Stages of Site Investigation

8/17/2019 Stages of Site Investigation

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Guidelines for Closure of Rouge River National Wet WeatherAbandoned Dump Sites Demonstration Project

I:rouge2:dumps:dumpdoc:chap5a.wpd5-1

CHAPTER 5 - CONDUCTING THE INITIAL SITE INVESTIGATION

hen the information gathered during the background investigation

Wsuggests that hazardous substances may be present on the site, an

investigation must be performed to determine whether and to whatextent the site is contaminated, and to identify exposure pathways that may

require assessment and remediation. This phase begins with a comprehensive

planning process that requires the participation of technical staff from various

disciplines. The process concludes with an evaluation of presumptive remedies

after completion of the initial site investigation. The data gathered during the

initial site investigation may show that a certain presumptive remedy is

appropriate and may be cost effective.

The initial investigation, as outlined in this chapter, begins with the development

of a conceptual model, followed by site screening and systematic planning process

to determine the scope of work which may include geophysical or remote sensingsurveys, soil borings, and monitoring well placement. The planning process

requires the participation of technical staff with various disciplines and expertises

(e.g., statistician, risk assessor, hydrologist, etc.) The strategy is to adequately

characterize the composition of the waste material and sample potentially-

impacted media in order to evaluate the typical exposure pathways associated

with dump sites. Examples of this strategy are: 1.) leachate, if observed or

detected, should be sampled, 2.) a geophysical survey is recommended for sites

where waste burial histories are unknown or where site boundaries are unclear,

and 3.) monitoring wells are drilled and screened in strategic locations to learn

whether groundwater exists, and if so, in which direction it is flowing.

The seven basic parts of an initial site investigation are:

1. systematic, comprehensive project planning to establish the scope of work;

2. evaluating information obtained during the preliminary investigation and

site visit;

3. site screening;

4. conducting an intrusive investigation to evaluate whether hazardous sub-

stances are present;

5. evaluating exposure pathways for the hazardous substances that are

detected;6. evaluating whether hazardous substances are detected at concentrations

that exceed the applicable clean-up criteria; and

7. evaluating whether further site investigation is necessary.


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5.1 EVALUATION OF INFORMATION GATHERED DURING THE BACK-GROUND INVESTIGATION

The information and data collected during the background investigation should

be carefully reviewed, focusing on the potential for undetected environmental

contamination on or migrating from the property. Conclusions drawn at this point

will form the basis for investigating these conditions and identifying the potentialhuman health or environmental risks. These conclusions are then summarized

in a conceptual site model (CSM), one form of which consists of an illustrated

overview of the site dynamics.

5.2 CONCEPTUAL SITE MODEL

The CSM is a depiction of a site that illustrates suspected sources and types of

hazardous substances present, contaminant release and transport mechanisms,

affected media, exposure points, exposure routes, primary receptors, and

secondary receptors. Generally, a CSM is based on evaluation of the existing data

and information and is developed before any field activities are conducted. The

CSM can be used as a tool to identify and/or possibly eliminate certain hazardoussubstances or exposure pathways from further consideration. For example, if it

is known that volatile organic compounds (VOCs) are not present at the site, it can

be assumed that inhalation of VOCs is not an exposure pathway. Typical CSMs

include the following:

! Suspected sources, types, and estimated quantities of contaminants

present,

! Geologic/hydrogeologic environment at and around the source area,

! Contaminant release, transport and fate mechanisms,

! Rate of contaminant release and transport,

! Affected media,

! Known and potential routes of migration,

! Extent of contamination.

! Known and potential human and environmental receptors,

! Potential for hot spots.

The CSM should be revised and updated as investigations reveal new information

and data about a site. Assumptions or hypotheses presented by the CSM are

tested, refined, and modified throughout the site investigation. The development

and use of a CSM typically includes the following steps:

1. Collection of Existing Site Data and Information - Site data and information

includes, but is not limited to, site sampling data, historical records, aerial

photographs, maps, and observations from the site visit.

2. Organization and Evaluation of Existing Site Data - If there is sufficient

existing data, perform a preliminary evaluation of potential exposure

pathways and receptors.


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3. Prepare a Preliminary Diagram of the CSM - Prepare an illustration of the

site conditions, including source areas, exposure pathways, and potential

receptors. An example of a CSM diagram is shown on Figure. 5-1.

A more sophisticated form of CSM is a flow chart that shows all the same

parameters as in the schematic diagram but also includes a listing of receptorpopulations, all pathways of exposure, whether or not each pathway is complete,

and which pathways are included in the site risk assessment. This format allows

changes in the CSM to be easily made and identified.

The CSM can be used to focus attention on the hazardous substances or areas of

concern that pose the greatest risk, and to help identify and evaluate preliminary

remedial action alternatives. In addition, the CSM is an internal part of the

decision-making process in choosing the appropriate elements of a presumptive

remedy.

5.3 SITE SCREENINGSite screening can be defined as utilizing investigative tools and instrumentation

that minimize disturbance to the site (i.e, are non-intrusive) to gather preliminary

information on whether hazardous substances are present on the site. Site

screening is conducted to identify areas of potential contamination, qualitatively

define the areal extent of fill or hazardous substances, identify potential transport

and exposure mechanisms, as well as areas which may require further

investigation.

Field screening also is an effective and economical tool for generating site data.

With the constraint of a limited sampling budget, field analytical screening, withlaboratory confirmation of the screening results, can produce a more

comprehensive analytical database at lower cost than by using offsite laboratory

analysis. Field Screening is typically done in the following manner:

5.3.1 SELECT SCREENING INSTRUMENTATION

Field screening instruments provide real-time or immediate reading capabilities.

These screening instruments can typically detect the presence of contaminants (if

present at high enough concentration) and narrow the possible groups or classes

of chemicals for laboratory analysis. Once an area of concern is identified using

field screening techniques, a subset of samples can be sent for laboratory analysis

to verify the screening results. When using field screening methods andinstruments, it is crucial to follow standard operating procedures, including

instrument calibration, performance checks, and record keeping. Table 5.1 lists

many of the common field screening instruments, their application, and

advantages and disadvantages.


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Table 5.1Field Screening Instruments

INSTRUMENT APPLICABILITY ADVANTAGES DISADVANTAGES

Flame Ionization Detects organic Widely used and Used for organic vapors only;Detector (FID) gases and vapor in available; can be used detection is non-specific in the

air, soil, and waste; for total detectable survey mode; requires experienceuseful in gases and vapors, or in to operate (especially in the GCdetermining areas of a gas chromatograph mode); detects in the ppm rangeconcern (GC) mode for a specific

compound; can beused in humid and coldweather; direct reading

Photo Ionization Detects organic and Widely used and Detection is non-specific;Detector (PID) some inorganic available; direct requires experience; not effective

gases and vapor in reading; detects some in humid or cold weather;air, soil, and waste; inorganic compounds affected by electrical sources;useful in does not respond to methane;

determining areas of depends on lamp eV; does notconcern respond to any compound with a

higher ionization potential thanits probe (probes with varyingionization potentials areavailable); detects in the ppmrange

Portable Gas Detects organic New portable GC’s are Requires specific “modules” forChromatograph gases and vapor in much like the PID but various compounds or to work in(GC) air, soil, and waste can also give PID mode, therefore, the user

compound specific must have an idea what to screenconcentrations of in advance; not effective at loworganic vapors temperatures; data tabulationimmediately; requires some experience

immediate results; candetect below 1 ppm forsome compounds; datacan be downloadeddirectly from theinstrument into acomputer; effective inhigh humidity

