While remaining mindful that, as I was saying to Classic, I am not suited to suggesting corrections... there are some difficult points from an intonation standpoint, which however also form part of the piece's aesthetics. At least as far as I can understand.
I will give you a sort of "walk-through" which, I repeat, is not a list of things you must correct, but rather a commentary on the most complicated points:
Bar. 17: Augmented triad, preceded by a diminished triad on A, to which a major seventh is then added (I interpreted the diminished triad of A as the second degree of a hypothetical minor mode on G#, and therefore an augmented chord on Bb, where rather than Gb there should be an F#... but nothing is certain in these situations, also because on the second quarter we have a D major)... the augmented triad is in itself a difficult chord to intonate; if we also add a prominent minor second between the altos and sopranos, it becomes even more complex. But that is the nature of this chord. The real problem in this bar, in my opinion, lies in the movement of the parts. There are choices I don't understand, but they may be aesthetic choices. Since you are moving in a situation that is inherently complex, I wouldn't have made that change between tenors and basses. You want to have a D major on the second quarter? You could have anticipated the natural A in the altos, rather than doubling the third. But the entire voice leading, in my opinion, is clumsy or enigmatic. Wide leaps make these chords more complicated.
Bar. 20: at the eighth note we have "harmonically" the superposition of two fifths, C-G and D-A. In reality, the voicing says G-D-A and then C. At the following eighth note, there is a major seventh chord on Bb in third inversion, and after that, the same chord on Eb, but in second inversion. The harmony changes again at the eighth note until the third eighth note of the following bar. I am not saying it is impossible, because it isn't at all, but all these harmonic changes so rapid are already complex to intonate. Dissonances of this type, in my opinion, make the piece very tiring. Imagine that these people must maintain a cappella intonation the whole time, and then at bar 22 you introduce another voice change with wide leaps again.
Bar. 23 et seq.: the complicated harmonic changes continue, but here the problem of textures and false relations is added. There is one between alto and tenor, where the tenors even arrive from an unresolved dissonance (the F is the seventh of a G7 chord). The sopranos, then, go an octave with the basses—actually at a distance of 3 octaves—to intonate on the downbeat of bar 24 a very strange chord, which is the delay of the subsequent Ab, with a very distant major seventh that gives me a headache just thinking about it :-) and everything culminates in the famous parallel octaves of bar 25... if the choir doesn't drop half a tone at this point, it's not a choir of real people :-)
Bar. 26-36: here I really don't know what to say. The harmonies change on the eighth or the quarter note, and they are not "transits," as in a chorale—meaning passing dissonances often on held notes of other voices. No, I mean, seriously, I started reading it and I couldn't believe it: you made different harmonies at EVERY change. Not all of them are complicated, but they are all different, and with part movements that are not always ideal. Direct and hidden fifths and octaves increase intonation problems, precisely because if they are not perfectly in tune, they transform into the worst existing dissonances (diminished fifth and major seventh). For instance, between bars 28 and 29, basses and sopranos make an ascending minor third at a distance of two octaves. Besides the fact that I keep wondering why you changed the voicing if you are leaving two Cs and an Eb in the previous bar; if that Eb at the beginning of bar 29 is not in tune for both basses and sopranos, it will be heard and it will sound terrible. Okay, you might not know that parallel octaves and fifths are difficult to intonate, but I'm telling you now :-)
Now enough, or I'll seem mean...
a me the piece doesn't suck at all, eh, but as it is, it is sooo much difficult to perform well