Thank you so much for your recommendations and thoughts. They were very helpful. I definitely plan to test the soil for heavy metals before doing any edible plantings. We're in Central PA in Lancaster County and I plan to contact our extension office on this. I had not heard before about constructing a swale to filter out pollutants and am interested in something like that as well. We are planning to put up a fence around our backyard to keep out some of the noise from the road and also for privacy purposes, but I think some kind of natural barrier would even be better as it might help filter some of the pollution from the road. Right now we have only a row of rather widely-spaced pine trees back there, which don't provide much privacy or noise reduction and I'm sure aren't doing much for the pollution factor either. And yes, I'm definitely interested in composting too.

As far as the deck is concerned, it's not in great shape -- it's about 25 years old, and the wood is peeling, chipping and cracking in different places. The previous homeowners (who lived here about 10 years) didn't seal it at all from what we can tell. We have lived here less than a year and haven't spent much time out there or done anything to it yet. Do you recommend any particular 'green' deck sealant or method? I'm afraid to sand it as that would probably send bits of toxic chemicals flying all over the place, but don't know how else to control the splitting and chipping wood, and am not sure that you could put sealant on top of that as it is.

If you don't mind my asking, how did you learn all of this stuff? Are you a professional landscaper? I really appreciate your help! I am new at this and kind of overwhelmed. Is there a book or website out there for first-time organic gardeners/property owners that you recommend, or just hanging out on these message boards? Thank you so much!

Unfortunately there is no one place to get the information gardengal provided, it is everywhere along with a lot of misinformation. it can take years of reading, thinking, reading, thinking, finding trusted places to obtain information from.
Given the age of your deck it most likely was made with CCA PT wood and the major problem with that was the arsenic that leached out which was then picked up by children and then ingested. If sealing cannot be done you might consider replacing (expensive yes) it with something with lower potential problems.
As gardengal alludes getting the level of organic matter in your soil up to optimum is the best method to control potential soil problems such as heavy metals because that seems to stabilize them. Studies show that some substances will not migrate in soil very far. Creosote has not been found much more than a few inches from the source in soil, Arsenic from the CCA PT wood also has not been found to move in soil very far, maybe about 6 inches.

If you don't mind my asking, how did you learn all of this stuff?

LOL!! A formal education in horticulture plus countless years self-educating :-) I am a professional in this field and I teach as well and I think teaching - if it is a passion - is probably the best way to stay well-informed, as you are constantly drawing in new information from all sorts of sources, even one's students.

As kimmsr states above, there is no single source for all the info one can or should assimilate. Read, read, read somemore and ask questions. There is tons of info available online, most of it good - some just junk. Some of the best info available is provided by the extension services - county agencies sponsored by land grant universities and intended to assist home gardeners - Penn State has a an excellent extension system. Get to know them, they will become your friends :-)

This may not be what you want to hear, but 25 years is well over the life expectancy of most wooden decks, especially if not mainatined properly on an annual basis, and it should probably be replaced rather than trying to bandaid existing problems. You might want to consider one of the recycled wood products when you do rebuild, rather than raw lumber. These are a combo of both recycled plastic and wood industry byproducts and last an extremely long time without the need for attention via staining or sealing. Although more expensive initially than raw lumber, there are virtually no maintenance costs associated with recycled wood products so less expensive over the long run and they are considered sustainable and very "green".

And we were all beginners at some point in time :-) Just keep at it and come back and ask more questions as they arise.

Here is a link that might be useful: Penn State extension service website

May I add a few points to the excellent comments from gardengal and kimmsr?

Re: a living screen to filter out pollutants from the roadway ... great idea. The denser, the better.

Re: testing for tainted soils ... I know I've seen references online about growing test plants to see from growth patterns which pollutants are present. But of course, can't find the reference.

Re: soil possibly tainted .... it seems to me that the same might also be true of commercial grower's soils. So the vegetables you grow in your [constantly improved] soil will be at least equal to and probably far better than store bought ... hope that helps you feel better about your veggies.

If you are concerned about runoff and pollutants from the highway, I'd encourage you to investigate the swales. These are really just wide planted ditches that collect runoff during high rains and filter out pollutants via the plantings. A little similar to rain gardens, although those are typically included within the garden proper.

There is a neighborhood in Seattle that has instituted a network of swales planted with native plants that has been extremely successful in both reducing the impact of stormwater runoff as well as filtering this runoff of pollutants that used to leach into groundwater and eventually local salmon spawning streams. It is called SEA streets (for Street Edge Alternatives). Check out this link to see details on this project and take a virtual tour of this neighborhood.

Here is a link that might be useful: Swales

O_N_G: I honestly don't mean to be a downer and appreciate your concerns as well as your earnest effort to deal with the things that concern your gardening area. I am mystified, are you equally concerned that you may be eating tainted foods that you purchase, not knowing their specific geographic origins such as near highways and so on?