X-Ray Field detection of Rapid analysis of Requires experience; 10 samplesFluorescence arsenic, antimony, metals; user can must be analyzed in lab for QA(XRF) barium, cadmium, analyze an unlimited level 2; site-specific calibration

chromium, copper, number of samples to curve is needed; results can vary iron, lead, mercury, generate data of known in heterogeneous samples; soil

nickel, selenium, quality (with lab cover of 0.5 cm may mask a hotand zinc confirmation) meeting spot; soil moisture affects result;QA level 2; can use a high detection limits, in the ppmgeneric calibration range; not widely available.model for locatingpoints for further labanalysis


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Field Detection Detects specific Rapid results; easy to Limited number of kit typesKits compounds, or use with some training; available; interference by other

specific properties, low cost; kits may be chemicals; colorimetricin soil, waste, and customized to user interpretation is needed;water (e.g., PCB or needs; semi- detection level dependent uponpesticide kits; Haz quantitative type of kit used; soil moisture canCat kits for affect results; some tests requireexamining experience to interpret resultsparameters such asreactivity, pH,flashpoint,ammonium,chlorine, cyanide,sulfides)

Real-time Aerosol Real-time detection Not much experience Cannot detect specificMonitor of particulate matter needed to use; can compounds(RAM)/mini RAM in air detect dusts, fumes,

smoke, fogs, etc., gives

direct reading

Detector Tubes Qualitative air Easy to operate; Must have specific tubesmonitoring for available for many available (must know what youspecific vapors different compounds; are monitoring for ahead of time);

gives direct reading of some tubes are cross sensitivevapor concentration; (e.g., HCL tube may detect CL orwidely available NO ); detection time is slow;2

there is no advance warningwhen vapor is present; accuracy is + 20%

Monitor Gas Detection of various Needs no experience; Certain monitors may be crossMonitor specific gases (e.g., passive; simple sensitive to other gases (e.g., the

H S, HCN, NO ) audible alarm if HCN monitor is cross sensitive to2 2

concentrations of the H S, HCl, and Cl )gas rises above TLV;widely available

2 2

Radiation Meter Detection of alpha, Allows immediate Most probes cannot distinguishbeta, and gamma detection of radioactive between beta and gammaradiation materials; direct radiation; many detectors may

reading; widely detect beta and gamma, but notavailable; needs little alpha (even if alpha is present);experience to operate; must have specific probe foraudible detection mode alpha; must be lab calibrated;

requires experience to interpretresults.

Combo meter Detection of Fully automatic; 3-way Used mainly for health and safety

(CGI, O , H S) combustible gas audible alarm; can give purposes and not2 2(CGI), O , and H S, TWA for H S; direct “environmental” screening,2 2in air reading; widely however, the ability to monitor

2

available; needs little H S is useful.experience to operate

2


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Mercury Vapor Analysis of mercury Direct reading with For vapors only; instrumentAnalyzer vapor in air real-time concentration probe cannot come in contact

levels with dust or liquid; requiresexperience to operate; not readily available

Conductivity Screening of Immediate detection of Not definitive; not compoundMeter groundwater potentially-impacted specific

groundwater; highconductivity is anindication of possiblecontamination

High volume air Used to determine Sample media available Requires experience; off- sitesampling pumps particulate and/or for many different laboratory analysis must be used

VOC type, size, and compounds and for channel testingquantity particulates

Personal air VOC and particulate Many sampling Requires training for use; off-sitesampling sampling for worker scenarios for VOC and laboratory analysis must be used

exposure and particulates for chemical testingcontaminantspecification

Notes:

H S=hydrogen sulfide Cl =chlorine gas2 2HCN=hydrogen cyanide O =oxygen2NO =nitrogen dioxide TLV=threshold limit value2HCl=hydrogen chloride TWA=time weighted average

5.3.2 SELECT THE SCREENING LOCATIONS

The selection of screening locations should be based on the results of theinformation investigation and the site visit. Examples of areas that warrant site

screening are: 1.) locations where wastes were buried; 2.) areas where there is

evidence of stressed vegetation; 3.) leachate seeps; 4.) points where there is evidence

of material spillage; 5.) areas with little or no site cover; and 6) areas with animal

burrows.

5.3.3 ANALYZE SELECTED SAMPLES AT AN OFFSITE LABSamples from known or suspected source areas should be submitted to an offsite

laboratory for full chemical characterization. The results will enable the

investigation team to evaluate potential contaminants at their method detectionlimits (MDLs), and confine future sampling and analysis to those substances that

are detected above the MDLs. It is important to ensure that laboratory data in all

phases of the investigation are of sufficient quality to allow the drawing of

conclusions regarding future investigation and eventual closure. In Michigan, the

MDEQ has provided guidance on MDLs in Operational Memorandum #6.


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Away from source areas, a limited number of indicator parameters may be selected

for analysis (e.g., lead, PAHs) based on the suspected hazardous substances.

Although approved sampling and laboratory methods must be used for all offsite

laboratory analysis, this approach will result in significant cost savings over a full

chemical analysis of each sample.

The USEPA recommends analysis of at least 10% of the screening samples at an

offsite laboratory to evaluate MDLs and the potential bias of screening methods

(USEPA, 1991). The samples chosen for analysis should be representative of

locations at which hazardous substances were detected by the field screening

instruments. If no contaminants were detected by the field screening instruments,

the samples submitted for laboratory analysis should be a random selection of

several media.

To meet screening objectives, USEPA quality assurance/quality control (QA/QC)

objective level 1 (QA1) is appropriate (USEPA, 1991). The QA1 objective applies

when a large amount of data are needed quickly and relatively inexpensively, orwhen preliminary screening data is not required to be chemical or concentration

specific. QA1 requirements are used with data from field analytical screening

methods to prepare a quick, preliminary assessment of site contamination.

Examples of QA1 objectives include:

! determining physical and/or chemical properties of samples;

! determining the extent and degree of contamination;

! conducting a preliminary health and safety assessment; and

! determining waste compatibility.

The Quality Assurance requirements for QA1 are:

! Sample documentation (e.g., chain-of-custody form)

! Instrument calibration data or a performance check of a test method

! Determination of detection limits, if appropriate

5.4 CONDUCTING THE INITIAL INVESTIGATION

5.4.1 DETERMINING THE SCOPE OF THE INVESTIGATION

The objective of the initial investigation is to detect hazardous substances, if they

are present, at a level of confidence sufficient to evaluate all suspect areas andpotential exposure pathways. At this point in the process, all available information

and data should be reviewed and evaluated for the purpose of developing an

investigative approach and a scope of work for this phase of the project. If

necessary, an additional site visit may be conducted to verify potential data gaps

and refine the proposed scope of work.


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The scope of work should define the methods that will be used to conduct the

investigation (a geophysical survey, leachate sampling, test pits, soil borings,

monitoring wells, etc.); the media that will be sampled (soil, groundwater, sediment);

the sampling locations and quantities; and the analytical parameters for laboratory

analysis. Detailed information on the application of these technologies is provided

in subsequent parts of this chapter.

5.4.2 PREPARATION OF A WORK PLAN DOCUMENT

A formal work plan document should be developed and should include: 1.) the

scope of the investigation; 2.) investigation methods; 3.) sampling locations; 4.)

analytical parameters; 5.) quality assurance procedures, 6.) a cost estimate; 7.) the

project schedule; and 8.) project deliverables.

The work plan document should identify field and management personnel, and their

duties and responsibilities. However, it should be remembered that, while it is

essential to have a well-defined plan, a good scope of work is flexible and may be

revised during the investigation, if appropriate.

5.4.3 PREPARATION FOR INITIAL SITE INVESTIGATION

Prior to conducting the site investigation, several preparatory steps, discussed

below, must be undertaken. They are essential to the success of the investigation

and should be considered carefully before commencing field activities.

