The reason I know so much about it is that the homes in our development (So Cal) have post tensioned slabs. One of our neighbors was adding a second story over his garage and the GC cut a cable while installing a footing. It cost 5G to fix! So when we had our kitchen remodeled and needed a trench for the plumbing for an island, before I even mentioned it to our GC he told me that we needed the x-ray done. It was about $300 and they marked the cable locations with spray paint. They were laid out on 4 foot centers. It took a little extra time because they hand chiseled near the cables, but it didn't prevent us from putting the plumbing in. Most likely you don't have a post tensioned slab. You should be able to find out at your local building department - are you hesitant because you're not permitting the job? If so, your builder must have a copy of the plans, the house isn't that old - they would be specifically shown on the foundation plan if they are there. An x-ray company can definitely distinguish cables, that's their specialty. If you have them, they would almost definitely hit them in digging a 10 foot trench because they criscross the slab at 90 degrees. Sorry to scare you, but if the plumber is asking for a waiver he most likely has encountered them in your area and knows it's expensive to fix if he cuts/damages one.

If you want to see my slab mess you can look at my demolition diary (scroll down from there). I'm in SoCal, with slab, but I have to admit I don't even know what "post-tension" is. There's some fill in the front of the house, but I don't think this was a concern in the kitchen. Regarding the floor after the trenching, there's goop my artisan tile setter used, called anti-fracture membrane. It takes a couple of days to put down, but not a month of curing. It's supposed to keep the tile from breaking if the new concrete expands and shifts at a different rate than the old. When you're considering the sink relocation, remember the plumbing vent and fall of the drain line, as well as running the water. It's important to be able to drain into your existing line (since you don't want to dig up the whole house), and vent somewhere feasible. For mine, before we even started demolition, the master plumber traced where the vents were, and sent the camera robot into the drains to see where they were, at what depth, and at what rate of fall. I was very lucky that they could tie into what was there without much trouble. It's much better to do it this way than just start digging and take your chances. The dust CAN be controlled. Just act a little hysterical around the GC. :-) Mine brought in the thin plastic sheeting from Home Depot, and put it over everything. Well, his helper did. :) It also drapes the open wall between the dining room and living room, and covers the kitchen door. There isn't an outside lock, so one of the guys comes in, opens the kitchen slider, comes back and tapes the kitchen door, then goes around. Too much dust escaped when they removed the dining room door, however, even though there were drapes between DR and LR. A solid barrier is...solid, and it took them awhile to get the shrouding just right. If you have an open plan, several separate layers become crucial. But it can be done. Although dust is inevitable, I've had remarkably little to deal with, and since I have respiratory issues I was expecting the worst.

Thank you for the explanation. You are right I don't like the column or the sump pump. Outside the house is a concrete patio adjacent to the foundation so that would have to come up in order to tunnel under from the exterior. Sounds like we may need to stick with the current U shape (with an island in the middle). My last hope is that when the house was built in 1996 the builder put in a pre-plumb for an island sink option that is hidden under the current island. I've been in a few of my neighbors houses and they don't have a sink in their island but I suppose there's a slim chance its there and most buyers didn't want to pay the tract builder extra money to put in the sink. It was common in the area at the time to pre-plumb for the sink and then charge $1K to finish it. I'll see if anyone on the HOA board knows before tearing things up to check myself.

AND.....the hits keep coming............ I have not seen any further activity in the house. I keep checking...but nothing. Holding my breath but hopeful. HOWEVER...today I decided to clean out my shed. It is an all wood 8x12 structure that I built myself in the corner of my backyard. It is built upon four 6x6 posts (embedded in concrete) and is four (to six) inches above the ground (suspended). I had a large hardwood tabletop and a big piece of butcher block countertop stored in there. As I was removing items I noticed a large blemish on the tabletop. I thought I might have scarred it with a bicycle that I'd had hanging next to it. Nope....termites. I pulled the tabletop (and butcher block) away from the wall and they were prettly well chewed up. I soaked them with bug killer (because I didn't want to unleash live insects into the wild) and hauled them to the curb. Then I noticed that tremites had chewed up the plywood inner wall of the shed. Mud tubes (might as well be..mud WALLS) were erected in the corner of the shed. One single mud tube went all the way to the ceiling. It had all been hidden by that giant tabletop. There was damage in one other area as well....and I could HEAR the termites munching away. The damage is pretty harsh but IS salvageable (and does not appear to be structural). I doused all the affected areas with Termiticide. The termites also munched on other pieces of scrap project wood I'd been storing in there. I trenched around the back and side of the shed and (in the back) found a LIVE cluster of termites and mud tubes centered around some decorative stones I'd placed around the base of the shed. This area is CONSTANTLY moist (due to rain and shade). I soaked the trench in termiticide (including the backfill) and will complete the treatment for the front and other side tomorrow. I am exhausted. If anyone else has gone through this...I feel your pain. The destruction of these little buggers is unreal. I am confident I can patch my shed up...but man....what a frustrating pest to deal with. Cheers.