Scraping the Bottom: Dredging for Coal on the Susquehanna

You can’t call the Susquehanna a lazy liver.

Inside 30 miles, just north and south of the Mason and Dixon Line, it fights its way over three big dams, turning out en route enough hydroelectric power for a goodly chunk of the metropolitan East.

Besides that, at the center dam—Holtwood, owned by the Pennsylvania Water & Power Company—the river is also made to supply the fuel for a steam plant. This fuel is coal, and it comes right off the river bottom, courtesy of the currents that wash down through the eastern Pennsylvania coal fields.

At Holtwood, just a few miles north of the Maryland-Pennsylvania boundary, engineers dredge up the coal for fuel to drive the steam plant and harness the river water for the hydroelectric plant at the same time.

This is believed to be the only such combined operation in the world.

Like a giant rain gutter, the Susquehanna has been collecting through the years the coal particles that flow with the breaker waste wash water and sluice off the culm heaps surrounding anthracite mines.

With the building of the Holtwood Dam in 1910 (both Conowingo (1928) and Safe Harbor (1930) dams came later), this steady trickle of coal began to settle on the bottom of the 8-mile-long Lake Aldred. The sand became black with coal particles.

Eventually, it occurred to engineers that perhaps a good fuel source was being overlooked—a systematic survey involved aerial photos and a close study of shorelines, eddies, and flood actions. Test borings and samplings were made of the material in the river bed.

From viewpoints—”stimes”—located every 1,200 feet along the shore, survey crews worked across the flow of water, sampling the bottom every two feet.

From all this, a blueprint was drawn showing where the thickest deposits lay.

Where the swift-flowing water rounded a bend, for instance, a skim of anthracite covered the outside of the curve. Where the currents met the quiet main body of the lake—just above Pinnacle Rocks on the east, or Lancaster County, PA shore—they tended to drop their burden of blackened silt.

In many areas, the bottom was stratified, with a few inches of coal, then sand, in alternating layers due to freshets that followed heavy rains.

The Pennsylvania Water & Power Company erected a steam plant at Holtwood in 1925. At first, it bought coal from an outfit operating in the Pequea region. Later, it began recovering the river coal itself on a large scale.

Engineers borrowed some of their techniques from systems developed by gold miners in the West and invented or perfected the rest of them as they went along.

Two million tons of anthracite have been recovered so far, and since 1937 the steam plant has operated entirely on riverbed gleanings. Burning this fuel creates the steam to turn two steam turbines, increasing the electric output of the Holtwood development by close to 25 percent.

With coal costing more than $8 a ton in the bunker at other regional steam plants, riverbed coal is well worth salvaging at less than $3 a ton.

The process begins several miles above the dam, where a string of dredges—steam, bucket, and clamshell—types go to work in 15 to 50 feet of water.

Great scoops of sand, silt, mud, water, and coal are either hauled or pumped to the surface and heaped in dripping gray mounds on flat wooden barges. There are about 30 barges, most twenty-tonners, but two 500-ton waddlers that take five or six hours to load. The smaller barges are anchored in clumps, looking like a flock of dirty ducklings until the pickup trip comes around.

A pair of steam tugs take turns picking up the barges, twelve or fourteen at a time, lashed securely together. The steamboat threshes its way up the lake, twin paddle wheels at the stern throwing spray in wide arcs, rounds up its flock of barges, and shepherds them downstream to Holtwood.

In rough weather, this task takes seamanship, and the two-or three-man crew has its hands full. On calm days the men relax and watch the beautiful scenery of the steep Susquehanna shores.

Bald eagles inhabit the cliffs, and deer come down to drink.

At Holtwood, the barge fleet sidles gently into the dock, and a hoist equipped with a clamshell bucket moves the silt into a row of gaping bunkers. The gray-black material feeds downward to the “table plant.” Each table, made of wood and steel with a rubber-covered deck and rubber or wood ridges, jiggles horizontally back and forth—like unpredictable fun-house floors—and is washed with a continual surge of water.

