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Plan for Evaluation and Remediation of Soils O'Henrv Laundry. Tutu St Thomas. USVI 1.0 Introduction The O' Henry Laundry is located on Highway 38, Tutu, St. Thomas, USVI. Contaminants, principally tetrachloroethene (PCE), have been detected in subsurface soils in the vicinity of the laundry. The purpose of this plan is to provide an overview of a method to evaluate soil contamination at the O' Henry Laundry based on existing data and, if warranted, to perform interim soil remediation based on appropriate criteria established during the evaluation. Preliminary descriptions of the proposed methods to evaluate soil contamination and to perform the soil remediation, if required, are provided for illustrative purposes and to provide a framework for discussion with regulatory agencies. 1.1 Background Six soil borings have been drilled and sampled at the O'Henry Laundry during investigations performed by others (Figure 1). Soil boring SS-1, located near the southwest corner of the laundry, was drilled and sampled in June 1990. The boring was drilled to a depth of approximately 24 feet, terminating at auger refusal. Five soil samples obtained from the boring were analyzed for volatile organic compounds of EPA's Target Compound List. The results of this analysis are summarized in Table 1. Five volatile organic compounds were reported. Three of these compounds, acetone, 2-butanone, and methylene chloride, were typically found in the associated laboratory method blanks and are common laboratory reagents. Therefore, the concentrations of these substances may not be representative. Further, there is no other evidence that these compounds contaminate environmental media at the laundry. The remaining compounds detected were PCE and xylenes (total); however, xylenes were also detected at concentrations near quantitation limits in the method blank for every sample. Because the sample analyses were conducted at secondary dilution factors, these low level background concentrations were multiplied by dilution factors ranging from 125 to 1,250. This may very likely account for the observed xylenes and their apparent depth correlation with PCE. The concentrations of PCE and xylenes appeared to follow similar trends with depth. In sample TW2, collected from depths between 2.5 feet and 4.0 feet, PCE was detected at a concentration of 5,400 ppb and xylenes were detected at a concentration of approximately 280 ppb. At a depth of approximately 6 feet (sample TW5), concentrations of both compounds increased by approximately one order of magnitude to their maximum reported values for the boring: PCE was reported at 59,000 ppb, and xylenes were reported at 11,000 ppb. Concentrations of both compounds decreased below this depth, and at a depth of approximately 19 feet (sample TW20), PCE was not detected. Xylenes were detected at an estimated concentration of 630 ppb. Five additional soil borings have been drilled and sampled at the O'Henry Laundry and are discussed in "Technical Memorandum II, Results of the Field Program, Tutu Service Station Investigation, St. Thomas, U.S. Virgin Island" (Geraghty and Miller, Inc., May, 1993). The soil borings are designated SB10, SB11, SB12, SB13 and SB13A in Figure 1. PCE was the only significant volatile organic compound detected. Concentrations above detection limits were as lb008.KL.cp *64508* 64508 follows: • 29 ppb from soil boring SB11 at 0.0 feet to 2.0 feet • 200 ppb from soil boring SB13 at 4.0 feet to 6.0 feet • 15 ppb from soil boring SB13A at 0.0 feet to 2.0 feet 1.2 Approach Criteria for soil remediation will consist of a risk-based Preliminary Remediation Goal (PRG) using a direct soil exposure scenario and a model-based determination of the maximum PCE concentration in soil that is protective of groundwater if not remediated. PCE-contaminated soils will be evaluated based on these criteria and on existing soil data to determine whether interim soil remediation is necessary. A Removal Action Memorandum (RAM) documenting the calculated cleanup standards and the soil evaluation will be prepared for EPA review. If soil remediation appears necessary, the RAM will also provide details of the removal action. On reaching a concurrence with EPA, the RAM will be implemented as a guide to the removal