Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 5.8
FIELD DOCUMENTATION

5.8 FIELD DOCUMENTATION

5.8.1 SURFACE SOIL SAMPLING LOGS

Accurate field logs are essential for evaluation and interpretation of analytical results and for preparation of the site investigation report. Details of all field activities, both during initial site inspections and during sample collection, should be recorded. The latter includes documentation of the possession and handling of samples from the time of collection through analysis and final disposition. Copies of the sampling logs, pertinent notes, and photograph logs should be included in the site investigation report.

Similar information should be recorded for borings, trenches, or pits installed to collect MI samples from subsurface DUs as well as the use of any discrete soil samples for initial screening purposes. Deviations from the sample plan caused by conditions encountered in the field (e.g. inadequate tools for sample collection, unanticipated surface debris or subsurface obstacles in sample collection, weather delays, etc.) are also important to document. Site visits to assess field conditions prior to mobilization for the collection of samples are essential and should also be documented in field logs.

An example of a surface soil sampling log is presented as Figure 5-47. Include similar information for any discrete soil samples collected. The intended use of the discrete samples and limitations regarding their representativeness should be clearly discussed in the investigation report (refer to Section 4.3). Copies of the field logbook, sampling logs, and (if available) photograph logs should be included in the site investigation report.

A log should be prepared for each DU included in the investigation. The logs should at a minimum include the following information:

Site name and identifier;

Name(s) of field personnel or sampler;

Date, time;

Unique sample ID or code;

Sketch map depicting DU shape, dimensions, adjoining DUs, landmarks, north arrow, etc;

Decision Unit coordinates (e.g., latitude and longitude of DU corners);

Photographs of DU areas;

Depth of DU sampling interval;

Increment spacing;

Number of increments collected for bulk Multi Increment sample(s);

Type of sampling equipment used;

Sample containers;

Approximate bulk sample mass;

Describe any field processing of sample(s);

Soil description;

Planned sample analyses;

General comments (e.g., odor, staining, etc.).

Figure 5-47. Example Surface Soil Sample Log

Adequate information should be included in the sketch map and sample information log to generate a to-scale map of DU locations in the final report (e.g., shape, dimensions, adjoining DUs, landmarks, north arrow, etc.). Depictions of DUs on high-altitude (e.g., satellite) maps or with low-altitude (e.g., drones) photos is acceptable and even preferred provided that distortion is not too great to prevent accurate estimation of dimensions (Figure 5-48). Draft DU maps can be made prior to sample collection and adjusted in the field as needed. Final DU maps depicted on aerial imagery can significantly aid in future re-identification of investigated areas.

Figure 5-48. Demarcation of Decision Units and DU Information Using a Google Earth Image

Coordinates determined via hand-held Geographic Positioning System (GPS) equipment is acceptable to record the boundaries of Decision Units (e.g. four corners of a rectangular-shaped Decision Unit). The accuracy of the equipment to be used should be documented in the SAP. Any potential variability caused by surrounding forests, structures, or other obstructions to the GPS unit acquiring satellite signals should be taken into account and documented in the investigation report.

A more detailed survey of the site and DU boundaries by a surveyor licensed in the State of Hawai‘i is required for maps to be included in an Environmental Hazard Management Plans (EHMP). This is necessary to more precisely document locations where contamination will be left in place for long-term management. The EHMP should include the latitude and longitude of key DU boundary points, along with ground surface elevation data determined within the Hawai‘i State Plane Coordinate System to an accuracy of 0.1 foot. Locations of existing buildings or other major landmarks should also be surveyed for reference to the targeted area under long-term management.

The basic rational for designation of the DU (e.g., suspect spill area, perimeter DU, etc.; see Section 3.4) should be noted in the site documentation. The tools and method used to collect Multi Increment (or other) samples should be described in the sample logs. Note the increment spacing used for each DU (see Section 4.2.4). Record any field processing of the sample(s) collected, including the need to reduce the sample mass due to the original bulk sample(s) being too large for lab processing (refer to Section 4.2.3).

Record information for field observations and field screening methods used to assist in the identification of potential contaminants of concern or test samples in the field (see Section 8). This might include visual and olfactory observations, or the use of tools such as a photo-ionization detector (PID), portable X-ray fluorescence device (XRF), immunoassay test kits or a field Gas Chromatography-Mass Spectrometry [GC/MS] unit. A dehumidification tip should be used with the PID. Field measurements should be recorded and included in the log for the targeted DU.

