The Silver Spring Transit Center is plagued by design, construction and management failures, some of which were known as early as 2010, the Montgomery County Inspector General’s Office reported Tuesday.

The 64-page document adds to a burgeoning library of research on the $120 million bus and train hub that was originally supposed to open in mid-2011.

Yet another construction consulting firm, Alpha Corporation, was hired, this time to assist Inspector General Edward Blansitt with the highly technical subject matter. While the final product is a little late and yields nothing brand new, it draws together the other volumes of data.

The report also provides a new platform from which County Executive Isiah Leggett’s challengers in next month’s Democratic primary, County Council member Phil Andrews and former county executive Doug Duncan, are likely to continue to attack the mishandling of the project.

The inspector general’s report illustrates how the transit center, envisioned as a key component in downtown Silver Spring’s rebirth, was plagued from the start: by unexpected underground obstacles at the site; questionable oversight of cement quality; pouring and hardening of concrete in winter temperatures below established limits, and structural steel supports that never made it into certain segments of roadway.

Overall, Alpha reported, 11 key controls that should be a part of every big construction project showed evidence of deficiency in design, implementation or effectiveness.

The study also revisits the months of fingerpointing and delay between the time a county inspector raised initial concerns about potential cracking (2010) and the decision to hire KCE Structural Engineers for a top-to-bottom forensic analysis of the structure (2012), after construction was 95 percent complete.

The inspector general said some problems might have been avoided had the county Department of General Services (DGS), the lead agency on the project, hired an independent, third-party construction manager at the outset to oversee the work. DGS retained Parsons Brinckerhoff, the engineering firm that designed the building.

Plans are underway for repairs to roadways and concrete beams and girders, work expected to push the eventual opening of the facility into 2015.

The back of the report includes four pages of responses from Montgomery Chief Administrative Officer Timothy Firestine. He agreed with the inspector general’s recommendation for independent construction management. His main message, however, repeated in several variations, is that the main contractors (Foulger-Pratt and Parsons Brinckerhoff, Robert Balter) and their subcontractors are responsible for the mess.

Firestine said they will be held accountable.