action. If soil remediation does not appear to be warranted, the RAM will be submitted to EPA to document this. 2.0 Calculation of Appropriate Soil Cleanup Levels Two criteria for the soil remediation will be developed. In the first method, the PRG for PCE in soil will be developed using a risk-based direct exposure scenario according to EPA guidance (USEPA, 1991). This method does not consider secondary impacts on groundwater. Therefore, the second criterion will involve calculation of the potential affect of PCE-contaminated soil on groundwater using modeling. Results of the modeling will be used to determine the maximum allowable PCE concentration in soil that will not result in unacceptable groundwater contamination. In developing the risk-based PRG, it is assumed that the O'Henry Laundry will be classified as a commercial/industrial site. Typical exposure pathways to be considered for a commercial/industrial site include incidental soil ingestion, inhalation of organic compounds volatilized from surface soil, and inhalation of particulates suspended in air due to site activities. In comparison, dermal contact may be a minor exposure pathway because most of the site is paved, and any workers involved in excavating contaminated subsurface soil will have adequate levels of personnel protective equipment. Therefore, this pathway may not need to be considered in the development of a PRG. Since PCE is a carcinogen, the PRG will be developed for a target risk of 10"6 cancer incidence in excess of background. The equation to derive the PRG is as follows (USEPA, 1991): C(mg/kg) = ______________TRxBWxATx365days/yr____________ EFxEDx[(SF0xl(T6 kg/mgxIR90il) + (SFiXlR^x [1/VF + 1/PEF] ) ] lb008.KL.cp where: C chemical PRO (mg/kg) TR target risk (KT6) SFi inhalation cancer slope factor (mg/kg-d)"1 SF0 oral cancer slope factor (mg/kg-d)'1 BW adult body weight (kg) AT averaging time (yr) EF exposure frequency (days/yr) ED exposure duration (yr) IRwil soil ingestion rate (mg/d) IR»ir workday inhalation rate (m3/d) VF soil-to-air volatilization factor (mVkg) PEF particulate emission factor (mVkg) Site specific values will be used for the parameters wherever applicable; otherwise, default values approved by EPA will be used in the calculation. Transport of PCE through vadose zone soils to groundwater will be evaluated using finite difference modeling. The modeling procedures will be similar to those described in Rosenbloom, et.al. (1993), which consider liquid advection, gaseous diffusion, liquid to solid phase sorption/desorption, liquid-gas partitioning and volatilization of the gas phase into the atmosphere. The modeling will be used to predict the mass of PCE per unit time that will reach groundwater for a range of conditions that will be based on existing data for the site. Finite difference groundwater modeling will then be used to determine the resulting concentrations of PCE in groundwater. These concentrations will be compared to drinking water standards to establish the maximum concentration of PCE in soil that will not require remediation to be protective of groundwater. 3.0 Removal Action Memorandum The suitability of the proposed soil remediation will be examined by comparing existing soil analyticaJ data to the criteria described above. If the proposed interim remediation is judged to be protective, expedient and cost effective, a RAM addressing excavation of PCE-contaminated soil (as described in the following sections) will be prepared and submitted to the EPA and, if appropriate, to DPNR for review. On receiving regulatory agency approval the RAM will be implemented. If soil removal does not appear to be warranted, this will be documented in the RAM. 4.0 Excavation A preliminary review of the data indicates that the risk-based PRO for PCE in soil using a direct exposure scenario may be approximately 18,000 ppb. Analytical results indicate that the maximum concentration of PCE in soil is approximately 60,000 ppb at a depth of six feet in soil boring SS-1, which is located near the southwest side of the laundry (Figure 1). The maximum concentration detected in other borings around the site was 200 ppb. This concentration was lh008.KL.cp in the vicinity of soil boring SS-1 may need to be remediated. Other preliminary assumptions are: The excavation will not require major