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Responses to EPA Comments on the Draft Work Plan for Evaluation and Interim Remediation of Soils, O'Henry Laundry, Tutu, St. Thomas, USVI General Comments Comment 1: Cleanup levels will be driven by the VLEACH modeling results rather than by direct soil exposure risk-based calculations, because more stringent cleanup levels will be necessary to assure groundwater protection than to assure human health from soil exposure. However, IT has not provided sufficient supporting evidence for some of the assumptions they elected to use in the model. In particular, documentation for the presumed thickness of the vadose zone (depth to water) must be provided. If the distance from the PCE soil source to water is less than the 20 feet assumed in the model, lower cleanup levels than 328 ppb may be needed to result in concentrations below the federal drinking water standard of 5 parts per billion at the water table. This in turn would result in a larger soil volume to be excavated. Response: Appendix B (VLEACH Modeling) will be augmented to provide additional supporting documentation. Please refer to Specific Comments 2 and 8. We acknowledge that if the actual vadose zone thickness is less than the 20 feet modeled using VLEACH, this will tend to drive cleanup levels to concentrations less than 328 ppb. However, the work plan has been designed so that soils will be removed to concentrations much less than this value (see Section 3.1) which could result in excavation of soil volumes greater than estimated in the draft work plan. The soil volume will be revised to 1575 ft3 in the work plan (refer to Specific Comment 1, below). Please note that all data collected by IT and previous contractors (with the exception of work performed as part of the site wide RI) was transmitted to the EPA on February 22, 1994. Comment 2: The plan admits that excavation may be limited by safety considerations or physical limitations imposed by buildings, not just PCE concentrations. No information is provided concerning structural support of the excavation by way of sheeting, bracing or some other method. As the excavation is immediately adjacent to the laundry facility and the soil is sandy clay loam, acceptable engineering practice and OSHA requirements for open excavations must be followed. Response: This comment is addressed below. Comments 3 and 4. Please refer to Specific TUT 004 23O6 *64540* 64540 Comment 3: Based on the PCE concentrations in soils reported for boring SS1, the area of excavation probably needs to extend south of the boundary shown in Figure 3-1. As shown, the perimeter of the excavation coincides with boring SS1. Response: Figure 3-1 will be revised to show the assumed perimeter of the excavation extending to the south of boring SS1. Specific Comments Comment 1: Section 1.1 - Scope and Objectives, Page 1-1, 1st Paragraph - The 100 ft3 volume of soil that is estimated for removal does not match the volume implied on Figure 3-1 - Soil Excavation and Storage Locations. Based on the area shown on this figure and the approximate 7-foot depth of excavation indicated in Section 3.1 - Soil Excavation and Storage, Page 3-1, the unit should be cubic yards instead of cubic feet. Response: Concur. The volume implied by Section 3.1 and Figure 3-1 is approximately 15 ft by 15 ft by 7 ft or 1575 ft3 (58 cubic yards). This revised volume estimate will be included in Section 1.1, Page 1.1, 1st Paragraph. Comment 2: Section 1.2 - Background, Page 1-1 - In order to adequately evaluate this interim remedy work plan, boring logs for the soil borings (especially SS1) should be included in this work plan to portray soil conditions, groundwater levels and contamination locations. Response: Section 1.2, Page 1-1 will