C.1.2.5 Use of Discrete Data to Identify Localized Spill Area

Further characterization of the landfill DU was warranted based on the initial, incremental sample PCB sample data. As part of the study, each of the 600+ discrete samples collected from the targeted intervals of the DU was tested in the field for PCBs. Tables C.1-1a through C.1-1c present a summary of the discrete data results. The discrete data indicate the presence of an approximately 3000 ft2 concentrated area of PCB-contaminated soil at depth in the center of the former landfill footprint (see Figures C.1-5 and C.1-6 and Tables C.1-1a through C.1-1c). This area was targeted for a more detailed ISM investigation. Additional soil samples were collected from a 5-foot grid established across the central spill area and for the 28–36 and 36–60 inches depth intervals (refer to Figure C.1-5). Seventy-four discrete samples were collected from each interval. ISM samples were prepared from splits of the discrete samples in the same manner as described above. Sieves were used to separate the soil samples into four size fractions for analysis, >2 mm, <2–>0.25 mm, <0.25–>0.063 mm, and <0.063 mm.

Table C.1-1a. Landfill DU PCB discrete data summary, 0–4 inch depth interval
(USCG 2009, Table B-1)

Y-Axis X-Axis
0 10 15 20 25 30 35 40 45 50 55 60 65 70 80
0 0.00 0.01   0.00   0.03   0.00   0.03   0.00   0.08 0.00
10 0.02 0.00   0.01   0.15   0.07   0.15   0.03   0.08 0.04
20 0.10 0.06   0.15   0.13   0.12   0.20   0.30     0.09
30 0.64 0.54   0.51   0.84   0.55   2.24   0.98   4.30 0.00
40 0.55 0.93   0.23   0.00   0.02   0.00   5.00   0.00 0.00
50 0.00 1.81   1.99   0.10   0.01   0.00   0.01   0.00 22.68
55     2.54 3.05 0.98 11.7 2.08 0.00 0.04 0.01 0.03 0.00 0.00    
60 0.35 0.51 1.21 0.84   1.42   5.27   0.11   0.00 0.02 0.06 0.00
65                         0.00    
70 0.09 0.31   0.58   0.24   0.00   0.84   0.00 0.03 0.07 0.00
75         2.80 0.32 1.71 2.29         0.02    
80 0.07 0.00   0.31 1.50 0.17 3.15 0.20   0.00   0.05 0.00 0.00 0.00
85         0.75       0.31 0.15 0.09 0.33 0.18    
90 0.06 0.00   0.11 0.54 0.08   0.08   0.01   3.11 0.20 0.00 0.04
95         2.38             0.02 0.10    
100 0.48 0.30   0.45   0.12   0.05   0.32   0.06   0.17 0.07
110 0.45 0.28   0.41   0.62   0.25   0.81   0.67   1.17 0.05
120 0.15 0.07   0.15   0.02   0.11   0.03   0.05   0.04  
130 0.21 0.17   0.12   0.07   0.29   0.03   0.07   0.02  
140 0.13 0.56   0.04   0.11   0.04   0.04   0.11      
150 0.19 0.18   0.15   0.04   0.07   0.04   0.05      
160 0.15 0.11   0.11   0.03   0.00   0.00   0.03      
170 0.11 0.12   0.11   0.00   0.00   0.00 0.11 0.12   0.11  

 

Table C.1-1b. Landfill DU PCB discrete data summary, 2836 inch depth interval
(USCG 2009, Table B-2)

Y-Axis X-Axis
0 10 15 20 25 30 35 40 45 50 55 60 65 70 80
0 0.00 0.01   0.00   0.03   0.00   0.03   0.00   0.08 0.00
10 0.02 0.00   0.01   0.15   0.07   0.15   0.03   0.08 0.04
20 0.10 0.06   0.15   0.13   0.12   0.20   0.30     0.09
30 0.64 0.54   0.51   0.84   0.55   2.24   0.98   4.30 0.00
40 0.55 0.93   0.23   0.00   0.02   0.00   5.00   0.00 0.00
50 0.00 1.81   1.99   0.10   0.01   0.00   0.01   0.00 22.68
55     2.54 3.05 0.98 11.7 2.08 0.00 0.04 0.01 0.03 0.00 0.00    
60 0.35 0.51 1.21 0.84   1.42   5.27   0.11   0.00 0.02 0.06 0.00
65                         0.00    
70 0.09 0.31   0.58   0.24   0.00   0.84   0.00 0.03 0.07 0.00
75         2.80 0.32 1.71 2.29         0.02    
80 0.07 0.00   0.31 1.50 0.17 3.15 0.20   0.00   0.05 0.00 0.00 0.00
85         0.75       0.31 0.15 0.09 0.33 0.18    
90 0.06 0.00   0.11 0.54 0.08   0.08   0.01   3.11 0.20 0.00 0.04
95         2.38             0.02 0.10    
100 0.48 0.30   0.45   0.12   0.05   0.32   0.06   0.17 0.07
110 0.45 0.28   0.41   0.62   0.25   0.81   0.67   1.17 0.05
120 0.15 0.07   0.15   0.02   0.11   0.03   0.05   0.04  
130 0.21 0.17   0.12   0.07   0.29   0.03   0.07   0.02  
140 0.13 0.56   0.04   0.11   0.04   0.04   0.11      
150 0.19 0.18   0.15   0.04   0.07   0.04   0.05      
160 0.15 0.11   0.11   0.03   0.00   0.00   0.03      
170 0.11 0.12   0.11   0.00   0.00   0.00 0.11 0.12   0.11  

