Vapor

.Pathway is of growing concern.

Don’t be caught off-guard!

Intrusion Pathway

Vapor

�Major factor in setting clean-up goals at some Oregon and New York drycleaning sites.

�Pathway guidance under development for Federal Superfund, UST RCRA facilities.

Intrusion Pathway

and

Area of concern is crack around perimeter of slab

wall crack

bottom slab

Problems Testing Interior Air

�Interior air samples subject to many false positives from consumer products �Interior Air samples costly…

– Possibly $1,000 to $2,000 per sample

�Collection of interior air samples Problematic from Public perception standpoint.

Washington State Results

�TCE Plume from Electric Heater Manufacturer

�Originally discovered as soil gas plume during installation of sewer lines

�State officials decided that they had to monitor indoors as result.

Washington State Results

�30 houses over the plume or near enough to be of concern. �(One school and one daycare monitored

as precaution). �Collected 65 Summa canister samples

from the 32 buildings.

Washington State Results

�Seven houses had basements (including daycare)

�23 houses had crawl spaces.

� One house had concrete slab-on grade construction.

Washington State Results

�15 of the 65 Summa Canisters had Detections.

�6 of these had higher detections in the basement/crawl space than in interior air.

Washington State Results

�5 of the 15 detectable concentrations do not appear to be due to vapor intrusion.

�33% false positives !

�Washington State has not yet shared results with residents because of uncertainty over what results mean.

Solution: Models to determine if Risk is present before doing indoor air samples.

�Computer Modeling is cheap and should focus attention to areas of site needing attention.

Use Computer

“Model Fails to Predict Indoor Air Concentrations”

Oft- Cited Case: Redfield Scope Manufacturing, Denver Colorado

“Many houses with indoor concentrations much greater than predicted by plume concentrations”

“Model Fails to Predict Indoor Air Concentrations”

�Redfield Site Groundwater Concentrations underestimated for portion of the plume because an uncharacterized gravel sub-surface feature is channeling plume in unexpected direction.

�Model correlates well with indoor concentrations when correct groundwater concentrations input.

Denver Post Headlines

� “EPA Toxic Gas Model Falls sort in England, Seattle” February 8, 2001

� “indoor pollution levels were at least 100 to 1000 times higher than predicted by … models”

Denver Post Headlines

� Model predicted concentrations in Seattle were actually 100’s higher than Detected after correct inputs put into model.

DENVER POST Headlines

� Site in England was Vapor Plume from filled-in rock quarry. � Data was being entered as

groundwater concentrations.

� Model highly accurate once error was realized.

Models get bad rap because of bad data

� Lots of Air Intrusion data/ Interior Air samples have been collected nationwide.

� Lot of Suspect data � Example: Denver

> 1000 interior air samples reviewed for quality control, data consistency

140 samples considered “valid”.

– API Paper by Johnson, et al.

CDOT Facility Site

Computer Models

� Johnson and Ettinger (J&E) originally developed in early 1990’s

� Now available from EPA as spreadsheet model Version 2.3

epa.gov/superfund/programs/risk/

airmodel/johnson_ettinger.htm

J&E Model

� Four components: GW_SCREEN, GW-ADV, SG-SCREEN, SG-ADV

� GW-ADV

– Can input specific parameters for soil types, depth of contamination, building air exchange rates, interior air space of the buildings, etc.

– Can run the model to back-calculate groundwater concentrations that would exceed specific risk levels.

Building Air Exchange Rate

� Every Building has passive ventilation through cracks, building joints, window and door openings, siding, mortar joints etc.

Building Air Exchange Rate ACH

� Key Component in the Model that has a direct influence on predicted interior concentration.

� ACH has direct Inverse Effect on indoor Air concentration.

� Doubling ACH decreases predicted indoor Concentration by half.

ACH – Air Changes per Hour

� Model default is 0.45 ACH � Range for Residential Houses based on

Perfluorocarbon Tracer Studies (2,844

houses) was 0.01 to 11.8 – Lower ACH values may be short-term

seasonal variations.

� Mean Value 0.76 ACH

� Earlier study found average to be 1.1.ACH

ACH

ACH – Air Changes per Hour

� Lowest Ventilation rates observed in Mild Winter conditions with windows closed and heating system not-operating.

� SURPRIZE! No trend of increased air-tightness in areas with severe winter climate with houses constructed after 1980.

� Tendency of Environmental Regulators to use lower ACH to be “conservative”

� Danger of modeling conditions inconsistent with quality of life.

� RAGs uses ventilation rate of 0.25 m3/hr

� Calculates out to ~ 0.001 ACH !

