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2.1 - Surface Soil Sampling

No changes to the SAP are needed to implement and complete the surface sampling effort. Procedures for conducting and collecting soil samples are provided in the original SAP. In addition to the original SAP, those AOCs which encompass large areas (AOCs 36, 38, 39, and 40) will require an established sampling grid be staked out prior to the actual sampling event. The grid size and density will be unique to each specific site, and will be predetermined prior to field mobilization.

Surface samples will be collected from each grid from a random depth between 0 feet and 2 feet below grade. Samples will be obtained using either properly decontaminated trowels or hand augers. Each sampling location will be surveyed using the CSSA global positioning system (GPS) receiver. Particular attention will be given to the accuracy of the surveyed coordinates of each grid system corner. Each staked sampling location will be clearly labeled on the wooden stake, and left in place for future reference.

At AOC 65, two surface samples will be collected from beneath the citrus-based cleaning vat inside of Building 90. This location will require concrete coring through cement by the drilling contractor. The samples will be obtained from locations which provide good access for equipment, and allows for the necessary for the field crew. during coring activities, the contractor shall use the minimal amount of water necessary to keep the coring bit cool. Once the core is removed, any excess water in the corehole should be removed. The sample should be collected from a reasonable depth below any gravelly backfill. Hand augers may be necessary to obtain a representative sample of fine-grained material beneath the zone that may have been impacted by the cooling water. Prior to abandoning the holes, the work site should be thoroughly cleaned by broom and mop to return the site to its previous condition. Each corehole will be neatly abandoned by emplacing a properly mixed batch of concrete.

A total of 82 surface samples (not including QA/QC) will be collected from the five AOCs with scheduled surface sampling. Table 2 lists the number of samples and parameters for each site. Table 3 lists the number of quality control samples required for the soil sampling effort.

Table 3 - Surface Sampling Quality Control

2.2 - Subsurface Soil Sampling

Several changes to the SAP are needed to implement and complete the subsurface investigation phase of the field effort. Procedures for conducting subsurface investigations are provided in Section 1.1.4 of the original SAP.All soil borings will be placed proximal to subsurface anomalies detected during the electromagnetic surveys. Two samples will be collected from each boring. One sample will be collected from the total depth of the boring. The remaining sample will be collected from the depth with the highest headspace PID reading or indications of visible contamination (which may include a surface sample). If there is no measurable or visible indicators of contamination, the sample from the midpoint depth of the boring will be retained for chemical analysis.

A total of 26 surface samples (not including QA/QC) will be collected from the 13 soil borings (2 per boring). The maximum depth of each boring is 10 feet below grade. Five borings each will be drilled and sampled at AOC 35 and AOC 42. Three borings will be drilled and sampled at AOC 43. Table 4 lists the number of samples and parameters for each site. Table 5 lists the number of quality control samples required for the soil sampling effort.

Table 5 - Subsurface Sampling Quality Control

All volatile organic compound (VOC) compound samples collected from unconsolidated subsurface materials will be obtained in special brass liners specifically fitted to the inside diameter of a standard split spoon (typically 1.5 inches). These liners allow recovered soils to be shipped to the analytical laboratory with minimal disturbance or exposure to the atmosphere. Because the brass liners are composed of an alloy of copper and zinc, laboratory samples to be analyzed for metallic compounds will not be submitted in the brass liners.

Since the brass liners are reusable, they will be decontaminated prior to each use by those methods described in Section 1.5 of the SAP. Extra care will be taken to ensure that ALL soil has been completely removed. Once the sample has been obtained inside the brass liner, excess soils will be trimmed from either end will a clean, stainless steel knife. Prior to snapping on the protective end caps, each end will be fitted with a square sheet of teflon to avoid contact between the sample and the plastic caps. The outside of the brass liner will be wiped clean, and a gummed sample label will be affixed to the container. The brass liner is then handled, stored, and shipped as any regular sample.

