Heat lingers on Whittier and Rosemead Boulevards long after a September sun goes down in Pico Rivera, and the lawns on the side streets are thirsty for the night. GreenCity Sprinklers is a sprinkler business helping those yards through the hot months, with irrigation work and lawn care for Pico Rivera homes. A sprinkler that reaches every corner — no brown crescent by the driveway, no stream wasted down the street — is a small piece of engineering most people notice only when it fails. Getting it right means a lawn that stays green from curb to porch through the last heat of the year. In a city stitched together in 1958 from two communities, Pico and Rivera, that even green runs through the blocks like a thread.