5.4.3.1 Obtaining Site Access

In order to conduct field activities, it will be necessary to obtain site access from all

affected property owners. This may include adjacent property owners, if access to

the site affects adjacent sites. Due to potential legal issues, it is recommended that

written permission be obtained from each affected property owner. An example of

a typical access agreement is presented in Appendix C.

5.4.3.2 Obtaining Utility Clearance

The locations of aboveground and underground utility corridors should be

determined using several sources of information. These sources can be

summarized as follows:

! Site Inspection: Visual inspection of the site may reveal sewer lines and other

buried utilities, and above ground power lines that may interfere with field

activities (i.e., drill rig)

! Utility Companies: Water, electric, and gas companies will provide detailed

information on locations of buried utilities.

! Current Site Owner(s): Blueprints or other detailed site diagrams, current

and historical, may be available from the current site owner(s).

! Miss Dig Utility Alert: In Michigan, a utility locating service known as Miss

Dig Utility Alert (800-482-7171) will mark all the known utility lines for a site.


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Similar services are available in other states.

5.4.3.3 Field Preparation And Mobilization

Proper field preparation is essential to the success of a field investigation. Field

preparation activities include equipment testing, calibration and decontamination

and acquiring and organizing sampling and testing equipment (i.e., tools, laboratory bottles, meters, protective clothing). In addition, prior arrangements should be

made for disposal of investigation-derived waste.

5.4.3.4 Preparation of an Investigation Schedule

A project schedule should be developed that includes the time required for each

work activity. A detailed schedule of the investigation activities can potentially

avoid unnecessary delays by identifying interdependent work tasks. Typically, the

site manager needs a detailed project schedule for purposes such as site planning,

development, health and safety, or regulatory requirements.

The project manager should carefully schedule field activities to ensure that allsubcontractors are well informed of their responsibilities, and to avoid delays

and/or potential conflicts. In addition, the project manager should provide any

required notification of field activities to regulatory agencies or other interested

parties.

5.4.3.5 Preparation of a Health & Safety PlanAny project involving field work for which the likelihood exists that a worker will

come in contact with hazardous substances or conditions, will require preparation

of a site-specific health and safety plan (HASP). The purpose of the HASP is to

provide information for site workers about the physical and chemical hazards that

may be encountered at the site. The HASP describes the health and safety guide-

lines for the protection of on-site personnel, visitors, and the general public. The

document should contain the following information:

! Summaries of the site background and scope of work.

! A list of the key personnel working at the site.

! Identification of personnel directly responsible for site health and safety.

! An analysis of safety and health risks for each task.

! Data sheets describing the potential chemical hazards.

! A description of personal protective equipment and medical monitoring

requirements.! Activities and corresponding level of protection.

! Air monitoring requirements and action levels.

! Site control, decontamination, and disposal.

! Delineation of work zones (i.e., hot zone).

! Hazard communication.

! Procedures for emergencies, accidents, and injuries.


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! Emergency response contingency plan.

! SOPs for any site monitoring, protective equipment, etc.

! Site maps to the nearest hospital.

! List of emergency contacts.

An outline of a typical HASP is located in Appendix D. Federal Occupational Safety and Health Administration (OSHA) standards (29CFR 1910 and 1926) dictate the

specific policies and procedures to be implemented at a site. In Indiana, Michigan,

and Minnesota, state OSHA regulations may apply.

5.4.3.6 Preparation of a Field Sampling & Analysis Plan with StandardOperating Procedures and a Quality Assurance Project Plan

The field activities and laboratory procedures for site investigation must be

documented in the form of written standard operating procedures (SOPs). Typically

SOPs are included as attachments to a field sampling and analysis plan (FSP), and

include field sampling procedures, sample handling and preparation, and sample

analysis. The USEPA has made several types of SOPs available electronically on theInternet at www.ERT.org. From the site homepage, click on products, the on the

link for “Compendium of ERT Standard Operating Procedures. This will lead to a

list of SOPs which can be downloaded or in some cases mailed after finalizing a

request. The SOPs available at this site include the following:

! Surface water sampling

! Sediment sampling

! Toxicity testing

! Waste sampling

! Field analysis

! Groundwater sampling! Soil sampling

! Air sampling

! Biota assessment

Laboratory SOPs are obtained from the laboratory selected to perform the analysis,

and usually are based on published procedures from sources such as USEPA or the

American Society for Testing and Materials (ASTM).

In addition, a Quality Assurance Project Plan (QAPP) should be prepared and

approved prior to the start of field investigation activities. The QAPP summarizes

the project objectives and outlines the data quality objectives for the investigation.An example outline of a QAPP is included in Appendix E.

5.4.3.7 Preparation of a Cost EstimateUsing the scope of work, a detailed cost estimate should be prepared. The cost

estimate provides information for the site manager to prepare budgets and cost

control procedures. A detailed cost estimate should include costs for the following


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items:

! Development of a site-specific work plan

! Field preparation and mobilization activities

! Field activities (i.e., labor, equipment, travel)

! Laboratory testing! Laboratory and field data review analysis and

! Preparation of required report(s)

An example of a cost estimate is included in Appendix F.

5.5 CONDUCTING THE INITIAL SITE INVESTIGATION The field investigation will be conducted according to the methods and procedures

outlined in the work plan. However, as additional site information and data are

collected, the project manager and other technical staff should continually evaluate

the appropriateness of the scope of work with respect to the objectives of the

investigation. The scope of work may be reduced or expanded based upon theevaluation of site data. If the scope of work needs revision, the project manager

should submit the revised scope of work and cost estimate to the site manager.

5.6 INVESTIGATION METHODS

The next several sections of this chapter describe in detail the methods that are

typically used to perform the site investigation. The specific sampling design or

combination of designs should be chosen so that risk assessment information will

be provided for all receptor populations. Thoroughness at the outset may reduce

the need for additional sampling. Preliminary or background data will likely be

useful in directing both the CSM and the sampling strategy.

5.6.1 STATISTICAL METHODS

Statistical methods are widely employed to evaluate sites of environmental

contamination and may be useful at several stages of the investigation of an

abandoned dumpsite:

! determining appropriate sampling locations;

! evaluating and organizing data;

! establishing confidence in data; and

! evaluating the appropriateness of a proposed investigation or closure of a

site.

This section focuses specifically on the use of statistical methods in the selection

of sampling locations from which the samples will be subjected to trace chemical

analysis. The choice of the most appropriate sampling approach is important; the

methods include judgmental, random, stratified random, systematic grid,

systematic random, search, and transect sampling. A sampling plan may combine


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two or more of these approaches. Table 5.2 summarizes several types of statistical

sampling designs.

This section is not intended to be an exhaustive treatment of this exceedingly

complex topic. Many important areas have not been included, namely determining

the number of sampling locations, specifying the specific location of samples, andprocedures for detecting outliers. During the planning stage of an investigation it

is crucial to involve a qualified statistician so that appropriate statistical methods

are selected.

5.6.1.1 Judgmental Sampling

Judgmental sampling is the subjective selection of sampling locations at a site and

is typically based on: 1.) historical information; 2.) visual inspection; and 3.) the

professional judgement of the sampling team. Judgmental sampling is conducted

to identify contaminants present at areas having the highest concentrations (i.e.,

worst-case conditions). It has no randomization associated with the sampling

strategy, precluding any statistical interpretation of the sampling results.

5.6.1.2 Random Sampling

Random sampling is the arbitrary collection of samples within defined boundaries

of the area of concern. Random sample locations are selected using a random

procedure (e.g., using a random number table). The arbitrary selection of sampling

points requires each sampling point to be selected independent of the location of all

other points, and results in all locations within the area of concern having an equal

chance of being selected. This randomization is necessary in order to maintain

statistical validity.


