'GERAGHTY
<S? MILLER, INC.
Environmental Services
Ground Water 
Engineering 
Hydrocarbon 
Remediation 
Education
August 26, 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 drillii*
conditions in the 70-foot deep corehole at this location. The coring was completed on My 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 fwt
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.
CO
As was agreed in a conference call between Caroline Kwan, USEPA; Sally Odtend,
CDM Federal Programs; and Thomas V. Danahy, Geraghty & Miller, Inc.; Monitoring MW-6
will be abandoned because the unsealed 70-foot deep corehole may result in anomalous water- 
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level or water-quality data. The well abandonment and sealing procedures are outlined below. 
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201 Vfe&t Passaic Street, 3rd Floor • Roctoelle Pkrk, New lensey 07662 • (201) 909-0700 • FAX (201) 909-0567/OS«
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GERAGHTY & MILLER, INC.
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 Hie 4-incfc
well will be drilled through to minimize further collapse of the formation. A 3-inch diameter
rotary bit will be extended to 70 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, Upoa
reaching 70 feet, the corehole will be tremie-grouted to the surface by placing a bentoni*-
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
win be placed in the upper 5 feet of the hole and the paving will be restored.
If you have any questions, please call.
c: 
Ana Gloria Ramos, TEIC
Sally Odland, CDM Federal Programs
Sincerely,
GERAGHTY & MILLER, INC.
Thomas V. Danahy
Senior Scientist/Project Manager
Daniel A. Nachman 
j
Vice President/Project Director
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