It should be clear why they did this. The other ones were dirty?
Well, one weekend about 18 months ago a resident of the small community I was chief in discovered his basement had about 3 feet of sewage in it. He called City Hall but this was a Saturday. he called the police department but unless an officer in the building and off patrol, there is no one in it on weekends. He didn't think to call Central Dispatch for the officer.
So he took it upon himself to pump out his basement full of sewage and dump it into the storm sewer system. Needless to say that on Monday our DPW crews were busy cleaning up a large portion of storm sewer before it migrated it's way into the county drain system. I estimate that it cost the City about $5000.00 in man-hours and equipment to fix this mistake.
I was so astounded that I wanted to open an investigation and possibly charge the moron or at least go for cost recovery but I was denied. You see, even members of the Council did not know that storm and sanitary sewers are separate lines.
Apparently the guys sewer had been stopped up in his house for months and he didn't discover the mess until his furnace quit working. I guess the smell wasn't a clue. The error was on his end and not the city's.
So, now the City will place similarly changed sewer grates as they do routine repairs.