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Table 5.2Summary of Sampling Designs

TYPE OF SAMPLING CONDITIONS WHEN THE SAMPLINGDESIGN DESIGN IS USEFUL

Haphazard sampling A very homogeneous population over time and space is

essential if unbiased estimates of population parameters

are needed. This method of selection is not recommended

due to difficulty in verifying this assumption

Judgmental sampling The target population should be clearly defined,

homogeneous, and completely assessable so that sampleselection bias is not a problem. Specific environmental

samples are selected for their unique value and interestrather than for making inferences to a wider population.

Stratified random sampling Useful when a heterogeneous population can be broken

down into sampling parts that are internally homogeneous.Multistage sampling Needed when measurements are made on subsamples or

aliquots of the field sample.

Cluster sampling Useful when population units cluster together (schools of

fish, clumps of plants, etc.) and every unit in eachrandomly selected cluster can be measured.

Systematic sampling Usually the method of choice when estimating trends or

patterns of contamination over space. Also useful forestimating the mean when trends and patterns in

concentrations are not present or they are known apriority, or when strictly random methods are impractical.

Search sampling Useful when historical information and site knowledge of

prior samples indicate where the object of the searchmay be found.

Because most approaches assume that the site is homogeneous with respect to the

parameters being evaluated (i.e., the contamination does not contain major patterns

or trends) other methods must be considered. The higher the degree of

heterogeneity, the less the random sampling approach will adequately characterize

true conditions at the site. Therefore, since hazardous waste sites are very rarely

homogeneous, other statistical sampling approaches may provide more suitable

means of subdividing the site into homogeneous areas, and thus would be moreappropriate than random sampling. Figure 5.2 presents an example of a random

sampling design.


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Figure 5-2 Random Sampling Design Example

5.6.1.3 Stratified Random SamplingStratified random sampling often relies on historical information, prior analytical

results, or field screening data to divide the sampling area into smaller areas, called

strata. Each strata is more homogenous than the site is as a whole. Strata can be

defined by various criteria, including sampling depth, contaminant concentration

levels, and contaminant source areas. The placement of sampling locations within

each of these strata is conducted using random selection procedures. Stratified

random sampling imparts some control on the sampling scheme, but allows for

random sampling within each stratum.

Different sampling approaches may also be selected to address the different strataat the site. Stratified random sampling is a useful and flexible approach for

estimating the pollutant concentration within each depth interval or area of

concern. Stratified judgmental sampling is another approach for dividing the

sampling area into smaller stratified areas.

Typically, sample depths are based on:

! field screening results;

! the presence of a permeable zone such as a sand lens;

! the location of the base of fill material; and

! the location just above the saturated or impermeable zone.


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Figure 5.3 Stratified Random SamplingDesign Example

Figure 5.3 shows an example of a stratified random sampling design.

5.6.1.4 Systematic Grid SamplingSystematic grid sampling involves subdividing the area of concern by using a

square or triangular grid and collecting samples from the nodes (intersection of the

grid lines or center of cell). The method starts with the selection of the origin and

direction for placement of the grid using an initial random point.

From that point, a coordinate axis and grid is constructed over the entire site. The

distance between sampling locations in the systematic grid is determined by the sizeof the area to be sampled and the number of samples to be collected.

Systematic grid sampling is often used to delineate the extent of contamination and

to define contaminant concentration gradients. Figure 5-4 presents an example of

a systematic grid sampling design.


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Figure 5-4 Systematic Grid Sampling Design Example

5.6.1.5 Systematic Random Sampling

Systematic random sampling is a flexible approach, useful for estimating the

average pollutant concentration within grid cells. Systematic random sampling is

conducted by subdividing the area of concern using a square or triangular grid,

then collecting samples from within each cell using random selection procedures.

Systematic random sampling allows for the isolation of cells that may require

additional sampling and analysis. Figure 5-5 presents an example of a systematic

random sampling design.

Figure 5.5 Systematic Random Sampling Design Example5.6.1.6 Search Sampling


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Search sampling utilizes either a systematic grid or systematic random sampling

approach to search for areas where hazardous substance(s) exceed applicable clean

up standards (i.e., hot spots). The number of samples and the grid spacing are

determined on the basis of the acceptable level of error (i.e., the probability of

missing a hot spot).

Search sampling requires that assumptions be made about the size, shape, and

depth of the hot spots. The smaller and/or narrower the hot spots are, the smaller

the grid spacing must be in order to locate them. Also, the smaller the acceptable

error of missing hot spots is, the smaller the grid spacing must be. This, in effect,

means collecting more samples.

Once grid spacing has been selected, the probability of locating a hot spot can be

determined. Using a systematic grid approach, Table 5.3 lists approximate

probabilities of missing an elliptical hot spot based on the grid method chosen and

the dimensions of the hot spot. The lengths of the long and short axes (L and S) are

represented as a percentage of the grid spacing chosen.

A triangular grid method consistently shows lower probabilities of missing a hot

spot in comparison to the block grid method. Table 5.3 can be used in two ways.

First, if the acceptable probability of missing a hot spot is known, then the size of

the hot spot which can be located at that probability level can be determined.

Second, if the approximate size of the hot spot is known, the probability of locating

it can be determined.

Examples of these two scenarios are presented below.


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Length of Short Axis as a Percentage of Grid Spacing

L e n g t h o f L o n g A x i s a s a P e r c e n t q g e o f G r i d S p a c 8

i n g

BLOCK GRID

TRIANGULAR GRID

0.97

0.95

10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

10% 0.97

0.95

20% 0.95

0.92

0.88

0.85

30% 0.92

0.87

0.83

0.78

0.72

0.66

40% 0.88

0.85

0.75

0.71

0.65

0.55

0.50

0.41

50% 0.85

0.82

0.69

0.63

0.54

0.44

0.38

0.27

0.21

0.08

60% 0.80

0.80

0.62

0.58

0.45

0.35

0.27

0.15

0.12

0.03

0.06

0.0

70% 0.77

0.77

0.56

0.54

0.38

0.29

0.18

0.12

0.07

0.0

0.03

0.0

0.0

0.0

80% 0.75

0.75

0.54

0.50

0.32

0.08

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

90% 0.72

0.72

0.51

0.45

0.30

0.21

0.1.0

0.06

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

100% 0.70

0.66

0.45

0.37

0.24

0.18

0.08

0.04

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

S=length of short axis

L

S

L = length of long axis

From tables in: Gilbert , 1987



Table 5.3 Probability of Missing an Elliptical Hot Spot

Example 1: Suppose the block grid method is chosen with a grid spacing of 25

feet. The decision maker is willing to accept a 5 percent chance of missing an

elliptical hot spot. Using Table 5.3 , there would be a 95 percent probability of

locating an elliptical hot spot with L equal to 80 percent of the grid spacing chosen

and S equal to 50 percent of the grid spacing chosen. Therefore, the smallest

elliptical hot spot which can be located would have a long axis L= 0.80 x 25ft = 20ft,

and a short axis S = 0.50 x 25ft. = 12.5ft.

Example 2: If 1.) a triangular grid with a 25 foot grid spacing is chosen, 2.) the

approximate shape of the hot spot is known, 3.) L is approximately 15 feet or 60percent of the grid spacing and 4.) S is approximately 10 feet or 40 percent of the

grid spacing, then, there is approximately a 15 percent chance of missing a hot spot

of this size and shape. Figure 5-6 presents an example of a search sampling design.


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Figure 5-6 Search Sampling Design Example

5.6.1.7 Transect Sampling

Transect sampling involves establishing one or more transect lines across the

surface of a site. Transect sampling is conducted by collecting samples at regular

intervals along the transect lines at the surface and/or at one or more given depths.

The length of the transect line and the number of samples to be collected determine

the spacing between sampling points along the transect. Multiple transect lines

may be parallel or non-parallel to one another. If the lines are parallel, the

sampling objective is similar to systematic grid sampling. A primary benefit of

transect sampling over systematic grid sampling is the ease of establishing and

relocating individual transect lines versus an entire grid.

