A brief explanation:
In the late 30's (as lend-lease was getting under way) The more military areas were kept away from the civilian facilities, and Brockton Bay was a much smaller city. It was mainly used as a staging point for freighters heading north to Halifax to join a convoy, but the US Navy had a small station there, mainly for some older destroyers and destroyer escorts for anti-sub work.
During that time, the USN was switching from ammonium picrate (Dunnite) to Picratol (Ammonium Picrate & TNT) because Dunnite was not completely shock insensitive, with shells detonating on impact with a surface instead of after penetrating (if they were AP rounds). There were issues with it deteriorating and becoming unstable when exposed to atmospheric moisture.
This lot had been awaiting storage when a storm hit, and the boxes containing the explosives - 20 US tons of it - were damaged and exposed to the elements. Now unusable, the boxes were carefully dried, sealed in paraffin, and carefully removed to a site further away from the city and docks as they existed in 1944, and entombed it in concrete, then built a building over it, and used it for storage of other things.
Then the war ended, and the old warehouse was cordoned off with a security fence on government property.
It took a couple of incidents in the 1950's and 1960's, one at Kittery (a fire) and one in Boston (records misfiled, then shredded), to lose any record of what was under the building. The property was sold to the Brockton Bay Dockworkers Association, who used it for tackle and rigging storage up until the riots. After the riots, use of the building dwindled to nothing, and it was eventually left to sit empty. A couple of fires during and after the riots and substantially weakened the concrete over the explosives, such that a 200 lbs. support beam hitting it from 20 ft. up end on would penetrate and strike a box with enough force to initiate a detonation.
The end result of 40,000 lbs of picratol going off will launch the concrete slab into the air in chunks, along with demolishing the surrounding buildings. Vista had already had an area 2 miles (3.2km) centered on the building in question warped to contain debris, and because the math for a sphere is much less complex than that of a cube, cone, or cylinder (yes, they exist. Quartic equations are not for the mathematically weak of heart), the warped area goes into the air, too. A bit of adrenaline might double that distance.
It will probably annoy Taylor, will have all sorts of unhappy federal officials running around scared, and the DWA trying to find out what might be under other buildings from that era.
What surprises me is no one caught the jellybean discussion.