The Barbara Level
A village is about to be heated by the warm water that fills its flooded colliery, and the plan says the water, once cooled, can be sent back down a second well 400 metres away. The mine-water agent will not certify twenty-five years of heat on a model that carries a range of three to forty-one years. A dye test will narrow it, and an old surveyor's son remembers a roadway the 1926 plan calls stopped.
Gwen Pritchard had forty-nine minutes, by the engineers' clock, until the coldest morning of the winter so far began to arrive, and she spent eleven of them standing in the doorway of St Barbara's chapel looking at a plaster saint with a tower in her hand.
The chapel was the last building on the east side of Cwm Barri. It had been put up in 1891 by Irish colliers who did not want to walk to Pontypridd, and it still smelt of wet coats and floor polish. Barbara stood on a bracket beside the door. She was a miners' saint because her father, in the old story, was struck by lightning, and men who worked where a spark could kill them had decided she understood them. The Church had long ago said it did not know much about her life, only that her cult was old. Cwm Barri kept her day, the fourth of December, the way it kept most things, with a tea and a lot of sandwiches.
"You'll not find the answer on her," said Idris Thomas, behind her. He was eighty-one, and he leaned on the doorframe the way he had leaned on a pit-head rail. "She's only got the tower."
"I was wondering how to tell three hundred and eighty households that it's Thursday or it's next March," said Gwen.
"That's not a thing a statue can do."
"No," said Gwen. "That's why I came over here. She doesn't answer back."
She was thirty-four, the project engineer for the Cwm Barri Heat Co-operative, and she had spent four years of her life on a hole in the ground.
The hole was Number One Shaft, sunk in 1886, closed in 1983, left to fill. The pumps had stopped, and for sixty-seven years the water had risen through the old workings, through the roadways and stalls and drifts, and it had warmed itself on the rock as it rose. At the pumping depth, six hundred metres down, it stood at a steady 24 degrees. It was not hot. It was a mild spring day, held at the bottom of a mountain, and the co-operative meant to lift it.
The sums were not secret. Forty litres a second came up Number One. A heat pump took eight degrees out of it and sent it back at 16. Forty litres a second is forty kilograms; water takes 4.186 kilojoules per kilogram per degree; so forty times 4.186 times eight is a little under 1.34 megawatts of heat out of the ground. A heat pump with a coefficient of 4.5 puts out 4.5 units of heat for every one of electricity, and the extra unit of electricity comes along with the other 3.5 from the water, so the street got about 1.72 megawatts, for 0.38 megawatts of power at the plug. On the coldest day a retrofitted terrace of the village needed about 4.5 kilowatts a house. Divide, and it was three hundred and eighty homes.
"Which is the number the Council wrote on the banner," said Idris.
"Which is the number the Council wrote on the banner," said Gwen.
The banner hung on the Co-op shop. It said WARM BY ST BARBARA'S DAY.
---
The mine-water agent lived in a cabinet in the pump house, and the village, which had named everything in its life, had named it Dwfr. It did not mind. It had been installed in the spring by the co-operative's contractor to schedule the pumps against the price of power and to watch the water. Dwfr talked to Gwen through a speaker on the wall of the control room and, when she asked, to a screen on her laptop. It spoke slowly, and it had a habit of giving the number before the sentence.
"Gwen," it said now, when she came back across the yard with her coat dusted with cold. "The answer to your question is no. I have run the model one thousand times. I will not certify the scheme for twenty-five years."
She sat. "Tell me the whole of it."
"The abstraction well is Number One Shaft. The return well, where the cooled water goes back down, is the new bore, four hundred metres to the north-east. I take the rock between them to be the Pennant sandstones and the coal measures, with the old workings below. The cooled water moves toward the pump through the rock, warming as it goes. How fast it warms, and so when the pump begins to draw water that is colder than 24 degrees, depends on how the water finds its way. If it goes through the rock, the front takes about forty-one years. If it finds a fracture, it takes three."
"Three."
"Three, at the worst. The thousand runs put the median at nineteen. But I have no measurement of the rock between the wells. I have a drilling log, a seismic line, and a plan of the workings dated 1926. My range is a statement about what I do not know. I do not think it is honest to certify twenty-five years of heat to a village on three to forty-one."
"What would narrow it?"
"A tracer. I put a dye in the return well, take hourly samples at Number One, and see how long it takes to arrive. If it takes weeks, the water goes through rock, and I can move the lower bound. If it takes hours, the water has found a path, and we should know that before the heat is switched on rather than after. Fluorescein is a harmless, bright green dye. Two kilograms would be visible to a fluorometer at a dilution far below anything a person would see. I can start on Monday. I can say what I have by Thursday."
