Yes, OVERSPILL is a Scrabble word!

Letter values in Scrabble US: O 1, V 4, E 1, R 1, S 1, P 3, I 1, L 1, L 1.

Is it a valid word?

OVERSPILL is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the relocation of people from overcrowded cities; they are accommodated in new houses or apartments in smaller towns
the occurrence of surplus liquid (as water) exceeding the limit or capacity