Others have already pointed out the hazards of using run-off water from the
road, so I won't repeat that.

Sandy soil: I had the same situation many years ago, in a house 2 blocks
from the (salt)water in Long Island. Great drainage because of the sand, but
barely organic. The landlord who owned the rental had installed flowers over
the years, and added bags of topsoil, so it wasn't pure sand, but pretty
close. We added lots of peat moss, topped with leaves which we ground up
with the lawnmower. In the relatively mild climate (zone 6), the leaves
broke down nicely over the winter.

In a pinch, people have used peat moss to stop wounds from bleeding. It acts
like a sponge, drawing moisture away. So, if you want to use it in your
garden, it's imperative that you do it this way:

1) Open the flat side of the bag like the way single-serve cereal boxes used
to be perforated. Fold back the flaps and dig out an amount of peat moss the
size of maybe 10 1-gallon milk jugs. This makes room for you to pour in
water. Set aside the peat moss you've removed, and moisten it later. Pour in
enough water to fill the hole you've made, and wait a day or two until the
remaining stuff has absorbed it. Remove it in chunks and rub it over some
metal hardware cloth (screen with 1/4" holes - home centers sell it, and
it's cheap. You'll find other uses for it in the garden). The goal is to
break the chunks into more of a powder. Add that to the soil, and dig it in.
Left on the surface, it'll dry and blow away. If you're not using all the
peat moss right away, enclose the bail in a couple of big lawn & leaf bags
to keep it moist.

2) Peat moss will make your soil acidic, maybe too much for some plants. Get
yourself a soil test kit and check it. You might need to sprinkle some lime
around to counteract the acidity. The kit will be needed over the years
because the pH is not a static thing - it'll change gradually. Unless it's
way off, it's nothing to obsess about, but since it's so easy to fix, you
may as well attend to it.

3) Find organic matter in addition to the peat moss. Are you near beaches?
Seaweed's good stuff, as are fallen leaves. Grass clippings can be sprinkled
on the rows, but watch two things: First, do NOT use clippings from lawns
that have been chemically treated. Second, don't let fresh, green clippings
come into contact with tiny seedlings. Keep it 3-4" away. Apply thin layers
of clippings. When it browns, add more. Besides adding some nutrients, it
helps keep dirt from being splattered onto the plants during heavy rains.