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^^TGERAGHTY '& MILLER, INC. nvironmental Services Ground Water Engineering Hydrocarbon Remediation Education September 11, 1991 Ms. Caroline Kwan Environmental Engineer U.S. Environmental Protection Agency Region II 26 Federal Plaza, Rm 737 New York, New York 10278 RE: Response to Draft Comments by USEPA on Tutu Service Station Investigation Workplan Dear Ms. Kwan: On behalf of the Tutu Environmental Investigation Committee (TEIC), Geraghty & Miller, Inc. has prepared this draft response to the incomplete and draft comments on the above- referenced workplan received from the U.S. Environmental Protection Agency (USEPA) on July 15, 1991. Most of the USEPA comments were relatively minor procedural issues and can be incorporated with little additional effort. If the USEPA is in agreement, these revisions will be included in the workplan and the revised workplan will be distributed. Geraghty & Miller would like to propose that the wastewater generated during field activities (i.e., development water, purged water, pump test water) be screened in the field using a field gas chromatograph (GC). The water will be temporarily stored in 55-gallon drums or larger storage tanks until the GC results are available for determination of the proper disposal methods. If field GC headspace readings indicate that concentrations equal to or greater than 50 parts per billion (ppb) are present, Geraghty & Miller proposes that this wastewater be disposed of at the wastewater treatment facility in Nadir. If concentrations less than 50 ppb are present, Geraghty & Miller has proposed that this water be disposed in the Turpentine Run. 201 West Passaic Street, 3rd Floor• Rochelle Park, New Jersey 07662-(201) 909-0700-FAX (201) 909-0567/0568 . ....... ............... ..-....,.„,-.,,.,...,.,„..-.-. ...._..........,......__,„,.,...,. ..... .. ....,.,.........„..,.,,_„..-...- .-.....-....,..„.,. TUT OO6 1906 *64920* 64920 GERAGHTY & MILLER, INC. GENERAL COMMENT #1 In response to the USEPA comment regarding well intake intervals that may straddle the bedrock/overburden boundary, Geraghty & Miller agrees that these wells should be completed with well screens. If at all possible, wells that straddle the bedrock overburden boundary will be avoided. Wells screened across bedrock/overburden boundaries may give misleading water- level readings. However, if the water table does seem to occur or fluctuate in this interval wells will be installed to check for floating product. SPECIFIC COMMENTS Comment #1 The Esso Tutu service station is only open for gasoline sale at the present time. Since 1989, no mechanical repairs have been conducted at the Esso station. Comment #2 Not provided by USEPA. Comment #3 Air monitoring during the investigation will consist of HNu readings and if necessary OVA readings. Occasional air samples will be collected for field GC analysis. Comment #4 A statement will be included that additional well installations (Phase II) may be proposed in a technical memorandum to the USEPA, depending upon the results of the initial investigation. TUT OO6 19O7 GERAGHTY & MILLER, INC. 4 treatment facility. Wastewater with concentrations less than 50 ppb will be discharged onsite to the Turpentine Run or nearest storm sewer. Geraghty & Miller has begun preliminary discussions with the U.S. Virgin Islands, Department of Public Works (DPW) regarding the potential disposal of wastewater at the wastewater treatment facility in Nadir. If acceptable to the DPW, the proposed disposal method would be the most implementable alternative due to time-consuming requirements associated with potential permitting of other alternatives (i.e., air stripping or surface discharge after treatment). Comment #9 The word "logs" will be replaced with "logging". Sonic and caliper logs will be run prior to casing installation. Comment #10 Not provided by USEPA. Comment #11 Top of bedrock structure contour maps will be prepared based upon the available information generated during the investigation. Geraghty & Miller believes that enough information regarding the top of bedrock will be available including bedrock outcrops subsurface boring logs, and existing production well logs. Comment #12 The project management structure has been clarified and project organization chart has been revised accordingly. Any communications between