SILVER CITY —The New Mexico Environment Department is looking into what caused a strange milky white rain to fall on Grant County Monday.
Area residents noticed the unusual rain as it left white puddles and a white, almost sticky residue everywhere.
"We're trying to determine what caused this event," said Marissa Stone, communication spokeswoman for the New Mexico Environment Department. "We are sending samples to New Mexico Tech and the University of Texas El Paso to be tested."
Stone said the NMED is looking at several possible reasons, including wind and weather patterns that might have brought the unknown substance to the area.
"We'll know what the substance is when we get the results back in one to three weeks," Stone said. "We want to know what it is as much as you do."
Silver City Town Councilor Tom Nupp, who runs a Community Collaborative Rain, Hail and Snow Network weather station, said he measured the pH levels of the milky rainwater.
The alkalinity of the substance was unusually high — a rating of 7.9 pH based on tests with a litmus strip.
"That is very unusual," he said. "Rain water should be around 7.0. The town's drinking water is around 7.2 and I've seen it as high as 7.6. A pH of 7.9
is unusually high."
PH testing classifies substances on a scale of 0 to 14. A rating under 7 is classified acidic — the level of acidity increases as the number drops. A pH level above 7 is considered alkaline, or base. A rating of 7 is considered neutral.
He said the particles in the rainwater were extremely small — indicating the substance was likely a dust.
"It didn't settle out," he said. "Normally it would have settled in the rain gauge in an hour or two, but four or five hours later, the water was still that milky color."
Nupp said he theorizes that the substance in the rainwater may possibly be calcium carbonate dust or a type of dissolved limestone rock, probably picked up from playas along the New Mexico/Arizona border by high winds and dropped on the area by the rain.
As NMED officials look into the cause of the rain, Stone said if the milky rain happens again, residents are encouraged to collect fresh samples and submit them to the NMED or the local field office in Silver City. The contact number for the Silver City field office is (575) 956-1544.