When I google NH dirt works a lot of hits but nothing on yours or direct to the company in the first page or two - a lot of yellow pages, manta, and other linked pages but not many direct to the web site. Yellow pages, business directory listings usually cost some $.
I know you can pay google for links but I dont have direct experience on how to make it more prominent.
You already likely have connections with other contractors so one tact is if they have a web page, create links from yours to theirs and vice versa - you know, like local building supply houses, home builders, and others that you might reference for larger jobs, plumbing contractors and so forth.
Create some fliers - a simple one page setup and get them printed in quantity and distribute to real estate offices, bulletin boards in supermarkets - there are lots of places to post these use your imagination.
Signage at your work site will also create word of mouth advertising especially along well travelled routes.