Transect sampling is often used to delineate the extent of contamination and to

define contaminant concentration gradients. It is also used, to a lesser extent, in

developing a sampling approach for selecting composite samples. For example, a

transect sampling approach might be used to characterize a linear feature such as

a drainage ditch. A transect line is run down the center of the ditch, along its full

length. Sample aliquots are collected at regular intervals along the transect line

and are then composited. Figure 5-7 presents an example of a transect sampling

design.


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Figure 5-7 Transect Sampling Design Example

5.6.1.8 Comparison of Statistical Sampling Approaches

Table 5.4 summarizes the various statistical sampling methods and ranks the

approaches from most to least suitable, based on the sampling objective. The table

is intended to provide general guidelines, but the approach can vary based on site-

specific conditions.

Table 5.4Comparison of Representative Sampling Approaches

SAMPLING APPROACH

SAMPLINGOBJECTIVE

JUDGMENTAL RANDOM STRATIFIED SYSTEMATIC SYSTEMATIC SEARCH TRANSECTRANDOM GRID RANDOM

IDENTIFY

SOURCES1 4 2 2 3 2 3A

DELINEATE THE

EXTENT OF

CONTAMINATION

4 3 3 2 1 1 1B

CONFIRM

CLEANUP4 1 3 B 1 1 1C D

Notes:

1--Preferred Approach A--Should be used with field analytical screening

2--Acceptable Approach B--Preferred only where known trends are present

3--Moderately Acceptable Approach C--Allows for statistical support of clean up verification if sampling over entire site

4--Least Acceptable Approach D--May be effective with composting technique if site is presumed to be clean


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I:rouge2:dumps:dumpdoc:chap5b.wpd5-22

5.7 THE GEOPHYSICAL SURVEY

Geophysical surveys include a wide range of physical measurements and can

assist in: 1.) defining hydrogeologic conditions; 2.) selecting sampling locations;

3.) identifying the locations of buried waste and underground storage tanks; 4.)

estimating quantities of waste; and 5.) tracing conductive plumes (Benson et. al.

1988). The methods are non-invasive and usually lead to increased projectefficiency and cost effectiveness. These physical measurements are based on the

physics of electromagnetic fields, electric current flow, magnetics, seismic wave

propagation, gravitational attraction, and radioactive properties.

Natural Site Conditions - Terrain and ground cover will influence the rate

of collection and geophysical sampling locations. In some instances, grid

lines will need to be physically cleared before the survey can commence.

Soil type(s) and depths to groundwater need to be considered when selecting

the appropriate geophysical method. Drilling records will aid in interpreting

the survey results.

Cultural Features - Cultural features (i.e., fencing, power lines, and surfacemetal) can create undesirable “noise” (i.e., interference) in the geophysical

measurements. These cultural features can interfere with electric,

electromagnetic, and magnetic measurements. Vibrations from busy

roadways, industrial complexes, or mining operations can also interfere

with seismic data collection. The presence of these features should be

considered when assessing the viability of data collection.

Survey Objectives - The objectives of the geophysical survey should be

clearly defined and may include: 1.) defining hydrogeologic conditions, 2.)

defining the extent of fill, 3.) locating buried metallic objects (i.e., drums or

underground storage tanks), or 4.) locating trenches. Defining theobjectives of the survey is vital to a properly designed survey.

Waste Type(s) - Waste or fill material present in the survey area will

influence selection of the geophysical method. Some waste types may not

be detected by the proposed geophysical method. Other waste types can

interfere with the assessment of hydrogeologic conditions at the site.

Survey Grid Size and Positioning - The survey grid must be accurately

laid out and linked to permanent features so that locations of interest or

concern can be relocated after the survey has been completed. The line and

station spacing of the grid will depend on the target size, estimated depth

of buried material, contrast in physical properties between the target and

host material, and the selected geophysical method. The orientation of thesurvey grid relative to the target should also be considered.


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Cost Effectiveness - Geophysical surveys may not be cost-effective in all

investigations of abandoned dump sites. Experienced and knowledgeable

members of the investigation team should evaluate the appropriate

approach for each site.

5.7.1 GEOPHYSICAL SURVEY METHODS This section contains descriptions of five commonly used geophysical methods for

the investigation of potentially contaminated sites: electromagnetic, magnetics,

ground penetrating radar, DC resistivity, and seismic. Table 5.5 contains a

comparison of these five geophysical survey methods. In some instances, other

less common geophysical methods may be more appropriate for investigating site

conditions, and the lack of mention of these other methods in this guideline

should not necessarily exclude them from consideration.

5.7.1.1 Electromagnetics (EM)

EM provides a method of measuring the electrical conductivity of subsurface soils,

rock, and groundwater. It also is useful for the detection of buried metals.

Electrical conductivity is a function of the soil or rock type, porosity, permeability,

and the presence of liquid that occupies pore spaces within the soil/rock (Dobecki,

1985). As a result, the method is often useful in locating contamination in

groundwater or soils and in differentiating soil types. Conductivity is defined as

the ability of a medium to transmit an electric current. A medium that can pass

an electric current easier than another has a higher conductivity. For instance,

clay typically has a higher conductivity than sand.

An EM instrument has both a transmitter coil and receiver coil. An alternatingcurrent passing through the transmitting coil generates a primary magnetic field.

This oscillating magnetic field induces alternating electrical currents, or eddy

currents, in the earth. These eddy currents create a secondary magnetic field. In

general, the magnitude of the secondary field is linearly related to the subsurface

conductivity. The receiver coil senses the secondary and primary field and

converts it to an instrument readout. This reading is a composite conductivity

reading from the surface to the effective penetration depth of the instrument. The

effective penetration depth is primarily dependent upon the coil spacing, signal

frequency, and soil type (Telford, 1976).

Electromagnetics is also an effective method for detecting buried metal. This isusually accomplished by measuring the “in-phase” component of the EM signal.

The secondary field has components that are in-phase and out-of-phase with the

primary field. The in-phase component of the secondary field increase in


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Guidelines for Closure of Rouge River National Wet Weather

Abandoned Dump Sites Demonstration Project


magnitude with good electrical conductors (i.e., buried metals). Measuring the

in-phase signal, therefore, identifies the presence of buried metals. The EM

technique is an excellent reconnaissance tool for tracking certain contaminant

plumes, locating buried metal, detecting pit and trench locations of bulk waste,

as well as locating buried metallic utility lines.

The EM method does not require direct ground contact, therefore, data acquisition

is rapid. The EM instrument is carried over the site as data is recorded. A one-or-

two person field crew is usually sufficient to conduct the field survey. EM survey results are typically portrayed as profile lines or contour maps.

Table 5.5Comparison of Five Geophysical Survey Methods

METHOD USES PROS CONS

Electromagnetic

1. Defining hydrogeologic 1. Very fast to implement 1. Conductive near surface soils

conditions 2. Relatively inexpensive may limit penetration

2. Locating buried waste 3. Shallow to moderate 2. Susceptible to interference from

3. Tracking conductive exploration depth metallic objects

plumes 4. Small field crew (1-2 3. Susceptible to interference from

4. Locating buried metallic person) power lines

objects

Magnetic 1. Locating buried metallic 1. Does not have to pass 1. Highly susceptible toobjects directly over target to interference from nearby

2. Mapping of igneous identify metallic objects and power lines

intrusive 2. Very fast to implement 2. Solar activity and

3. Deep exploration depths thunderstorms can interfere

4. Small field crew (1-2 with data acquisition

person)

GPR 1. Mapping near surface 1. High resolution 1. Limited exploration depthstratigraphy 2. Picture Like Graphic 2. Rough Terrain May Cause

2. Locating trenches Display Misinterpretations

3. Locating buried metallic

objects

4. Underground utility

locations

5. Location of voids

DC Resistivity 1. Defining hydrogeologic 1. Good depth of exploration 1. Cumbersome data processingconditions 2. Both sounding and and analysis

2. Tracing conductive plumes profiling capabilities 2. Susceptible to large conductive

objects (metal fences, Railroad

Tracks, etc.)

