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Drinking water at tap is OK; Manteca works on TCP issue at wells

A notice mailed recently to Manteca residents about the quality of their drinking water alarmed some residents who were caught off guard by the state-mandated notice.

And while other residents online tried to calm fears by noting that these notices – which have to be sent out when the city exceeds the maximum containment level for a given sample – the substance at the base of the concern is something that has never before been on the city’s radar.

Trichloropropane – or TCP – is a chemical compound and byproduct of the manufacturing process of certain pesticides and soil fumigants. While it was detected in Manteca’s drinking water in 2016, the State of California didn’t require routine monitoring until December of last year – after they set a maximum containment level of 5 parts per trillion for the byproduct believed to be created by the Dow and Shell Chemical Companies.

According to Manteca’s Deputy Public Works Director George Montross – who is in charge of utility services for the city – there are two wells that serve the city’s system that are testing above the MCL for TCP, and that the city exceeded those levels during their first quarterly tests back in February.

In order to limit the usage of that water while long-term solutions and funding were sought, those two wells, Montross said, became “last on and first off” when it came to meeting the demands of the city’s water system and its thousands of customers. When the wells were retested in July, the concentration spiked to upwards of 8 times the amount of TCP that was evident earlier in the year – something that Montross said could be attributed to the lack of use of those particular wells, and the infrequent testing that is done to meet state guidelines.

In the month of July, the two wells combined to provide 4.9 million gallons of water out of the 554 million gallons of water that was produced – further diluting that concentration even more. Those numbers were even better in June when only 3 million of the 517 million gallons that were pumped to provide drinking and residential water to residents came out of the ground.

But even when that water is pumped out of the ground for residential usage, it’s almost impossible that the concentrations of TCP that exceed the MCL are anywhere near that level by the time they reach the tap. Manteca’s well water is pumped out and then combined with water from other, healthier wells – blended together before it is sent to distribution pipelines or water tanks for peak-demand storage.

Montross said that the city can’t legally say whether the water is safe to drink or not, but noted that the state form that was distributed to residents and property owners detailed that there is no need to switch to a supply of bottled water.

“This is not an immediate risk,” the notice announced. “If it had been, you would have been notified immediately. However, some people who drink water containing 1,2,3-trichloropropane in excess of the MCL over many years may have an increased risk for getting cancer.”

Montross also confirmed that the city is currently involved in litigation with the party or parties believed to be responsible for the TCP in local groundwater as a way to ensure that the purchase and installation of treatment methods and media isn’t something that has to be covered by ratepayers.

And unlike other elements in drinking water that can be prohibitively expensive to remove – if it’s possible to remove them at all – TCP filtration only requires the use of granulated activated carbon.

To contact reporter Jason Campbell email or call 209.249.3544.