The combination of water and agitation floats the lighter coal bits off to one side and the heavier sand to the other side into a drainpipe, where it is flushed away. The oozy coal goes up a conveyer, draining out most of the water and dumping the remainder into a coal car on the siding beneath.

Coal from the finest size of river-bottom silt goes through a unique process. Where the agitation tables would not be equal to the cleaning task, the material passes through an elaborate set-up: a hydraulic concentrator, a set of stainless-steel screens, a thickener, and a conditioner. In the conditioner, fuel oil is added, and pine oil is used as a frothing agent.

The coal particles, it seems, have an affinity for this oil. They cling like Daisy Mae, but the sand—like Li’l Abner—remains aloof. Then, in the final step, the mixture passes through a series of ten Denver cells, revolving paddles like an old-fashioned butter churn, scrape off the scum of coal, and the stubborn sand’s hold is finally broken.

At the far end, in the settling pits, all is black anthracite, and no trace of yellow sand remains. The product of this processing is known as “flotation coal.”

Up comes another clamshell, snatches the settled coal from the pits, transfers it to a coal car, and then the lot is dumped on top of a small mountain of coal already waiting in the storage yard.

Just now, 65,000 tons are in storage, and there will be more before December’s ice shuts down the workings on the lake. Enough must be stockpiled to keep the steam plant going 24 hours a day until the spring thaw permits the resumption of dredging.

Emerging from the cleaning or “table” plant, the coal goes to the preparation plant. Here it is fed to another sky-high row of bunkers, piped through a drying unit and into huge revolving bins containing a railroad carload of steel balls which cascade down on the coal and crush it into a fine dust.

This black powder is piped to the next-door furnaces, where, blazing at fierce heat, it converts water to steam. The steam turns the turbines which turn the generators—which turn out electricity—which turns on anything from your waffle iron to the welder in a shipyard.

Holtwood’s engineers say the Susquehanna is considerably cleaner than it used to be, and less coal per ton of silt is being recovered. Nevertheless, when one of the 500-ton barges docks at the table plant, they figure that up to half of its load is coal.

They predict Lake Aldred’s black gold will not give out for perhaps 25 more years. By that time, Lake Clarke—the lake behind Safe Harbor Dam, 10 miles north—may have its own quota of coal.

Safe Harbor, only opened in 1931, has not been a coal catch-all for very long; however, a lone dredge is already scouring its lake bottom, and, in time, company officials expect to enlarge the Holtwood steam plant and extend the recovery facilities.

In an average year, the steam plant puts out about 180,000,000 kilowatt-hours of electricity from about 181,000 tons of coal.

That is only a couple of dipperfuls in the bucket of Holtwood’s total 640,000,000 kilowatt-hours output. The significant part of the job is hydroelectric—the power of falling water instead of steam.

But then, no other river does two such jobs at once.

Resources

• Scraping the Bottom

Scraping the Bottom is a short pamphlet written in 1948 describing how coal dredged from the bottom of the Susquehanna River was used to produce electricity in a plant built in the Holtwood area. The booklet comes courtesy of Albert Lynch, who donated it from his private collection.

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A Brief History of ‘Black Diamond’ Dredging on the Susquehanna

Between the early 1900s and 1972, numerous coal dredging outfits operated on the lower Susquehanna. During the preceding decades, millions of tons of waste anthracite from coal mines near Wilkes-Barre had washed downriver. The coal eventually settled on the bottom, where dredges began drawing them out in the last years of the nineteenth century. Click here to read more.

Ice Found on the Susquehanna…in August!

Imagine finding a giant chunk of ice nearly five feet long in the Susquehanna. Not hard if it’s February and below freezing. What about August when it’s almost 100 degrees out? David Rankins did it four times in 1926 while dredging for coal. Its discovery revived many of the old mystery tales surrounding the ancient river. Click the link to read more.