Project Planning

This section provides an overview of the planning process for conducting soil sampling. Included is a discussion of sampling strategy, development of a site-specific SAP, and QA considerations.

Before soil sampling can begin, clear and concise objectives regarding the intent of the sampling program need to be developed. The objectives provide the framework for developing a sampling strategy for the site and preparing the SAP. Once the objectives are established, a sampling strategy can be developed.

4.3.1. Sampling Strategy

The sampling strategy is designed around the objectives of the project and should begin with a review of the conceptual site model. The model

takes into consideration historical site use, known or suspected pollutant releases, and the geology of the area. The conceptual site model is dynam-ic and is constantly revised as new information is collected and processed. The model focuses on contaminant fate and transport processes, the control of geologic materials on the contaminant pathways (e.g., depositional environments, geo-logic structure), the types of contaminants present (e.g., hydrophobic versus hydrophilic), and the processes that influence the concentrations of contaminants present (e.g., dilution, biodegrada-tion, dispersion).

The detail of the conceptual site model will de-pend greatly on the availability of information including historical site uses, native soil type, areas where fill materials may be present (e.g., utility trenches), and the direction of surface water flow. Specifically, the conceptual site model should describe:

 Physical characteristics of the site, including locations of buildings, paved areas, subsurface utilities, overhead utilities, significant

topographical changes (e.g., steep banks), exposed bedrock, standing water, stained soils, areas of depressed vegetation, equipment maintenance and storage areas, manufacturing locations, waste disposal areas, and expected depth to groundwater

 Types of contaminants to be sampled (e.g., volatile organic chemicals (VOCs), semi-VOCs, metals) and factors that could bias sampling results (e.g., organic contaminants that are tightly bound to soil particles)

 Lateral and vertical distribution of

contamination (e.g., contaminants distributed throughout an entire unit being monitored versus localized distribution controlled by small-scale features).

The sampling strategy and the information ga-thered from the conceptual site model will be-come the framework for development of the site-specific SAP. Key issues related to the

concep-tual site model are presented in more detail in the following subsections.

4.3.1.1. Types of Contaminants

The sampler or Site Manager may be able to predict the types of soil contaminants present and the duration of contamination by consulting site historical records and information on previous manufacturing practices, fuel or chemical usage, and any reported spills. This information can be used to determine sample collection locations.

For instance, heavy metals such as oxidized lead or organic chemicals such as pesticides which are relatively insoluble in water may be limited to the top few inches of soil and will not have spread far from their source in undisturbed sites. However, if sites are affected by soil erosion or construction activities, the contaminants may have moved from their source, and sampling program planners should account for these changes in site condi-tions. The extent to which the underlying groundwater is contaminated also would be a function of the solubility of the organic liquid in the water. Dense non-aqueous liquids, such as chlorinated solvents (e.g., trichloroethylene, tetrachloroethylene, carbon tetrachloride) or heavier chlorinated organic liquids (e.g., chlori-nated benzenes, PCBs), can permeate the subsur-face until they reach a confining layer, such as clay or bedrock.

For soil contaminants such as soluble metals found in metal plating wastes or from spills of concentrated organic chemicals (e.g., gasoline, aviation fuel, solvents, and transformer oil), the presence and extent of contamination may not be easily predictable due to a number of factors.

Soluble metals and organic liquids often are carried through soil by percolating rain water.

The extent of contaminant movement is affected by a number of factors, including:

 Density of Organic Liquids. Light organic liquids (e.g., gasoline, diesel fuel, and waste oils) will settle through soils that are not saturated with water until they reach a confining surface such as clay, bedrock, or groundwater. It is not unusual to find a

concentrated layer of organic liquid moving along the surface of a tilted clay layer or forming a pool or lens on the groundwater.

Therefore, the extent to which the underlying groundwater is contaminated, is a function of the solubility of the organic liquid in the water.

Dense, non-aqueous liquids, such as

chlorinated solvents (e.g., trichloroethylene, tetrachloroethylene, carbon tetrachloride) or heavier chlorinated organic liquids (e.g., chlorinated benzenes, PCBs) can continue to sink through groundwater until they reach a confining layer, such as clay or bedrock.

These chemicals can flow along tilted surfaces or pool in the cracks in bedrock and then slowly leach into groundwater.

 Susceptibility to Biodegradation.

Microorganisms in the soil can degrade many contaminants. However, for contaminants like fuels or other petroleum distillate products, the microorganisms require oxygen and generally are not active at depths of more than 1 foot.

Therefore, the surface soils may be relatively uncontaminated by these organic chemicals due to biodegradation, while deeper soils may be contaminated due to the lack of oxygen needed for biodegradation.

