Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 5.2


Physical clearance of DUs to permit and expedite the collection of surface samples and/or allow access to subsurface boring locations will be necessary for many if not most projects. Subsurface utility clearance will normally be required for subsurface soil investigations.


It is important to visit a site prior to finalization of a site investigation work plan. This is necessary to refine and finalize the designation of DUs and also helps ensure that the need to remove debris or clear vegetation prior to sample collection is identified and addressed prior to field activities. Multi Increment sampling methods require access to dozens or even hundreds of systematic random locations within a site for the collection of samples (refer to Section 4.2.4). Attempting to clear vegetation, or move debris, large equipment, vehicles, and other obstacles after the field team has already been mobilized to the site can significantly increase sample collection time and pose hazards for field workers (Figure 5-1).

Figure 5-1. Large Equipment Interfering with Access to a DU Targeted for MI Sample Collection

The need to maneuver around debris and skip or alter increment collection locations can also compromise the representativeness of samples. Debris can also serve as a home for wasps, centipedes, fire ants and other stinging insects. Request the property owner to remove such material from the area well ahead of time. Check the site to make sure that this has been completed prior to mobilizing a field crew.

Thick grass and other vegetation can considerably slow down sample collection. Certain types of tall grasses can have thin sharp blades that require long-sleeve shirts for protection. Clearing of vegetation prior to sample collection can usually be done at a minimal cost in comparison to the overall investigation (Figure 5-2). Heavy equipment (e.g., bulldozer) can be used to clear DUs in heavily overgrown areas (Figure 5-3). Care must be taken not to significantly disturb or remove soil immediately beneath the surface vegetation root zone if the DQOs for the investigation target the area just below the surface root zone as part of the DU vertical layer. Where the site investigation DQOs includes sampling soil through the root zone, vegetation should be cut off just above the ground surface to allow access, rather than scraping the surface with a bulldozer.

Figure 5-2. Clearing of Thick Grass from a Targeted DU Prior to the Collection of MI Sample Increments

Figure 5-3. Bulldozer used to Cut Access Paths and Clear 59 Lot-size (5,000 ft2) DUs within a 500-Acre Field (Photo from Bureau Veritas)

Clearing prior to field work can also help identify otherwise unnoticed dump areas or suspect areas of elevated contamination within a designated DU that should be investigated as separate DUs. If clearing a site is not possible before site inspection or site investigation, then carry tools to do so in the field as necessary. This might include gas-powered weed trimmers, swing blades, saws, clippers or similar tools. A breaker bar (o’o), essentially a long metal bar with a flattened and sharpened tip, can sometimes be used to punch holes through old asphalt for the collection of increments if a power tool is not available. Check with nearby hardware stores for daily tool and equipment rentals in order to minimize the amount of equipment that must be transported between islands. Note that vegetation can grow rapidly in many areas (especially the windward areas), with up to several feet of grass appearing in an area that was cleared only weeks before.

Characterization of DUs within very large heavily overgrown areas that cannot be cleared can be especially challenging. Strategically located paths corresponding to increment collection grid lines can be cut through large heavily overgrown DUs to provide access and stake out increment location points ahead of time (Figure 5-4). This can be time consuming but can also significantly improve the efficiency of field work and help ensure that representative samples are collected.

Figure 5-4. Path Matching Increment Grid Locations Cut Through Thick Vegetation Covering a 50-acre DU; Increment Locations Pre-staked to Expedite Sample Collection

5.2.2 SUBSURFACE UTILITY CLEARANCE Information Gathering

An effort must be made prior to subsurface field work to gather information on underground utilities or features at the investigation site. This primarily involves activities below a depth of three feet, but could also pertain to shallow utilities in the vicinity of buildings. Intrusive activities can involve drilling to collect soil cores, collection of soil gas samples and installation of monitoring wells as well as excavating and trenching. The goal of the information gathering and potential underground geophysical survey is to accomplish either or both of the following tasks:

  • Locate subsurface utilities or features that may be targets of the investigation, (e.g., potentially leaking underground storage tanks) in order to aid in identifying the proper location, arrangement, and depths of subsurface samples to best investigate the identified object.
  • Identify other subsurface utilities or features that should be avoided by the intrusive activity in order to minimize the potential for damage to underground utilities and other functional structures (e.g. utility lines) and to minimize potential for associated physical injury.

Pertinent information sources should be contacted prior to any field effort in order to obtain as-built plans, historical photos, utility maps and other available information concerning subsurface utilities and/or subsurface features at a site. Such information sources can include but should not be limited to the following:

  • Utilities (e.g., Board of Water Supply, Hawaiian Electric);
  • Communication companies (e.g., cable/telephone companies);
  • Landowners or property management companies;
  • Facility or site managers;
  • Department of Defense or other federal agencies owning or controlling facilities;
  • Utility Notification Center – One Call Center.