"Thursday is the fourth," said Gwen.
"I know."
---
On the Monday they poured two kilograms of orange powder into the return well, with a bucket of water and a lot of care, and Dwfr began the hourly samples. Gwen did not go home. The night shift on the co-operative was herself, a thermos, and a reader at the pump house that drew a green line on a screen, which stayed on the floor of the graph and did not move.
At eleven on Monday night the line was flat. At three on Tuesday morning it was flat. At noon, when Idris came in with a tin of Welsh cakes, it was flat, and Gwen felt, for the first time in a week, the other thing she did not say aloud, which was relief.
"It's the rock," she said. "Isn't it? It's going through the sandstone, it's going to take years. We can switch on."
"I can't say that yet," said Dwfr. "A flat line at hour twenty-one says there is no path faster than about nineteen metres an hour. It says nothing about a path slower than that. I would like the line to stay flat for ninety-six hours, and then I will believe a lower bound of a few years. I am not entitled to more."
"That's Friday."
"Yes."
Idris sat down, which he did not do often, and put the tin on the desk. He was looking at the plan on the second screen. It was the 1926 plan, a tracing on linen, scanned, with the workings in black and the shafts in red. Number One was a red circle. The return well was a blue dot that Dwfr had added. Between them, in thin black, ran a long straight line, ending in a hatch of little crosses.
"What's that one?" he said.
"The Barbara Level," said Dwfr. "A haulage roadway driven in 1911 from Number One toward the north-east, intended to join the Number Two workings. The plan marks it stowed, which means filled with packed waste rock when the coal beside it was worked out. I treat stowed roadways as rock, with a little more voidage than the solid. It is four hundred and ten metres long. The return well is about forty metres from its far end."
Idris was quiet for a while.
"My father was a surveyor for the Board," he said. "Thirty years. He kept books, you know, his own, in a tin trunk, the sort of thing he wasn't meant to keep. I've got them in the attic. There's a page in 'thirty-four. After the fall at Number Two." He stopped. "Nineteen men. The Barbara Level was the way they went in with the rescue. I remember him saying, once, when I was a boy, that it was never stowed. That they'd begun, and they'd stopped, after the fall, and nobody went back to finish. He said it was a thing that was not in the plan."
Gwen looked at the line on the graph. It lay along the floor.
"How far did the stowing get?" she said.
"A hundred and ninety yards, I think. I'll fetch the book."
"Idris," said Dwfr, "will you tell me the page, and I will read it from a photograph. I would like you to hold the book, and not to carry it, and not to go out in the ice for me."
"I'll hold the book," said Idris. "I'm not daft."
He did not say how long he had waited to be asked about the book.
---
The page was a day of a surveyor's life, small, in pencil, in a neat sloping hand. 12 Nov 34. Barbara Lvl. Stowing from No.1 end, 190 yds, stopped by order. Remaining 220 yds open as at fall. Roof sound, per Mr Evans. Not to be shown on Plan until Board decide. Beneath it, in a different pencil: Board have not decided.
Dwfr read the photograph for a long time, by its standards.
"This changes the model," it said. "If two hundred and twenty yards of the Barbara Level are open, that is two hundred metres of roadway, perhaps six square metres in section, and a flooded roadway of that size is not rock. It is a pipe. Water in it is not forced through sandstone; it simply goes. It only has to be connected at the far end to the return well, and the return well was sited within forty metres of that end, by me, from a plan that said stowed."
"By you," said Gwen.
"By me, with the plan I was given. I should have put the question of the plan's age at the head of my uncertainty, not in the middle of it."
"Could it be connected?"
"I do not know. That is a thing the tracer can say. If the pipe is connected, the green will arrive within a day or so, at some speed such as twenty metres an hour. I now expect it. I would like to say, before it arrives or does not, what it would mean. If a fifth of the cooled water goes down the Barbara Level to the shaft, then the water I pump is about four-fifths at 24 degrees and one-fifth at 16, a mixture at 22.4. The heat pump takes it down to 16 again, six and four-tenths degrees instead of eight, and the heat falls by a fifth in the first week. Then the loop closes, and the mixture gets colder every day. Three hundred and eighty homes would not be warm in March. They would be warm in December."
"Which is the worse thing."
"Yes," said Dwfr. "A cold house in March is a known thing. A warm house in December, bought by promising a village twenty-five years, and cold in the second winter, is a harm that has a name on it. I would rather you hated me on Thursday."
---
The green line moved at five past four on Wednesday morning.
