Soil and groundwater contamination of real estate is a problem that is receiving more attention as developers and property purchasers discover the risks and liabilities resulting from historical chemical spills and buried wastes found on their sites.  The application of environmental regulations and common law to real estate transactions can impose devastating responsibilities and impairment liabilities on the unwitting purchaser and/or generator of soil and groundwater contamination.

Contamination of property can take many forms including contaminated soil and groundwater, buried wastes, exposed asbestos, waste stored in drums, PCBs in electrical equipment, leaking underground storage tanks, and migration of contamination onto the site and underlying groundwater.

Upon determination that there is a reason to suspect that contamination may exist or that the environmental integrity of the subject or adjacent properties may have been impacted by the presence of contamination, it is necessary to sample the soil and groundwater for the presence of such contamination. 

Site Sampling Plan

A Site Sampling Plan must be established for the collection of soil and groundwater samples.  This plan must contain information about the chemical nature of the suspected contaminants and their approximate locations.  This plan must also address other physical, chemical and biological parameters associated with the site location and the suspected contamination.  The following is a list of some of the important considerations that must be addressed when designing a comprehensive sampling plan:

• Chemical and physical properties of the contamination (vapor pressure, density, water solubility, chemical composition, physical phase, Henry's Law constant, concentration, organic carbon distribution coefficient, viscosity, dielectric constant, boiling point, and molecular weight);

• Site location (physical size of the site, availability of space, etc.);

• Type of samples required (soil and/or groundwater, grab and/or composite samples);

• Type of field measurements required (temperature, water level measurements, electrical conductivity, and pH);

• Type of soil/sludge sampling equipment required (Shelby Tube, Split-Tube Sampler, Benthos Gravity Corer, Alpine Gravity Corer, Phleger Corer, Air Hammer Rig, Diamond Drill Top Drive Rotary Rig, Shipek Grab Sampler, and Birge-Ekman Dredge);

• Type of groundwater sampling equipment required (Waterra Power Pump, Kemmerer Sampler, Teflon Bailer, Sampling Iron, Van Dorn Bottle, and Bladder Pump/Controller Sampling System);

• Rigorous field Quality Assurance and Quality Control (QA/QC) for field measurements, sampling procedures, sample storage and transport;

• Rigorous laboratory Quality Assurance and Quality Control (QA/QC) for analytical procedures;

• Types of analyses required;

• Number of samples required for plume delineation;

• Sampling methodology and integrity; and Methodology for recording of field data (station location description, station description, detailed sketch of station location and mapping).

Site Execution Plan

Upon completion of the Site Sampling Plan, a Site Execution Plan is prepared and subdivided into phases.  This approach is flexible, practical, and cost-effective.  These phases illustrate the schedule of services that Great White North Environmental Services Limited offers; every site may not require all of these services.  Given the complex nature and extensive scope of such studies, Great White North Environmental Services Limited is prepared to constantly review and interact with our client on a regular basis through meetings and progress reviews.

The following represents the phases that constitute a basic Site Execution Plan:

• Phase 1:     Conduct a soil vapour survey for plume delineation of volatile constituents;

• Phase 2:     Install monitoring wells in the four (4) cardinal directions around the contamination and take soil and groundwater samples for laboratory analysis;

• Phase 3:     Computer modeling of groundwater flow and contaminant transport in the near surface (vadose and saturated zones) and deep aquifers;

• Phase 4:     Data interpretation to determine the nature and extent of contamination;

• Phase 5:     Evaluation of mitigative measures;

• Phase 6:     Evaluation of hazardous materials disposal options; and

• Phase 7:     Long-term groundwater quality monitoring, if required.

Phase 1:          Soil Vapour Survey

Soil vapour measurement is a useful tool in subsurface investigations.  Its most popular use is in mapping the extent of groundwater and unsaturated zone contamination related to surface spills, leakage from underground storage tanks and/or waste disposal sites, and leachate from landfills.  This technique has potential application in most site investigations because many of the most frequently observed contaminants are volatile organics. This technique is extremely cost effective because preliminary plume delineation can be accomplished without monitoring well installations.

