what is your soil... and what does your septic expert say???? would they be more informed than a tree expert???? if you were to tell me that you have 3 inches of soil.. atop bedrock... it might make a difference i really have no idea what the answer is ... playing the advocate here .... but the guys who dig fields.. would surely know more.. than the guy who plants trees .... since most of us tree guys .... never see the roots the diggers will see ... ken

with most conifers... once all the green is cut off .. the trunk and roots are technically dead ... there are no dormant buds, so there is little chance it will regrow ... how long will it take to rot .. well ... in my dry sand.. forever .... in moister soil.. shorter .. and BTW.. enjoy the mushroom show that is on its way as they rot ... it is hard work .. but you shouldn't have all that hard a time digging some new holes for trees .... especially if you move 10 to 15 feet from the stumps .... and if you cant handle it.. hire a couple of strapping young men to go at a couple holes .... sometimes its easier to pay .. lol ... sharpen your shovel ... get a good tree saw ... and some pruning shears .....and just start digging ... and if you run across a giant root... shift the hole over a bit and keep going ... until you have a decent sized hole ... a lot of the bigboxstores get in fresh stock in the fall ... DO NOT BUY STOCK THAT HAS BEEN SITTING THERE ALL SUMMER .... buy them now.. leave them in the shade in the pots.. until about October or so ... i do this in my zone 5.. i think you can still do it in zone 6 in fall .... and plant them once they lose their leaves... untangle the bigger roots in the pot ... spread them out.. water it well through thanksgiving.. water deeply ... into the rootball .. when ever your finger inserted 3 to 6 inches indicates it is dry ..and then water it deeply all next summer.. and they should take off like rockets.. in the alternative.. do it in April, as soon as the soil thaws .... and stock is available .. add 3 to 4 inches of good mulch ... speaking of which .. do NOT let them take away the wood chips from those pines.. free mulch for your new trees ... the trunks are poor firewood .. and not worth using indoors ... but if you like campfires... keep that also ... good luck ken

I am removing these roots. Almost every resource says to just make sure to plant a few feet away, and many testimonies say their new tree is doing fine years later, but even 8ft away I am hitting like 3x3 fresh lumber I can make furniture with lol. Ultimately I think this is a unique scenario because I checked youtube vids like below and although some of those trunks are much smaller than the Silver Maple, the ratio of roots-to-trunk size seems way different as if this Silver Maple made clusters of much thicker and longer roots for its size - I think it's because the sandy/clay grading soil when they built the development makes things root shallow in this location. This is how a lot of developments are built, they use cheap sandy/clay stuff for the main grading and then only about 18" of good soil on top for the grass and trees, and also I've heard this whole side of town was basically a swap or something once upon a time, google maps even shows a blue line (river) along this fence line but there's never been a river, maybe an underground spring or something hence the map's river line starts and ends with no body of water and I've replaced fence posts here when it hasn't rained and basically hit an underground river (the wood underground was solid because no oxygen is why fence posts usually rot at the base only). I removed the stumps and roots of a row of blue point junipers that were chopped down like 7 years prior and they were still solid. If the roots look like the below vids, then yes go ahead and plant close and don't even worry about that little amount of roots in fact yes it'll just add organic matter I'd prefer to leave some roots if it's sandy/clay which is what I'm doing adding small roots back into the mix and mixing the sandy sub soil with the dark rich compost topsoil. Green giants are well-rooted and unlikley to tip over from windthrow, and they might root deeper into the sandy/clay stuff just below the old maple roots, but bottom line is there's too much big roots in the way that I know it'll be better without them, I can't even dig a 1ft wide hole for a new tree without hitting something decent. Some trees cost too much to risk it IMHO at least get some of the old roots out, setting up irrigation, transporting the trees, fertilizing etc better to not risk it if the conditions and old roots are like this. Another thing is if a previous tree/roots had disease, it could enter the new tree, but as long as there's not a ton of old root mass, then maybe it's not a big deal and the soil microbes will correct it, but just wanted to note that about planting near an old stump. And well, you can't just make quick work of roots with a chainsaw because it'll dull in 5 seconds and you'll spend more time sharpening than cutting (although I might sacrifice a chain for this and test my dremel chainsaw bits for once because usually I just hand file), but it's not too too bad removing roots. It rained hard and turned my project into a pool that I bucket'd mostly out and then filled the finished areas back with soil and it was like working on quicksand but it's getting there and the farther away from the stump the easier it becomes. Sawsall pruning blades dull really fast too and I resharpen them on a bench grinder but it's still takes a while. I've been picking at them with an axe, splitting wedges etc, rain-soaked compost topsoil makes it a lot heavier and everything slippery, been going at it with a jack hammer with a sharpened chisel bit does decently. This Silver Maple stump was like 3ft wide at the base. I just removed a different maple's stump and roots from the sidewalk grass strip area to plant new sweetbay magnolia and that was about a 1ft maple stump but the ratio of those roots to the large silver maple doesn't correlate, I was able to rather easily remove the whole stump and what seems like the only main roots it put out due to being confined between the sidewalk and street compared to the large Silver Maple really put tons of big roots out. sorry so long, Another things though is Green Giants are an extremely QUICK growing tree so I would still prefer not to have even medium sized roots near them. Tree services should offer the option to grind the roots too if they're this big. The Silver maple roots I'm removing are much bigger for the trunk-to-roots ratio than these trees it seems likely because of the site conditions https://youtu.be/N3RUifC7Uo8?t=310 https://youtu.be/Fjg7ieBY7Lk?t=434 https://youtu.be/bRTIwWUg4fc?t=152 https://youtu.be/vM24klVyxFk?t=477

The chemical you refer to is for stump removal. The stump is cut as low as possible, holes are drilled in it and the chemical is poured into the holes. After several weeks the stump becomes soft and can be removed in chunks, but nowhere can I find any information as to what if anything happens to the roots. As long as ficus trees don't re-sprout from their roots you shouldn't have a problem. However, removal of any large tree leaves roots in the ground. Some tree roots rot away quickly and some tree roots take longer. If you want to plant another tree or shrub next to the remains of the ficus trees, you will have to cut out any roots that are in the way of planting.