4.3.1.2. Type of Soil

Soil type can have a significant impact on the mobility of pollutants. For example, clay layers create relatively impermeable barriers, retarding groundwater flow and in some instances prevent-ing surface contaminants from affectprevent-ing ground-water. However, clay particles also can absorb certain types of hazardous chemicals, resulting in increased pollutant concentrations in localized areas. Organic liquids can form pools in the low reaches of clay layers, or can flow down the surface of tilted clay layers.

Soils that contain large amounts of organic ma-terial, such as peat, can absorb and concentrate hazardous chemicals. A layer of organic soil, therefore, may be more contaminated than the soil layers above and below it.

Porous non-organic soils, such as sand or gravel, do not absorb pollutants and allow for rapid surface and groundwater movement. In such soils, PCBs from spilled transformer fluid and from buried electrical capacitors have been found several hundred feet from the source of the con-tamination. Gasoline from leaking USTs can be carried hundreds of feet by moving groundwater.

Bedrock may provide a confining layer beneath groundwater. Fractured bedrock, however, may provide channels for the movement of groundwa-ter and heavy organics or low spots for the accu-mulation of pools of heavy organic liquids.

Soil characteristics such as pH, can change the chemistry of the surrounding water, which in turn can affect the solubility of some pollutants, in-cluding heavy metals. For instance, acidic stormwater can dissolve metals on the ground surface. However, as the dissolved metals pass through the soil column, they may encounter areas with elevated soil pH (e.g., limestone) that cause the metals to become insoluble precipitates again.

4.3.1.3. Presence of Groundwater

Moving groundwater can carry hazardous conta-minants for considerable distances; see Figure 4-1.

Figure 4-1. Contaminated Groundwater

The rate at which groundwater will cause conta-minants to spread is affected by both the speed at which the groundwater moves through the soil

and the extent to which the soil absorbs the con-taminants. One of the most serious effects of accidental spills and improper disposal of hazard-ous chemicals is contamination that precludes the use of a groundwater source for drinking water.

4.3.2. Site-Specific SAP

A soil sampling program should collect soil samples at a specific locations and depths that are representative of the site. Procedures that result in the collection of an undisturbed soil column will yield the most representative soil samples.

The development of a site-specific SAP is the first step toward collecting a representative soil sample (see Chapter 2 for a detailed discussion of SAP development applicable to all sampling programs). Each SAP is an instruction manual for field personnel, and should be built around the objectives and sampling strategy. The discussion below focuses specifically on SAP development for soil sampling programs.

Ideally, the SAP should be based on knowledge of which contaminants are likely to be present and how the distribution of the contaminants may be affected by the soil characteristics of the site.

The purpose of the fieldwork also may be to define the soil characteristics and obtain chemical data for determining compliance with federal, state, or local requirements. It is possible for soil sampling to be conducted in a number of phases, with the field observations and field test results providing data to guide subsequent work. If knowledge of contaminants and site soil characte-ristics is limited, then dynamic sampling tech-niques and field measurements can be used to locate sampling points.

Dynamic sampling relies on individuals in the field to interpret field data as it becomes available and revise the sampling strategy accordingly.

Dynamic sampling can quickly provide signifi-cant amounts of information needed to develop the conceptual model for the site. Dynamic sampling in many instances, however, is consi-dered a first step toward developing a more fo-cused soil sampling program for a particular area within the site.

The SAP should consider a variety of factors, including, but not limited to, the physical features of the site (e.g., locations of buildings, tanks, buried utilities, roadways), the types of contami-nants and their potential mobility and biodegra-dability, soil types, the accessibility of potential sampling locations, the size of equipment needed to collect samples at depth, suspected pollutants, field screening requirements, DQOs, analytical methods and detection limits, soil collection methods, sample handling procedures (e.g., pre-servation requirements, COC), containment and disposal procedures for contaminated soils gener-ated during sampling activities, and safety.

The SAP cannot be implemented effectively if field personnel do not understand its contents.

Many times the primary reason that sampling events are problematic is that the person who prepared the SAP is not the person in the field.

One method that alleviates this problem is assign-ing a Samplassign-ing Team Leader who is responsible for all activities in the field. The Sampling Team Leader will work closely with those individuals preparing the SAP to understand fully the objec-tives of the program. The Sampling Team Leader then will be responsible for all individuals in the field. He or she also is responsible for providing additional training to field personnel, if required, before fieldwork begins.

4.3.3. QA

Soil sampling programs encompass a variety of information sources and include both primary and secondary data collection. These data sources are used to continuously update the conceptual site model and allow site managers to make decisions regarding further investigation, additional moni-toring, remediation alternatives, or site closure.