Preliminary sampling is performed to determine vertical profiles of subsurface organic vapour concentrations at several locations within the site to be surveyed.  Based on the preliminary vertical profiles, a sampling depth is chosen that appears likely to provide gas concentrations large enough to be readily quantified by available analytical techniques.  Soil-gas samples are then collected over the survey area on a predetermined grid at the uniform sampling depth.  This is accomplished utilizing soil vapour probes.  Figure 3.1, Soil Vapour Probe, depicts a graphical representation of this device.  The samples are analyzed on site or transported to a laboratory for analysis.  Data analysis consists of plotting the concentrations on a map of the survey area and interpolating the iso-concentration lines of the organic vapour. 
Figure 3.2, Soil Vapour Isoconcentration Map, illustrates soil vapour contamination that was modeled by computer to define the most impacted areas of an industrial site.  The final objective of the soil-gas survey is the siting of monitoring wells to obtain representative measurements of groundwater concentrations of the contaminants and/or to obtain core samples to determine the concentrations of the contaminants in the soil.
 

Figure 3.1
Soil Vapour Probe

 

Figure 3.2
Soil Vapour Isoconcentration Map
Corrected to Conditions of
Standard Temperature and Barometric Pressure

 

 

 

Phase 2:          Soil and Groundwater Sampling

Great White North Environmental Services Limited conducts all soil and groundwater sampling in accordance with the Environment Canada publication, "Sampling for Water Quality."[1]  This manual is designed to help water and soil/sediment quality investigators in the field.  It outlines procedures that are currently practiced and recommended by staff of the Water Quality Branch.  The sample containers, preservatives, and sampling procedures described are those commonly used for physical, chemical, and bacteriological analyses.

During the monitoring well installation process, soil samples are collected for laboratory analysis.  Typically, this is accomplished utilizing a Lynac Heavy-Duty Split Tube Soil Sampler.  Please refer to Figure 3.3, Subsurface Soil Sampling, Lynac Heavy-Duty Split Tube Soil Sampler for a graphical depiction of this device.

The quality and integrity of collected soil samples is greatly influenced by the degree to which Quality Assurance/Quality Control (QA/QC) procedures are performed and adhered to during the soil sampling process.  Strict Quality Assurance/Quality Control procedures include the following:

• All personnel collecting soil samples don two (2) pairs of surgical Latex gloves, the outer pair of which are removed and disposed of after the collection of each and every sample;

• All disassembled sampling equipment (e.g., Lynac Heavy-Duty Split Tube Soil Samples, cement trowels, hammers, etc.) are washed thoroughly with Liquinox, a phosphate free laboratory detergent, used for cleaning laboratory glassware.  This process is followed by a distilled water rinse.  The soil sampling device is then reassembled and once again distilled water is poured over the outside and inside of the device.  This water is collected into a USEPA approved soil jar and labeled as a “sampler blank.”  The concentration of contaminants found, if any, in this rinsate represents the amount of cross-contamination remaining on the soil sampling device;

• Soil samples are collected in duplicate.  The core sample collected from the split tube soil sampler are split longitudinally along its axis into two (2) equal halves.  The first half is placed into an USEPA approved soil jar fitted with a Teflon lid and filled full to avoid any head space and degassing of the sample.  This sample is placed into a cooler, filled with gelled ice packs and preserved for potential laboratory analysis.  A “V” notch cut is then scribed into the remaining half of the core, and this sample is then also placed into an USEPA approved soil jar, however, this time the jar is only filled to fifty (50) percent total volume, allowing for volatile vapour to accumulate into the headspace of the jar.  Aluminum foil is then placed over the jar opening and the lid is sealed over the foil.  The contents in the jar are then allowed to come to equilibrium with room temperature and the lid is removed.  The aluminum foil lid is then punctured with the tip of a photoionization detector to determine the concentration of any accumulated volatile vapour.  The samples are screened in this way to determine which samples, if any, will require laboratory analysis.  Figure 3.4, Lynac Heavy-Duty Split Tube Soil Sampling Protocol, illustrates the above noted process; and

• The individual auger flights/drill pipe are steam cleaned with a hot pressure cleaning device, such as a “Hotsy.”

