I'm also going into my junior year, and I am building my mileage to 60-65 miles per week also.
This is my fourth week of training, I should hit about 48 miles this week, possibly more. I will take an easy week after this, then I will start incorporating tempo runs, and some intervals around my LT pace. Also, I did a speed workout today which consisted of 9x300m @ 800m pace, this was my first speed workout of this training cycle. I recommend doing a speed workout every few weeks, just to sharpen up and allow your body to remember how to run fast. One every 2 weeks really wont hurt you.
Examples (Tempo)
-25 min tempo, starting at AT, working down to LT.
-20 min tempo @ LT
-5-6 mile tempo @ AT
Example (Fartlek)
-60 min (20 min E, 20 min of (3 min hard, 2 min E), 20 min E)
-5 miles of (1/2 mile hard, 1/2 mile easy)
Enjoy your summer training and make sure to be disciplined!