand/gravel C gw ~ 100 μg/l Unconfined Aquifer 16
Sampling Description ID Description Purpose IR Indoor rep. breathing zone risk assessment IP Indoor pathway pathway assessment OP Outdoor at HVAC intake mass balance BKG Offsite background outdoor sources 17
Study Methods Identify potential indoor/outdoor TCE sources Conduct Site survey and tenant interviews Sample duration = 12-hour integrated sample Sample with 6-L Summa canisters Two rounds of sampling/event (season), 1 week apart Analyze for chemicals of concern in GW (e.g. TCE) Analyze using EPA Method TO-15 Select Ion Monitoring (SIM) 18
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Breathing zone sample Pathway sample 20
Breathing Zone Sampling 1/4 SS cane 3.5 ft ags Duplicate Sampling (Section 2) Air sampling in office (Section 1) 21
Pathway Sampling 1/4 Teflon tubing Sampling of bathroom floor drain with the ceiling fan turned on! Floor Drain Building Section 1 bathroom 22
Pathway Sampling 1/4 SS cane 3.5 ft ags Floor crack 1/4 Teflon tubing Floor crack Building Section 2 Shop Area 23
Outdoor HVAC Intake Sampling HVAC Outdoor air intake Vacuum gauge Flow controller 24
Meteorological Conditions Sample Date Meteorological Conditions Building Section 2 Condition May 6, 2003 Cloudy, with occasional rain Wind from West @ 5 mph T out ~ 54-62 o F Poor ventilation system, stagnant air Doors were periodically open T in ~ 69-72 o F / ΔP <0.001 H 2 O May 13, 2003 Partly cloudy Wind from North-Northwest @ 6.5 mph T out ~ 59-67 o F Poor ventilation system, stagnant air Doors were periodically open T in ~ 69-72 o F / ΔP <0.001 H 2 O SPRING CONDITION September 4, 2003 September 11, 2003 Sunny Wind from North-Northwest @ 8.2 mph T out ~ 65-74 o F Sunny Wind from North-Northwest @ 3.9 mph T out ~ 65-90 o F Ventilation on full-time (24-hours/day) ΔP ~ 0.01 H 2 O T in ~ 73-75 o F Ventilation on full-time (24-hours/day) ΔP ~ 0.02 H 2 O T in ~ 71-73 o F HOT SUMMER CONDITION December 23, 2003 Rain, heavy at times Wind from Southwest @ 8.2 mph T out ~ 55-58 o F Ventilation on ½ hour before sampling ΔP ~0.02 H 2 O T in ~ 64-70 o F COLD STORM CONDITION Abbreviations: T out = Outside Temperature T in = Inside Temperature mph = miles per hour o F = degrees Fahrenheit H 2 O = water ΔP = Pressure difference between inside and outside the building measured in inches of water ( H 2 O), where positive pressure means greater indoor air pressure. 25
Data Evaluation BASELINE DATA SUMMARY SECTION 1 - VACATED OFFICES Parameter Observation Building pressure 0.01 H 2 O TCE - breathing zone <0.18-0.35 μg/m 3 (8 Samples) TCE -pathway 0.37, 0.5 μg/m 3 (2 Samples) SECTION 2 - OCCUPIED OFFICES Parameter Observation Building pressure <0.001 H 2 O TCE - breathing zone 0.53-1.4 μg/m 3 (6 Samples) TCE -pathway 17, 49 μg/m 3 (2 Samples) 26
Data Evaluation Pathway vs. Breathing Zone Attenuation Effects of Ventilation and Pressurization 27
Baseline Air Sampling Results - Building Section 1 1 0.9 May 6th May 13th TCE Concentration (ug/m3 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Bathroom Floor Drain 0.5 0.35 0.37 0.21 <0.18 <0.18 <0.18 0.19 <0.18 <0.18 <0.18 <0.18 0 BZ-1 BZ-2 BZ-3 BZ-4 Pathway Outdoor Sample Location 28
Baseline Results - Building Section 2 Breathing Zone sample 0.9 μg/m 3 EPA Sample @ 1 ags 1.1 μg/m 3 3.5 ft Pathway sample 6-inch (assumed) 49 μg/m 3 29
Typical HVAC System Components 30
HVAC Repairs in Building Section 2 Repairs included replacing parts, fluids, filters Conducted pressure/flow testing Added outdoor air intake to one HVAC unit Conducted air balancing Air Exchange Rate = 1.2 ACH Indoor-to-outdoor pressure difference = 0.01 H 2 O 31
1.6 1.4 TCE Concentrations in Indoor Representative and Outdoor Air Samples - Building Section 2 1.4 UN-PRESSURIZED BLDG Before HVAC Repairs PRESSURIZED BLDG After HVAC Repairs Sample Locations Indoor Breathing Zone - Cubical Indoor Breathing Zone - Above Pathway 1.2 Outdoor HVAC Intake Sample TCE Concentration (ug/m 3 ) 1 0.8 0.6 0.9 0.61 0.84 EPA Region IX Provisional PRG 10-5 Cancer Risk (0.48 ug/m 3 ) 0.66 0.4 0.34 0.3 Average Lab Reporting Limit (0.19 ug/m 3 ) 0.27 0.3 0.2 0 <0.19 <0.19 <0.18 <0.20 <0.19 <0.18 5/6/03 5/13/03 9/4/03 9/11/03 12/23/03 Sample Date 32
TCE Concentration in Pathway Samples Before and After HVAC Repairs - 60 TCE Concentration (ug/m 3 ) 50 40 30 20 UN-PRESSURIZED BLDG Before HVAC Repairs 17 49 PRESSURIZED BLDG After HVAC Repairs Ventilation system operated all week, 24-hrs per day Ventilation system operated only weekdays, 12 hours/day 10 0 <0.19 0.23 0.62 5/6/2003 5/13/2003 9/4/2003 9/11/2003 12/23/2003 Sample Date 33
Conclusions HVAC C OP = 0.3 μg/m 3 Not Pressurized C IR = 0.9 μg/m 3 Pressurized C IR = 0.3 μg/m 3 C BKG = <0.19 μg/m 3 EW C IP = 49 μg/m 3 C IP = 0.62 μg/m 3 Paved surface 14 (no seasonal fluctuations) sand/gravel low permeability alluvial deposits sand/gravel Vadose Zone sand/gravel C gw ~ 100 μg/l Unconfined Aquifer 34
Conclusions Vapor Intrusion was REAL! Attenuation from slab surface to breathing zone: 20-60 times under minimal building pressure Proper ventilation and building pressurization effectively minimized vapor intrusion (negligible TCE detection). 35
SOME QUESTIONS & CHALLENGES: Is soil gas and sub-slab sampling useful and/or necessary if one can perform indoor pathway sampling? What level of TCE vapor results in an unacceptable risk? Is pressurization adequate as a sole mitigation measure? How reliable is pressurization in the long-term? 36
Contact Information: Alborz Wozniak, P.E. Johnson Wright, Inc. (925) 284-9001 alborz.wozniak@johnsonwright.net 37
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