Recording the spacing of increments is important in order to document that the sample was collected in a systematic random manner. As discussed in Section 4.2.4, the specific locations of individual increments do not need to be recorded or included on a map of the DU. This is in part because individual increments cannot be assumed to be representative of the immediately surrounding soil, due to uncertainties from random small-scale variability (refer to Section 4.1.2 and Section 4.2.4). The exact location of any given individual increment collection point therefore does not need to be documented.

A basic soil description and classification should be included with the sample log (see Subsection 5.8.3). Additional and more detailed information regarding soil taxonomy, geotechnical properties and other characteristics that might be required to meet the project objectives should be included as appropriate. A brief overview of consistency, cementation, structure, rock classification, and other information is provided in Subsection 5.8.4.

5.8.2 SUBSURFACE SOIL SAMPLING/BORING LOGS

Logs for samples collected from subsurface DUs should include the same type of information noted above for surface soil samples regarding site conditions, sample collection methods, boring spacing, etc. Record the rational for the selection of targeted DU layers in the same manner as done for surface soil (refer to Section 3.5.6). This might include the anticipated known or anticipated depth of contamination, visual or olfactory evidence of contamination during test borings or abrupt changes in soil characteristics. Field processing of samples is typically required for subsurface Multi Increment samples due to the mass of individual core increments and should be described in the logs (refer to Subsection 5.4.2).

Additional information is required for exploratory borings or borings to be used for the installation of wells. A log for each boring should be prepared which includes the following items, as applicable:

Name of drilling contractor;

Borehole coordinates – latitude and longitude;

Sketch showing the borehole location (including reference distances);

Diameter and total depth of borehole;

Type of drilling equipment used (e.g., direct push, auger, air or mud rotary);

Drilling fluid and angle (if applicable);

Blow counts/Resistance;

Depth to water table

Important stratigraphic boundaries encountered (e.g. depth bedrock);

Hydrogeologic information (e.g. transmissivity, etc.);

General comments (e.g., odor, staining, etc.);

Field measurements (e.g., PID, XRF, etc.);

Designated DU layers for sample collection;

Sample collection equipment used;

Core recovery and portion submitted for analysis;

Sample identification number;

Planned sample analyses

Figure 5-49. Example Log for Exploratory Borings or Borings Used for the Installation of Wells

An example boring log is depicted in Figure 5-49. The soil descriptions should also include information on density or consistency (primarily when borings are conducted using hollow stem auger) and appearance descriptors of cementation, structural appearance of layers and other features, and other appearance descriptors as applicable to the project.

5.8.3 SOIL DESCRIPTION

Soil descriptions for soil sampling events should be made by a trained geologist, geotechnical engineer or soil scientist. The Unified Soil Classification System (USCS) is recommended for basic soil descriptions (ASTM, 2006d; see also ASTM, 2006e; USDA, 1987, USDA-NRCS, 2007; Nielsen, 2006; US Navy, 2007).

The level of detail appropriate for soil descriptions for a given site is tied to and should be addressed in the site investigation objectives (DQOs). At a minimum the color and estimated nature of the soil in terms of average particle sizes (e.g., gravel versus sand versus clay) should be recorded using a standardized approach. More detailed soil descriptions, including laboratory-based measurement of particle size distribution, might be required for more detailed investigations of contaminant fate and transport or to design remedial actions. Maps with taxonomic names for soil on each island are published by the US Department of Agriculture (USDA, 2015). The accuracy of the maps in highly developed, urban area where soil from other areas may have been imported should be verified.

A summary of key elements of the classification system is provided below. If an alternative classification scheme is used then a summary of terms used and particle size categories should be included in the report.