The level of data quality for each soil sampling program, and for each specific sampling event, depends on the intended use of the data. For example, the level of QA/QC needed to estimate the volume of soil that may need to be removed for a corrective action might be different than for samples needed for site closure. It is important to remember, regardless of the level of QA/QC for

any soil sampling event, that sample integrity must be maintained during sample collection.

Laboratory analysis, no matter how sophisticated, is defensible only if the sample supplied to the analyst has retained its integrity.

To ensure quality data, site managers and those responsible for data integrity should begin with a systematic planning process that helps define the DQOs. The DQOs clarify the study objective, define the most appropriate type of data to col-lect, determine the most appropriate conditions for data collection, and specify tolerable error limits that will be used as the basis for program decision making. Detailed information on QA/QC, including the systematic planning process, development of DQOs, and preparation of SAPs, is available in Chapter 2 of this hand-book.

Some specific QA/QC issues related to soil sam-pling programs include equipment specifications, equipment decontamination, and QC samples.

Each of these is discussed briefly in the following sections.

4.3.3.1. Secondary Data

Secondary data are those data collected in addi-tion to sampling data. For a soil sampling pro-gram, secondary data may include items such as historical records regarding site use, spills, and corrective actions on neighboring properties, current and historical subsurface utility maps, locations of previous above-ground and below-ground structures as well as possible disposal areas and areas containing fill materials or other antidotal agents. These data aid the Site Manager in selecting soil sampling locations or determin-ing possible pollutants.

For secondary data, acceptance criteria are used instead of the measurement performance criteria typically used for laboratory data. In general, acceptance criteria are used to assess secondary data adequacy and evaluate uncertainty in the results derived from the use of secondary data sources. For example, the Project Manager for the soil sampling program may require interviews of former employees to validate the location of

disposal areas found on historical site maps. In this case, the acceptance criteria are the verbal confirmation of the disposal areas by the former employees. The SAP for each soil sampling program will explain the acceptance criteria for determining which sources of data are sufficient to support the project objectives. See Chapter 2 for more information.

4.3.3.2. Equipment Specifications for Quality Control

The selection of appropriate materials for soil sampling equipment is critical to ensuring data quality. The materials that come into contact with the sample are as critical as the composition of the laboratory sample containers. Selecting the appropriate materials for sampling equipment should be based on the type of expected pollu-tants. It is important that the sample equipment not add or remove target pollutants. For example, if collecting samples for analysis of low-level metals, carbon steel sampling equipment should not be used. If samples are being collected for low-level organic constituents, plastic sampling equipment should be avoided because plastics have the potential to absorb organic pollutants.

The recommended materials for hand augers, split spoons, trowels, and other sampling devices are as follows: polytetrafluoroethylene (PTFE) (Tef-lon®), stainless steel, polypropylene, linear po-lyethylene, polyvinyl chloride (PVC), Viton®, and conventional polyethylene. Because soil sampling typically requires more rugged equip-ment compared with other types of sampling, stainless steel equipment is typically the material of choice.

4.3.3.3. Equipment Decontamination

Decontamination of existing and new equipment is required prior to use in the field. Section 4.9 describes decontamination procedures for various types of soil sampling equipment. Decontamina-tion procedures must be followed and docu-mented to prevent cross-contamination between sites and within the site. Rinsate blanks may be collected at the start and end of the sampling event to determine the cleanliness of the sampling

devices and evaluate the cleaning techniques used in the field. Decontamination procedures for all equipment that contacts soils must be included in the SAP.

4.3.3.4. Quality Control Samples

Field duplicates or splits are collected in the field in double the number of bottles required for the regular sample. A duplicate sample is a sample collected concurrently, under comparable condi-tions, with a first sample. Duplicate samples are QC samples that are used to assess data repeata-bility based on field conditions. Duplicate sam-ples provide a total precision of field sampling precision and lab analysis. Duplicate samples should not be identified as duplicates to the la-boratory. Split samples are two or more repre-sentative portions taken from one sample in the field or in the laboratory and analyzed by differ-ent laboratories. Split samples are QC samples that are used to assess analytical variability and comparability. Samples sent to the same laborato-ry are duplicates, and samples sent to a different laboratory are splits. Split samples shall be field homogenized. To ensure that split samples are representative, the soil sample collection must follow Pierre Gy’s Sampling Theory and Sam-pling Practices. However, for VOC samples, split samples shall be collected as field duplicates to minimize loss of volatile components.

Procedures for obtaining split soil samples are included in Section 4.7.4.3.