Above Pawtucket Falls the Merrimack keeps up a low white noise all summer, and Benicio Landscaping and Construction INC works the yards that live within earshot of it. Mowing starts early, while the grass still holds the river's damp, and the lines come out straight enough to read from the sidewalk. Trimming and edging follow, so every walk and foundation ends in a clean seam instead of a shaggy guess. Cleanups in spring open the beds back up; in fall the leaves come off before they mat down and sour the turf. It is ordinary work done carefully, and a Lowell lawn that shows it is a small, satisfying thing.