5.8.3.1 Recommended Parameters for Soil Descriptions

Classification of soil in accordance with the USCS involves a group symbol, name, and complete word description (ASTM, 2006d). Key descriptive parameters include:

  • Relative proportion of gravel, sand and fines and USCS classification name and symbol;
  • Color (Munsell method preferred);
  • Consistency;
  • Moisture content;
  • Staining/discoloration/odor;
  • Glass, wire, porcelain fragments or other debris indicative of disposal or fill;
  • Other descriptive terms

Descriptive terms denoting the geologic nature of the soil can also be added, including such terms as "saprolite" for soil directly derived from weathered rock or "sediment" for soil associated with unconsolidated terrestrial or marine sediments. Additional soil descriptors can be included as needed based on the DQOs of the investigation (e.g., plasticity, angularity, etc.; refer to ASTM, 2006d). Properties regarding the in situ structural nature of the soil might be required in projects that include a geotechnical component (e.g., density, structure, etc.). A review of properties commonly recorded as part of subsurface borings is provided in Subsection 5.4.

Include notes regarding odors and other observations during drilling, even if these are not apparent in the samples collected. Field aids that combine the USCS classification system with examples of particle sizes, percent estimation of individual components, color, particle angularity and other descriptive criteria are available commercially.

Classification Group Name

An abbreviated summary of the USCS classification scheme is provided in Figure 5-50 (after ASTM, 2006d). Soils are initially classified as "coarse-grained" or "fine-grained," depending on the dominance of gravel and/or sand-size particles versus silt and/or clay-size particles. The term describing the dominant particle size is further modified based on the abundance of other particle sizes, with a code applied to each grouping. The classification scheme somewhat confusingly uses a minimum of 12% clay + silt to describe a sand or gravel as "with fines" but a minimum of 15% sand + gravel to describe a fine-grained soil as "with sand" or "with gravel."

Figure 5-50. USCS Soil Classification Scheme (after ASTM 2006d)
Major Divisions Code Description
Coarse-Grained Soils More than 50% retained on a 0.075 mm (No. 200) sieve Gravels 50% or more of course fraction retained through a 4.75 mm (No. 4) sieve Clean Gravels (<5% fines) GW Well-graded gravels, sandy gravels or gravels with sand; little to no fines
GP Poorly-graded gravels, sandy gravels or gravels with sand; little to no fines
Gravels with Fines (>5% fines) GM Sandy gravels with silt, gravels with sand and silt
GC Sandy gravels with clay, gravels with sand and clay
Sands 50% or more of course fraction passes through a 4.75 mm (No. 4) sieve Clean Sands (<5% fines) SW Well-graded sands, gravelly sands, or sands with gravel; little to no fines
SP Poorly-graded sands, gravelly sands, or sands with gravel; little to no fines
Sands with Fines (>5% fines) SM Silty sands, sands with silt
SC Clayey sands, sands with clay
Fine-Grained Soils More than 50% passes through a 0.075 mm (No. 200) sieve Silts and Clays ML Silt, sandy silt, clayey silt, silt with fine sand and clay
CL Clay, silty clay, clay with silt and fine sand
OL Organic silt and clay (loam)
Highly Organic Soils PT Peat and other highly organic soils
Notes:
  1. Gravel: >5.0mm to <75mm), sand: 0.075-5.0mm, silt: 0.005-0.075mm); clay: <0.005mm.
  2. Grading refers to the range of particle sizes in the soil. “Well-graded” gravels and sands contain a wide range of coarse particle sizes, poorly graded soils do not.
  3. Describe coarse-grained soils as “with fines” if >12% silt and clay; combine terms if between 5% and 12% fines (e.g., GW-GM). Describe soil as “with sand” or “with gravel” if the soil contains >15% sand or gravel.
  4. Silts and clays can be further defined in terms of liquid limit and plasticity as well as other criteria (see ASTM 2006d).

If the second-most dominant grain size makes up >30% of the soil type then include that grain size with the name. For example a soil composed of 30% fines and 75% sand is described as a "silty-clayey sand (SM)." If dominance of the fines by silt versus clay is known then a more specific code can be assigned, for example "SM" for a silty sand or "SC" for a clayey sand. Note that it can be difficult in the field to distinguish between fine sand, silt and clay without significant experience.

A sand with 12% to <30% silt and clay is described as "sand with fines (SM-SC)." Sands with 5% to 12 % fines require dual symbols that include a description of grading, for example "well-graded sand with silt (SW-SM)". A sand with <5% fines is simply described in terms of grading, for example "poorly graded sand (SP)".