the USEPA (or the USEPA oversight subcontractor) should be routed through the TEIC designated coordinator, Ana Gloria Ramos. TUT OO6 1908 GERAGHTY & MILLER, INC. 5 Comment #13 Not provided by USEPA. Comment #14 The correct number of wells is seventeen. The workplan will be changed to reflect this. Comment #15 The CLP Statement of Work (SOW) will be updated to the most recent March 1990 (3/90) version. Vinyl acetate will be removed from the list of VOCs. Comment The 3/90 SOW will be referenced. Comment #17 The size of the sampling containers will be specified. Comment #18 Deep wells 6D, 11D, 12D, and 13D will be included in the list of wells to be cored. Comment #19 See response to Comment #5. TUT 006 GERAGHTY & MILLER, INC. 6 Comment #20 See response to Comment #8. Comment #21 See response to Comment #9. Comment #22 See response to Comment #8. Comment #23 See response to Comment #14. Comment #24 See response to Comment #8. Comment #25 Geraghty & Miller takes issue with the need for replicate soil samples. Soil quality, unlike ground-water quality, is very heterogeneous and replicate analyses are likely to give different results. Ground-water replicate samples are useful for assessing laboratory and sampling variability. However, replicate samples of soil will not yield any useful information regarding these factors; instead, the results will likely indicate the heterogeneity inherent with soil quality. However, if required by the USEPA, Geraghty & Miller proposes that blind soil replicate samples be collected for 5 percent of soil samples. TUT 006 191O GERAGHTY & MILLER, INC. Comment #26 This comment indicates that the USEPA will be performing the risk assessment. However, it is not clear whether the risk assessment will be performed during the investigation or during the subsequent feasibility study. The risk assessment must be completed before beginning the feasibility study. HEALTH & SAFETY PLAN COMMENTS Geraghty & Miller agrees with and will incorporate the comments on the Health & Safety Plan numbered HI through H6. In response to Comment H5 the procedures for equipment decontamination will be included in the Health & Safety Plan. These procedures will be revised to comply with the USEPA-Region II CERCLA QA Manual, Revision 1, dated October 1989. We hope this draft response addresses your comments. If you have any questions or comments, please contact us. Upon USEPA approval of these revisions, the workplan will be revised and distributed in final form. Sincerely, GERAGHTY & MILLER, INC. ^tK^^^k^y^ Thomas V. Danahy (/ Senior Hydrpgeologist/Project Manager Daniel A. Nachman Vice President/Project Officer TVDrgv #PR01301/082791.1et TUT OO6 19.11 GERAGHTY & MILLER, INC. Comment #5 The monitoring wells will be installed to document if the water table fluctuates between the unconsolidated materials and consolidated rock. Initially, wells will be installed straddling the observed water table during the initial investigation. If the water table rises above the screened interval, additional shallow wells may be necessary. Due to the thin unconsolidated deposits, shallow wells in the unconsolidated unit may require screen lengths less than 20 feet. Due to seasonal water-table fluctuations of approximately 20 feet, it may not be feasible to have monitoring well screens intersecting the water table at all locations during the entire year. Critical areas (i.e., where the potential for floating product exists) will be selected for additional well installation (if necessary), based upon the ground-water level measurements. Comment #6 Two pump tests will be performed. This will consist of one pump test at one well location and another pump test at a different well location. The wells will be selected after evaluation of initial water quality results. Comment #7 Geraghty & Miller agrees that reducing the list of sample parameters is a potential modification. Comment #8 Wastewater disposal methods will consist of either disposal offsite at the wastewater treatment facility in Nadir or disposal onsite of waters containing concentrations less than 50 ppb of total VOCs based upon field GC headspace analyses. Wastewater will be temporarily stored in 55-gallon drums or tanks onsite until field GC analyses are available. Wastewater with headspace readings equal to or greater than 50 ppb will be disposed of offsite at the wastewater TUT OO6 1912