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SAP Addendum Specific to Field Sampling Plan for AOC-65 Treatability Study Under AETC TO 0058
Section 7 - Sample Collection Procedures
Sampling to be conducted during the treatability study includes soil, groundwater, and soil gas. Additional testing to be conducted includes rainfall measurements, groundwater elevation measurement, geophysical surveys and packer extraction tests.
Surface soil samples will be collected from the excavation performed west of Building 90 during the removal actions in that area. The soil samples will be collected to quantify the concentration of volatile constituents in the soil material after completing excavation and prior to placement of backfill material. Specific details for the surface soil sampling is included in Section 4.5.2 of the Environmental Cleanup Plan for Area of Concern (AOC)-65, Parsons, April 2002. No changes to the sample collection methodology described in the SAP are required for this sampling event.
7.2 - Subsurface Soil Sampling
Changes to the SAP are required to implement and complete the subsurface investigation phase of the removal action to be conducted at Building 90. Procedures for conducting subsurface investigations are provided in Section 1.1.4 of the SAP.
Up to 12 shallow soil borings will be advanced inside Building 90 to assess the concentration of volatile compounds in the soils beneath the building and to permit the construction of VEWs/vapor monitoring at the drilling locations. A maximum of 12 soil borings will be conducted west of Building 90 to assess the presence and concentration of volatile constituents in the shallow soils.
The soil borings completed inside the building will be drilled using a skid-mounted rotary drill rig equipped with hollow stem augers. The soil borings completed west of the building will be conducted using the skid-mounted drill rig placed on a trailer. The borings will be advanced until auger refusal is encountered. Where possible soil samples will be collected from the borings using a split-spoon sampler and field screened using a photoionization detector (PID) to assess the presence and relative concentration of volatile compounds. Potentially, one sample from each boring will be submitted for laboratory analysis. The selection of the sample from each boring for analysis will be based on PID readings or field observations. In the absence of field observations indicative of elevated volatile concentrations, the sample from the bottom of the boring will be selected for analysis. If however, difficult drilling conditions are encountered and representative samples cannot be collected, then no sample will be taken. The PID used for screening purposes shall have an ionization potential greater than 9.0 electron volts and be calibrated daily in a ordance with the manufacturer's recommendations. Data collected from the soil boring sampling activity is considered screening, and therefore, duplicate, MS/MSD, and equipment blanks samples are not required.
The subslab VEW/VMPs installed within the building will require concrete coring through the floor slab by the drilling contractor. The vent wells will be installed in areas where soil contamination was identified during previous soil gas sampling event that allow good a ess for equipment, and allow for the necessary a ess and level of safety required for the field crew and do not impact the mission of the o upants. During concrete coring of the floor slab, 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 borehole should be removed.
Upon completion of the subslab drilling and VEW installation, the work site will be thoroughly cleaned by broom and mop and returned to its previous condition. To protect indoor workers, installation of the Building 90 Subslab Ventilation System will be conducted in the evenings and/or on weekends to minimize potential exposures to contaminants beneath the building.
Changes to the SAP are required to conduct the groundwater sampling to be conducted during the groundwater recharge study. Procedures for collecting groundwater samples are provided in Section 2.1.5 of the Sampling and Analysis Plan, Volume 1, Environmental Encyclopedia.
As discussed in Section 4.0, groundwater samples will be collected from the piezometers and VEWs during the baseline assessment phase of the groundwater recharge study. Groundwater samples will be collected and analyzed to assess the distribution of dissolved constituents, evaluate natural attenuation capacity, and to establish a baseline groundwater quality for comparison during subsequent sampling events. Subsequent samples will be collected from the piezometers when significant rainfall events occur to assess changes in concentration with rainfall amounts as well as changes over time.