The disadvantage of the brass liner is that they limit the amount of the observable soil available for detailed lithologic logging, there is an appreciable amount of time involved with extruding and decontaminating used liners, and often liners are damaged beyond repair by gravelly material or after normal long-term use.

As part of this firm fixed-price contract, no provisions were given in the SOW for addressing any groundwater that may be encountered. Therefore, no borehole groundwater samples will be collected. In addition, in the unlikely event that groundwater is encountered, no monitoring wells can be installed without a formal change in the SOW.

2.3 - Soil Gas Sampling

No changes to the SAP are needed to implement and complete the soil gas sampling effort. Procedures for conducting and collecting soil samples are provided in the original SAP. The soil gas surveys will require an established sampling grid be staked out prior to the actual sampling event. The grid size and density will be unique to each specific site, and will be predetermined prior to field mobilization. As a general rule, the sampling grid will be based on 100-foot grid system.

2.4 - Geophysical Surveys

No methodologies for EM surveys deviate from the original SAP. However, this delivery order also includes the use of ground penetrating radar (GPR) as part of the geophysical surveys. The procedures for conducting a GPR survey are outlined below.

GPR surveys will be conducted using a Geophysical Survey Systems, Inc. (GSSI) SIR-2 instrument with a 300 MHz antenna. Ground-penetrating radar is a subsurface-geophysical technique which uses high-frequency (radio frequency) electromagnetic radiation to acquire subsurface information. A radar pulse sent into the ground from an antenna at the ground surface is reflected back to the receiving antenna at the ground surface by an interface between materials with differing dielectric constants. The radiated energy encounters differentials in electrical properties which are characteristic of the subsurface media through which the signal passes. These differentials cause some energy to be reflected back to the receiving antenna and some to be transmitted downward to deeper material. The reflected signal is amplified, transformed to the audio-frequency ranges, recorded, processed, and displayed. The record shows the total travel time for a signal to pass through the subsurface, reflect and return to the surface. If the antenna array is moved along the ground surface, a continuous cross-sectional profile of the subsurface is obtained. The subsurface profile shows features such as bedding, voids, fractures, faults, water table, and buried objects.

Optimal conditions for application of this technique are sandy or rocky soils in the vadose zone or bedrock with low permeability where water is not permanently present; poor results are obtained in clay or conductive soils. For practical purposes, the signal will not penetrate below the water table. This technique gives the highest resolution among the various geophysical techniques but also generally has the poorest penetration. Resolution ranges from inches to several feet, depending on frequency used. Specific antennas cover frequencies of 80-1000 MHz. The lower frequencies provide greater depths of penetration; the higher frequencies provide better resolution.

The complete GPR system contains the following components:

During the GPR survey, the antenna array is towed along the ground surface by hand or by vehicle to produce a continuous subsurface cross-section. The depth of a reflecting object can be calculated from the travel time of the signal and the electrical properties of the subsurface materials, but in practice the equipment is generally field calibrated against a test pit or boring for each project site. If subsurface conditions are heterogeneous, depth determinations can be difficult and of limited value.

Prior to conducting a GPR survey, a grid system must be established and constructed on the site so that any detected subsurface anomalies can be accurately located in the future. The grid spacing is set at the discretion of the field investigator. Generally, ten-foot spacing between grid lines will adequately cover an investigation site.

The initial setup and operation of the GPR system will include the procedural steps outlined in the manufacturer�s operation manual. The initial settings are determined on a site by site basis and must be correct in order to collect accurate and usable data.

Equipment function checks and instrument calibration are described in detail in the operation manual. "Real time" data are displayed on the Digital Control Unit and shall be monitored during survey operations to ensure accurate data collection.

GPR data are recorded and stored in the Digital Control Unit. Each survey line is recorded as an individual file. Logbook entries must be made at the time of data collection. These entries should contain information regarding file name, the direction that the survey was conducted, starting and ending points of each survey, distance between reference markers, and any other information that will aid in data interpretation.

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