Even though interior browning is normal on established trees, it's often a signal that new trees are short of water. The reason is that the roots are still confined within the original rootball. Thus, the rootball dries much more rapidly that does the surrounding soil. One key to success is where the soaker is placed. Right now, it should be ON TOP of the rootball. If the soaker is farther out than that, the water WON'T go sideways into the rootball. So go out and stick a finger into each & every original rootball. What's the status of each one -- dry, moist, or wet? My bet is that many are dry.

My comment on perhaps being too wet was mostly based on 1) your irrigation system, 2) Im kind of assuming where you live in Pa gets similar rainfall to Columbus, Ohio which isnt that far away, and 3- I think the "foliage drop" on the bottom of a few is probably due to being too wet. I believe browning from the bottom up is a sign of too much water(thats what people on here told me a while back). My land happens to be fairly wet as I have leaches living in my soil and the water table is usually pretty high. I have a cistern so it is easy to measure how far down to reach water. In addition, overwatering is the number one way people hurt/kill their plants/trees/etc. I am just 4.5 years into this hobby and Ive learned that not much happens in the first year, sometimes 2 years, and even 3-3.5 years. Usually (always in my case, my Horstmanns Siblerlocke Korean Fir, my last holdout, finally TOOK OFF after 3 years of not doing much at all) by year 4 the trees are settled, fill out nicely, and their growth rate is what it is supposed to be. While I generally dont fertilize, I do on occasion. Ive had good luck with Hollytone (and millorganite) and you can use it any time of the year. I bet it would help green those up if that is what you want to happen in the near term. My guess is they will green up naturally in time. This particular "linear mound" has been fertilized on occasion since I dont know how far into the "orginal ground surface" the roots go. I also added a bunch of cow manure when I got rid of my Subaru (see bare spot toward back of mound) about a month or two ago. Let me find a pic of an emerald green that has never been fertilized to see how its color is (from left to right weeping white pine, baby blue eyes, emerald green arborvitae, techney arborvitae (possibly dark green arborvitae, not sure), columnar Norway spruce). These pics were taken on the same day about 2 weeks ago and it does appear the ones that were fertilized are a darker green. As you can see, deer have been snacking on the emerald green.

I love walls of emerald green arborvitae, especially their texture, color, and fullness/density. Here is a pic I took about an hour ago at Muirfield golf course(Memorial tournament). Love the wider spacing, this is gonna be a killer wall in 10+ years(road is to left of bike path, need to focus on putt). Looks like they disregarded the internet, which generally suggests 2’-3’ spacing for wall, when deciding on spacing(check out the dead one). If Jack Nicklaus approves Thuja Occidentalis Smaragd as a privacy screen, then they must be good lol. Id say 21, 5-6 footers for 850 is a good deal. Still small enough to “become one with the ground/established” rather quickly. Even the 10+ footer I planted 5 years ago did good, though the smaller the tree, the quicker they get established. I have seen tiny tots outgrow larger trees on more than one occasion. I didnt believe what people were telling me until I witnessed it. All the $5, 1.5-2 foot Smaragd I planted 4-5 years ago are gettin close to 5’, some might be more. In looking at the pic, and knowing that there are lots of deer here, (some of) these may be getting deer pruned, though just a bit. The right two perhaps.

Thuja are a titch more demanding than most trees in the fertilization department, being fast-growing, but don't generally require a specific fertilization. But it's certainly an option if the OP would want to. In my case, I pushed mine from three feet to twenty in eight years to cover a particularly obnoxious neighbor, but that was an exception to the general rules... Although I'd recommend a low-powered organic one and in smaller amounts due to the lower amount of space available and on the lower end of the pH scale due to the preferences of the family to begin with. As I think on it, pH can be an issue, but most Thuja adjust well and aren't that particular about it. Still, as noted, excessive salt additions not only add sodium but boost the pH toward the alkaline. Which can cause some spotty browning. It's not of any concern, and the standard fix (yellow sulfur) is generally ineffective. But it's another possibility. And the only way to be sure is, again, a formal soil test. The home ones aren't accurate enough to be sure. Off the cuff, a small amount of Holly-Tone or Milorganite (fairly neutral, but does contain plenty of iron sulfate, which is acidic and the sulfates happily locate calcium, magnesium, and sodium and bind to them and remove them as highly soluble salts) wouldn't be taken amiss. But, of course, it's absolutely optional. If all this were me? I'd be out there with a fine clippers removing the brown tips. Because I'm seriously that picky. Been there, done that on my Green Giants.