Since groundwater levels will be measured continuously to assess fluctuations with rainfall infiltration, the monitoring wells will not be purged prior to sampling to minimize impacts to the groundwater level measurements. Each sample will be collected utilizing dedicated, disposable �mini-bailers� of a sufficiently small diameter to allow collection of the sample from the 4-inch piezometers without removing the pressure transducer. Data collected as part of the Groundwater Recharge Study is considered screening data. Therefore, no soil samples are proposed for collection during the installation of nested piezometers. In addition, duplicate, MS/MSD, and equipment blanks are not required.
Soil gas will be sampled during the extraction packer test, during the groundwater recharge study, and from VEWs and VMPs installed for the AOC-65 SVE and the Building 90 subslab systems. Two levels of soil gas sampling data will be collected, field screening and qualitative sampling. A brief description of qualitative soil gas sample collection for soil gas surveys is described in Section 1.1.3.2 of the Sampling and Analysis Plan, Volume 1, Environmental Encyclopedia. A description of soil gas sample screening in included in Section 1.1.3.3 of the Sampling and Analysis Plan, Volume 1, Environmental Encyclopedia. Both procedures require modification for the AOC-65 Treatability Study activities.
During the extraction packer test, field-screening soil gas sampling will be conducted prior to collection of qualitative soil gas sampling to assess the vertical distribution of contaminants in the unsaturated zone. Collection of the soil gas screening samples will be consistent with the methodology described in Section 1.1.3.3 of the Sampling and Analysis Plan, Volume 1, Environmental Encyclopedia, with the exception that a PID and O2/CO2 meter will be connected to a vacuum pump specifically extracting soil gas vapor from the packer interval.
Screening soil gas sampling will also be conducted prior to initiating the AOC-65 SVE treatability test and the evaluation of the Building 90 subslab ventilation system. The purpose of the screening soil-gas sampling is to assess the concentration and distribution of contaminants prior to initiating SVE operations. Prior to the start of the AOC-65 SVE initial system check, screening soil gas sampling will be collected from the VEW, VMPs, and piezometers located west of the building to assess the relative distribution of contaminants across the area.
Soil gas samples will be collected using an electric vacuum pump, flexible tubing, a vacuum dessicator, and/or Summa canisters. Soil gas will be extracted from each sample point by connecting flexible, tubing to the sample point (VMP, VEW, piezometer, etc.). The other end of the tubing will be connected to a clean Tedlar sampling bag, which is placed inside the dessicator. Another section of tubing runs from the dessicator to a vacuum pump capable of exerting a sufficient vacuum on the dessicator to draw air from the sampling port and into the Tedlar bag.
The dessicator contains three openings or �ports.� The Tedlar sampling bag is placed inside the dessicator. Tubing connects the Tedlar bag to the sample point, passing through one of the dessicator ports. The vacuum pump is connected to an another dessicator port, and the third port is used to regulate vacuum on the dessicator and Tedlar bag.
Using the vacuum pump flow rate and the volume of the sample point (i.e., VMP), an estimate will be made of the time required to purge the ambient air from the sample point. The ambient air within the sampling point will be purged using the vacuum pump to exert a vacuum on the dessicator. With the third port of the dessicator closed, soil gas is pulled into the Tedlar sampling bag from the sample point. When a sufficient amount of soil gas has been collected into the sampling bag, the vacuum is broken by opening the third dessicator port. The sampling bag is then closed and the tubing is removed. Field screening of the soil gas samples are made by connecting the Tedlar bag to the direct read field instruments.
Soil gas samples that will be submitted for laboratory analysis shall be collected into Summa canisters for transport to the laboratory. Summa canisters are pre-evacuated, metal canisters with one inlet. To transfer the soil gas sample from the Tedlar bag to the Summa canister, the sampling bag is connected to the Summa canister inlet port with a short piece of flexible tubing, and bag's inlet port is opened. The Summa canister port is then opened and the soil gas sample is pulled from the sampling bag and into the canister. The port on the Summa canister is then closed before disconnecting it from the Tedlar bag. Samples that will be transferred to Summa canisters will be collected in clean, dedicated Tedlar bags.
