So I'm a tac officer. So I was planning thus.

2 Eng, 1 Sci, 1 Tac.

What is the conventional wisdom for the ground powers? It's been so long that I'm not even sure what I used is good any more.

It depends entirely what you want to do. I always run an away team that comprises of one Tac, 2 Sci and 2 Eng (including my character). This gives a healthy amount of damage with good healing to add a little survivability to your BOffs. My BO layouts changed a lot after S4 released but all my characters seem to have settled into the same skills and BO layouts. For powers I usually use;

This gives a buff to HP, a flash heal, HoT and debuff clearer and NHM is just awesome at everything (whilst active it checks for damage and heals you up to 3 times when health drops below 75%). I'll usually run 2 of these, most of the heals will be used on your BOffs who will do very little to protect themselves from grenades and Cold/ Fire DoTs. I'll use only one of these on my Sci character but two on the others, especially against the Breen and Borg as the major debuffs they use are cleared by VR (Cold) and NHM (Assimilation) respectively.

CMB is a nice area denial weapon, if you place them manually you can catch the weaker NPCs and reduce up to 50% of there health through shields, on normal they usually won't make it. SRII is a nice shield heal that can be shared, they'll spam this on you and it's a real help if you're under a lot of fire as it'll buy a few seconds to get into cover.RRS is a self heal and important for BOffs, I've noticed they tend to use it before they place turrets and mortars so the shield resistance buff it grants usually keeps there shields up long enough to not be defeated whilst deploying the turret. And Quantum Mortars are just brutal, place them well out of sight and they'll rain down death from above, best Engineering BOff skill IMO.
I'll use two of these unless I'm playing my Engineer then I'll have only one.

This gives a powerful AoE kinetic attack with the grenades, they work very well against NPCs that seem to have very little kinetic resistance. Suppressing Fire gives a slow and DR debuff that's very nice against lunging Swordmasters but useful everywhere, TOII is optional, I use it on a Bolian Tac BOff with Superior Luck so the increased CrtH and CrtD works nicely with that trait. Lunge is just impressive and is capable of insane numbers (highest I've seen so far is 1450 from a Tac with TO running and a Tricorder Scan from my Sci character).
I'll use two if these unless I'm playing Tac myself (it's fun having two with the Tac too but lacks healing and usually ends badly on Elite).

that's all set to the way I like to play though so it may not work for you. The BOffs are cheap and easy to reskill though so just experimenting with them to see what suits you won't cost the world.

I always run with two Sci boffs, one a dedicated healer and one a dedicated attacker. I put both in the best defensive armor I can get (usually Polyalloy Weave) and equip both with Expose weapons.

I don't always take a Tac boff; much of the time, I'll fill the other two slots with Eng boffs. I ensure that both have Power to Shields OR Shield Turret, and then one additional damage-dealing turret apiece (either one Phaser turret and one Quantum Mortar or a Phaser turret apiece). I play around with the other two slots to see what makes sense given the team's abilities. On some toons, I go with more defensive Eng powers (e.g. Medical Generator) and on others, I go with more attacky powers. One Eng boff will get an Expose weapon; both might, depending on how the team shakes out. Often, the Eng Expose weapon is the CRM 200 freezie cannon, assuming we're not going up against Breen.

If I take a Tac boff, I go turret-heavy on the solo Eng boff. The Tac boff then gets heavy attack powers that buff his Exploit attacks, which are going to get the benefit of lots of Exposes provided by the other three boffs. I like to equip Tac boffs (again, if I take one at all) with Compression pistols or pulsewave assault rifles (which do their best damage up close), particularly if they have Aggression, Superior Aggression or some form of Rage as a trait. A boff with that trait is going to run in for the attack, so you might as well take advantage of that with close-in weapons.

I like Tac boffs that have inherent attacks, like Breen or Caitians; you get an extra attack form out of them without having to train them in a power. Aenar are also helpful; their Project Image ability draws a lot of aggro and can distract enemies effectively so you can cut them down. I try to avoid Aggression or Rage traits in all other boffs; I don't need my healer running up to a mob boss and beating him over the head with the butt of his rifle (yeah, that happened to me when I started playing).

When it comes down to it, your captain is going to be the chief damage-dealer in the away team, so I find it useful to find ways for the boffs to support that goal, whether it be with heals, Exposes, AoE attacks or just staying the heck out of my line of sight.

This is how I have my away team set up;

2x Tactical Officers; Battle Strategy, Target Optics, Suppressing Fire, Overwatch.
-- This gives my tactical officers a wide range of buffs, debuffs, and exposes.

1x Science Officer; Medical Tricorder x2, Vascular Regenerator, Nanite Health Monitor.
-- Set up for pure heals to keep everyone up.. it helps a lot because BOs are dumb.

1x Engineering Officer; Chroniton Mine Barrier, Phaser Turret Fabrication x2, Quantum Mortar Fabrication
-- Lots of toys for the enemy to attack instead of me, and those toys do good damage too!

Equipment wise all of them use AOE-style Expose weapons to maximize the damage of my AOE-style Exploit weapon. I also outfit my BOs with the best defense-focused shields and armor to help mitigate how stupid they are.

QFT. ^^^^^^

4 Engineers (or take 1 Sci for Assimilation clearing), and load up on as many Phaser turrets as you can on them. The turrets deal nice damage while taking a significant chunk of aggro.