be revised to include a reference to Appendix B. A cross section of the O'Henry site will be included in Appendix B. Refer also to Specific Comment 8. Comment 3: Section 3.1 - Soil Excavation and Storage, Page 3-1, 1st Paragraph - See General Comment 2. Response: A Health and Safety Plan for the soil excavation will be developed and included as an appendix to the work plan. OSHA compliance will be addressed in the Health and Safety Plan. The text of the work plan (Section 3.1, Page 3-1, 1st Paragraph) will be amended to include a statement that the excavation work will be conducted according to OSHA requirements. Also, excavation will be performed according to accepted engineering practices to ensure that the structural integrity of the laundry is not compromised. This will be done without sheet pilings or other structural support for the building and excavation. Costs of these measures have TUT OO4 2307 been evaluated and were found to be prohibitive. Therefore, the dimensions of the excavation will be limited according to OSHA and engineering standards in such a way that structural supports will not be needed. This may result in inability to remove contaminated soil in the immediate vicinity of the foundation. This will be addressed by sampling and analysis of soils near the foundation to be conducted during the removal action. The results will be submitted to the EPA and evaluated to determine whether an in situ remedy is necessary. Samples will be collected for on- site VOC analysis and for VOC analysis (CLP method) at a fixed based laboratory. Comment 4: There is no indication that a Health and Safety Plan will be used during the excavation. Response: A Health and Safety Plan will be developed and will be incorporated into the work plan as Appendix A. The text of the work plan (Section 1.0 - Introduction, Page 1-1, 1st Paragraph and Section 3.1, Page 3-1, 1st paragraph) will be revised to include the Health and Safety Plan by reference. Comment 5: Section 3.1 - Soil Excavation and Storage, Page 3-1, 3rd Paragraph - As the final remedy and remediation schedule for soil removed from the excavation is undetermined at this time, excavated soils could be contained more securely, for example, in roll-off containers. Response: The costs associated with storage of excavated soil in roll-off bins has been evaluated and was determined to be prohibitive due to the uncertain length of storage; likewise, the use of 55-gallon drums was evaluated and decided against due to the potentially large number of drums that might be required. The excavated soil will be stockpiled within an envelope of 4 millimeter plastic sheeting surrounded by a locked security fence. The fenced soil stockpile will be located on private land, which will be posted to prevent trespassing. Comment 6: Section 3.2.2 - Soil Screening Analytical Methods, Page 3-2, 4th and 5th Bullets - As the total number of samples is unknown at this time, the minimum number of analytical duplicates and matrix spikes should be 1 per 20, not a total of 3. [Note - comment refers to Page 3-3, 5th and 6th bullets.] Response: The text as reviewed by EPA states that analytical duplicates and matrix spikes will be analyzed for 1 in 20 samples and that a minimum of 3 samples will be analyzed as analytical duplicates TUT 004 2 Comment 7: and matrix spikes. The text will be revised to state this more clearly. Section 3.5 - Investigation-Derived Waste, Page 3-4 - Although the method for storing decon fluids is indicated, the method for collection is not. This should be identified. Response: Section 3.5 of the work plan will be amended to include a description of the decontamination area. A decontamination area will be constructed by lining an appropriate area with 4-millimeter plastic sheeting. Straw