Up to six piezometers will be installed for the groundwater recharge study. The piezometers will be constructed with 25-foot screened intervals set at varying intervals to monitor the upper 150 feet of unsaturated material at the site. The wells will consist of 4-inch diameter slotted PVC screen material and extended to land surface with 4-inch, schedule 40 PVC riser pipe. Piezometer installation and construction will follow procedures outlined in Section 1.2.1 of the SAP for monitoring well installation with the exception that modifications will be made to the top of the well to allow for the installation of a pressure transducer for the groundwater recharge study. Details for the modification of the piezometers depicted on Figure 3.2 of the AOC-65 Treatability Test Plan, Parsons, April 2002.
Up to six VEWs and six multi-depth VMPs will be installed in the vicinity of Building 90 for the AOC-65 SVE treatability test. Additionally, up to 12 combined VEW and VMP wells will be installed inside Building 90 as part of the subslab ventilation system to be installed during the removal actions. Installation and construction of the VEWs and VMPs will be performed following the procedures for monitoring well construction in the SAP with minor modifications to surface completion details as necessary.
For the AOC-65 VEWs outside Building 90, the procedure will be modified for the surface completion of the well to include connection of the well head to the SVE piping network. The AOC-65 VMPs will consist of four one-inch diameter PVC well screens set a varying depths within a single borehole and extended to land surface with 1/4-inch diameter tubing. The combined VEW and VMP wells installed inside Building 90 will consist of one-inch diameter PVC well material set at the maximum drilling depth at each location and extended above the concrete floor to the building rafters with PVC piping. Details for the construction of the AOC-65 VEWs and VMPs are presented on Figures 3.6 and 3.8 of the AOC-65 Treatability Test Plan, Parsons, April 2002. Details for the construction of the Building 90 subslab combined VEWs and VMPs is presented on Figure 3.3 of the AOC-65 Treatability Test Plan, Parsons, April 2002.
Extraction packer testing will be performed on the deepest piezometer borehole drilled as part of the groundwater recharge study. A packer consists of a rubber sleeve, which expands against the wall of the borehole when pressure is applied. The testing of isolated sections of a borehole requires the use of two pneumatic isolation packers separated by a length of perforated pipe. The double-packer assembly and inflating line are lowered into the borehole on a string of pipe so the perforated section is at the depth interval to be tested. The perforated piping is fitted with an airtight cap and sampling port, and connected via tubing to an aboveground pump.
The borehole must be cleaned of all cuttings and drilling mud (if used) prior to testing. To initiate the test, the packers are inflated to isolate the desired depth interval. Prior to collecting the sample, ambient air within the perforated piping and associated tubing is purged using the vacuum pump connected directly to the tubing. After the ambient air has been purged from the sampling string, the soil gas sample is collected using the vacuum dessicator sampling apparatus in accordance with the procedures described in Section 7.4.
At the rates of vapor extraction anticipated, it may be difficult to maintain either a constant rate of extraction or a constant extraction pressure during field operations. It is therefore imperative that both pressure and extraction rates be measured and recorded over time throughout the test. Measurements should be made as frequently as possible during the early moments of the test.
The period of extraction should continue as long as necessary, but should not be longer than 20 minutes per interval. As the time of extraction continues, changes in pressure and injection rate will occur more slowly and frequency of measurement may be decreased. However, field measurement should be taken at least every 3 minutes until the end of the extraction period. Pumping times and pressures depend on the depth and requirements of the test and the nature of the materials being tested. The test will be run until equilibrium has been established which will be determined by four or five consecutive readings of pressure and flow that are essentially constant.
The spacing of packers (which governs the length of the test section) is generally between 5-10 feet apart, depending on the diameter of the hole. The minimum spacing of packers should be governed by the following guideline:
Sp/D > 5
Where:
Sp = the spacing, or length between packers, and
D = the diameter of the borehole.
Up to eight separate packer intervals are proposed within the deepest piezometer. As presented in Table 1.1, soil gas samples will be collected from each interval and analyzed for VOCs in accordance with EPA analytical method TO-14. Soil gas samples will be collected utilizing the methods described in Section 7.4.