Seismic 1. Mapping stratigraphy 1. Good resolution 1. Cumbersome data processing2. Mapping water table 2. Good depth of exploration and analysis(refraction technique) 2. Relatively expensive

3. Locating lateral 3. Susceptible to existing ground

discontinuities (reflection vibration

technique)

5.7.1.2 Magnetics


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Magnetics utilizes a magnetometer that measures the intensity, in nanoteslas, of

the earth’s magnetic field. Ferromagnetic objects cause local variations in the

earth’s magnetic field. A buried ferrous object such as a steel drum or iron tank

distorts the earth’s magnetic field and results in a magnetic disturbance. The

magnetic method can also be used to map certain geologic features, such as

igneous intrusions, which may play an important role in the hydrogeology of asite. The magnetic method is effective for detecting buried steel drums, ferrous

containers, iron pipes, and iron tanks (Breiner, 1973).

A variety of magnetometers are commercially available. Most magnetometers

measure the total magnetic field strength, but a few measure a component of the

total field dependent on the sensor orientation. Some magnetometers require the

operator to physically stop and register discrete measurements, while others allow

continuous data acquisition while the instrument is transported across the site

at a fixed height. A dual sensor magnetometer may be used to conduct a

magnetic gradient survey.

Generally, the magnetic method can effectively detect ferro-magnetic materials at

a greater depth than other geophysical methods. However, the magnetic method

is more susceptible to interference from ferromagnetic objects and power lines

than other geophysical methods. In addition, natural sources of noise from sun

spot activity and thunderstorms can also interfere with magnetic surveys.

A one or two person field crew can conduct a magnetic survey in a relatively short

period of time. The shape of magnetic anomalies is dependent upon the geometry,

orientation, and magnetic properties of the object, as well as the direction and

intensity of the earth’s field. This variability in the shape of the anomaly increasesthe difficulty of data interpretation.

5.7.1.3 Ground Penetrating Radar (GPR)

GPR is a type of electromagnetic method. GPR involves use of a transmitter that

introduces an electromagnetic pulse of energy into the ground at a known

frequency. Reflections of the electromagnetic pulse occur when a contrast in the

dielectric constant between two media is present. A receiving antenna at the

surface measures the reflected portion of the transmitted energy pulse. Depth of

the signal penetration is principally controlled by soil conductivities.

GPR is generally an effective method for mapping stratigraphy, locating trenchesor buried objects, and determining the depth to the water table (Beres, 1991).

Typically, buried metallic objects such as underground storage tanks or drums

are readily detected in the GPR record due to strong contrast in electrical


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properties between the metal and surrounding soils. GPR has also been used to

map non-aqueous phase liquids floating on the water table. Data acquisition is

conducted by dragging an antenna across the ground. A two person crew is

typically required.

5.7.1.4 DC ResistivityDC Resistivity is the direct current (DC) resistivity method which has been

developed to determine lateral and vertical variations in the earth’s resistivity.

Resistivity surveys are conducted by inserting electrodes into the earth. DC or low

frequency alternating current (AC) is injected into the earth through electrodes.

Other electrodes measure the potential difference (voltage). The potential

measured is a function of the location and geometry of the source electrodes

relative to the potential electrodes.

Conduction of electric current is primarily through water in the pore spaces and

by clay minerals in the soil and rock. Factors controlling earth resistivity are: 1.)

the porosity of the medium; 2.) the amount of pore water; 3.) the concentration of dissolved solids in the pore water, and; 4.) the clay content of the soil or rock.

Cultural features that are conductors such as metal fencing, railroad tracks,

buried metal pipelines, and heavily salted roadways, will alter the measured

resistivity values and should be avoided.

There are two main types of resistivity surveys: sounding and profiling. A

sounding survey (also known as electrical drilling) has the electrode array expand

over a common center point. A sounding survey delineates depth and thickness

of layers of variable resistivity. The resistivity sounding method is intended foruse in uniformly horizontal-layered geologic conditions, but can yield useful

information in complex geological environments. A profiling survey (also known

as electric trenching) maintains a constant electrode spacing as the array moves

laterally across the site. Profiling surveys are performed when mapping lateral

variations in the subsurface or the boundaries of a conductive plume.


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A 3-4 person field crew is typically utilized when conducting DC resistivity

surveys. Data acquisition is relatively slow due to the direct ground coupling

requirements of the method. Depth of exploration using the DC resistivity method

is virtually unlimited provided that a powerful current source is available, but

resolution will diminish with depth. Data processing is required in order to

interpret survey results.

5.7.1.5 Seismic Method

The seismic method is used to determine the depth and thickness of geologic

layers. Two commonly used seismic techniques are seismic refraction and seismic

reflection. Both techniques measure the travel time of seismic waves propagating

through the subsurface. In the reflection technique, the travel time of a wave that

reflects off an interface is measured. In the refraction technique, the travel time

of a wave that travels along a subsurface interface is measured.

When conducting a seismic survey, an array of seismic energy detectors known

as geophones are implanted in the earth’s surface. The geophones are connectedto a seismograph which measures the travel times of seismic waves from an

energy source. The energy source for seismic surveys range from striking a

hammer against a steel plate to the use of explosives.

The seismic method has an excellent depth of exploration and yields fair to good

resolution of stratigraphy. The refraction technique can also map the surface of

the water table. The seismic reflection technique can locate lateral discontinuities

in lithologic units and can locate fractures or voids in bedrock. Generally, a three

to four person field crew is utilized when conducting seismic surveys. The seismic

method is expensive relative to other geophysical methods. In addition, dataprocessing requirements are typically time consuming. Seismic surveys are

susceptible to existing ground vibrations and generally are not suitable for depths

less than ten feet.

5.8 SOIL VAPOR SURVEYS

Soil vapor surveys can assist in site investigations when the investigation team

suspects that volatile organic compounds (VOCs) have been released. There are

two fundamental reasons why the concentration of contaminants detected in soil

vapor surveys cannot be used to estimate the concentration of contaminants in

soil or groundwater (Nielsen, 1991). First, the method relies on indirect

measurement of subsurface conditions, and second, soil vapor concentrations arethe result of complex relationships of highly variable soil or groundwater

contaminant properties. Therefore, the value of using this procedure should be

carefully considered. Ultimately, the applicability of soil vapor surveys is


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dependent upon soil composition, the depth to groundwater, and the properties

of the contaminant of concern. Common uses of soil gas surveys are:

! Locating subsurface release sources

! Mapping areal and vertical distribution of volatile liquids and gases

! Determining the direction of contaminant flow! Optimizing soil and groundwater sampling locations

! Evaluating whether biodegradation is occurring

! Measuring the potential for vapor migration into buildings

5.8.1 FACTORS INFLUENCING THE APPLICABILITY OF SOIL VAPORSURVEYS

Vapor pressure is a measure of the tendency for molecules to transform from a

liquid phase into a vapor phase. The higher the vapor pressure, the greater the

tendency for a specific contaminant to volatilize. Volatilization can occur from

single component liquids (i.e., benzene), multi-component liquids (i.e., gasoline),

or an aqueous solution. Many common organic contaminants are volatile.

The solubility of a contaminant also affects its vapor phase concentration in the

subsurface. Contaminants with low solubility and high vapor pressure are can

be most readily measured by soil vapor surveys. Contaminants with high

solubility will tend to go into solution in soil moisture and groundwater rather

than transforming into the vapor phase.

