final mottolo geophysics - newmoa

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Bedrock CharacterizationMottolo Pig Farm Superfund Site

Andrew “Drew” Hoffman, PE

NH Department of Environmental Services

andrew.hoffman@des.nh.gov

603.271.6778

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Acknowledgments

� GZA GeoEnvironmental (lead consultant)

� Hager-Richter (sub for geophysics)

� EPA, Region 1

� NH Geological Survey (regional bedrock)

� USGS (geochemistry / arsenic expertise)

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� Site Orientation & Defining the Problem

� TCE Investigation

� Geophysical Surveys

� 3D Model (Representation)

� Groundwater Hydraulics & Geochemical Studies

� Results

� Questions & Discussion

What’s Ahead

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Site Location & Orientation

Randy Lane

North

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Former Piggery Buildings

FORMER DRUM

DISPOSAL AREA

SHALLOW BEDROCK

FLOW TO BROOK A

SHALLOW BEDROCK MWs

Site Features & EPA Cleanup Actions

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EPA’s 3rd Five-Year Review

� Completed August 2008

� Questioned the Protectiveness of Remedy– Increasing concentrations of TCE & arsenic in

several on-site monitoring wells

– Increased residential development

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Residential sampling

began in 2003

2009 Expanded Residential Well Sampling

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2009 TCE Concentrations

Detected

below

standard

Detected

above DW

standard

Non-Detect

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Arsenic Concentrations

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Unanswered Questions

1. Does the TCE found in residential wells

originate from the Mottolo Site?

2. Any of the arsenic Site-related?

3. Extent of remedy?

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� Site Orientation & Defining the Problem

� TCE Investigation

� Geophysical Surveys

� 3D Model (Representation)

� Groundwater Hydraulic Studies

� Conclusions & Findings

� Lessons Learned & Options for Scale-Down

� Questions & Discussion

What’s Ahead

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Bedrock Groundwater Contours

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Brook A

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� Site Orientation & Defining the Problem

� TCE Investigation

� Geophysical Surveys� Surface geophysical methods

� Borehole geophysical methods

� 3D Model (Representation)

� Groundwater Hydraulic Studies

� Conclusions & Findings

� Lessons Learned & Options for Scale-Down

� Questions & Discussion

What’s Ahead

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Geophysical Surveys

Surface Geophysical Methods:

� Very Low Frequency Electromagnetics (VLF)

� Electromagnetic Induction - EM34

� Earth Resistivity Imaging (ERI)

Borehole Geophysical Methods:

� Optical Televiewer (OTV)

� Acoustic Televiewer (ATV)

� Fluid Temperature & Fluid Resistivity

� Heat Pulse Flow Meter (HPFM) Ambient & Pumped Conditions

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Surface Geophysical Methods:VLF & EM34 Fracture Interpretation

Former DrumDisposal Area

N

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Former DrumDisposal Area

Perspective View

Looking Northwest

Surface Geophysical Methods:Earth Resistivity Imaging

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9

Geophysically Logged Wells

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Blue Fracture Plane

in 3D Model

Borehole Geophysical LoggingFracture & Flow Interpretation

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Perspective View

Looking Northeast

Former DrumDisposal Area

3D Geophysical Conceptual Model

Well or Borehole Logged by Hager-Richter or USGS

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North

Area of

concentrated

groundwater

withdrawals

Former DrumDisposal Area

Surface Traces of Modeled

Fracture Planes

N

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� Site Orientation & Defining the Problem

� TCE Investigation

� Geophysical Surveys

� 3D Model (Representation)

� Groundwater Hydraulics & Geochemical Studies

� Results

� Questions & Discussion

What’s Ahead

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Pump Test

� Pumped from Site Well

� 30 gpm for First Two Days; 50 gpm Remaining Five Days

� Treated Extracted Water for VOCs and Arsenic

� Measured Groundwater Level Response at 27 Locations

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Pump Test Drawdown

Pumping well

5’ 10’15’

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Perspective View to the

Southeast Looking Down-Dip

Of Modeled Green Fracture Plane

Pumped WellMOT_MW-103

Former DrumDisposal Area

3D Geophysical Conceptual ModelWith Pump Test Results

Well with Immediate Drawdown

Well with Delayed or No Drawdown

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Area 1 – Remedial Area

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Results

� Bedrock groundwater flow and contaminant migration largely influenced by a dominant set of fractures and pumping of residential wells

� TCE generally detected in wells intersecting the dominant bedrock fractures

� Water line remedy addressed residences that were impacted or likely to be impacted

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Results (continued)

� Predictions of plume contraction since 2012

� 9 of 25 former drinking water wells became additional site monitoring wells

� Have not detected site-related VOCs since pre-water line

� Continued sampling of residential wells and site wells support remedy decision

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Lessons Learned

� Data from residential wells critical

� Multiple lines of evidence inform decisions

� 3D model can be kept simple to explain the primary bedrock fracture network

� Integration of multidiscipline team was key to decision making process

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Questions and Discussion

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