 

Table C.1-1c. Landfill DU PCB discrete data summary, 3660 inch depth interval
(USCG 2009, Table B-3)

Y-Axis X-Axis
0 10 15 20 25 30 35 40 45 50 55 60 65 70 80
0 0.00 0.01   0.00   0.03   0.00   0.03   0.00   0.08 0.00
10 0.02 0.00   0.01   0.15   0.07   0.15   0.03   0.08 0.04
20 0.10 0.06   0.15   0.13   0.12   0.20   0.30     0.09
30 0.64 0.54   0.51   0.84   0.55   2.24   0.98   4.30 0.00
40 0.55 0.93   0.23   0.00   0.02   0.00   5.00   0.00 0.00
50 0.00 1.81   1.99   0.10   0.01   0.00   0.01   0.00 22.68
55     2.54 3.05 0.98 11.7 2.08 0.00 0.04 0.01 0.03 0.00 0.00    
60 0.35 0.51 1.21 0.84   1.42   5.27   0.11   0.00 0.02 0.06 0.00
65                         0.00    
70 0.09 0.31   0.58   0.24   0.00   0.84   0.00 0.03 0.07 0.00
75         2.80 0.32 1.71 2.29         0.02    
80 0.07 0.00   0.31 1.50 0.17 3.15 0.20   0.00   0.05 0.00 0.00 0.00
85         0.75       0.31 0.15 0.09 0.33 0.18    
90 0.06 0.00   0.11 0.54 0.08   0.08   0.01   3.11 0.20 0.00 0.04
95         2.38             0.02 0.10    
100 0.48 0.30   0.45   0.12   0.05   0.32   0.06   0.17 0.07
110 0.45 0.28   0.41   0.62   0.25   0.81   0.67   1.17 0.05
120 0.15 0.07   0.15   0.02   0.11   0.03   0.05   0.04  
130 0.21 0.17   0.12   0.07   0.29   0.03   0.07   0.02  
140 0.13 0.56   0.04   0.11   0.04   0.04   0.11      
150 0.19 0.18   0.15   0.04   0.07   0.04   0.05      
160 0.15 0.11   0.11   0.03   0.00   0.00   0.03      
170 0.11 0.12   0.11   0.00   0.00   0.00 0.11 0.12   0.11  

Identification of central spill area using discrete sample data.

Figure C.1-6. Identification of central spill area using discrete sample data.
Isolated sample points >1.1 mg/kg PCBs indicate heterogeneity of PCB distribution in area outside central spill area at
the scale of a laboratory aliquot (i.e., 5 g). See also Figure C.1-5. Source: Modified from USCG 2009, Figure 6-1.

Elevated concentrations of PCBs were also reported in four isolated, discrete sample points, outside of the central spill area (Figure C.1-6). It is important to recognize that the presence of elevated PCBs at these sample points indicate heterogeneity of PCB distribution in area outside of central spill area at the scale of a laboratory aliquot (i.e., 5 g). These sample point locations do not represent plottable spill areas and cannot be treated as such (e.g., potentially excavated and removed as part of a future cleanup action (refer to HDOH 2008b, Section 4.3.5)). Instead, the presence of elevated PCBs in four, single-sample points outside of the central spill area more likely indicates that the reported concentration of PCBs in any given discrete sample collected within this area is likely to exceed 1.1 mg/kg a small percentage of the time. Removal of soil around the four, isolated sample points that happened to be identified during the study would not remove all sample-size spots above this screening level outside of the central spill area or reduce the overall mean concentration of PCBs in the soil for this area.