As the borehole is advanced with a hollow stem auger drilling rig, samples are collected and their lithologies are described utilizing the Modified Unified Classification (MUSC) System for Soils.  Figure 3.5, Modified Unified Classification System for Soils, illustrates the MUSC System.  These descriptions are logged and presented as Driller’s Log Reports.  Figure 3.6, Typical Driller’s Log Report, illustrates a typical soil/rock description utilizing the MUSC System.  Upon completion of all Driller's Log Reports, stratigraphic cross-sections are constructed to define subsurface geologic conditions, such as faulting, direction of subsurface flow, and continuity of geologic structures.

After soil samples are screened for volatile vapour with a photoionization detector, the relationship between Soil Total Volatile Vapour (S_TTV) and Soil Total Petroleum Hydrocarbons (S_TPH) can be determined.  In this way, the depth to which soil exceeds the Risk Management Guidelines can be estimated.  In Alberta, the “Risk Management Guidelines for Petroleum Storage Tank Sites,”[2] and in Saskatchewan, the “Risk Based Corrective Actions for Petroleum Contaminated Sites,”[3] have set the risk based criteria for Total Petroleum Hydrocarbons, for soil that requires remediation to 3,380 ppm.  Typically, soil contaminated with petroleum hydrocarbons that exceed this criteria must be remediated and therefore, determining the depth to which soil does not exceed this criteria is crucial.  Figure 3.7, The Relationship Between Soil Total Volatile Vapour (S_TVV) and Soil Total Petroleum Hydrocarbons (S_TPH), plots a typical relationship between these two parameters.

Figure 3.8, Typical Stratigraphic Cross-Section, illustrates the relationship of geological strata, piezometric data, and chemical contamination.

Failure to follow strict Quality Assurance/Quality Control procedures in the field, can result in biased, skewed, or unrepresentative data, the integrity of which can then be in question.  Additionally, if a soil sampling device is not decontaminated thoroughly between soil sample collection, it is possible to spread or smear the contamination to a depth below grade that is not at all contaminated.  This may lead the investigator to believe that the contaminated soil plume is deeper than is actually the case, causing an over-estimation of the total volume of contaminated media to be calculated.  Figure 3.9, Quality Assurance/Quality Control (QA/QC) Procedures in Soil Sampling, The Exponential Relationship Between Actual versus Potential Contaminated Media Volume Requiring Remedial Activity, demonstrates the exponential relationship of the volume of soil that would need to be excavated and/or treated on-site due to an over-estimation of the volume of contaminated media by poor QA/QC procedures conducted in the field.

Monitoring Well Installation

Great White North Environmental Services Limited conducts monitoring well installation and design in accordance with the U.S. National Water Well Association publication, “Manual of Groundwater Sampling Procedures”[4] and the, “Alberta Environmental Protection and Enhancement Act, Water Well Regulation.”[5] 
Figure 3.10, Typical Piezometer Nest/Monitoring Well Completion, illustrates the construction design of a typical piezometer nest.

Phase 3:          Modeling of Groundwater Flow and Contaminant Transport

Computer modeling of groundwater flow and transport can provide valuable information that can reduce the costs associated with monitoring well installation.  This process may help to delineate the contaminant plume, thus demarcating the approximate "zero contour" beyond which contamination does not exist.  As a result, costly monitoring well installations may be kept to a minimum.

Great White North Environmental Services Limited employs Surfer, a grid-based contouring and three-dimensional surface plotting graphics program, for modeling the piezometric surface of the groundwater.  This program interpolates irregularly spaced XYZ data onto a regularly spaced grid and uses this data to generate contour and surface plots.  Figure 3.11, Typical Contoured Piezometric Surface of the Groundwater, illustrates a typical plot showing the direction of groundwater flow. 
Figure 3.12, Typical Groundwater Isoconcentration Map for Dense Non-Aqueous Phase Liquids (DNAPL), illustrates a typical distribution of DNAPL contaminants observed in the groundwater.

