Recharging history

Posted on October 1st, 2009 by Water Nymph in Phil Says

RechargeWe at Rainwater are working on our third major project designing groundwater recharge systems below buildings to mitigatethe deterioration of wood pile foundations.

One building we’re working under is irreplaceable; a 250-year-old building where foundations, if left unchecked, would deteriorate to a perilous state. It’s not the fault of the nineteenth century engineers. They knew that wood in water doesn’t rot—the water keeps out the air, bugs, and fungus that cause wood to decay. They drove the wood piles (essentially hardwood trees that had all the branches trimmed off, were turned upside down, and driven into the ground) to below the natural groundwater level, pumped the water back in, and thought they’d created foundations to last eternity.

The problems started when more city construction came in—infrastructure such as deep storm sewers, subway tunnels and the like—and despite best efforts, made an unintended but undeniable path for water to drain away, leading to lowering of groundwater levels below structures with wood pile foundations and exposing these foundation elements to air—and the natural wood predators that come with those moist environments. These groundwater leaks have enormous financial repercussions. For example, the recently completed, $7-billion state-of-the-art Deer Island sewage treatment plant in Boston actually processes an enormous amount of clean groundwater that leaks into sanitary and combined sewers on the way to the plant—some estimates put the infiltration of groundwater at approximately 1/3 of the approximately 300 million gallons of water flowing to the plant, per day, where it is subject to advanced and costly water quality treatment before being discharged into the Massachusetts Bay. Beyond the unfortunate cost of the treatment of this normally clean groundwater, the consequential damage associated with these leaks are the deterioration of wood pile foundations under some of Boston’s most cherished historic structures. The cost of repairing or mitigating this problem is almost incalculable— so the work of stemming the problem has become very serious indeed.

But what about our beautiful 250-year-old building and its foundation? Once the water’s gone, so goes the protection from rot.

For the parts of the pilings that are no longer strong enough to do the work of holding up the building, they can use underpinning and replace the rotted part with a splice of concrete or metal.

But once that’s done, steps must be taken to prevent the other pilings from rotting. That’s where we come in, bringing up the water, restoring the ground water level under the building to where it was when it was built, recharging it with rainwater when possible from the building’s roof and other nearby catchment areas. That could add up to a savings of millions of gallons a year of fresh drinking water. Smart clients look to Rainwater Recovery, to show them how to use their roof water as the initial source.

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