Possible contamination of water supply by over use of herbicide

Hey y’all! Any advice or guidance on this situation is greatly appreciated. My parents live within Harris county limits next to the radio antennas for Univision. For many years they have been spraying herbicides along the fence line next to my parents property. Of all four sides of their property they only spray on that one side. I complained to them before because they kept over spraying into my parents property and the smell would be so strong that it made my mom dizzy and even killed some of her plants that were about 50ft away. Fast forward to today and a couple of mature trees on my parents property have started to die off. The water pump for my parents house is next to that fence line. I am suspecting that the water is contaminated. They have never stopped spraying even thou the fence is clean. I want to help them but I honestly don’t know where to start or who to contact first. Any advice is greatly appreciated.