Working The Same Muscle Groups
They both work the same muscle groups, as you know.
Exercise Order
The first exercise in a training program is going to elicit a greater training effect than the one that follows.
Your program has to some degree taking that into consideration.
However, let's break it down some more.
Training Both On The Same Day
The Deadlift take more out of the Squat than the Squat take out of the Deadlift.
That is the primary reason in Powerlifting, the Squat is the first lift and the Deadlift is the third lift.
In the beginnning of Powerlifting the lift order was...
1) Bench Press
2) Squat
3) Deadlift
The order was eventually changed to...
1) Squat
2) Bench Press
3) Deadlift
Since the Squat and Deadlift employ the same muscle groups. it allow more recovery for the Deadlift.
With that said, here are some other alternatives...
Combined Squat-Deadlift Training
1) Monday
A Llight Squat followed your Heaverier Deadlift Training.
With this method, the Squat is essentially a Warm Up for your Deadlift.
2) Friday
A Heavy Deadlift followed by a Very Light Squat; due to the muscle fatigue from the Deadlift.
3) Wednesday
No Squat or Deadlift.
Here's Why
1) Ressearch by Dr Fred Hatfield determined that the Larger Muscle Groups in the Lower Body require longer more days; with up to 6 says of recovery necessary.
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2) Research by Dr Tom McLaughlin found that the Lower Back is quickly and easily OverTrained; more so for Conventional Deadlifter due to greater lower back invovmement than Sumo Deadliftss, with less lower back involvement.
3) Also, what many fail to consider is how much the Lower Back is taxed with the Squat.
The Lower Back (core) is also worked to lesser degree with Standing Movement Exercises; which which contributes to OverTraining, muscle fatigue.
Powerlifter Deadlifting Training
Many Powerlifter only train the Deadlift once ever 7 - 10 days, sometime only every other week due to the Lower Backs need for recovery. There appraoch is based on anecdotal, partical exerience from decades of training.
Thus, a Training Program more in line with a Powerlifting Plan would be...
1) Monday: Squats
A good Auxiliary Deadlift Exercise following the Squat would be Moderate Repetition Kettlebell Swings with a Moderate Load, Hip Extension/Back Raises, etc.
2) Friday: Deadlifts
Good Auxiliary "Squat" Exercise following the Deadlift for the Squat would be movement the minimize the work load on the Lower Back, placing the workload on the Legs: Belt Squats, Step Up, Bulgarian Split Squats, etc.