It is always difficult to diagnose an issue from pictures, but the two major suspects that are easy to eliminate are drought stress and pH. If you suspect drought could be an issue, water the tree every ten days when significant rain is lacking--you want to saturate the soil around the tree in a 6' circle and wet the soil quite deeply--this may mean watering for 3-4 hours. It is important not to water too frequently, be sure the soil is allowed to completely dry between each watering. Typically, larger trees don't require supplemental watering, but I know some regions have been under drought this season.
To check pH, send in a soil sample from around the base of the tree. If you send it to the MSU Soil and Plant Nutrient Lab, they will provide you with recommendations on how to correct the pH as needed. There may be labs closer to you that you want to use as well.
If you are looking for more info on chestnuts, please visit www.chestnuts.msu.edu.