The Ryan Ranch area is the easternmost part of the Monterey system. While the rest of the Monterey system (closer to the coast) is often shrouded in coastal fog during hot summer days, the Ryan Ranch area is sunny and hot. Furthermore, the 500,000 gallon Ryan Ranch tank receives an average of 100,000 gallons per day of water from three wells in the area. These wells were known to have bromine levels around
70 ppb.

The combination of warmer temperatures and lower turnover had made it difficult to maintain an adequate level of chlorine disinfectant residual. As such, operators had periodically spiked the tank with additional disinfectant and frequently flushed the tank and surrounding system in an attempt to control THMs.