Diffusion is the primary mechanism for soil vapor migration. Diffusion is the

migration of vapor in response to a concentration gradient. Diffusion in soil is less

than diffusion in air due to the presence of grains, soil moisture, and organicmatter. The migration of soil vapors will vary with changes in site geology.

Diffusion is greatest in dry, coarse grained, high porosity soils with low organic

content. The diffusion rate of vapors in tight soils, such as clays, will be very

slow. Site features such as paved areas, buildings, and utility corridors may

create vapor flow barriers or preferential migration pathways.

Soil vapor samples are collected by applying a vacuum to the probing rod. The

soils must have a high enough air permeability to allow a sufficient flow of soil

vapors into the sample collection system. Soil air permeability depends upon soil

grain size, moisture, and organic content.


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Soil air permeability is greatest in dry, coarse grained, high porosity soils with a

low organic content. Soils with low air permeabilities (clays and silts) will

significantly increase the difficulty of sample acquisition.

5.8.2 SOIL VAPOR SURVEY SAMPLING STRATEGIES

Soil vapor sampling locations can be selected by the judgment, statistical, orhybrid strategies. The sampling depth interval may depend upon the water table

depth. Soil vapor survey design should take into account the following:

! Purpose and objectives of the investigation,

! Site hydrogeology,

! Nature of contaminants of concern,

! Anthropogenic influences on contaminant and vapor migration,

! Parameters to be monitored and detection limit,

! Method of probe installation,

! Site accessibility,

! Project budget and time constraints, and! QA & QC.

5.8.3 SOIL VAPOR SAMPLE COLLECTION

Vapor samples are acquired by hand driving, hand augering, power augering, or

hydraulically pushing a hollow probing rod into the earth. The probing rod may

be open ended or screened at its tip. Care must be taken to ensure the tip does

not become clogged during installation. The probing rods need to be installed in

a manner that prevents ambient air from migrating down the boring, outside of

the probing rods, or through joints in the rods.

A vacuum is applied to the probing rod at the surface. The amount of air

evacuated (purged) from the probing rod must be greater than its initial volume.

If a field instrument is to be attached directly to the probing rod, the vacuum

pressure required to draw soil vapors into the probing rod cannot exceed the

capabilities of the instrument. Often the sample is collected in a sample bag

(Tedlar or Teflon), canister, or syringe prior to being subjected to field screening

and/or laboratory analysis.

The information recorded during sample collection should include:

! Sample location,! Date and time,

! Pre-sampling instrument response,

! Sample purge volume and flow rate,


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! Difficulty in purging,

! Presence of water in the probe, and

! Peak instrument response during purging.

5.8.4 SOIL VAPOR SAMPLE ANALYSIS

Soil vapor surveys can generate either qualitative or quantitative data dependingon the method of analysis selected. The sample analysis method selected must

be capable of detecting the contaminants of concern or their break down products

at the desired detection levels. Common field analytical instruments include:

! Photoionization Detector,

! Flame Ionization Detector,

! Field Gas Chromatograph,

! Combustible Gas Indicator,

! Detector Tubes,

! Oxygen Meter, and

! Carbon Dioxide Meter.

Table 5.1 in this guideline contains detailed information about these field

analytical instruments. Soil vapor samples may also be collected in bags,

syringes, or canisters, and sent to an off-site laboratory for analysis. The

concentration of contaminants in soil vapor cannot be correlated with a volume

or concentration of contaminants in soil or ground-water because it is an indirect

measurement. Therefore, the results should be used as a screening tool to assist

in the evaluation of an area requiring further investigation.

Use of an oxygen meter or carbon dioxide meter serves a dual purpose. Typically,oxygen levels are slightly depressed and carbon dioxide levels are slightly elevated

in soil vapor relative to ambient air (21% O and 0.5 % CO in ambient air).2 2Vapors entering the probing rod may be from leaks or ambient air migrating down

the boring. Including an oxygen and/or carbon dioxide survey with the VOC

screening can help distinguish between ambient air and soil vapors. At locations

where aerobic biodegradation is occurring, oxygen levels will be greatly depressed

and carbon dioxide will be highly elevated.


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5.8.5 DATA REPORTING

Soil vapor survey results are usually depicted as contour maps of contaminant

concentration or instrument response. Variations of less than a factor of 10 in

soil vapor survey may be insignificant. In addition, single point anomalies should

not be over emphasized.

5.9 GROUNDWATER SEEP SAMPLE COLLECTION

Generally, groundwater seep samples are collected to obtain information on

groundwater that may have been impacted by hazardous substances present

within the interior of the abandoned dump and surface water that may be

receiving groundwater seepage originating from the abandoned dump site.

Groundwater seepage generally follows a cyclic pattern that is associated with

local rainfall quantities and surface runoff. Leaching of chemicals in waste

material to groundwater is usually the contaminant release method of greatest

concern at abandoned dump sites. Breakouts of groundwater seepage at the

ground surface is a potential transport mechanism through groundwatermovement or surface runoff to onsite surface water, sediments, and nearby

wetlands.

If encountered at a site, groundwater seep samples should be collected as

“judgmental” grab samples. A discrete sample should be collected from each

observed seep. At a minimum the sample should be screened in the field for

conductivity and pH. The sample should also be screened for VOCs in the sample

container headspace.

The type of laboratory analysis required will vary with individual site conditions,

but the team will need enough information to evaluate whether hazardous

substances may be present in the leachate. At a minimum, groundwater seep

samples should be analyzed for the following parameters:

! Priority Pollutant Metals (13 elements),

! Volatile Organic Compounds (EPA Method 8260), and

! Surface Water Quality Parameters (see Section 5.15.4 for a list of possible

surface water quality parameters).

5.10 SURFACE SOIL SAMPLE COLLECTION

Generally, surface soil samples are collected to determine whether hazardoussubstances are present in surface soil and whether a direct contact exposure risk

is present. Surface soil sampling methods and sample quantities will be based on

several factors, such as the size of the site or area of concern, the amount of site


32/131



cover (i.e., pavement, buildings, vegetation), and the current or future use of the

property. In addition, surface soil sampling is typically focused on locations where

groundwater seeps are observed, stains or discoloration are present, or stressed

vegetation is observed.

A combined judgmental and statistical approach is often taken. However, if apresumptive remedy such as a cap is being considered, the amount of surface soil

sampling needed may be very limited.

For the purposes of this guidance document, a surface soil sample is any sample

that can be gathered using sampling equipment such as a spoon, shovel, trowel

or spade. Surface soil is typically described as being from the surface to six

inches below ground surface (bgs). Surface soil samples should be tested for the

following parameters, at a minimum.


! Polynuclear Aromatic Hydrocarbons (EPA Method 8270), and! Polychlorinated Biphenyls (EPA Method 8080).

Because volatile organic compounds would not be expected to persist in the top

six inches in soil, this parameter is not typically tested for in surface soil, unless

existing data or knowledge infer that they may be present.

5.11 SURFACE WATER AND SEDIMENT SAMPLE COLLECTION

Because surface water and sediment may be affected by migrating contaminants

originating within the site, surface water and sediment samples should be

collected if there are surface water bodies (i.e., ponds, streams, ditches, lakes)within the perimeter of the site or immediately adjacent to it.

5.11.1 SURFACE WATER SAMPLING

Conditions that may make surface water sampling necessary include:

! A river channel or former river channel cuts through the area of concern.

! A river channel or other surface water body is adjacent to the area of

concern and groundwater is suspected of being contaminated.

! Leachate seeps are observed at the riverbank or the margin of another type

of surface water body.

! Surface drainage passes over the area of concern and leads to a surfacewater body.

