In the News: 1,2,3-Trichloropropane (TCP)

March 6, 2017

1,2,3-Trichloropropane (TCP) is a manmade organic chemical that was used mostly as a soil fumigant, which eventually ended up in groundwater supplies. Soil fumigants in use today no longer contain TCP. The State Water Resources Control Board has set a draft maximum containment level (MCL) of 5 ppt for TCP for all public water systems in California.

Cal Water is committed to meeting whatever maximum contaminant level is eventually set for TCP, and ensuring water provided to our customers meets all federal and state water quality standards. Even before the State began to set a regulation for TCP and while not required to do so, Cal Water was proactively monitoring for TCP in our wells and designing treatment in anticipation of the State establishing a maximum contaminant level. This will enable us to more quickly and efficiently meet the new standard.

The determination of whether the water is safe to drink and use is made by public health experts. They have calculated the theoretical health risks of TCP at this draft MCL at a 1-in-142,857 cancer risk over a lifetime of exposure. Five ppt is the level that the State has established as the detection reporting limit using currently approved testing methods.

A few quick facts about TCP and Cal Water:

  • We have conducted thorough research on TCP removal methods, and have determined that granular-activated carbon will most efficiently remove the TCP in our service areas.
  • In areas where we have GAC installed already, we are able to utilize that to remove TCP. In other areas, the MCL would dictate the level of treatment needed and, subsequently, the design of the treatment facility.
  • More information is available on the 1,2,3-Trichloropropane page.