For the most part, the listed information sources will provide information only on a single type of utility (e.g., buried power lines owned by Hawaiian Electric) but will not provide the same information for other utilities or subsurface features at an individual facility. Additionally, the utilities might not provide information on lateral connections to their main service corridors. Conversely, landowners or facility managers might have information on multiple utilities or features but only for a single facility within the property or only for the immediate area around individual buildings at the facility.

One Call Center Background

Hawaii's One Call Center, established in 2006, is similar to other centers operating throughout the nation requiring mandatory participation by both excavators (e.g., contractors) and operators (e.g., public utilities). The One Call Center system provides advanced warning to excavators of the location of underground lines before they begin digging. This mandatory "Call Before You Dig" program provides excavators with a single phone number to call for locating and marking underground lines, including lines for electric, gas, telecommunications, cable, water and sewer facilities. (

Hawai`i One Call Center Telephone Number
(Toll Free) 1-866-423-7287
(online; One Call Center Notification

Use of the Hawai‘i One Call Center service is required by Hawai‘i state law, under Hawai‘i Revised Statute (HRS) Chapter 269E, enacted in 2006 (HRS, 269E). The law includes two requirements related to subsurface utilities in the State of Hawai‘i:

  • That the State of Hawai‘i establish a one call center …"that provides advance warning to excavators in this State of the location of subsurface installations in the area of an excavation for the purpose of protecting those installations from damage."
  • That excavators within the state of Hawai‘i notify the one call center of the location of subsurface intrusive activity at a work site at least five working days before the activity.

The One Call Center in Hawai‘i (HOCC) is administered by the Hawai‘i Public Utilities Commission (PUC). Information on the HOCC, as well as answers to common questions, is contained in a handbook available from the PUC and One Call Center entitled "Dig Safely Hawai‘i" (PUC, 2008;

The phone number for the Hawai‘i One Call Center is 1-866-423-7287. Information can also be submitted online ( The service requires the following information by phone and in writing with respect to the site to be excavated or sampled:

  • Site address;
  • Maps and related information that identify the site location;
  • The specific location(s) that subsurface work is to be conducted at the site, including marking proposed intrusive locations on the ground surface in the field with white paint;
  • Contact information for the individual/agency responsible for or performing the subsurface work;
  • The type of intrusive work being performed;
  • The client or landowner for whom the work is being performed.

After receiving the information, the One Call Center will notify the publicly-owned utilities to mark the locations of their subsurface utilities or other features in and around the specific site work locations. The Utility Notification Center website states that: "…under normal circumstances it takes between 2 days to 5 days from the time you call (not counting weekends or holidays) to have the underground lines marked." No fees are charged for this service.

Note that the HOCC does not cover federal facilities or other utilities or facilities not listed as "Participating Facility Operators" in the HOCC handbook (PUC, 2008).The HOCC is also not required to identify inactive subsurface utilities, even though these could interfere with subsurface activities. Field Evaluation of Potential Subsurface Features

It is advisable to conduct an independent field effort to identify subsurface utilities or features in addition to contacting the HOCC. This should include a site inspection by a person knowledgeable of indications of subsurface utilities. Inspections with persons familiar with the facility since its inception can be invaluable. The site-specific SAP and Health and Safety Plan should define the clearance procedures that are necessary to identify the presence of subsurface utilities or other features that could impact or be impacted by sampling activity.

Facility construction diagrams can be a useful initial indicator of active or inactive subsurface utilities (e.g., a suspected former fuel pipeline). Field indications of potential subsurface utilities should be compared to information obtained earlier from HOCC and other sources. Manholes indicate access points to subsurface utilities. Long, linear patches in pavement often represent trenches dug for installation or subsequent repair of subsurface water, fiber optic or electric lines, or other types of pipeline (e.g., stormwater). Rectangular patches a few hundred square feet or smaller in area might indicate the location of an existing or former underground storage tank (UST). A U-shaped vent pipe extending from the ground surface and attached to the side of a building might indicate the presence of a current or former UST.

These features may or may not be present on construction drawings, particularly if the diagrams are out-of-date and site surface features used for orientation on the diagram such as buildings or fence lines have been subsequently removed or altered. If the linear patch in the above example corresponds to a fuel pipeline on the diagram and leads directly to a fuel valve pit then confidence in the construction diagram might be considered high. If the patch leads to a fire hydrant then the location of the fuel line, if indeed present, comes into question and further toning of the area may be required.

