lecture 4: contaminated site characterizationbaiyu/engi 9621_files/lecture 4.pdf · when the...

Spring 2015 Faculty of Engineering & Applied Science

Lecture 4: Contaminated Site Characterization

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9621 – Soil Remediation Engineering

Site characterization a systematic investigation aimed at obtaining appropriate and adequate data in order to define the type and extent of contamination as well as to assess the fate and transport of contaminants under various scenarios (1) Information required for site characterization

4.1 Introduction

Geologic data Hydro-geologic data Contamination data

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(2) Questions to be answered by site characterization

Nature and extent of contamination where is it? What is future migration and control where is it going? What are receptors and their risk what harm will it do? What are technical options for remediation how do we fix it?

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(3) General methodology for site characterization

Source: Sharma and Reddy, Geoenvironental Engineering, 2004

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4.2 Preliminary and exploratory site assessment

to collect and review available or published site-specific or regional data involves two tasks: literature review and site visit

(a) Literature review

(1) Phase I: Preliminary site assessment

site use and history site permits water well logs and records aerial photos other sources

site personnel interviews geological maps and reports topographic maps soil survey maps

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Action I Get a topo map understand geographic setting, topography, nearby water bodies Action II Get background geologic data through

Effective actions:

consulting ground-water atlas of Canada getting reports on geology, hydrology, meteorology checking for reports from province and national geological surveys

Action III Investigate regional geology and hydrogeology help to understand site geology and hydrology understand effects on contaminant movement

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Where were chemicals handled or disposed? What site structures or activities are potential sources? What chemicals are and were handled? Prevention of costly mistakes such as multi-aquifer wells

(b) Site visit observe/record all potential important surface site features + collect surface water and near-surface soils

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to confirm findings in the preliminary assessment to obtain preliminary site-specific data to facilitate design of a detailed site investigation program

(2) Phase II: Exploratory site investigation

sampling and testing procedures sampling locations and frequency QA/QC plan health and safety (H&S) plan schedule cost assessment

a written work plan for phase III

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More information about H&S plan , visit http://www.worksafebc.com/publications /health_and_safety/by_topic/assets/pdf/howtoimplement_ohs.pdf

Health and Safety Levels

Source: Rast, Environmental Remediation Estimating Methods, 1997

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http://www.worksafebc.com/publications/health_and_safety/by_topic/assets/pdf/howtoimplement_ohs.pdf

http://www.worksafebc.com/publications/health_and_safety/by_topic/assets/pdf/howtoimplement_ohs.pdf

4.3.1 Methods of obtaining soil and rock data

4.3 Detailed site investigation

Phase III : detailed site investigation a comprehensive field and laboratory test program, along with S&H and QA/QC plans

Direct methods Geophysical methods Drive methods

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bucket augers; spiral or ram’s horn auger

Direct methods – near surface soil sampling

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Direct methods – soil sampling by solid-stem auger drilling


Power-driven solid-stem augers: (a) solid-flight auger; (b) relationship of surface cuttings and subsurface

Drilling stop at the desired depth augers remove from the borehole a sampler is attached to the end of the drill put the entire string back to the borehole a sample is taken from the bottom flight by

Only for sampling from soil, not applicable to saturated zones

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Direct methods – soil sampling by hollow-stem auger drilling


Typical components of a hollow-stem auger: a hollow pipe with a continuous ramp of upward-spiraling flight welded around them

Drilling a center rod (with a pilot bit and plug) is lowered inside the auger till the sampling position is reached the center rod/bit/plug are removed soil sampler is applied

Applicable to soil/uppermost level of groundwater sampling

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Presenter

Presentation Notes

The plug is prevent the soil from entering into the hollow stem

solid-stem (left) and hollow-stem (right) augur flights

a hollow-stem augur in action Source: DeJong & Boulanger, 2010

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Direct methods – popular samplers

A split-spoon sampler

Thin-walled tube samplers

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Drilling boreholes drilling fluid is pumped down hollow rotary drill rods the fluid circulates back to surface by moving up the annular space between drill rods and borehole wall stabilization of the borehole wall installation of the piezometer/monitoring wall

If the circulation medium is air instead of water air rotary drilling


Direct methods – Installing piezometers and monitoring wells by wet rotary drilling

Direct mud rotary circulation system

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Geophysical methods

Borehole geophysical methods a probe into the borehole using a cable transmit signals to surface instruments generate logs or charts

Surface geophysical methods no requirement of boreholes conduct electric/seismic/electromagnetic surveys as well as the use of ground penetrating radar

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Geophysical methods – Electrical resistivity

Source: van Ea, Geophysical Techniques for Sensing Buried Wastes and Waste Migration, 1985 18

Presenter

Presentation Notes

Direct-current (DC) resistivity and conductivity sensors measure the apparent ability of soils and sediments to conduct an electrical current. This property varies with soil or sediment type, and it is often used in conjunction with data from pressure sensors to further refine soil stratigraphy measurements. During resistivity surveys, electrical current is passed into the earth through a pair of current electrodes on the surface of the tool. A second pair of electrodes (potential electrodes), also on the tool surface, measures the resulting difference in voltage as the current travels through the ground, and the apparent resistivity is calculated. The resistivity of soils is a complicated function of porosity, permeability, the ionic content of pore fluids, and degree of clay mineralization. As a sideline, drastic differences in apparent resistivity may be noted when the probe encounters free product, providing an indication of contamination; this technique was initially for petroleum exploration. The apparent resistivity is the bulk average resistivity of all soils influencing the flow of current. It is calculated by dividing the measured potential difference by the input current and multiplying by a geometric factor specific to the array being used and the spacing of the electrodes. Different kinds of tools use different arrangements of current and potential electrodes for different applications. Examples are the dipole-dipole, Schlumberger and Wenner arrays.

