Site Field Investigation

As a result of the uncertainties associated with the modeling results (in particular the leaching portion of the site conceptual model), a Supplemental Field Investigation was implemented. This investigation focused on better defining the source areas with respect to soil contamination and determining site-specific leaching potential to compare to OLM results. The following sections present an overview of the field investigation.

1. Development of Area-Specific Soil Boring Locations

The first task associated with the soil boring program was to establish a sampling grid over each potential source area. The locations of the soil boring grids were approved by EPA V in September 1991 based on the source areas defined in the 1986 RI report and in the site-modeling effort.

The original grid spacing for all four investigative areas was approximately 100 ft by 100 ft. However, some sampling was done in areas not corresponding to grid loci, as a result of field limitations or greater data needs in a given area. Limitations for this spacing were introduced by the railroad right-of-way and paved areas. Boring locations were established at less than the 100 ft by 100 ft grid due to asphalt paving (along the west side of the southeastern area), site buildings, and property lines or fence lines. The boring affected by paving and a site building was G-17. Borings G-51, G-52, and G-53 were located only 60 ft from borings G-13, G-26, and G-28, respectively, because of the property or fence line. Borings G-l through G-13 and G-51 are located along the eastern property line. Figure 10 shows the four investigative areas and their respective sampling locations.

2. Drilling Methodology

Each soil boring was drilled using the hollow-stem auger method of drilling with a truck-mounted rig. Soil samples were collected continuously using a 24-in. split-spoon device as the hole was advanced to the termination depth of 6 ft at each boring location.

Samples were collected continuously so the soils could be classified with respect to textural composition and the presence or absence of visually identifiable potential site-related constituents. Samples were collected using a 3-in. OD split-spoon sampler, logged in the field by the site hydrogeologist, composited for the individual spoon sample interval, and placed in clean laboratory-prepared jars with Teflon-lined lids for submittal to the analytical laboratory. All soil samples were classified according to the Unified Soil Classification System.

Following completion of each boring, the borehole was sealed to the surface using a cement/bentonite grout. The split-spoon sampler was cleaned after collection of each sample using a soapy water bath followed by a clean water rinse. Between boreholes, and prior to leaving the site, the drilling rig, hollow-stem augers, drilling rods, and associated drilling tools were steam-cleaned at the on-site decontamination area. The cuttings from the drilling operations were contained on site in roll off boxes for eventual treatment or disposal.

3. Chemical Analysis

The soil samples collected from each depth interval of the grid boring locations were submitted to a certified laboratory for chemical analysis. The samples were analyzed for cPAHs using EPA Method SW846 8270, a high-resolution gas chromatographic, low-resolution mass spec-trometric (GC/MS) method of analysis. Mass spectrometric detection allows for nearly absolute identification of the cPAHs as opposed to other methods of detection. Samples that exhibited concentrations of less than 700 mg/kg of cPAHs were also submitted for TCLP extraction and subsequent leachate and analysis for cPAH by Method SW846 8270 to determine the actual leaching potential of the sample. An analytical sampling summary is presented in Table 28.

Table 28 Analytical Sampling Summary

Soil cPAH analysis TCLP/cPAH analysis

Table 28 Analytical Sampling Summary

Soil cPAH analysis TCLP/cPAH analysis

No. of

Total No.

Rinsate

Lab

No. of TCLP

Lab

Area

borings

of samples

blanks

blanks

MS/MSD

Duplicates

samples

blanks

MS/MSD

Duplicates

Southeastern

53

162

8

11

9

4

158

9

8

1

Southwestern

16

48

2

4

3

4

46

4

3

4

Northeastern

13

39

2

1

4

2

39

3

4

0

Northwestern

5

15

1

1

2

1

15

1

2

1

As part of the study, a quality assurance/quality control (QA/QC) sampling program was completed that consisted of collecting matrix spike/matrix spike duplicate samples and field blanks. A laboratory audit was also conducted by EPA to ensure the legitimacy of the analyses.

Site soil samples subjected to TCLP extraction did not produce detectable concentrations of any cPAH in the corresponding leachate. The majority of soil samples contained total cPAHs in excess of the soil cleanup goals obtained by the modeling effort. Soils containing as much as 1200 mg/kg of total cPAHs did not leach, suggesting that site leaching potential is at least a factor of 4-12 times lower than predicted by the site conceptual model. Samples containing more than 1200 mg/kg total cPAHs were not subjected to TCLP extraction.

The following paragraphs and Figures 11-13 present a spatial presentation of source area soil cPAH concentrations. Discussions concerning remediation are related to the direct-contact soil cleanup goal of 700 mg/kg total cPAHs since site-specific data suggest that this value is also protective of the no leaching potential. Areas requiring remediation were delineated on the assumption that the extent of impact is midway between a "clean" point and an adjacent impacted point. The volume of soils exceeding the remedial goal of 700 mg/kg was calculated based on the depth at which the exceedance was noted.

The analytical results of the samples collected from 53 soil boring locations in the southeastern area were used to delineate the horizontal and vertical extents of soils for remediation (Figure 11). The locations in this area that exhibited total cPAH concentrations greater than 700 ppm were grid locations G-60, G-5, and G-61; G-64, G-67, G-9, G-22, G-23, G-24, G-25; and G-73. Soils delineated for remediation are confined to the upper 2 ft, except for three locations. Locations G-73 and G-22 show soils exceeding 700 ppm total cPAHs in the 2-4-ft interval, and G-61 showed total cPAHs exceeding 700 ppm in the 0-4-ft interval. Approximately 24662868 cu yd of soil in this area exceed the remedial goal.

A total of 16 soil borings were drilled in the southwestern area. The analytical results are presented in Figure 12. Grid sampling locations G-80, G-81, G-82, G-83, G-35, and G-36 exhibited total cPAH concentrations above 700 ppm. Soil intervals delineated for remediation are limited to a small portion of this area and are generally from 2 to 6 ft. Boring location G-83 exhibited cPAH concentrations above 700 ppm in the 0-2 ft interval, boring G-81 exceeded the remedial goal in the 2-4-ft interval, and borings G-80, G-82, G-35, and G-36 exceeded the goal in the 4-6-ft interval. Approximately 626-1588 cu yd of soils in this area exceed the remedial goal.

In the northern area, grid samplings locations G-46 and G-87, between 0 and 2 ft, exceeded the risk-based criteria of 700 ppm for total cPAHs (Figure 13). Approximately 5581177 cu yd of soils present in this area exceed remedial goals.

No grid sampling locations in the northwestern area exhibited total cPAH concentrations above 700 ppm (Figure 13). Remediation of soils in this area is therefore not necessary.

0 0

Post a comment