ACH – Air Changes per Hour

� 0.35 ACH is Minimum recommended by American Society of heating, Refrigerating and Air Conditioning Engineers (ASHRAE) to avoid indoor air problems associated with poor air quality (mold, CO2, CO Odors, Moisture).

ACH – Air Changes per Hour

Building Air Exchange Rate ACH

� Tyvek House Wrap used to claim that it was possible to achieve the 0.35 ACH ASHRAE standard if properly applied during construction of the house.

Climate Inputs

� Model uses Henry’s Law to predict the amount of vapour that move off of a contaminant plume.

� Henry’s Law uses Temperature in o K

(o C + 273)

Groundwater Temperature

� Many people assume that higher temperatures in Summer will lead to increase volatilization and higher indoor concentrations

� Groundwater temperatures usually vary by no more ~0.5 EC.

� Near-surface GW temperature closely estimated by yearly Average Air Temperature.

Groundwater Temperature

� Yearly Difference in groundwater is small % when converted to o K

� Difference in volatilization because of temperature change over year is insignificant!

Soil Temperature

� Not a component of GW model; however, is factored into the SG-ADV component.

� Soil Temperatures may be more variable in northern climates, especially if under black asphalt.

� Soil Temperature may be major impact on model if a “Vapor Plume” exists.

J&E Model

� Changing soil types in spreadsheet model does not automatically change soil moisture inputs.

Caution A lot of Model

“failures” due to incorrect moisture

values

Including Seattle site reported in

Denver Post

wall crack

bottom slab

Limited by calculations to less than 2 cm.

Crack width in Model default set at 0.1 cm around the perimeter of the house.

Crawl Spaces

� Crawl Spaces cannot be modeled with existing J&E because of amount crack width.

� Crawl Space modification of model to be presented at Batelle Conference.

Interior Air Sampling

� Worst Case Samples Preferred

� Within Reason!

� One state’s protocol calls for sealing windows with tape and modifying furnace to draw in air from basement.

Interior Air Sampling

� Reasonable Worst case (from Massachusetts’s protocol)

� Moderate Steady Wind 5-10 MPH

� Inside temp 10o higher than outside

� Low or Steady barometer over course of sampling

� Doors and windows shut

Validation of J&E Model

� Ian Hers, et al, compares model to >2000 interior air samples at 12 sites

� Only 1 interior sample had concentration > predicted by model.

– Lowry AFB, Colorado – East Montclair Neighborhood • Website information indicates interior air

samples are an order of magnitude less than reported in Hers.

Validation of Model

� Washington State Heater Manufacturer site.

� Model predicted concentrations approximately an order of magnitude higher than detected.

Factors that may skew Worst Case Indoor samples

� Asphalt pavement

� Ice capping

� Air Conditioning ???

Comparison Of Model in SC

� 3 interior samples collected over 8 hour period from unoccupied units on first floor.

� Side of building facing the drycleaning plant.

� Soil gas samples also collected simultaneously.

� No detections in interior air space samples.

Comparison of Model in SC

� One site- Navy Base, Charleston SC

� “Smoking” PCE plume resulting from base Drycleaning Plant

� Adjacent building is 3 story temporary housing apartments

� Similar construction to motel.

Comparison of Model in SC

� Weather conditions not recorded during sampling event.

� Obtained from US Weather Service.

� Conclude that samples collected during probable worst case conditions

Validation of Model in SC

� Model Predicted interior concentrations at least 33 times higher than detection levels.

� Looking for more sites to compare model with.

SCDHEC Drycleaning Fund DRAFT INDOOR AIR Procedure

� Computer Model using site specific inputs – Modeling only if basements and/ slab-on

grade construction

– Crawl Spaces in SC are well-ventilated because of moisture concerns so should be no interior air concerns

DRAFT INDOOR AIR Procedure

� If Model predicted risk exceeds “acceptable risk” – Screen around houses with passive Soil

Gas method

• Most likely Gore Sorbers

DRAFT INDOOR AIR Procedure

� If Detectable with Passive Soil Gas Samplers – Perform Active Soil Gas Survey

• Samples probes to be collected around buildings from depth greater than slab or basement floor.

DRAFT INDOOR AIR Procedure

�IF Active Soil gas levels exceed Health Risk values

� Then interior samples will be collected with Summa Canisters for minimum of 8 hours.

J&E model may be overly conservative for large regions of the country.

� No Degradation in Model (factor more important for petroleum components).

� Clean Surficial water layers overlying contaminant plumes.

� Assumes house vacuum pulls vapors from sub-surface; however, easier for air flow through cracks, etc.