Figure 3.3
Subsurface Soil Sampling
Lynac Heavy-Duty Split Tube Soil Sampler

 

 

 

Figure 3.4
Lynac Heavy-Duty Split Tube Soil Sampling Protocol

 

 

 

Figure 3.5
Modified Unified Classification Systems for Soil
 

 

 

Figure 3.6
Typical Driller's Log Report

 

 

 

Figure 3.7
The Relationship Between Soil Total Volatile Vapour (S_TVV)
and Soil Total Petroleum Hydrocarbons (S_TPH)

Figure 3.8
Typical Stratigraphic Cross-Section

 

 

 

Figure 3.9
Quality Assurance/Quality Control (QA/QC) Procedures in Soil Sampling, The Exponential Relationship Between Actual versus Potential Contaminated Media Volume Requiring Remedial Activity

 

 

 

Figure 3.10
Typical Piezometer Nest/Monitoring Well Completion

 

 

 

Figure 3.11
Typical Contoured Piezometric Surface of the Groundwater

 

 

 

Figure 3.12
Typical Groundwater Isoconcentration Map for Dense Non-Aqueous Phase Liquids (DNAPL)

 

 

 

Phase 4:          Data Interpretation

All soil and groundwater data must be thoroughly reviewed to investigate:

• the nature and extent of the contamination, if present;
• the chemical characterization and composition of the contamination;
• the volume of contaminated soil requiring remedial action (plume delineation);
• the volume of contaminated groundwater requiring remedial action (plume delineation);
• the direction of groundwater flow; and
• the environmental and public health risk resulting from the contamination.

The findings resulting from this phase of the investigation will have a profound effect on the mitigative measures and disposal options available.

Phase 5:          Mitigative Measures

Upon completion of all analytical data interpretation, a thorough review is conducted to determine potential mitigative measures for soil and groundwater contamination.  This will include methods to lessen the impact from contamination on the underlying aquifer, subsurface soil, human health, and the environment.  Mitigative measures are generally employed to reduce the risks and liabilities associated with contamination migration prior to and during the initiation of remedial action.

Phase 6:          Evaluation of Hazardous Materials Disposal Options

Disposal options must be evaluated as to their efficacy, advantages and/or limitations, cost, remedial time frame, risk to the environment and public health, and feasibility.  A summary of soil treatment and disposal options is available, from the Alberta Environment publication, “Remediation Guidelines for Petroleum Storage Tank Sites, 1994.”

Phase 7:          Long-term Groundwater Quality Monitoring

If contamination is found to have reached the groundwater, a long-term groundwater quality monitoring program may be required.  This will allow for the determination as to whether remedial progress, due to natural biodegradation, is being achieved, as groundwater quality is observed with respect to time.  This monitoring program will reveal important information to determine if aquifer remedial action is required.

Quality Assurance/Quality Control (QA/QC)

All field measurements are conducted in accordance with the Environment Canada publication, “Sampling for Water Quality.”

All subsurface soil and groundwater sample collections are conducted in accordance with the United States National Water Well Association publication, "Manual of Groundwater Sampling Procedures."

Field Quality Assurance

The Field Quality Assurance Program used, is a systematic process that, together with the laboratory and data storage quality assurance programs, ensures confidence and integrity in the data collected.  This program includes the following:

• all equipment, sampling apparatus, and containers are clean and in good working order;
• records are kept of all repairs done to instrumentation and sampling devices;
• conditions are maintained in the work environment that encourage safety; and
• necessary precautions are taken to protect samples from cross-contamination and deterioration.

Field Quality Control

Quality control is an essential element of a Field Quality Assurance Program.  This program requires the submission of blank and duplicate samples.  These samples are used to check the purity of chemical preservatives, to check for contamination contained within sample containers, filter paper and filtering equipment, and sampling devices, as well as to detect other systemic or random errors in sampling procedure of protocol.  The various types of blanks and duplicates and the frequency with which they are required are as follows:

• Bottle Blanks - are used to detect contamination caused by the bottle washing process.  One (1) bottle for every ten (10) is filled at random with ultra-pure distilled water, preserved and analyzed in the same manner as field samples.
• Sampler Blanks - are used to detect cross-contamination from the field sampling apparatus.  Ultra-pure distilled water is passed through the sampling apparatus and analyzed for the same parameters as the field samples.  These blanks are collected periodically.
• Filter Blanks - are used to detect contamination caused by filtering surface water.  These blanks are collected daily by passing ultra-pure distilled water through pre-washed filters, collecting, preserving and analyzing this water in the same manner as field samples.
• Trip Blanks - are used to detect contamination caused by the transportation process.  One (1) blank for every five (5) field samples are required only for analyses requiring field preservation.  These blanks are prepared at the end of each day by pouring ultra-pure distilled water and preservative into a clean bottle and analyzing these samples in the same manner as field samples.
• Field Blanks - are used, for groundwater, to detect contamination caused by on-site background sources.  These blanks were prepared, throughout the day, by pouring ultra-pure distilled water into a clean USEPA approved glass jar and handled in the same manner as field samples, near the well being sampled.
• Duplicate (Split) Samples - are used to determine the magnitude of errors owing to contamination, systematic and random errors, and any other variabilities that maybe introduced from the time of sampling until the samples arrive at the laboratory.  These samples are split into sub-samples and are prepared periodically.
• Spiked Samples - are used to reveal any systemic errors or bias in the analytical methodology.  These samples are prepared by spiking a four-way split of a single water sample with three different concentrations of the parameters of interest, within the concentration range capability of the analytical method employed.