Fine-grained soils with >30% sand or gravel are described as "sandy" or "gravely." Fine-grained soils containing 15% to <30% sand or gravel are described by adding "with sand" or "with gravel" to the group name (e.g., silt and clay with sand, ML-CL). Although not called for in the ASTM document referenced above, it is reasonable for the purposes of an environmental investigation to add "with sand" or "with gravel" to fine-grained soils that contain 5% to 15% coarse-grained particles. Dual classification of a soil type is appropriate if a sample has properties that do not distinctly place it into one group (e.g., SC/CL). Refer to the documents referenced above for additional soil descriptive terms.

Visual Estimation of Grain-Size Distribution

In practice the accurate classification of soils with a large fraction of fines can be challenging in the field without first drying and sieving the sample. Detailed analysis of particle size distribution is most accurately carried out in the laboratory if required as part of the investigation DQOs (e.g., Method D422; ASTM, 1998). As an alternative, field estimation of particle size distribution can be carried out in the following manner:

  • Select a representative sample (Multi Increment sample preferred).
  • Remove all gravel-size (>75mm or approximately three inches) or larger particles from the sample. Estimate and record the percent by volume of these particles. Only the fraction of the sample smaller than 75mm is classified.
  • Estimate and record the percentage of gravel.
  • Considering the rest of the sample, estimate and record the percentage of sand particles, typically the smallest particle visible to the unaided eye.
  • Assign the remaining percentage to "fines"; do not attempt to separate silts from clays.

Estimate percentages to the nearest 5 percent. If one of the components is present in a quantity considered less than 5 percent, indicate its presence by the term "trace." Percentage composition figures can assist in estimation of different size or particle type makeup of a sample. More precise lab methods might be required to accurately distinguish fine sand from silt and accurately determine clay composition if this information is required for completion of the field investigation.

Munsell Color

Color is described by hue and chroma using the Munsell Soil Color Chart (Munsell, 2000). For uniformity, the HEER Office recommends that investigators utilize this chart for soil color classification. This assists in comparisons of soils from different areas of a site or between sites. The Munsell Color Chart is a small booklet of numbered color chips with names like "5YR 3/4", a specific type of reddish brown. The first part of the code (e.g., 5YR) describes the sample in terms of the basic color group ("hue"). The second part of the code (e.g., 3/4) describes the color in terms of lightness and darkness ("value") and color intensity ("chroma").

Descriptors should also note layering, mottling, gradation, or banding of colors. It is important to note and describe staining that might be related to contamination, particularly if the observation is correlated with other observations of odor, moisture, or appearance (e.g., presence of apparent petroleum liquids or green staining possibly related to contamination with copper-chromium-arsenic).

Consistency

Consistency describes the strength at which soil particles are held together. Descriptors include:

  • Loose – Soil easily falls apart;
  • Friable – Soil initially holds together but easily crushed with gentle pressure;
  • Firm – Soil crushes under moderate pressure and resistance is noticeable;
  • Very Firm – Strong pressure required to crush soil; difficult to accomplish with thumb and forefinger.

Soils that are loose and easily crumbled even when wet are usually indicative of a low clay content. Dry soil that is very firm is usually indicative of a moderate amount of clay.

Moisture Content

The moisture content of the soil should be described qualitatively using the following terms and the corresponding definitions:

  • Dry - Absence of moisture, dry to the touch.
  • Moist - No visible water but moisture is sufficient to bind soil matrix.
  • Wet - Visible water, usually when soil is sampled from a water table. In other instances, the wetness may also indicate the presence of non-aqueous phase liquid (NAPL), if accompanied by strong odor or unusual liquid color or viscosity.

Submit samples to a laboratory for followup moisture analysis.

Staining, Odor and the Presence of Contamination

Unusual odors should be noted in logs and soil descriptions if detected when sampling, as they may be related to hydrocarbons, solvents, or other chemical contamination in the subsurface. Hydrocarbon odor may range from gasoline to lubrication oil. Contaminant-related odors also might have a distinctive smell of decaying vegetation or a stronger astringent or sweet odor that could be indicative of solvent compounds.