structural supports, such as sheet piling Soils near the foundations of the O'Henry Laundry and the Liquor Barn will not be excavated or disturbed (Figure 1) No modifications to existing footings, foundations or other structures will be made The removal action will involve only vadose zone soils The PRG for PCE in soil will drive the remediation Soils will be excavated to a depth at which concentrations are less than the PRG but will proceed at least to the depth at which PCE was detected in excess of the PRG in SS-1. Based on these preliminary assumptions, soils in the vicinity of soil boring SS-1 will be excavated in stages to depths of approximately 1 foot, 5 feet, 7 feet and 10 feet. At each depth, soil samples will be collected and analyzed in the field by gas chromatography. Excavation will be halted when PCE concentrations, as indicated by the field screening, have fallen below the PRG but will proceed at least to the depth at which PCE contamination in excess of the PRG was detected in previous soil borings. Five soil samples will then be collected from the walls and floor of the excavation. These will be sent to a fixed-base analytical laboratory for confirmation that no further excavation is necessary. The samples will undergo expedited analysis for VOCs according to EPA's Contract Laboratory Program 1990 scope of work. Pending review and approval of the confirmatory analysis results by EPA, the excavation will remain open but will be enclosed within a security fence. On receiving approval from EPA, the excavation will be filled using clean soils transported to the site from an appropriate source. Excavated soil will be stockpiled on visqueen, covered with visqueen (weighted) and surrounded by a security fence. No further action will be performed on the excavated soils at this time. The final remedy for soil removed from the excavation will be consistent with the final remedy for the Tutu site considered under the RI. 5.0 Schedule Table 2 is a preliminary work schedule. Based on regulatory concurrence, soil excavation could be conducted in November-December, 1993. 6.0 References: Geraghty and Miller, 1993, "Technical Memorandum II Results of the Field Program Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands," February 1993. lh008.KL.cp Rosenbloom, J., P. Mock, P. Lawson, J. Brown and H.J. Turin, 1993, "Application of VLEACH to Vadose Zone Transport of VOCs at an Arizona Superfund Site", Ground Water Monitoring and Remediation, Summer 1993, Vol. 13, No. 3, pp. 159-169. USEPA, 1991. Human Health Evaluation Manual, Part B: Development of Risk-Based Preliminary Remediation Goals. OSWER Directive 9285.7-01 B. lb008.KL.cp HIGHWAY 36 MW02 MW03 MW01 a SB10 HARVEY WELL, MW04 Scale 25 SO Legend • Existing Monitor Well B Existing SoH Boring O Water W«fl FIGURE 1 SITE MAP O'HENRY LAUNDRY ST. THOMAS U.S. VIRGIN ISLANDS WTEMUnoNAL TECHNOtMV COHMNATION •TTMOMASVUSBM^I OHW*V-J»« Table 1 Summary of Soil Analytical Results from Boring SS-1 June 1990 O'Henry Laundry St. Thomas, U.S. Virgin Islands Project Number 409440 Compound (ppb') Acetone Methylene Chloride 2-Butanone Tetrachloroethene Xylenes (Total) Sample Number and Depth TW2 2.5 - 4.0 Ft. NDb 270 DBJC 370 DBJ 5400 D 280 DBJ TW5 5.0 - 6.5 Ft. 3000 DJ 3100 DBJ ND 59000 D 11000DB TW5DUP 5.0 - 6.5 Ft. ND 3000 BJ ND 22000 4700 BJ TW8MS 8.5 - 10 Ft. 2000 880 B 440 BJ 230 J 450 BJ TW8MSD 8.5-10 Ft. 1900 ND 310 BJ 150 J 520 BJ TW20 19.0 - 19.5 Ft. ND 1300 BJ ND ND 630 BJ •ppb- "ND- B- J - Parts per billion (ng/Kg). Not detected. Compound analyzed at secondary dilution factor. Compound detected in method blank. Compound detected below contract required detection limit. olK«ry \XLOOI.j.i ACTIVITY DESCRIPTION EARLY START EARLY FINISH 1993 SEP 1994 OCT I NOV I DEC JAN I FEE MAR DRAFT REMOVAL ACTION MEMORANDUM (RAM) 1SEP93 EPA REVIEW 27SEP93 FINAL REMOVAL ACTION MEMORANDUM (RAM) 18OCT93 EPA APPROVAL OF RAM 1NOV93 SOIL EXCAV/ STOCKPILE SOIL 29NOV93 REQUEST APPROVAL TO BACKFILL EXCAVATION 6DEC93 BACKFILL EXCAVATION 3JAN94 24SEP93 15OCT93 29OCT93 12NOV93 3DEC93 24DEC93 6JAN94 PtotDale 9AUC93 D*UD«le 1SEF93 Project Surt 1SEP93 Project Finish 6JAN94 (c) Piinuvera Systems, Inc ./PU, Aovny LHtN • 9M I «< PROPOSED L'HENRI INTERIM SOIL REMOVAL ACTION SCHEDULE BAR CHART -----PROJECT SCHEDULE--- Dale Revision Checked Approved TABLE 2