Soil Sampling Methodology

To collect valid soil samples, sampling devices and procedures must be designed to represent accurately the water/soil system being studied.  The procedures and apparatus employed for soil sampling depend on the type of soil being sampled.  The methodology and the equipment used for sampling sandy soil is different from those required for soil containing gravel.

Sample Collection

Soil samples are collected to determine the physical and chemical characteristics of the soil.

The type of soil sample collected is influenced by the following factors:

• The objectives of the study and the accuracy and precision required to meet those objectives;

• The characteristics of the system under investigation (i.e., site conditions) and the analytical parameters of interest; and

• The resources available (i.e., manpower, equipment, and materials).

Types of Soil Samples

The types of soil samples are as follows:

• Grab Samples - are taken at a discrete location, depth and time.  With regards to soil sampling, it may be used to determine soil composition and/or heterogeneity.

• Composite Samples - are obtained by mixing several discrete samples of equal or weighted volumes prior to analysis.  These samples are used to determine average soil composition for the location and parameters of interest.

Sample Integrity

For some purposes soil samples can be disturbed, i.e., the individual particles can be rearranged relative to each other and it is unimportant that the volume and shape of the sample has been altered from the actual conditions of the deposit.  However, for most purposes undisturbed samples are required.  When the purpose of the sampling is to obtain information related to vertical composition of the deposits or on distribution of contaminants from a certain depth, undisturbed core samples must be taken.

Field Equipment and Techniques

Great White North Environmental Services Limited has at its disposal numerous sampling devices to meet any sampling requirement.  The sampling devices available are listed in the following subsections.

Soil Samplers

Core Samplers - are used to collect undisturbed samples.  Samplers of this type are essentially tubes that are forced into the soil system.  Samples are retained inside the barrel of the sampler and retrieved by a partial vacuum formed above the sample and/or by a core retainer at the lower end.  The various types of core samplers are listed below:

1. Shelby Tube;

2. Split-Tube Sampler (with core retainer);

3. Benthos Gravity Corer;

4. Alpine Gravity Corer;

5. Phleger Corer;

6. Drilling Systems AP 1000 Becker 180 Hammer Drill Rig;

7. Hollow or Solid Stem Auger Drill Rig; and

8. Diamond Drill Top Drive Rotary Rig.

Wherever possible, we recommend that soil sampling be conducted with a split-tube sampling device.  This method allows the samples to be observed as to their heterogeneity, colour, odour, and lithological characteristics.

Groundwater Sampling Methodology

The use of good equipment and proper sampling techniques are critical to obtain representative water samples.  The quality and integrity of the sample will greatly influence the subsequent laboratory analyses.  The sampling procedures outlined herein address some of the practical sampling considerations:

• the co-axial tubing attached to the sampler should be secured to a fixed point;

• sufficient tubing should be allowed to reach the required depth of investigation;

• when sampling, the sampler must never be allowed to contact the bottom, thus avoiding contamination from agitated sediment;

• the sampler must be rinsed three or four times with the water to be sampled unless the sample bottle contains a preservative;

• the required volume must be obtained for field and laboratory analyses; and

• the required preservation procedures must be performed for all samples.

Monitoring wells to be sampled should be done in an organized fashion.  Wells that are located upgradient, and therefore represent background water quality, should be sampled first, thereby reducing the risk of cross-contamination.   Following, the wells located downgradient should then be sampled as they may, if fact, contain contaminants from the site.  All sampling devices should be rinsed thoroughly with a 1% solution of Liquinox laboratory detergent followed by two (2) distilled water rinses, the latter of which should be saved to check cleaning efficiency and labeled as a sampler or equipment blank.