Methods for surface water sampling vary from simple grab sampling using


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suitable sample containers to more complex methods that enable the investigators

to collect samples from discrete depth intervals. Several types of discrete interval

samplers are available, including Kemmerer bottles and Alpha and Beta bottles.

Surface water samples are typically collected up gradient and down gradient of

any known groundwater/drainage seeps. It is critical to identify other possible upgradient or historical sources of contamination (i.e., industrial or municipal

sources). If intermittent streams are present on or adjacent to the site, it may be

necessary to conduct stream sampling during or immediately following a heavy

rainfall. In addition, on-site ponds or adjacent lakes may be impacted by surface

water runoff and/or groundwater seeps from the dump site. It is also possible

that contaminated groundwater could recharge to nearby ponds or lakes. Surface

water samples should be tested for the following parameters, at a minimum.

! Priority Pollutant Metals (13 elements), and

! Surface Water Quality Parameters (see section 5.15.4 for a list of surface

water quality parameters).

5.11.2 SEDIMENT SAMPLING

Sediment sampling may be necessary when any of the following conditions are

observed:

! Migration of contaminated leachate to the surface water body is ongoing.

! Earlier surface water sampling has been inadequate to characterize the

contamination.

! Groundwater is discharging into an on-site pond, lake, or wetland.

Sediment sampling methods generally include two categories: grab sampling and

core sampling. Grab samplers, such as Ponar and Ekman dredges, are useful for

collecting samples of surface sediments only. While these are generally easy to

collect, they are only useful for characterizing relatively recent impacts reflected

in the youngest sediments.

Core samplers are required for collecting deeper sediments when historical

deposition data is needed. There are a variety of types available, including vibro-

corers, piston corers, and gravity corers.

As with surface water samples, sediment samples are typically collected upgradient and down gradient of any known groundwater/drainage seeps. The other

factors affecting the selection of surface water sampling locations pertain to

sediment sampling as well. Sediment samples should be tested for the following


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parameters, at a minimum.


! Polynuclear Aromatic Hydrocarbons (EPA Method 8270), and

! Surface Water Quality Parameters (see section 5.15.4 for a list of surface

water quality parameters).

5.11.3 CAP INVESTIGATION

At most abandoned dump sites, little or no cover may be present on the waste

material. However, a cover or cap investigation should be conducted to determine

if an adequate cover is present at the site. The degree of sophistication of the cap

investigation depends to a great extent on whether the existing cap is going to be

used or incorporated into a new cover system. If the existing cap will not be used,

little investigation is necessary.

If the existing cover may be used for the cover system, it is important to

investigate the following aspects of the existing cap.

! Type of cover material(s),

! Thickness of cover material(s),

! Areal extent of cover,

! Whether hazardous substances are present in the cover,

! Integrity of cover, and

! Potential settlement and stability of waste material, depending on plans

for future use of it.

5.12 EXCAVATION OF TEST PITSExcavating test pits can be a reliable, fast, and efficient tool for investigating

subsurface conditions at abandoned dumps because fill material is typically

heterogeneous (i.e., not distributed uniformly) near the surface.

The primary purpose of excavating test pits at an abandoned dump site is to

identify and characterize, through physical inspection, the types of materials

within the dump. Information obtained from the preliminary investigation (i.e.,

results of the geophysical survey) should be used to select the test pit or trench

location(s).


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Information that can be obtained from excavating test pits includes:

! Confirmation of dump boundaries,

! Verification of geophysical interpretations,

! Verification of the presence of groundwater,

! Potential presence of continuing sources of contamination (e.g., drums,underground tanks),

! Soil composition,

! Thickness of fill and/or waste material, and

! Distribution of fill and/or waste material.

The excavation of each test pit should be conducted slowly and with utmost care

for safety. Site activities should be conducted in accordance with a health and

safety plan prepared for activities at each specific site. A complete description and

field sketch of the test pit should be recorded and should include the following

information:

! Location,

! Approximate surface elevation,

! Test pit dimensions,

! Soil descriptions (refer to soil descriptions below),

! Presence or absence of groundwater,

! Results of air monitoring or soil sampling screening results, and

! A detailed description of the type(s) and distribution of waste(s).

All test pits should be abandoned in a manner that prevents them from acting as

future conduits or infiltration points for contaminated surface water. As a generalrule, the test pit should be backfilled with material that is at least an order of

magnitude less permeable than the material that was excavated. Typically, a

mixture of soil (i.e., the material that was excavated) and bentonite is used for

backfilling. If significant amounts of waste material or hazardous substances (e.

g., drums containing liquid waste) are encountered during the excavation of the

test pits, disposal and/or treatment of excavated material at a licensed facility will

be required.

The advantages and disadvantages of excavating test pits are outlined in Table

5.6 . To minimize health and safety concerns during the excavation of test pits and

to ensure a proper surface seal following completion of the test pit, this activity should be specifically addressed in the health and safety plan and only

experienced personnel should conduct and direct the excavation.


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Additional information regarding the excavation of test pits and/or trenches is

described in USEPA, 1987 and OEPA, 1995.

Table 5.6Advantages and Disadvantages of Test Pits

ADVANTAGES DISADVANTAGES

Cost effective Health and safety concerns

Possible to inspect large areas of concern Potential disturbance of surface and cap

Allows visual inspection of waste material Limited excavation depth (20 feet)

Potential disposal requirements

5.13 SOIL BORINGS

Soil borings are drilled to collect soil samples for chemical testing, geotechnical

testing, and determination of soil composition and characteristics. They are

drilled to varying depths beneath the ground surface. Information obtained from

soil borings is used to characterize the source of contamination and the areal

extent of contamination. They are also routinely used for the installation of

groundwater monitoring wells. There are generally two purposes for drilling soil

borings. The first is to collect representative soil samples to evaluate the

concentration and distribution of hazardous substances. The second is to collect

data concerning the fate and transport of hazardous substances within andbeyond the boundaries of the dump (i.e., the presence of groundwater). To

accomplish these goals soil borings may be drilled within the dump, in areas

immediately surrounding the dump, and possibly at the interface of groundwater

and surface water. Soil borings are also routinely used for the installation of

groundwater monitoring wells. If groundwater is encountered in any of the soil

borings, monitoring wells should be installed.

5.13.1 LOCATION, NUMBER, AND METHODS OF DRILLING SOIL BORINGS

The number of soil borings to be drilled at an abandoned dump will vary from site

to site. However, it is recommended that a minimum of three soil borings be

drilled within the dump and a minimum of four soil borings be drilled outside thedump in natural soil layers. Depending on the results of the initial investigation,

it is likely that more soil borings and/or monitoring wells will be required to

adequately characterize subsurface conditions at an abandoned dump. Additional


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soil borings may be required due to the size of the dump site or the presence of

several “hot spots” located in separate areas of the dump site.

The purpose of drilling soil borings within the interior portion of the dump is to

evaluate:

! Types and distribution of waste material,

! The potential presence of leachate,

! Soil composition,

! Cap thickness and characteristics (soil classification, grain size distribution,

density and permeability),

! The potential presence of groundwater, and

! The potential for contaminant migration.

The purpose of drilling soil borings beyond the boundary of the dump in the

natural soil layers is to evaluate:

! Soil stratigraphy;

! Confirmation of dump boundaries;

! The potential presence of groundwater; and

! The potential for contaminant migration.

The abandoned dump should be carefully evaluated before drilling the boring to

ensure that the boring is drilled at a preferred location, and potential health and

safety concerns are minimized. Site activities should be conducted in accordance

with a health and safety plan prepared for activities at each specific site.

Soil borings can be drilled using numerous methods. However, southeastern

lower Michigan is dominated by unconsolidated Pleistocene glacial and glacial-

lacustrine deposits that may be as thick as 400 feet. Therefore, soil borings to be

drilled at abandoned dumps within the River Rou

Stages of Site Investigation

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