G-Sump

The G-Sump is a filtration chamber situated at the base of Annex G, occupying the whole of the sub-basement designated G-0 and extending a further eleven metres below the lowest surveyed course of the annex's east wall. It exists to capture page-dust: the fine, pale, mildly alkaline residue shed continuously by the bindings, fore-edges and shelving of the upper annexes. The G-Sump is not a place where water is kept, a point of persistent confusion in the visitor's guides, and the small brass notice at the head of the descent stair states it plainly: This is not a well. Do not lower a bucket. The notice is reproduced from the original of Year 288 and has been renewed four times.

Construction and fabric

The chamber is circular, twenty-three metres across at the rim, narrowing to a bowl of seven metres at the collecting floor. Its walls are of unglazed pressed brick to a height of four metres, above which the fabric changes to the pale riveted panels customary in the lower annexes. The collecting floor is slightly dished and perforated at its centre by a grate of Annex G's own manufacture, beneath which the settled dust is drawn off in linen sacks at intervals set by the Librarians and, in practice, by the weather.

Access is by the descent stair from G-1, or by the maintenance gallery that runs beneath Annex Δ and joins the chamber at its western quarter. The gallery is unlit, low, and carries no handrail. It is the shorter route and is discouraged, though nothing in writing forbids it.

Operation and the dust harvest

Dustfall arrives at the G-Sump by three routes: settling through the annex's ventilation shafts, washing down the drainage channels after a cleaning of the upper galleries, and — in the view of the Sump's own keepers — arriving of its own accord. The chamber's function is to hold this material until it can be classified, and the classification is the labour for which the G-Sump is chiefly known. Settled page-dust is sifted into four grades, of which the third is the most variable and the fourth is not used.

The harvested dust is not discarded. Coarse first-grade material is pressed into brick for the repair of annex walls; second-grade is returned to the Gutterwell store for packing; third-grade is held indefinitely pending a ruling. A body of opinion among the keepers holds that the third grade is mostly the first grade with a long journey behind it, and a smaller body holds the reverse.

The G-Sump is staffed by a keeper and two assistants, a complement unchanged since Year 301. The present keeper, Warden Sable Orr, has held the post since Year 344 and has twice declined promotion. Her standing grievance concerns the descent stair, which is swept by the annex's cleaners on the third day of each month and which she maintains should be swept by the G-Sump's own staff, on the grounds that the dust on the stair belongs to her chamber and is being removed before it can be counted.

The relationship to the wider sump network

The G-Sump should not be confused with the larger hydraulic and conceptual works with which its name shares a syllable. It is not connected by any channel to the Oblivion Sump on Floor 5017, nor does it feed the Aorta of Thirst at the Sump of First Want on Floor 712, although a persistent error in the older floor-lists places it in that drainage. The confusion is partly the fault of the G-Sump's own seal, which depicts a descending stream, and partly the fault of the Fifth Spiral Watercourse, whose first surveyors included the chamber in an appendix of "associated falling waters" and then omitted the footnote that would have explained why.

Its nearest kin in function are the Sump-Gargoyle network and the Filtration Mask Grade Ii, both of which address airborne dust before it reaches a chamber of this kind. The G-Sump is what those devices are for; it receives what they miss. It is the last place in the annex at which page-dust is still dust and not yet a category of thing.

Dispute of record: the Second and Fifth Concordances

Two rulings govern the G-Sump and they do not agree. The Fifth Concordance, Annex 9, provides that "material captured in any sump of the G-class shall be assessed in the sump that captured it, and shall not be removed for assessment elsewhere, nor retained uncounted past the third settling."

The Third Concordance, Annex 11, provides, in language equally firm, that "nothing captured below the course of a wall shall be assessed above it," which the keepers of the G-Sump have always read as requiring that the chamber's dust be carried up to G-1 for counting. The two annexes have stood unreconciled since Year 271. The effect is that the G-Sump's third-grade dust is held uncounted in the chamber, which satisfies the Fifth and offends the Third, and is carried up to G-1 only when an inspector of the older school is expected, which offends the Fifth and satisfies the Third. Warden Orr has described the arrangement, in her annual return for Year 356, as "a compromise of long standing and no great harm."

"The chamber does not care which annex prevails. The dust settles either way. It is only the counting that moves."

— Warden Sable Orr, annual return, Year 356

Incidents

The chamber has flooded twice: once in the winter of Year 281, when the gallery beneath Annex Δ took seepage from an unattended cistern and carried it into the bowl, and once in Year 309, from causes the record describes only as "a fault above." The first flooding is remembered for the loss of eleven sacks of uncounted third-grade dust and the second is not remembered at all, which the keepers consider the greater insult.

In Year 331 a junior assistant, Tamsin Well, spent a season compiling a register of the G-Sump's contents by probable origin, tracing settled dust to the bindings it had left. The register ran to four hundred folios and was judged, on review, to be a work of history rather than filtration, and was transferred to the Sump of Withdrawn Premises, where the Bureau of Counterfactual Integrity maintains its secondary registry. Well did not appeal. Copies of her register are still consulted by keepers of the G-Sump, who find it useful and say so carefully.

The chamber is inspected on the first of the month by a Librarian of the annex, who signs the rim ledger and is not required to descend further than the fourth landing.