Use of a field organic vapor analyzer for screening purposes is recommended when volatile or semi-volatile organic contaminants are expected at a site (refer to Section 8). Direct inhalation should be avoided if odors suspected to be related to contaminants are detected. A health and safety plan should be prepared for sites where volatile or semi-volatile contaminants are anticipated. A respirator may be required under some circumstances, in additional to other personal protective equipment (e.g., gloves, tyvex suits, safety boots, etc.).

Note and describe staining or unusual moisture found in combination with unusual odors, as the combination of characteristics is often indicative of solvents, petroleum or other Non-Aqueous Phase Liquid (NAPL) contamination in soil (i.e., separate phase liquid not dissolved into water). The staining or moisture indicative of NAPL is often gray to brown in hue but can range in appearance from clear to completely black. Gasoline sometimes imparts a greenish to bluish hue to soil. Along with unusual odor and color, the moisture indicating NAPL contamination most often has an unusual textural aspect. For example, hydraulic fluids may feature a tacky or sticky feel accompanied by a sweet odor, while lubrication oil is most commonly much more viscous than water and accompanied by a dark color and a heavy, musky odor.

Appearance of coarser fragments

Angularity of coarser particles is often an indicator of mode of deposition. The following criteria describe the angularity of coarse sand and gravel particles:

  • Rounded particles have smoothly-curved sides and no edges;
  • Subrounded particles have nearly plane sides, but have well-rounded corners and edges;
  • Subangular particles are similar to angular, but have somewhat rounded or smooth edges;
  • Angular particles have sharp edges and relatively plane sides with unpolished surfaces. Freshly broken or crushed rock would be described as angular.

Note that both angular and rounded particles can be associated with depositions of volcanic ash.

5.8.3.2 Example Soil Descriptions

Description of coarse-grained soil samples

A coarse-grained soil is one that is primarily composed of sands and/or gravel particles. A soil is classified as a sand if greater than 50 percent of the coarse fraction is "sand-sized." It is classified as a gravel if greater than 50 percent of the coarse fraction is composed of "gravel-sized" particles.

The written description of a coarse-grained soil should contain the following information:

  • USCS classification name based on soil properties (particle size and percentage, plasticity, and other parameters as defined by USCS);
  • Munsell color and color number;
  • Moisture content;
  • Relative density (if determinable);
  • Coarse particle angularity and makeup by predominant particle type (e.g., coralline or basaltic).

An example coarse-grained sample description is presented below:

POORLY-SORTED SAND WITH SILT, medium- to coarse-grained, SW/SM (minor silt with approximately 80 percent coarse-grained sand-sized shell fragments, and 20 percent medium-grained basalt sand, and 5 percent to 15 percent ML), light olive gray, 5Y 6/2, moist, no odor, subrounded grains.

Description of fine-grained soil samples

Fine-grained soil is subdivided into clays and silts according to its plasticity. Clays are plastic while silts have little or no plasticity. The written description of a fine-grained soil should contain similar information as noted above, in addition to information on plasticity An example fine-grained sample description is presented below:

SANDY CLAY WITH TRACE GRAVEL, CL (70 percent fines, 30 percent fine sand, with minor amounts of basalt gravel [< 5 percent]), light olive gray, 5Y 6/2, moist, faint odor, firm, moderately plastic.

5.8.4 ADDITIONAL SAMPLE INFORMATION

Additional sample information that might be required for a project includes moisture content, density/consistency, cementation, structure, and rock classification. A brief overview of these topics is provided below (see also Nielson, 2006, US Navy, 2007).

Density/Consistency (borings)

Density and consistency describe a physical property that reflects the relative resistance of a soil to penetration. The term "density" is commonly applied to coarse to medium-grained sediments (i.e., gravels, sands), whereas the term "consistency" is normally applied to fine-grained sediments (i.e., silts, clays). There are separate standards of measure for both density and consistency that are used to describe the properties of a soil.

