OMFG, I just don't know where to start. I'm talking about...
A GIANT SINKHOLE THE SIZE OF A CITY BLOCK. *headdesk*
I feel the need to put on my engineer-hat for this one:
Geology: Sea.ttle is underlain by gravels, sands, silts and clays left behind by several rounds of glaciation. Not particularly susceptible to massive sinkhole development. Especially a massive sinkhole 50 feet deep.
Engineering: A water main break going for weeks without anyone noticing? Water main breaks have a pretty good way of letting you know they exist. You know, by flooding the area where the break occurred. I can't come up with a reason why a water main would be buried so deep that it wasn't found for weeks, and it managed to scour enough soil away to form a void the size of a city block. Water mains are buried only a few feet underground. Not 50 feet.
More Engineering: Where did they get the clean, dry sand to bury that kid in? If it were truly a sinkhole caused by a water main break, I'm pretty sure that all the soils would be saturated.
More Geology: Sea.ttle has the Cas.cadian Subd.uction Zone Earthquake to worry about. The Juan de Fuca plate is being pushed under the North American plate resulting in the potential for a 9.0 Magnitude (or higher) earthquake. This is a real geologic hazard, and quite frankly, they should have done this story. Maybe that'll be the season finale?