Locations of potential subsurface features should be marked on the ground surface by whatever means is appropriate for the surface cover at the sampling location. Multiple subsurface utilities or features can also connect or overlap at different depths, further complicating the investigation. The situation can sometimes create a complex subsurface environment as illustrated in Figure 5-5. Initial hand digging may be required at such locations if samples are to be collected. Hand digging, or other methods such as air or water jetting, may be required at some facilities. The latter can pose problems with the integrity of the samples collected and must be discussed in the investigation work plan.

Figure 5-5. Field Indicators of Underground Features

The photograph depicts field indicators for subsurface utilities or underground features as follows:

  • Potential subsurface feature running left to right indicated by the cut in asphalt in the upper left center portion of the photo. This surface indication does not continue in the right center portion.
  • Manhole and potentially associated cut suggest a storm drain parallel to the previous feature. In this case the field indicator was found to relate to a subsurface feature. Subsequent comparison to as-built plans showed the cut was unrelated to the storm drain and instead indicated yet another subsurface feature.
  • Surface cut in the yellow curb, an associated break in asphalt cover associated with the curb cut, and an apparently connected asphalt patch in the upper right corner of the photo suggest yet another potential subsurface feature. Subsurface Survey Methods

A wide variety of commonly available surface-based survey methods can be used to identify and evaluate potential subsurface features at a site. Common survey methods used in Hawai‘i include the following:

  • Resistivity/Electromagnetics;
  • Magnetometer; and
  • Ground-Penetrating Radar

Electromagnetics and resistivity (EM) are the general name for a variety of methods to measure for changes in subsurface electrical conductivity. The methods provide a means of measuring the electrical conductivity of subsurface soil, rock, and ground water. Electrical conductivity (the inverse of electrical resistivity) is a function of the type of soil, porosity, permeability, and the conductivity of fluids in the pore spaces. The EM method can be used to map natural subsurface conditions and conductive contaminant plumes. Additionally, trench boundaries, buried conductive wastes such as steel drums, metallic utility lines, and steel underground storage tanks, might be located using EM techniques (see Figure 5-6). Equipment and operators for EM methods are readily available in Hawai‘i. Under ideal circumstances the methods are able to penetrate several hundred feet of soil or bedrock for mapping of large-scale, subsurface changes (e.g., soil or rock interfaces). The methods are more commonly regarded as good to excellent for detecting single objects (e.g., pipelines or 55-gallon drums) at depths of 6 to 8 feet below ground surface (bgs) (Nielsen, 2006). The disadvantage to the methods is that they are potentially affected by metal fences, piping, buildings and vehicles at the surface.

Figure 5-6. Subsurface Survey to Identify Underground Features

Example of survey to identify features prior to intrusive sampling. The photograph depicts use of an EM detector to identify subsurface utilities. Painted arrows on the asphalt surface mark the location of a utility line.


Magnetometers measure the intensity of the earth’s magnetic field. The magnetometer will respond only to ferrous materials, including differences between subsurface soil and rock types (Nielsen, 2006). The presence of boulders, drums, underground tanks or pipes in the subsurface can cause measurable changes in the field. Magnetometers are readily available and typically have a depth penetration of 25 to 50 feet, depending on the type of instrument and the size, type, and number of objects in the subsurface. The presence of multiple drums in a burial pit will, for example, create a larger signal than a single drum.

Ground-Penetrating Radar

Ground-Penetrating Radar (GPR) uses electromagnetic waves from the high frequency radar spectrum (100 to 1,000 megahertz [MHz] range, radiated downward into the ground from a transmitter and reflected back to an associated receiving antenna, to identify subsurface changes in layering, cementation, moisture, and density, including the presence of voids and fractures (Nielsen, 2006). The receiver and antenna are usually towed in tandem over the area to be surveyed. Reflections of the radar wave occur whenever there is a change in dielectric properties of the subsurface materials.

GPR has both advantages and disadvantages over other subsurface survey methods. Under ideal conditions GPR can produce a much higher resolution of subsurface features (down to inches) in comparison to other geophysical methods. A continuous plot of subsurface data over time and location can produce a relatively rapid and picture-like image of subsurface features. "Echoes" from dense material can, however, obscure imaging of deeper features. High soil moisture, particularly in saltwater or brackish environments, can also mask subsurface features.

A GPR investigation performs best in coarse or massive material that is dry (e.g., unconsolidated coralline sediments, sandy soils and unweathered basalt formations). Subsurface penetration of 15 to 30 feet bgs can often be obtained, an effective depth for most environmental investigations. The high electrical conductivity of expansive clays or saprolite derived from volcanic rock can limit the usefulness of GPR in some areas of Hawai‘i. Clays can cause the GPR signal to rapidly attenuate and limit penetration to only a few feet. Consult an expert with experience in Hawai‘i prior to initiating full-scale use of this method. Experienced operators and GPR equipment can be expensive and difficult to obtain in Hawai‘i.