The density or consistency of a subsurface soil is determined by observing the number of blows required to drive a standard 1 3/8-inch (35 mm) inner diameter (ID) split barrel sampler (commonly termed a standard penetrometer test [SPT] or terzaghi sampler) 18 inches using a drive hammer weighing 140 lbs (63.5 kilograms [kg]) dropped over a distance of 30 inches (0.76 meters). Record the number of blows required to penetrate each 6 inches of soil in the field boring log during sampling. The first 6 inches of penetration is considered to be a seating drive; therefore, the blow count associated with this seating drive is recorded, but not used in determining the soil density/consistency. The sum of the number of blows required for the second and third 6 inches of penetration is termed the "standard penetration resistance," or the "N-value." The observed number of blow counts must be corrected by an appropriate factor if a different type of sampling device is used (e.g., most commonly in Hawai‘i, a Modified California Sampler [MCS] with liners). For a 2-inch ID MCS equipped with brass or stainless steel liners and penetrating a cohesionless soil (sand/gravel), the N-value from the MCS must be divided by 1.43 to provide data that can be compared to the 1 3/8-inch ID SPT sampler data (University of Southern California, 2001).

For a cohesive fine-grained soil (silt/clay), the N-value for the MCS should be divided by a factor of 1.13 for comparison with 1 3/8-inch ID SPT sampler data (US Navy, 2007).

Drive the sampler and record blow counts for each 6-inch increment of penetration until one of the following occurs:

  • A total of 50 blows have been applied during any one of the three 6-inch increments; a 50-blow count occurrence shall be termed "refusal" and noted as such on the boring log.
  • A total of 150 blows have been applied.
  • The sampler is advanced the complete 18 inches without the limited blow counts occurring, as described above.

If the sampler is driven less than 18 inches, record the number of blows per partial increment on the boring log. If refusal occurs during the first 6 inches of penetration, the number of blows will represent the N-value for this sampling interval. Tables 5-3 and 5-4 present representative descriptions of soil density/consistency verses N-values.

Table 5-3. Measuring Soil Density with Standard Penetration Test and Modified California Sampler – Sands, Gravels
Description Standard Penetration Test Sampler Modified California Sampler
Field Criteria (N-Value) Field Criteria (N-Value)
1 3/8 in. ID Sampler 2 in. ID Sampler using 1.43 factor
Very Loose 0–4 0–6
Loose 4–10 6–14
Medium Dense 10–30 14–43
Dense 30–50 43–71
Very Dense > 50 > 71
Table 5-4. Measuring Soil Density with a Standard and California Sampler – Fine Grained Cohesive Soil
Description Standard Penetration Test Sampler Modified California Sampler
Field Criteria (N-Value) Field Criteria (N-Value)
1 3/8 in. ID Sampler 2 in. ID Sampler using 1.13 factor
Very Soft 0–2 0–2
Soft 2-4 2-4
Medium Stiff 4-8 4-9
Stiff 8-16 9-18
Very Stiff 16-32 18-36
Hard >32 >36

Cementation

Cementation is used to describe the friability of a soil. Cements are chemical precipitates that provide important information as to conditions that prevailed at the time of deposition, or conversely, diagenetic effects that occurred following deposition. Seven types of chemical cements are recognized by Folk (1980). They are as follows:

  1. Quartz – siliceous;
  2. Chert – chert-cemented or chalcedonic;
  3. Opal – opaline;
  4. Carbonate – calcitic, dolomitic, sideritic (if in doubt, calcareous should be used);
  5. Iron oxides – hematitic, limonitic (if in doubt, ferruginous should be used);
  6. Clay minerals – kaolinite, chlorite;
  7. Miscellaneous minerals – pyritic, collophane-cemented, glauconite-cemented, gypsiferous, anhydrite-cemented, baritic, feldspar-cemented, etc.

Of these, only 4 through 6 are commonly encountered in Hawaiian substrate.

If the clay minerals are detrital or have formed by recrystallization of a previous clay matrix, they are not considered to be a cement. Only if they are chemical precipitates, filling previous pore space (usually in the form of accordion-like stacks or fringing radial crusts) should they be included as "kaolin-cemented," "chlorite-cemented," etc.

The degree of cementation of a soil is determined qualitatively by utilizing finger pressure on the soil in one of the sample liners to disrupt the gross soil fabric. The three cementation descriptors are as follows:

  • Weak – friable (crumbles or breaks with handling or slight finger pressure);
  • Moderate – friable (crumbles or breaks with considerable finger pressure);
  • Strong – not friable (will not crumble or break with finger pressure).