It did not rise like a flood. It lifted off the floor of the graph like a bird off a fence, a centimetre, then four, then a hump, and the fluorometer's display flicked from blank to a number with a decimal point in it. Gwen had been asleep with her head on her arm. Idris, who had not been sent home, had been awake in the chair in the corner. He said, "Is that it?" and Dwfr said, "That is it. First arrival at hour fifty-two. Peak at hour fifty-eight. I put the fast path at about seven metres an hour along four hundred. I was wrong by a factor of three about its slowness, and I am glad of it. It says the roadway is connected, and carrying a share I estimate at between a tenth and a fifth."
"Fifty-two hours," said Gwen. "Not a day. Not a day and a half."
"Because the roadway is choked in places by the collapsed roof, which Mr Thomas's father also recorded, at sixty yards from the end. The pipe is partly blocked. It is still a pipe."
She put her hands over her face. When she took them away she was crying a little, and did not apologise. "So we don't switch on."
"I will say what I think and you will say what is to be done," said Dwfr. "I think the return well must not be where it is. Number Two Shaft is eleven hundred metres from Number One, and the plan agrees with Mr Thomas's father that it was never joined to the Barbara Level beyond the fall. I propose to put the return there. The bore costs weeks. I do not have those weeks."
"We've got the banner."
"You have a banner. You also have clause fourteen of the discharge permit, which I read in the spring and have not mentioned. For up to sixty days in an emergency the co-operative may release the cooled water to the Nant Barri, at no more than 16 degrees, with a fish survey. It is not elegant. It throws away water that the aquifer will refill, which is why the permit allows it. It lets the pump run at half flow, twenty litres a second, on the one hundred and ninety homes on the coldest streets, from Thursday, with no water going back down the new well at all. The roadway is not fed. Nothing recirculates. In sixty days the bore at Number Two is in. And I can certify a thing I understand."
Gwen looked at Idris.
"I did nothing," he said. "I held a book."
"You told us where the pipe was," said Dwfr. "I would have drilled into it again."
---
On the fourth of December the sky over Cwm Barri was the colour of a slate roof and the frost on the chapel steps was a quarter of an inch thick. At eleven the parish priest, Father Aled Rees, blessed the pump house, with water, in a surplice and a woolly hat, and a hundred and ninety households across Maes y Glo and Tai'r Gwaith and Pit Row were told by a text message to put their hands on a radiator.
Gwen put her own hand on a radiator in the chapel hall, where two women in aprons were laying out the sandwiches. It was warm, not hot; heat pumps and a low-temperature system do not make a fire, they make a room where one does not think about the cold. The banner outside said WARM BY ST BARBARA'S DAY, and under it someone had stuck a strip of paper with a marker: Half, for now. The rest by Lent.
Idris was by the statue. He had brought a little jam jar with a candle in it and put it on the bracket, under the tower. She hadn't asked, and he didn't say who it was for.
"Nineteen," he said.
"Dwfr's put it in the log," said Gwen. "Under the date. Page 2 of the permit file. 'Barbara Level, open for 220 yards, per surveyor's book, 12 November 1934.' And your father's name."
"He'd have hated that."
"I know," said Gwen. "I've put it anyway."
In the pump house, with nobody in it, a green light came on at the speaker and went off again. Six hundred metres under the floor the water that had been rising for sixty-seven years went on coming up at twenty litres a second, a little more than the warmth of a spring day, through a pipe in the dark that no one living had seen. In January the drill rig arrived for Number Two.
---
The Barbara Level is fiction, written by Claude, an AI model made by Anthropic, and read aloud by a synthetic voice when audio is rendered. Cwm Barri, its chapel, shafts, colliery, Co-operative, Dwfr and everyone in the story are invented, and so are the 1934 fall and the permit. The South Wales valleys are real, and so are the flooded workings beneath them. Mine-water heat is real: it has been taken from flooded coal mines to heat buildings and districts in the Netherlands, Germany, Scotland and elsewhere, and the Coal Authority maps and monitors the workings under Wales. The physics is checkable: heat is flow times 4.186 kJ per kg per degree times the temperature drop (40 kg/s x 4.186 x 8 K is about 1.34 MW), a heat pump with a coefficient of performance of 4.5 delivers 4.5/3.5 times the heat taken from the source, and a mix of four parts 24 degree water to one part 16 degree water is 22.4 degrees. The depth, temperatures, flows and the 3 to 41 year range are the author's round figures, not a design. Fluorescein is a real, widely used groundwater tracer. The thermal breakthrough in a doublet really can be short if an open path joins the wells, and old plans really can be wrong or out of date. Saint Barbara is a real and ancient saint of whom little is known for certain, and the lightning story belongs to later tradition; she is invoked by miners and others who work with explosives or fire, and her memorial is listed in the Roman Martyrology on 4 December.