Mapping of contaminants in geologic formations
View Patent ↗An apparatus and method for evaluating chemicals of interest in a subsurface bore hole, such as a groundwater sampling well. An absorbent member is attached to a flexible liner, and the liner is everted by fluid pressure down the borehole. The everted liner presses the absorbent member against the wall of the borehole. Any chemicals of interest are absorbed into the absorbent member from the media surrounding the borehole. The liner, with associated absorbent member thereon, is then extracted from the borehole. The absorbent member may then be subjected to any suitable laboratory analysis to evaluate the type, spatial distribution, and concentration of chemicals of interest, such as water contaminants occurring in the borehole.
1. An apparatus for evaluating underground contamination, the apparatus disposable in a borehole having a borehole wall, the apparatus comprising:
a flexible first liner, defining a tube with a closed end, disposable by eversion in the borehole;
a retrieval cable, attached to the closed end inside the tube, for retracting the liner from the borehole by inversion; and
an absorbent member disposed upon the liner, the absorbent member comprising:
an outer layer, comprising a flexible material of low permeability to water, for preventing immediate saturation of an absorbent material by ambient water residing in the borehole;
the absorbent material disposed between the liner and the outer layer; wherein when the apparatus is at least partially everted in the borehole, at least a portion of the liner is urged toward the borehole wall by a fluid pressure inside said liner, and at least a portion of the absorbent member is pressed against the borehole wall by the portion of the liner, whereby any contaminants at the borehole wall are at least partially absorbed by the absorbent material; and
a diffusion barrier, comprising a thin metal film, disposed between the liner and the absorbent material.
2. An apparatus according to claim 1 wherein the liner comprises a flexible plastic liner.
3. An apparatus according to claim 1 wherein the thin metal film comprises aluminum.
4. An apparatus according to claim 1 wherein the outer layer is hydrophobic.
5. An apparatus according to claim 1 wherein the outer layer comprises perforated polyethylene felt.
6. An apparatus according to claim 1 wherein the absorbent material comprises activated carbon felt.
7. An apparatus according to claim 1 wherein the absorbent material comprises a composition selected from the group consisting of cotton felt, polypropylene fibers, and granular carbon in a supporting gel.
8. An apparatus according to claim 1 wherein the diffusion barrier further comprises a thin film of MYLAR biaxially-oriented polyethylene terephthalate.
9. An apparatus according to claim 1 wherein the diffusion barrier comprises a laminate of the thin metal film and a plastic substrate.
10. An apparatus according to claim 1 wherein the absorbent member is detachable from the liner.
11. An apparatus according to claim 1 wherein the at least one absorbent member extends continuously substantially the length of the liner.
12. An apparatus according to claim 1 comprising a plurality of discrete absorbent members disposed at separate locations along the length of the liner.
13. An apparatus according to claim 1 comprising a plurality of at least two absorbent members extending continuously substantially the length of the liner.
14. An apparatus according to claim a 1 wherein the diffusion barrier substantially completely surrounds circumferentially the liner.
15. An apparatus according to claim 14 wherein the complete absorbent member substantially completely surrounds circumferentially the liner.
16. An apparatus according to claim 1 wherein the absorbent member is segmented to define gaps between segments, and wherein segments of the absorbent member are overlapped so to position portions of the diffusion barrier within the gaps to prevent migration of contaminants between segments.
17. An apparatus according to claim 1 further comprising a second liner disposed into the borehole alongside the first liner.
18. An apparatus for evaluating underground contamination, the apparatus disposable in a borehole having a borehole wall, the apparatus comprising:
a flexible liner disposable in the borehole by eversion, the liner comprising a long tube with a closed end;
a retrieval cable, attached to the closed end inside the long tube, for retracting the liner from the borehole by inversion; and
at least one absorbent member removably attached to the liner, the absorbent member comprising:
an outer layer, comprising a flexible material of low permeability to water for preventing immediate saturation of an absorbent material by any ambient water residing in the borehole while the liner is being everted down the borehole;
the absorbent material, disposed between the liner and the outer layer, for absorbing any contaminants occurring at the borehole wall; and
a diffusion barrier, comprising a thin metal film, disposed between the liner and the absorbent material for substantially preventing chemical transport by diffusion from the liner into the absorbent material;
wherein the at least one absorbent member is carried by the liner when the liner is disposed by eversion down the borehole.
19. An apparatus according to claim 18 wherein the outer layer comprises a tightly woven fabric.
20. An apparatus according to claim 18 wherein the outer layer comprises polyethylene felt.
21. An apparatus according to claim 18 wherein the outer layer is hydrophobic.
22. An apparatus according to claim 18 wherein the absorbent material comprises activated carbon felt.
23. An apparatus according to claim 18 wherein the absorbent material comprises a composition selected from the group consisting of cotton felt, polypropylene fibers, and granular carbon in a supporting gel.
24. An apparatus according to claim 18 wherein the diffusion barrier comprises a laminate of thin metal film and plastic substrate.
25. An apparatus according to claim 24 wherein the thin metal film comprises aluminum.