bales will be placed around the perimeter of the area (beneath the sheeting) to contain runoff, which will be collected in a shallow sump. The fluids will be pumped from the sump to 55-gallon DOT-approved drums as described in the work plan. Comment 8: Appendix B, the input printout for the VLEACH model appears to indicate a 20- foot thick vadose zone (0.2-ft/cell X 100 cells) has been modeled. This is probably a reasonable assumption based on the depth to water reported by Geraghty and Miller for upgradient wells in Technical Memorandum II. However, no site-specific information (boring logs or water level elevations) has been provided for the O'Henry property in this work plan to confirm the accuracy of this assumption. In borings B-11, B-12 and B-13, installed by Geraghty and Miller, the top of bedrock is inferred at 3.5 ft, 8.4 ft and 6.4 ft, respectively, so we presume the water table is within bedrock. The geologist's log indicated wet samples at 24 feet during drilling of O'Henry's monitoring well MW-3. However, EPA has never seen monitoring well elevations or water level measurements for this property. As indicated in General Comment 1, more stringent soil cleanup levels will be necessary if the distance from the PCE source to the water table is less than 20 feet. Response: Appendix B will be revised to include a cross section and accompanying text. The cross section will include the area to be excavated, and will show geologic conditions, water level measurements for three periods (August 1990, March 1993 and May 1993) and contaminant concentrations as detected in SS-1. TUT 004 23O9 .,., ."}; .4~GERAGHTY Aa, & MILLER, INC. .4if Environmental Services PROJECT SCHEDULE PRO.ECT: LOCATION: DESCRIPTION: REVISED PHASE II REMEDIAL INVESTIGATION IMPLEMENTATION SCHEDlLE TIJTU WELLS SITE ST. THOMAS, U.S. VIRGIN ISLANDS PROJECT NO. PR0013.038 AUlHORIZA TION NO. LEGEND: GERAGHlY a, MILLER IMPLEMENTATION •••••••• POlENTIAl.l Y RESIPONSIBLE PAAlY RE\IIEW □□□□□□□ USEPA RE\IIEW * MILESTONES LAB ANALYSIS REVISED FIGURE 7-2 SYM RE\1SIONS DAlE SOi'D BY: D. NACHMAN DATE: 3-11-94 CHK'D BY: T. DANAHY DAlE: 3-11-94 APPV'D BY: D. NACHMAN DATE: 3-11-94 llEM NO. 19931 DEC JAN FEB MAR APR 1994 I 1995 MAY JUNE JULY AUG SEPT OCT NOV DEC JAN FEB MAR APR MAY JUNE 11 21 2 I fl 2J JO I 1J 20 27 I 1J 20 'D J 10 17 24 1 I 1122 211 12 fl) 21 3 10 17 2-4 31 7 14 21 21 ♦ 11 11 21 2 I 11 23JO I 13 20 V 4 1111 215 1 I 11 22 ~ I 12 ,. 21 g 12 !!_~2 I 11 23 JO 7 14 21 ♦ 11 11 26 PROPERTY ACCESS PROCUREMENT 2 I EARTH CHANGE PERMIT APPLICATION AND APPROVAL 3 I TASK 1 SITE INSPECTIONS 4 I TASK 2 SITE INSPECTION REPORT 5 I TASK 3 SOIL-GAS SURVEYS 6 I TASK 4 SOIL-GAS SURVEY REPORT 7 I TASK 5 MONITORING WELL AND SUPPLY WELL SURVEYING B I TASK 6 SUPPLY WELL INSPECTION 9 I TASK 7 PUMPAGE IMPACT MONITORING 10 I TASK 8 MONITORING WELL INSTALLATION AND STORM SEWER INVESTIGATION 11 I TASK 9 WATER-LEVEL MEASUREMENTS 12 I TASK 10 COMPREHENSIVE GROUNDWATER SAMPLING EVENT 13 I TASK 11 DATA VALIDATION 14 I TASK 12 MONTHLY REPORTS 15 I TASK 13 DRAFT RI REPORT 16 I TASK 14 FINAL RI REPORT 17 I TASK 15 ANALYSIS OF REMEDIAL ALTERNATIVES 18 I TASK 16 DRAFT FEASIBILITY STUDY EXPLANATION B:TU-311 PROJECTED SCHEDULE AS INCORPORATED MARCH 9, 1994 ORIGINAL SCHEDULE IN PHASE II REMEDIAL INVESTIGATION WORK PLAN LAB ANAL-.iis 1 •.•. _ .•. _.@._._._._._1 I:::- -- C iii D 11. :>:.:: .... /: .. :.::::::: ❖ !.i•: H (. ff flt n ~~s : .~,;: 1:.:.,/·.·.··· I I I* f ff '~Th 11 ltl 11 ~ 11 ~ 11 1+1 11 ~ 11111111111111 ' ' ' ' ' ' ' ' ' ' ' ' ' ' ~ It •. ,m¢:icjJcjc ASSUMPTIONS: 1. CONDENSED DRILLING (TASK B) FROM 12 WEEKS TO 9 1/2 WEEKS FOR 13 WELLS. 2. TASK 10 ASSUMES 2 WEEK TURNAROUND OF LAB DATA (INSTEAD OF 4 WEEKS). _:;:~;: ... _.,:_:_:,. -=~::::::;~,:-:-:-·-· --~- -~=:=:.-:·::,:;:: ··:;:xs· ·~