Letter regarding Abandonment of Monitoring Well MW-6, Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands
./ •-" & MILLER, INC. Environmental Services Ground Water Engineering Hydrocarbon Remediation Education September 1, 1992 Caroline Kwan U.S. Environmental Protection Agency 26 Federal Plaza, Room 737 New York, New York 10278 Re: Abandonment of Monitoring Well MW-6 Tutu Service Station Investigation St. Thomas, U.S. Virgin Islands Dear Ms. Kwan: As you know, Monitoring Well MW-6 was installed after incurring difficult drilling conditions in the 65-foot deep corehole at this location. (Please note the total depth was previously incorrectly stated to be 70 feet.) The coring was completed on July 23, 1992. This 3-inch diameter corehole was intended to preceed the reaming and installation of Monitoring Well MW-6D. However, as the corehole was being reamed to a diameter of 10 inches, formational collapse occurred. Collapsed rock and soil filled the 10-inch diameter hole from approximately 25 to 35 feet below grade. In order to minimize re-drilling efforts, the field crew decided to set the shallow Monitoring Well MW-6 in the remaining drill hole rather than abandon the hole. …
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./ •-" & MILLER, INC. Environmental Services Ground Water Engineering Hydrocarbon Remediation Education September 1, 1992 Caroline Kwan U.S. Environmental Protection Agency 26 Federal Plaza, Room 737 New York, New York 10278 Re: Abandonment of Monitoring Well MW-6 Tutu Service Station Investigation St. Thomas, U.S. Virgin Islands Dear Ms. Kwan: As you know, Monitoring Well MW-6 was installed after incurring difficult drilling conditions in the 65-foot deep corehole at this location. (Please note the total depth was previously incorrectly stated to be 70 feet.) The coring was completed on July 23, 1992. This 3-inch diameter corehole was intended to preceed the reaming and installation of Monitoring Well MW-6D. However, as the corehole was being reamed to a diameter of 10 inches, formational collapse occurred. Collapsed rock and soil filled the 10-inch diameter hole from approximately 25 to 35 feet below grade. In order to minimize re-drilling efforts, the field crew decided to set the shallow Monitoring Well MW-6 in the remaining drill hole rather than abandon the hole. Monitoring Well MW-6 consists of a flush-mounted 4-inch diameter stainless steel casing and screen. The screened interval is from 4 to 24 feet below grade. As was agreed in a conference call between Caroline Kwan, USEPA; Sally Odland, CDM Federal Programs; and Thomas V. Danahy, Geraghty & Miller, Inc.; Monitoring MW-6 TUT OO6 1741 201 West Passaic Street, 3rd Floor• Rochelle Park, New Jersey 07662-(201) 909-0700-FAX (201) 909-0567/0568 ^b 3 *64880* 64880 GERAGHTY & MILLER, INC. will be abandoned because the unsealed 65-foot deep corehole may result in anomalous water- level or water-quality data. The well abandonment and sealing procedures are outlined below. The borehole will be reamed to the original depth using air-rotary and/or wash-rotary techniques. Initially, the drill crew will attempt to remove the 4-inch diameter stainless steel casing. If unsuccessful, the casing and screen will be left in place and the bottom of the 4-inch well will be drilled through to minimize further collapse of the formation. A 3-inch diameter rotary bit will be extended to 65 feet. Potable water will be used to cool the bit and remove cuttings. If necessary, bentonite mud may be used to remove cuttings from the hole. Upon reaching 65 feet, the corehole will be tremie-grouted to the surface by placing a bentonite- cement grout using the drill string or a tremie pipe. After grouting, the stainless steel casing will be cut-off at least 5 feet below grade (if it is not entirely removed). Clean backfill material will be placed in the upper 5 feet of the hole and the paving will be restored. If you have any questions, please Sincerely, GERAGHTY & MILLER, INC. Thomas V. Danahy a Senior Scientist/Project Manager Daniel A. Nachman Vice President/Project Director c: Ana Gloria Ramos, TEIC Sally Odland, COM Federal Programs TVD:cmw PR01301-wp3/082592a.ltr TUT 006 1742