A friend of mine asked me how he should approach a 4 week taper to an IM (Placid in this case). I responded with an outline of a four week taper block. It should be noted that this is for a well-trained, fit athlete that is accustomed to high volume training. Also, if it seems Friel-esque; that's because it is.
A standard four week taper/Peak period for an IM includes key workouts every 72-96 hours while allowing recovery and reducing duration; not intensity; throughout).
Something along the lines of:
Monday-Thursday: easy to recover from Build you just completed (in your case; four solid weeks)
Friday: Long run; duration should be the longest you completed during your build (but no more than 2.5 hours). The idea here is to log as much steady state time as possible. It might be a good idea to do a 60-90 minute easy/steady ride to get the most our of your run time. I run nearly the entire duration within my IM HR ranges when I do this session.
Friday: recovery day
Sunday: Key long ride; 5 hours with 4 hours or work done at IM effort; 15 min run off bike
Monday+Tuesday: Recovery days
Wednesday: 90 min steady ride; 1:45 run off bike; (75 minutes steady; 30 minutes very easy).
Thur and Fri: reco days
Saturday: Good one hour swim with quality; 4 hour long ride with 3 hours of IM work done within; 15 min run off bike
Wednesday: 90 min ride with 60 min steady; 75 min run off bike; 45 min steady; 30 min easy
Thur + Fri: Recovery
Saturday: Solid one hour swim; 3 hour ride with 2 hours of IM work done within; 15 min run off bike
Monday: Normal duration swim; 60 min ride with 1,2,3,4 minutes @ IM effort on equal rest duration (i.e. one minute off; one min easy).15 min run off bike
Tuesday: 45 min run with 5 x 90 seconds at HIM effort on 3.5 min easy jog recoveries; 45 min recovery spin
Wednesday: Swim only; include 5 x 90 seconds (100s -150s based on fitness) at HIM effort with 3 minutes of easy swimming in between.
Thursday: 30 min easy run. 45 min ride with 1,2,3 minutes at IM effort on equal recovery
Friday: Swim only; very easy
Saturday: Prerace SBR of 15/30/15 with a couple pickups in each sport
Sunday: Win your AG.
You might be wondering what to day on reco days. Here's what I suggest.
Place the normal frequency of your running, cycling, and swimming within those extra days of the week (peak workouts count for a session in each). The only caveat is that you keep the duration shorter and the intensity lower (swimming excepted). The only times you want to pick it up are on your 'peaking' days (aside from swimming). I would keep your frequency rides in the 60-90 min range and make them spins. The runs I would keep at 40-50 minutes in week three and 30-40 in week two (assuming those are normal durations).
I wouldn't think of your final four weeks as a time to do "speedwork." Your primary goal is to strip away fatigue (by lowering volume) and maintain peak fitness (with peak workouts that don't back off the intensity).