III. ALTERNATIVES

A. Alternative A. No Action

This alternative would leave the boreholes blocked and prevent future geophysical measurements, including temperature measurements.

B. Alternative B. Clear Borehole Blockage by Impact

One way to potentially break up an ice blockage is to repeatedly drop a heavy metal rod onto the ice plug. This was attempted during 1993. However, it proved to be ineffective and the alternative is no longer considered reasonable.

C. Alternative C. Mechanical Drilling of Blockage

In principle, it should be possible to clear the ice blockages by mechanically drilling through them. However, additional ice blockages may exist deeper in the holes than those detected during November 1993. Blockages must be cleared for the total depth of the boreholes.

Mechanical drilling would require erecting a derrick and lowering tens of meters of drill pipe down each hole, displacing DFA to the surface where it would need to be recovered. Although a small drill motor potentially could be developed that could be lowered down inside the hole casing to the depth of an ice blockage, there would be no way to extract the drill bit and motor from the hole should the bit become stuck during drilling (a common occurrence when drilling ice). Locating the drill motor on the surface would involve less technical risk. However, the logistics requirements of moving the drill pipe, motor, and the derrick to each site are much greater than necessary to gain the information needed from the temperature profiles. For these reasons, this alternative was not considered to be a viable means to clear the ice blockages in the boreholes.

D. Alternative D. Thermal Drilling to Remove Blockage

To remove the ice blockage, hot propylene glycol would be sprayed on an ice blockage by members of the S-171 science group until the blockage melts and breaks up. The proposed hot glycol delivery system would use components from proven melter technologies modified for use in narrow diameter boreholes. The glycol would be heated on the surface using an Alkota Model 3850 heater which burns JP-8 fuel at a rate of 7.6 to 11.4 liters (2 to 3 gallons) per hour to heat fluid in a set of coils. An electric pump, powered by a 5-kW mogas-driven generator, would than pump the heated glycol down to the blockage in a thick-walled hose at pressures up to 17.6 kilograms per square centimeter (250 pounds per square inch). Pressure would be controlled by the size of the nozzle attached to the end of the hose. The system would operate as an open system with the displaced propylene glycol and DFA being collected through a hose connected to an extension of the borehole casing at the surface and drained to a waste drum (see Attachments 2 and 3).

Because both water and ice are more dense than DFA, the remnants of the ice plug would sink to the bottom of the hole as the melted water refreezes. If deeper blockages exist, the proposed equipment should be adequate to clear ice blockages down to the full depth of the boreholes.

IV. ENVIRONMENTAL EFFECTS AND MITIGATING MEASURES

The environmental effects refer to Alternative D unless otherwise specified.

A. Protection of the Environment Adjacent to the Boreholes During Clearing

The following mitigation measures would be implemented before hot glycol pumping begins:

1. Tarps and petroleum absorbent pads would be placed on the soil or ice surface; and

2. The configuration of the well-head on the borehole would be modified so that all fluid (DFA and propylene glycol) dispaced from the borehole during pumping would go into a 208-liter (55-gallon) collection drum near the borehole.

These measures would contain any chemical spillage, preventing DFA and/or propylene glycol from contaminating the local soil or affecting the ecosystem.

It is estimated that one 208-liter drum of propylene glycol would be sufficient to melt and remove the ice blockages in each of the boreholes. Past experience indicates that approximately 20 to 75 liters of glycol would be required for each borehole. However, it is not known if the ice blockages are uniform throughout the depth of each borehole. There is a possibility that additional fluid would be required to adequately melt all of the ice blockages in each borehole. Additional fluid added would result in a corresponding volume of fluid being displaced and collected in the waste drum. The transportation to the proposed sites and installation of equipment pose no unique or unusual circumstances for operation in the Dry Valleys as supported from McMurdo Station, Antarctica.

B. Modification of the Boreholes

The proposed clearing would alter the contents of each borehole in the following ways:

1. 20 to 75 liters of propylene glycol would be added to the fluid contents of each borehole;

2. The fluid level in each borehole would change; and

3. The ice which is now located high up in each borehole would settle and likely reform at the bottom of each borehole.

The boreholes are cased with steel pipe and are therefore effectively closed systems. Thus, the addition of propylene glycol to a borehole should not affect the ambient environment outside of the borehole. Similarly, changing the fluid level in a borehole should not affect the surrounding environment. As a precaution, the fluid level would be lowered to below the maximum depth of the active layer (that portion of the permafrost which seasonally thaws) upon completion of the clearing operation. There are no foreseen environmental effects associated with transferring the contents of the ice plugs to the bottom of the boreholes.

In addition, the elevations of the top of casings relative to the lake levels would be reviewed. Borehole casings which are at risk of being inundated within several years will be conservatively scheduled for casing extension or other appropriate repairs to prevent the release of DFA and propylene glycol to the environment.

C. Retrieval of Scientific Information

In Alternative A, potentially valuable paleoclimatic information would not be obtainable. In Alternative D, the heated boreholes would have to remain undisturbed for one year before meaningful geophysical measurements could be made. It is assumed that borehole temperatures would readjust with depth from the surrounding strata during an austral summer and winter. By the 1995-1996 field season, the boreholes should have adequately readjusted to ambient temperature profiles such that useful measures could be made. The contents of the closed-system boreholes are not anticipated to interfere with any known scientific investigations planned within the boreholes or within the immediate area of the boreholes.

V. CONSULTATION WITH OTHERS

National Science Foundation/Office of Polar Programs: (703) 306-1030

Mr. Bob Cunningham	NEPA Compliance Manager rcunning@nsf.gov Tel: (703)306-1031
Mr. Peter Karasik	Associate Compliance Manager pkarasik@nsf.gov
Ms. Joyce Jatko	Environmental Officer jjatko@nsf.gov
Dr. Polly Penhale	Manager, Polar Medicine and Biology ppenhale@nsf.gov

Antarctic Support Associates: (303) 790-8606

Mr. Terry Johnson	Environmental Manager johnsote.asa@asa.org
Ms. Vicki Kraus	Environmental Engineer krausvi.asa@asa.org

Polar Ice Coring Office: (907) 474-5585

Mr. Bruce Koci	Senior Engineer
Mr. Dave Giles	Field Engineer

U.S. Geological Survey: (415) 329-5179

Mr. John Kennelly	Engineering Technician
Dr. Gary Clow	S-171 Co-Principal Investigator clow@astmnl.wr.usgs.gov
Dr. Edward Waddington	S-171 Co-Principal Investigator edw@geophys.washington.edu

VI. ATTACHMENTS

1. Map of the McMurdo Dry Valleys

2. Ice Melter Block Diagram