They have 5 parking garages (all 24 hours), each with at least 1 cashier and 1 valet. That's 10 employees each getting a $6.00/hour raise, for a total cost of $1440. But is one valet really enough during peak times? Let's say for half the day, they have 2 valets per garage. That adds another $360 for a total of $1800, which is getting pretty darn close to the extra $1980 they are making if they park 2,000 cars a day.
If any of the shuttle drivers make less than minimum wage or they ever have more than 1 cashier or more than 2 valets at one garage, they probably aren't even fully recovering the added cost.
Alternatively, you can calculate the hours needed to park "thousands" of car. Let's say it takes 5 minutes to park + return a car. If thousands is 2,000, that is $1,000 in valet hours + $720 in cashier hours (assuming 1 cashier). Again fairly close to the $1980 extra revenue, so better hope those valets have 0 downtime during their 8-hour shift.
If thousands = 3,000, they are making $2970 per day and paying an extra $1,500 in valet hours + $720 in cashier. The more cars they park, the more likely they are actually making money, assuming again, the shuttle drivers were already making $15.00 and they run with a minimum staff of 1 cashier + minimum number of valets to park "x" cars at 5 minutes per car with 0 breaks.
All-in-all, I'd bet they aren't fully recoupling the extra cost in wages, which is consistent with the company's statement that the surcharge covers a "portion" of the increase in costs.