The document discusses the rapid delineation of a soil gas plume in a small Indiana town using Hapsite technology and various evidence lines, revealing significant PCE contamination in groundwater and soil vapor. It highlights the efficient installation of soil vapor probes and Hapsite sampling, with a notable increase in plume dimensions compared to conventional methods. Additionally, it emphasizes the cost-effectiveness and speed of Hapsite compared to traditional approaches, resulting in better data density and insightful decision-making.

1. 1 Presentation Title
Rapid, Efficient Delineation Of VI Potential From Large Soil Gas Plume
Using HAPSITE and Other Lines of Evidence (Single Slide Summary)
Chris Lutes, CH2M Hill Christopher.Lutes@ch2m.com
• Small town in Indiana; Residential and Commercial areas (pop. = ~5,000)
• Five of 36 monitoring wells screened over the “shallow” aquifer (5‐23 ft bgs) have PCE
concentrations in groundwater greater than the residential VISL (~26 µg/L) (14% of wells
exceed)
• Permanent soil vapor probes (SVP) installed to a depth of one foot above the top of water
table. Top of water table ranged from 8 to 12 bgs. A total of 15 of 18 SVPs have PCE
concentrations that exceed the residential subslab VISL (~360 mg/m3). (83% of SVPs
exceed)
• HAPSITE 80 soil gas locations around the site, to delineate the extent of the soil vapor plume
and guide EPA Emergency Response (size, shape, chemical nature of plume);
• 80 points completed in 5 days; 8 ft depth (42% exceeded VISL). Comparison presented to 8
confirmatory lab samples
• Plume size – 4 acres (GW); 13 acres (permanent soil gas points); 87 acres (after HAPSITE Soil
gas). Plume shape differed.
• HAPSITE provided efficient, economical delineation consistent with TRIAD principles of field
adaptive decision making.

2. Rapid, Efficient Delineation From VI Potential
of A Large Soil Gas Plume Using HAPSITE
and Other Lines of Evidence
Chris Lutes and Jennifer Knoepfle, Ph.D., P.G

3. 3 Presentation Title
•Small town in Indiana; EPA led NPL Site
•Residential and Commercial (pop. = ~5,000)
•Unconsolidated sand and gravel aquifer (0‐~90 ft bgs) overlies shale
bedrock
•Municipal water extracts (~10‐20 µg/L) (drawn from entire aquifer 15 – 90
ft bgs) exceed the MCL (5 g/L) for PCE
•Five of 36 monitoring wells screened over the “shallow” aquifer (5‐23 ft
bgs) have PCE concentrations in groundwater greater than the residential
VISL (~26 µg/L) (14% of wells exceed)
•Permanent soil vapor probes (SVP) installed to a depth of one foot above
the top of water table. Top of water table ranged from 8 to 12 bgs. A total
of 15 of 18 SVPs have PCE concentrations that exceed the residential
subslab VISL (~360 g/m3). (83% of SVPs exceed)
•Some residents still use private wells screened in the shallow aquifer
Site Setting

4. 4 Presentation Title
Basic History
•1986‐1991: Industrial dry cleaner (source)
was operational (PCE contamination)
•2003 – 2008: EPA removal action (soil
excavation + AS‐SVE in and adjacent to
source)
•2010: IDEM noticed PCE impacted municipal
wells exceed PCE MCL and town treats
water through carbon filtration
•2015: Region/CH2M began RI efforts (4 field
events)
•2016: Subslab and Indoor Air Sampling
Underway by EPA

5. 5 Presentation Title
Recent Investigation Approach
•August 2015: PCE (and TCE) soil vapor plume – 15 of 18 permanent
SVP exceeded the PCE VISL
•Five locations exceeding the IDEM action levels and EPA Removal
Management Levels (RMLs) for PCE (2 locations for TCE)
– Soil Vapor Max concentrations 170,000 g/m3 (PCE) and 12,000
(TCE)
•August 2015: Bulk soil concentrations (discrete depth) for PCE and
TCE exceeded residential RSLs in one permanent SVP location. Soil
considered delineated.
•October 2015: PCE “residual” groundwater plume – considered
delineated (120 g/L= max GW PCE concentration)

6. 6 Presentation Title
December 2015: HAPSITE soil vapor investigation
•80 soil gas locations around the site, to delineate the extent
of the soil vapor plume and guide EPA Emergency Response
(size, shape, chemical nature of plume);
•80 points completed in 5 days; 8 ft depth (42% exceeded
VISL). Project included 8 confirmatory lab samples
•2016 Removal branch/START has recently performed targeted
subslab and indoor air sampling (results pending)
•May 2016: 2nd HAPSITE soil gas investigation is proposed
based on results from December 2015 to complete soil vapor
delineation

7. 7 Presentation Title
Comparison of Effected GW/Soil Vapor Plume Dimensions
•Plume based on locations were GW PCE concentrations exceeded
VISLs
– ~9 buildings
– ~164,000 ft2 (two small plumes 60,000 ft2 and 104,000 ft2 each)
– ~3.9 acres (two small plumes 2.4 acres and 1.4 acres each)
•Plume based on results from results from permanent soil gas points
– ~18 buildings
– ~585,000 ft2 plume area
– ~13.4 acres
•Plume based on results from First HAPSITE investigation
– ~178 buildings
– ~3,796,900 ft2 plume area
– ~87.1 acres

8. 8 Presentation Title
Plume Map Based on Groundwater VISL Exceedances

9. 9 Presentation Title
HAPSITE Planned Locations –Based On Permanent Soil Gas Results

10. 10 Presentation Title
HAPSITE Results Substantially Increases Soil Gas Footprint in Several Directions

11. 11 Presentation Title
Temporary Soil Vapor Probe Installation and Sampling Set-Up

12. 12 Presentation Title
HAPSITE Instrument

13. 13 Presentation Title
Cost Comparison
•Conventional Approach: 18 permanent soil vapor points
installed to 9-12 ft. bgs; one round of laboratory analysis =
$43K about $2,400 a point.
•HAPSITE/TRIAD Approach: 78 temporary soil vapor points,
installed to 8 ft bgs, with HAPSITE analysis on all, 8
confirmation samples $74K about $950 a point.
•This comparison does not include the additional benefits of
speed and eliminating unnecessary sample points with field
decision making.

14. 14 Presentation Title
HAPSITE Output

15. 15 Presentation Title
Methods Inter-comparison (Eight samples)
2 Points
1
10
100
1000
1 10 100 1000 10000
HAPSITE Result (ug/m3)
Laboratory Result (ug/m3)
Comparision of HAPSITE to Confirmatory Laboratory Samples for PCE
data
Ideal Agreement
VISL (PCE)
VISL (PCE)

16. 16 Presentation Title
Lessons Learned
•HAPSITE provided efficient delineation consistent with
TRIAD principles of field adaptive decision making.
•HAPSITE with temporary soil vapor probe mobilization
was rapid – 2 months for planning and mobilization.
•External soil gas sampling with HAPSITE allowed a
greater density of data points then the permanent
monitoring well network.
•Soil gas points appear to exceed corresponding VISLs by
greater ratio then shallow groundwater. Soil gas has
higher percentage of exceedances and larger plume
footprint mapped.