Butyl Acetate (nBA) is a volatile fluid used to prevent the bore hole from collapsing under the weight of the ice cap. It has been chosen as a fluid which best meets several criteria: it does not corrode or contaminate the core, it is relatively safe for humans, it is relatively safe for the environment, and it is relatively inexpensive. It is, however, volatile and flammable, may cause headache and nausea, and has a slight narcotic effect. Care must therefore be used. Butyl acetate is metabolized efficiently in the body and is quickly eliminated. There are no known or suspected long term effects. All personnel working in positions where nBA exposure is possible will wear respirators as a precaution. The concentrations in work areas have not been measured to exceed the 150 ppm long term average exposure levels set by the EPA and are typically < 30 ppm in the drill dome where levels are the highest. Sensitivity to nBA varies from individual to individual, with some being very sensitive. Respirators will be provided and fitted by PICO for anyone who wants/needs one.
The use of butyl acetate as a drilling fluid in 1990 and 1991 was a success and well received by drillers and CPL personnel. It does not appear to pose a significant fire or explosion hazard, it evaporates quickly from the core, appears to cause no significant contamination, and was a reasonable compound to work with from a safety and convenience point of view.
A goal of the pre-CPL storage areas is to provide core which is free of nBA. We came close to this goal in 1990 and 1991. Our experience in the past two seasons indicates that butyl acetate evaporates in minutes to hours from an exposed surface. However, the butyl acetate will remain for several weeks at least, and possibly longer if it gets trapped in the core . There are two main places that nBA will be trapped: between core breaks, if they are fit closely back together, and in fractures which are large enough to allow nBA to enter. The nBA on the core break surfaces may be effectively removed by meticulous wiping by the Core Handlers in the drill dome, and by leaving the breaks separated with as much space as possible while the core is being stored prior to entering the CPL.
The nBA in the fractures is more difficult to deal with. Since the fractures cannot be opened without injuring the core, they cannot be easily exposed to allow evaporation. A solution to this problem has not been developed yet. This was not a significant problem in the 1990 season, or in the core processed in the 1991 season. In 1991 the brittle ice zone was encountered. The highly broken and fractured core from this zone was left to relax over the winter 1991 -1992. The early 1992 CPL personnel will be processing this core, our expectation is that this core will also be predominantly nBA free.
Once cutting begins in the CPL, the ice dust produced from the saws may contain nBA from either core breaks (should be very unlikely) or fractures (more likely). This dust may hold the nBA with the core as pieces move through the trench. Therefore, as cutting proceeds, the ice dust should be removed with brushes. This will help reduce any chances of any residual nBA making it very far in the CPL.
Information about the core is recorded in a combination of the core cards and data sheets located along the CPL. All the information from these sources is collected and entered into a data base by the Data Manager.
There are three main databases:
Core Break Notation
Information about the core is required both in the CPL and afterward to develop effective sampling plans and to assure that sample depths are accurate and comparable for different samples. Of critical importance in the CPL - and afterward - is a knowledge of the depth of the top and bottom of a piece of core, the location, size, and nature of breaks. The notation and pictorial representation below is intended to make recording and reading this type of information as accurate and easy as possible.
For example: If the meter from 456 to 457 is noted with “.62 G .77” it would mean that on that piece of core, there is a gap between 456.62 and 456.77 with clean perpendicular breaks at each end. If one of the ends was diagonal rather than perpendicular, the notation might read; “.57 B .62 G .77” indicating that there is a diagonal break from 456.57 to 456.62 and a gap from 456.62 to 456.77.
Below is an example of the pictorial representation of this information as it might appear on a core card. It describes the piece of core in the above example with additional features. For sections of core with ends that extend beyond the 0.00 or 1.00 marks, either negative numbers (-.01) or numbers greater than 1 (1.02) should be used.
If the core is damaged in such a way that chips, or pieces of core, are produced that cannot continue in the regular CPL, they should be placed in a bag and labeled with the depth range that the chips came from: CBXXX.XX-XX. Again, using the example above, if there was ice from the gap between .62 and .77, it would be put in a bag, and the bag labeled "CB 456.62-.77". The notation would also be written on the core card in the chip bag section. These bags are then placed in ISC boxes and will be available for future use.
The following categories, developed by the physical properties group, should be used to rank the core in the “Drill Dome Quality” and “Stratigraphy Station Quality” sections of the core cards.
Excellent: 0 to 1 core breaks, no fractures.
Very Good: 0 to 2 breaks, 90% or more un-fractured.
Good: 0 to 3 breaks, 50% or more un-fractured. At least one 26-cm long piece without fractures.
Fair: At least one 10-cm long piece without fractures.
Poor: At least one 10-cm long piece with no through-going fractures.
Trash: No 10-cm long pieces without through-going fractures.
Definitions: A break separates the core into distinct pieces; “fractures” occur within a single piece of core; and a “through-going fracture” occupies more than half of the cross-sectional area of the core piece.
Information about Samples
Every non-continuous sample that is taken from the core must be recorded on the core card at the time the sample is removed from the core. This includes all samples except ARC01, CON02, RAM02, ISO04, and TAY03.
This is done by writing the sample type ID (e.g. BEN01, etc.), the actual top depth of the sample, the actual bottom depth of the sample, the date the sample was taken, and any notes that are pertinent on the core card. There is a unique cross section associated with every sample type and this information along with the top and bottom depth of the sample yields complete information about the status of the core and sample distribution. With this information, a sampling plan may be developed that accommodates the many interests in the GISP2 core, that maximizes the scientific return, and does not require a physical, tube by tube inspection.
It is very important that sampling be done according to plan. Samples may be allocated next to each other so that inaccurate sampling may destroy another sample. Changes to the plan can and should be made in the field to respond to varying core quality, evolving scientific strategies, and interesting sections of core, but should only be done after discussion with the Chief Scientist. This provides a mechanism for representing the wide range of interests in the GISP2 core.
Any observations or notes about the core should be written in the notes section on the core card. This section should be used at any point in the CPL as necessary to record pertinent information that is not recorded elsewhere.
DRILL DOME DATABASE
Date, Run number, Run length, Time of core break, (this information is requested from drill operator while core is coming up) Time out of top of hole, Core length measured by Core Handlers, Time down doghouse, Dome temperature, Notes
TUBE TABLE DATABASEFeeder Trench,Freezer In: Date, Time, Tube numbers, Feeder trench temperature, Freezer temperature. Relaxation Trench In: Date, Time, Tube numbers, Relax trench temperature. CPL In: Date, Time, Tube number, CPL temperature, Core wall temperature. ECM: Date, Time, Tube number, Core temperature, Core wall temperature. Packing Table/Storage In: Date, Tube number, Time, Core wall temperature, at packing table. Time in, Temperature in, Storage Trench
Index cards have been used in other projects to mark a section of core that has been removed or other unusual core activity that should be brought to the attention of those further down the CPL. This is a reasonable practice which was incorporated to a degree during the 1990 and 1991 season. It should be used to the extent that it is valuable and worthwhile to those in the CPL.
During the processing of brittle core, index cards and even large pieces of ice in plastic bags will be encountered. These samples should be incorporated into the core that is processed on the CPL. The existence of these samples should be recorded on the core card and the position of these pieces noted carefully so that they can be removed from the Main Core Archive after processing on the CPL.