EXPLANATION OF DIFFERENCES IN SAMPLING RESULTS FROM CHEVRON AND THE PLAINTIFFS IN THE JUDICIAL INSPECTIONS

Transcription

1 EXPLANATION OF DIFFERENCES IN SAMPLING RESULTS FROM CHEVRON AND THE PLAINTIFFS IN THE JUDICIAL INSPECTIONS Prepared August 22, 2008 by Stratus Consulting Inc.

2 There are often differences between the Plaintiffs and Chevron s sampling results at the same site. There are two primary explanations for the observed differences: Differences in sampling depths or locations relative to contamination. At some sites, Chevron collected samples at shallower depths than the Plaintiffs, and these soils were less contaminated than those at depth. For example, at the Aguarico Station, samples were collected by Chevron in the shallow fill material that had been placed over a pit, while the Plaintiffs collected samples from the pit itself below the fill material. Soil samples from Pits 1, 2, and 3 collected by Chevron were from depths ranging from 0 to 0.3 m. Concentrations of TPH (as DRO + GRO) ranged from below detection (at 4 mg/kg for DRO and 0.69 mg/kg for GRO) to 812 mg/kg. In contrast, samples collected by in the same pits were from depths ranging from 1.0 to 5.6 m. Concentrations of total TPH in their samples ranged from 433 to 9,578 mg/kg (Stratus Consulting, 2007). In addition, at some sites, Chevron collected samples away from sources of contamination. Although collection of background samples is an important element of site investigation, it is critical to find the highest concentrations at a site when evaluating impacts to the environment and planning for remediation (U.S. EPA, 1988). For example, at the same location, Aguarico Station, the Plaintiffs sampled two large contaminated areas (referred to as Contaminated Areas 1 and 2 in Stratus Consulting, 2007, Figure 4.15). Chevron did not sample either area but instead sampled west and east of Pit 2 and north of Pit 1. The Plaintiffs results for the contaminated areas ranged from 393 to 333,262 mg/kg TPH. Chevron s results for the areas outside of the pits ranged from 4.65 to 98.7 mg/kg TPH (as DRO + GRO). In summary, soil TPH results for Station Aguarico demonstrate how differences in sampling depths or locations relative to contamination can explain differences in concentrations reported by Chevron and the Plaintiffs. Chevron s selection of sampling locations in the shallow portions of pits in fill material and in areas outside of pits avoided contamination, while the Plaintiffs chose sampling locations to identify areas with the highest degree of contamination. Differences in analytical methods The differences in the analytical methods used by the Plaintiffs and Chevron, especially those for TPH, may also contribute to the differences observed in sampling results. Chevron typically measured TPH-DRO and TPH-GRO, while the Plaintiffs measured total TPH. TPH-DRO and TPH-GRO capture only a portion of the total hydrocarbons related to petroleum because the residual range organics, which have higher molecular weights than diesel-range organics, are not included. Page 2

3 Even when TPH-DRO and TPH-GRO values are summed, the totals of the samples reported by the defendants are generally lower than those reported by the proposed experts for the Plaintiffs. The experts for the defendants collected split samples of the Plaintiff s samples (same location and depth) and analyzed them for a number of parameters, including TPH-DRO and TPH-GRO. A comparison of results for 12 split samples (those of experts proposed by the defendants are indicated by SS in the sample identification) collected at Sacha 13 shows that the results of the experts for the defendants for TPH DRO+ GRO are less than the Plaintiff s results for total TPH for almost every sample (Table 4). Three sample sets meet the acceptance criteria of +/-30% RPD, and results of another sample were below detection for both parties. However, for twothirds of the samples, the TPH values reported by the experts for the Plaintiffs were higher than TPH DRO+ GRO values reported by the experts for the defendants. These results indicate that the analytical methods are not comparable, and that the results reported by the experts for the Plaintiffs are measuring the higher-end petroleum compounds above C35 that are present in unrefined crude. Therefore, the results reported by the experts for the Plaintiffs are a better measure of the total amount of petroleum hydrocarbon (Cabrera Vega, 2008, Annex B). Regardless of the differences in the concentrations reports by Chevron and the Plaintiffs, both datasets clearly demonstrate that oil exploration and production operations in the Concession have caused extensive environmental contamination. References Cabrera Vega, R.S Technical Summary Report. Expert for the Court of Nueva Loja, Expert Opinion. March 24. Annex B: Evaluation of Data Usability, Table 4. Stratus Consulting History of Contamination at Oil Well Lago Agrio 11A, Oil Well Sacha 94, and Production Station Aguarico in the Napo Concession, Ecuador. Prepared for Kohn Swift & Graf, P.C. by Stratus Consulting Inc., Boulder, CO. November. U.S. EPA Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA. Office of Emergency and Remedial Response. EPA/540/G-89/004OSWER Directive October. Page 3

4 Table 4. Comparison of split samples at Sacha 13: Plaintiff vs. Texaco soil TPH values Sample Data source Parameter Result (mg/kg) Depth 1 Depth 2 RPD a Between acceptable limits? (+/-30% RPD a ) Which is higher? SA13-P1( m)_sv Plaintiffs TPH 2, JI_SA_13_PIT1_SS(0,6) Texaco TPH (DRO+GRO) No Plaintiff SA13-P1( m)_sv Plaintiffs TPH 2, JI_SA_13_PIT1_SS(1,4) Texaco TPH (DRO+GRO) 1, No Plaintiff SA13-PA1( m)_sv Plaintiffs TPH JI_SA13_PA1_(SS) Texaco TPH (DRO+GRO) No Plaintiff SA13-PA2( m)_sv Plaintiffs TPH 2, JI_SA13_PA2_(SS) (2,0) Texaco TPH (DRO+GRO) 1, No Plaintiff SA13-PA2( m)_sv Plaintiffs TPH JI_SA13_PA2_(SS) (3,0) Texaco TPH (DRO+GRO) Yes Plaintiff SA13-PA3( m)_sv Plaintiffs TPH JI_SA13_PA3_(SS) Texaco TPH (DRO+GRO) No Plaintiff SA13-PA4( m)_sv Plaintiffs TPH < JI_SA13_PA4_(SS) Texaco TPH (DRO+GRO) NA NA Plaintiff SA13-SE1( m)_sv Plaintiffs TPH 15, JI_SA_13_SE1_SS(1,0) Texaco TPH (DRO+GRO) 3, No Plaintiff SA13-SE2( m)_sv Plaintiffs TPH JI_SA_13_SE2_SS(1,2) Texaco TPH (DRO+GRO) 1, No Texaco SA13-SE3( m)_sv Plaintiffs TPH 5, JI_SA_13_SE3_SS Texaco TPH (DRO+GRO) 3, No Plaintiff SA13-SW3( m)_sv Plaintiffs TPH JI_SA_13_SW3_SS(1,0) Texaco TPH (DRO+GRO) Yes Plaintiff SA13-SW3( )_sv Plaintiffs TPH 2, JI_SA_13_SW3_SS(3,15) Texaco TPH (DRO+GRO) 2, Yes Plaintiff a. RPD (relative percent difference) = [((Valor 1 Valor 2)/Media) 100]. Source: Cabrera Vega, Page 4

5 Page 5 Differences in Sampling Results