The list of 37 companies named by the Department of Energy today as grant recipients in the federal government’s first-ever ARPA-E competition contained many local companies, but was topped by a name that virtually no one has heard: Foro Energy

The Littleton, CO, startup is developing a “hybrid thermal/mechanical drilling technology” that could make it much easier to tap the geothermal heat coursing through the layers of deep, hard, crystalline rock that geologists call “basement” rock, according to a Department of Energy summary. To help perfect the drilling technique, which the department said “could open up cost effective access to…a potentially huge new source of domestically available, carbon-free baseload power,” Foro will receive the largest grant of any ARPA-E winner—$9,151,300, to be exact.

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It was the only grant awarded to a geothermal energy company under the ARPA-E program, which stands for Advanced Research Projects-Energy. Foro was in deep stealth mode prior to the Energy Department’s announcement—not a word about the company’s drilling technology has leaked into the media. But Xconomy has learned that Foro was incubated in Cambridge, MA, and has raised roughly $12.5 million in venture funding from Waltham, MA-based North Bridge Venture Partners and CMEA Capital of San Francisco. The company’s president is Joel Moxley, a former entrepreneur-in-residence at North Bridge.

The information comes from an e-mail that Moxley sent today in response to congratulatory notes about the ARPA-E grant. The note, a copy of which was obtained by Xconomy, lists North Bridge and CMEA as Foro’s funders, and says that the Department of Energy grant brings the startup’s total funding to $22 million—implying that the venture firms’ contribution comes to somewhere between $12.5 and $13 million.

“We take our commitments to our funding partners North Bridge, CMEA, and likely now the DOE extremely seriously,” Moxley wrote in the e-mail. “Although we are excited about the significant progress made to date, we continue to focus on ruthless execution to achieve our next milestones to ensure that our now $22M in total funding will dramatically impact U.S. energy security over the coming years.”

Beyond this note—which also quoted Winston Churchill’s famous lines, “Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning”—Moxley has not commented publicly on Foro Energy or the technology it is developing. Reading between the lines, however, it’s possible to form a general picture of the company’s goals.

Geothermal energy is already in important source of energy in a few regions near the edges of the planet’s tectonic plates, where magma melted by radioactive decay deep within the Earth brings heat closest to the surface. But in other areas, drilling wells deep enough to reach these heated layers is a vexing technological challenge. Such wells often need to be several miles deep, and need to penetrate through soft sedimentary layers atop the Earth’s crust into harder, crystalline rock layers that quickly dull or destroy drill bits.

Foro Energy is evidently working on technology that uses thermal energy to soften crystalline rock so that drill bits can penetrate it with less wear. Exactly what methods Foro is using to deliver this thermal energy is unclear, but based on thermal drilling techniques tried by others, its system could include technologies such as electrical heaters; pressurized liquid, gas, or steam; or even lasers.

Cambridge-based Greatpoint Ventures is also one of Foro’s funders, although the extent of its involvement is not clear. A PowerPoint presentation from Greatpoint Energy lists Foro as another GreatPoint Ventures portfolio company, but incorrectly locates the startup outside Chicago.

The connection between North Bridge Venture Partners and Foro Energy has actually been a matter of public record for some time, but no observer (including this reporter) put the necessary pieces together. Massachusetts registration papers filed for the company in December, 2008, list Carmichael Roberts as one of its directors. Roberts is a general partner at North Bridge. Roberts couldn’t immediately be reached for comment.