Geophysical methods – Seismic reflection


Presenter

Presentation Notes

Seismic survey technologies are based on the principle that a portion of acoustic energy introduced into the ground at a specific location is reflected back to the surface when materials of different density are encountered. Sources of acoustic energy include power-assisted hammers, dropped weights, or explosive charges (such as shotgun shells). The acoustic waves travel into the ground at a velocity dependant on the density and elastic properties of the material through which they travel. When the waves reach an interface where the layer velocities change significantly as a result of changing physical properties, a portion of the energy is reflected back to the surface, and the remainder is transmitted into the lower layer. Where the velocity of the lower layer is higher than that of the upper layer, a portion of the energy is also critically refracted along the interface. Critically refracted waves travel along the interface at the velocity of the lower layer and continually refract energy back to the surface. Geophone arrays determine the time of travel. The angles of reflection and refraction are determined from arrival information. Using this information, the position of geologic units may be determined. With CPT seismic sensors, seismic waves are generated at the ground surface using a beam attached to the CPT rig. Geophones in the cone recognize the arrival of waves generated at the ground surface. Software then plots the wave amplitude versus travel time, and wave velocities are calculated. The seismic sensor may be used to measure compression and shear wave velocities for layers of known depth and thickness. These factors are key parameters for the analysis of soil behavior in response to dynamic loading from earthquakes, ice, vibrating machine foundations, waves, and wind.

Geophysical methods – Electromagnetic Induction


Geophysical methods – Ground penetrating radar


Drive methods e.g. cone penetrometer technology

CPT a method of providing real-time data for use in characterizing the subsurface, as opposed to older methods of analyzing subsurface conditions in the laboratory It consists of a steel cone that is hydraulically pushed into the ground at up to 40,000 pounds of pressure Sensors on the tip of the cone collect data

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4.3.2 Methods of obtaining hydrogeologic data

Piezometers and monitoring wells Water-level measurement In-situ hydraulic conductivity test Packer test Slug test Pumping test

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Installing Piezometers with a Manual Slide Hammer Structure of a piezometer

Piezometers a small-diameter observation well used to measure the hydraulic head of groundwater in aquifers

Source: Shanahan, Waste Containment and Remediation Technology, 2004 24

Monitoring wells -- Structure

Source: Shanahan, Waste Containment and Remediation Technology, 2004

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Monitoring wells -- Development


Well development by surge block


A surge block closely fits the casing interior and is operated like a plunger beneath the water level it has a very direct positive action on the movement in the well

Water-level measurement


(a) Applying a bailer a portion of the water is removed from the bore hole after which measurement can commence The rise rate of the groundwater is determined by using a measuring tape with a float and a stopwatch (b) The determination of the saturated water permeability using the Guelph permeameter.

In-situ hydraulic conductivity test

(a) (b) Source: Eijkelkamp, Agrisearch Equipment, 2010 (http://www.eijkelkamp.com/)

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Sources: Groundwater data collection, USGS Illinois Water Science Center Searchable Publications Database, 2010, http://il.water.usgs.gov/pubs/ofr01-50_chapter4_8.pdf (Left) Cutting Edge Drilling , 2010, http://cuttingedgecoredrilling.com/_wsn/page4.html (Right)

(a) The schematic of a packer test apparatus (b) Field packer test

Packer test

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Presenter

Presentation Notes

Packer tests consist of isolating specific sections (usually 10 ft) of a bedrock borehole with inflatable packers (bladders) so that water-quality samples can be collected and aquifer tests can be conducted. A series of such tests allows definition of the vertical distribution of water quality (usually contaminants) and hydraulic conductivity (pathways for water and contaminant movement) in an aquifer. Monitoring water levels in nearby wells while pumping packed intervals can identify permeable intervals within the aquifer. Information from the packer tests can be used to properly site the future location of monitoring wells.

http://il.water.usgs.gov/pubs/ofr01-50_chapter4_8.pdf



Source: Butler, et al., Analysis of slug tests in formations of high hydraulic conductivity, Ground Water, v. 41, no. 5, 620-630, 2003

Slug test

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Presenter

Presentation Notes

A slug test is a particular type of aquifer test where water is quickly added or removed from a groundwater well, and the change in hydraulic head is monitored through time, to determine the near-well aquifer characteristics. It is a method used by hydrogeologists and civil engineers to determine the transmissivity/hydraulic conductivity and storativity of the material the well is completed in.

Pumping test

Single well pumping test Source: Sharma and Reddy, Geoenvironental Engineering, 2004

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4.3.3 Methods of obtaining contaminant data

Contaminant in soil analyze the samples from soil sampler

Contaminant in water analyze the samples from piezometers and/or monitoring wells

Contaminant in soil vapor analyze the samples from soil gas sampler

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3.4 Case study

The Cantuar Field Scrubber Site located in southwest Saskatchewan

Leaking underground storage tank of natural gas condensates site contamination

Source: Zhang et al., 2007

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