Hey! I'm not sure if I lift as heavy as you do, but I do lift weights and run. My weekly schedule is about 25-30 miles per week of running and 2 days per week of lifting. I find that any more lifting than that interferes with my running - especially lunges, deadlifts and squats!! During my spring HM training, my week usually looked like this:

Monday - off
Tuesday - 3-4mi run + lifting
Wednesday - hills or speed training
Thursday - 4-5mi easy run
Friday - 3-4mi run + lifting
Saturday - 6mi easy run
Sunday - long run (8-13mi, depending on the week)

Good luck with your training!

Your week looks very similar to mine. I guess I need to figure out a way to make the lifting quicker on the days I'm also running.

I go with the Matt Fitzgerald philosophy: Go in, Lift Heavy, Go home. He recommends not hitting the same area a bunch of times or doing too many sets.

So I lift twice a week these days, once at home and once at the gym. At home I use 15-20lb dumbbells and then at the gym I use the heavy lifting area.

I have become kinda fluid about which days I go. I use to lift on the second of two rest days and then on an easy run day, but now I just fit it in when I can, sometimes it's after a long run, sometimes its on the day I run a double. I haven't felt any detrimental effects from this...

I am very familiar with this philosophy. In fact, I'm one of the only women in my gym that lifts more than 15lb dumbbells or body weight squats. However, at this point in my training for my race, lifting that heavy just isn't feasible within my time limits. As my long runs are now at 10 miles and getting longer, I don't have time lift afterwards. I guess I just need to let go of my beloved HEAVY lifting for now and just lift...

If your weekly mileage is 30-40 miles per week, I am guessing that is running 4-5 days a week. That is going to mean that you are going to have to lift on running days. That will be very hard and I expect you will not be able to maintain it for very long.
I lift and I run. I find that the runs I take the day after lifting are very hard and very slow, particularly after deadlifting.
If I were to make a suggestion, I would say 'give up the heavy weight-lifting while you train for the race.' You can do two days of cross-training with your running -- push-ups, pull-ups, air squats, yoga, sprints, and jumps, etc. -- and that will be much less likely to interfere with your running.
Heavy lifting takes the strength out of your body (legs) both the day of the lifting and the day after, and then you get in the habit of being slow and not challenging yourself when you are running. You don't want that before a race. You want to train to improve your speed and stamina. You do that best by doing more miles.
You can take up lifting again after the race.

Yes, I currently run 5 days a week. 1 complete rest day and 1 active rest day that usually consists of lifting. I do lift on my shorter run days currently but am still trying to lift what I was during the winter (which I shouldn't be). So I have identified one part where I can reevaluate my routines. I don't run after leg day. NEVER. I wouldn't make it more than 1/4 mile.

I'm not looking to give up lifting completely, just asking more about how runners lift while training for races to maintain muscle mass (or lose as little as possible).

I run ~25 miles a week (4 - 5 days per week). I lift every other day and am following the Stronglifts 5x5 program at the moment. On lifting days I warm up for 15 - 30 minutes on a cardio machine, do my lifts, and then run 3 miles easy on the treadmill. On running days my partner, Haley the 90 pound black German Shepherd, and I pound the pavement for 5 - 7 miles in the wee hours of the morning. I have actually found that the longer I have followed this lifting program the better my running has become. Prior to Stronglifts I was following my own (i.e. concocted) circuit training proram - it gave me a really nice workout but didn't really have any long term goal and it didn't do much, if anything, for my running. I much prefer what I am doing now and intend to keep following this routine for the foreseeable future. Lift heavy! Run strong! - Doug

Finally!! I know how much my weight training has helped in my running and I don't want to give it up. You are the first one to mention how it can help your running! I will have to look into the stronglifts program that you mentioned. I haven't heard of that.
But if it is what I assume it is (5 sets of 5 reps), I am definitely interested! Thank you for your comment!!