Structure

This variable is most appropriate to the vertical extent observed in borings and sometimes to lateral extent observed in trenches. The variable is used to qualitatively describe physical characteristics of soil that are important to incorporate into hydrogeological and/or geotechnical descriptions of soil at a site. Appropriate soil structure descriptors are as follows:

  • Granular – spherically shaped aggregates with faces that do not accommodate adjoining faces;
  • Stratified – alternating layers of varying material or color with layers at least 6 mm (1/4 inch) thick; note thickness;
  • Laminated – alternating layers of varying material or color with layers less than 6 mm (1/4 inch) thick; note thickness;
  • Blocky – cohesive soil that can be broken down into small angular or subangular lumps that resist further breakdown;
  • Lensed – inclusion of a small pocket of different soil, such as small lenses of sand, should be described as homogeneous if it is not stratified, laminated, fissured, or blocky;
  • Prismatic or Columnar – particles arranged about a vertical line, ped is bounded by planar, vertical faces that accommodate adjoining faces (prismatic has a flat top, columnar has a rounded top);
  • Platy – particles are arranged about a horizontal plane.

Other sample appearance descriptors include:

  • Mottled – soil that appears to consist of material of two or more colors in blotchy distribution;
  • Fissured – breaks along definite planes of fracture with little resistance to fracturing (determined by applying moderate pressure to sample using thumb and index finger);
  • Slickensided – fracture planes appear polished or glossy, sometimes striated (parallel grooves or scratches).

Rock Classification

The purpose of rock classification is to thoroughly describe the physical and if possible, mineralogical characteristics of a rock sample collected through rotary sampling, or significant rock fragments encountered in a soil matrix drilled into by hollow stem auger, or in a trench, and to classify it according to a common system. Because rock classification systems vary, and to date there is no universally accepted rock system equivalent to the soil USCS, the HEER Office recommends a general rock classification system similar to the US Navy standard operational procedure developed for description of rock types; however, it is modified because the Navy system includes rock types not found in the state of Hawai‘i (US Navy, 2007).

Rock descriptions preferably should be made by a trained geologist or geotechnical engineer. The items essential for classification include: Rock Name (e.g., coral limestone), Color (according to the Munsell code), Texture/Grain size (e.g. fine-grained, porphyritic), Structure (e.g., fractured, massive, porous), degree of weathering, and overall Classification according to the following general rock types:

  • Conglomerate (CG) – Coarse-grained, consolidated sedimentary rock, including conglomerate and breccia.
  • Sandstone (SS) – Consolidated sedimentary rock composed primarily of sand-sized particles.
  • Mudstone (MS) – Consolidated sedimentary rock composed primarily of silt-sized or finer particles.
  • Carbonates (LS) – Chemical or biological precipitates including coralline limestone, algal limestone, cemented shell limestone.
  • Basalt (IE) - Although it is conceivable that very deep borings may encounter intrusive igneous rock, the predominant igneous rock that will be encountered in Hawai‘i is basalt. The description of basalt should include an identification of the encountered rock as predominantly a’a or pahoehoe. Descriptions of basalt should also have an indication of degree of weathering (if possible) and any identifiable dominant zones, depths, identifiable fracture orientations, clinker zones in a’a, or interconnected / elongated vesicles in either lava type. All of these may indicate preferential pathways for groundwater travel.
  • Tuff (T) – Descriptions of tuff should include boring structure characteristics as described previously, degree of friability, and degree of weathering.

Where possible, rock types should also be identified according to depth range below ground surface. Descriptions of rock type should pay primary attention to characteristics that potentially affect groundwater behavior (e.g. basalt fracturing, carbonate porosity). An example rock description is as follows:

Tuff (T), dusky red, 2.5 YR 3/2, welded, horizontal layers (~0.5 inch) of sand-sized ash/rock fragments grading upwards to laminated fine grained ash, 5 to 6 feet bgs, no fracturing with upper laminations highly weathered and altering to clay.

Other Subsurface Boring Soil/Rock Information

Optional but desirable associated information to accompany the boring logs would be photographs of boring locations, and for deeper borings, photographs of recovered samples. Each photograph should have a unique qualifying identification number or code. This code and some of the pertinent boring/soil sample information indicated on the list above should be written down and included within the photograph. A common method to include the information is to write it on paper or a reusable dry-erase type of board and to place the paper or board within the view of the photograph along with a common object (e.g., pen) for scale.