Representative sampling is the result of the execution of a carefully planned sampling protocol that establishes necessary hydrogeological and chemical data for each sample collection effort.   An important consideration for maintaining sample integrity after collection is to minimize sample handling that may bias subsequent determinations of chemical components.  Since opportunities to collect high quality data for the characterization of site conditions may be limited by time, it is prudent to conduct sample collection as carefully as possible from the beginning of the sampling period.  It is preferable to risk error on the conservative side when the doubt exists as to the sensitivity of specific chemical compounds to sampling or handling errors.  Repeat sampling or analysis cannot makeup for lost data collection opportunities.

Water Level Measurement

Prior to purging and sampling, the determination of the water level in a monitoring well is an extremely important source of information.  It provides information concerning the volume of water required to properly purge the well of stagnant water.  Furthermore, information is obtained concerning natural recharge events and the hydraulic conditions at the site.  For example, in relatively shallow monitoring settings, high water levels from recent natural recharge events may dilute the total dissolved solids in a collected sample.  Conversely, if contaminants are temporarily held in an unsaturated zone above the zone being monitored, recharging may "flush" these contaminants into the shallow groundwater system resulting in higher concentrations of some constituents.

The depth to the groundwater level is determined utilizing a flat tape water level meter, commonly referred to as a Depth Sounder device. The device incorporates an insulating gap between a pair of electrodes.  When contact is made with static water the circuit (battery operated) is completed, sending a signal back to the reel.  The water level is determined by taking a reading directly from the cable, at a pre-determined measuring point.  The distance from the top of the well casing to the water level is recorded.  Additionally, the total depth of the well is also measured.  This allows for the calculation of the free water standing height and volume.  This information is utilized to determine the minimum volume of water required to purge the well of stagnant water.  It should be noted, however, that this volume of purged water is only used as a guideline and that much greater emphasis is placed on the stability of the groundwater chemistry as the determining factor prior to sample acquisition.

Purging of Monitoring Wells

A sufficient volume of stagnant water must be removed from the monitoring well to ensure that a representative sample of groundwater is obtained.  Rule of thumb guidelines, as to the volume of water required to obtain a representative sample of groundwater (e.g., three, five, or ten well volumes), are inaccurate procedures leading to non-representative data.  Sufficient groundwater should be purged from the monitoring well until stable measurements (+/- 10%) of pH, electrical conductivity, and temperature are obtained.

The quality and integrity of collected groundwater samples is greatly influenced by the degree to which Quality Assurance/Quality Control (QA/QC) procedures are performed and adhered to during the groundwater sampling process.  Strict Quality Assurance/Quality Control procedures include the following:

• All personnel collecting groundwater samples don two (2) pairs of surgical Latex gloves, the outer pair of which is removed and disposed of after the collection of each and every sample;

• All disassembled sampling equipment (e.g., Bladder Pumps, Waterra Power Pumps, Submersible Pumps, co-axial tubing, etc.) are washed thoroughly with Liquinox, a phosphate free laboratory detergent, used for cleaning laboratory glassware.  This process is followed by a distilled water rinse.  The groundwater sampling device is then reassembled and once again distilled water is poured over the outside and inside of the device.  This water is collected into a USEPA approved jar and labeled as a “sampler blank.”  The concentration of contaminants found, if any, in this rinsate represents the amount of cross-contamination remaining on the groundwater sampling device; and

• Groundwater samples are collected in duplicate and the appropriate chemical preservative added to each sample jar.  All samples are placed into coolers containing gelled freezer packs prior to transport to the analytical laboratory.

Failure to follow strict Quality Assurance/Quality Control procedures may lead to the collection of groundwater samples that are unrepresentative of the  concentration of contaminants actually found in the aquifer under investigation.  Collection of groundwater samples with, for instance, a Teflon bailer, may lead to samples that contain an inordinately high concentration of volatile organic compounds.  This technique removes a small quantity of stagnant groundwater over a long time span, resulting in an infinite dilution of the stagnant wellbore volume.  That is to say, that the stagnant groundwater is never actually removed, and is infinitely diluted by the groundwater flowing into the wellbore.  For example an overlying layer of LNAPL [light non-aqueous phase liquids (i.e., (gasoline)], within the wellbore, is actually agitated and is further dissolved into the underlying groundwater layer resulting in the collection of a groundwater sample that is higher in concentration in contaminants than a representative sample of the groundwater, deep within the formation, which has come into equilibrium with the overlying contamination.

A better technique is to remove the stagnant water by utilizing a submersible pump or a Waterra Power Pump.  This procedure removes the stagnant groundwater within the wellbore quickly and also removes any overlying light non-aqueous phase liquids (LNAPLs), such as gasoline, so as to prevent cross-contamination from such non-soluble liquids from samples selected for laboratory analysis.  Actual groundwater sampling should be conducted with a Bladder/Waterra Power Pump System that collects a groundwater sample, to surface, without pulling a negative pressure on the sample and hence does not degas the sample.  One should monitor the groundwater chemistry, such as pH, electrical conductivity, and temperature, prior to collection of a groundwater sample, to ensure that only groundwater that has achieved equilibrium with the overlying LNAPL contamination is being taken as a representative sample for laboratory analysis.  Failure to follow strict Quality Assurance/Quality Control procedures in groundwater sampling may result in the collection of unrepresentative groundwater samples for laboratory analysis.

Figure 3.13, Quality Assurance/Quality Control (QA/QC) Procedures in Groundwater Sampling, illustrates the importance of utilizing the monitoring of groundwater chemistry prior to the collection of groundwater samples.

Figure 3.14, Purging of Monitoring Wells, Determination of Stable Groundwater Chemistry, illustrates how groundwater parameters, such as pH, electrical conductivity, and temperature, are plotted to determine that stable groundwater conditions have been achieved prior to the collection of representative samples.

 

Figure 3.13
Quality Assurance/Quality Control (QA/QC) Procedures in Groundwater Sampling

 

 

 

Figure 3.14
Purging of Monitoring Wells
Determination of Stable Groundwater Chemistry:  Monitoring Well I

 

 

Sample Collection and Handling

Water samples should be collected only when the solution chemistry, as indicated by measurements of pH, electrical conductivity, and temperature, has stabilized over five (5) or more successive wellbore volumes.  Samples that are expected to contain volatile compounds should be sampled first.  These samples should not be filtered in the field as doing so reduces the concentration of volatile organics by evaporation thus rendering these samples as "unrepresentative".  Samples that require field filtration should be collected next, followed by large volume samples (such as those collected for extractable organics).  Figure 3.15, Generalized Flow Diagram of Ground-Water Sampling Steps, depicts a priority order for a generalized sampling effort.

 

Figure 3.15
Generalized Flow Diagram of Ground-Water Sampling Steps
(Barcelona et al, 1985)

 

*    Denotes samples that should be filtered in order to determine dissolved constituents.  Filtration should be accomplished preferably with in-line filters and pump pressure or by N2 pressure methods.  Samples for dissolved gases or volatile organics should not be filtered.  In instances where well development procedures do not allow for turbidity-free samples that may bias analytical results, split samples should be spiked with standards before filtration.  Both spiked samples and regular samples should be analyzed to determine recoveries from both types of handling.

**  Denotes analytical determinations that should be made in the field.

 

Samples can be held for the U.S. Environmental Protection Agency (EPA) recommended maximum holding times after proper preservation.  These are shown in
Table 3.1, Recommended Groundwater Sample Handling and Preservation Procedures for a Detective Monitoring Program, which has been modified slightly from Scalf et al (1981).

Sample Storage and Transport

The storage and transport of soil and groundwater samples are important elements of sampling protocol.  Due care must be taken in sample collection, field determinations, and handling.  Sampling and transport need to be planned in advance so that sample holding times do not exceed those required for proper laboratory analysis.  Laboratory staff must be informed, in advance, when to expect samples arriving from the field so as not to exceed recommended storage times.  Often this may require that sampling schedules be altered so that samples arrive at the laboratory during working hours.

Procedures for handling and preserving soil and groundwater samples depend on the specific analyses needed.  Often chemicals, such as acids, oxidizing agents, etc., must be added to those samples requiring field preservation.

 

Table 3.1
Recommended Groundwater Sample Handling and Preservation Procedures for a Detective Monitoring Program