GRA SACTO BRANCH MEETING: Factors Affecting 1,2,3-Trichloropropane in Groundwater in California

September 11, 2019 @ 5:30 pm – 8:30 pm
Aviator's Restaurant
6151 Freeport Blvd. Sacramento
CA 95822

1,2,3-TCP is a volatile organic chemical of eminent concern due to its carcinogenic, mutagenic, and reproductive effects, and its frequent occurrence at concentrations of concern worldwide. California recently established a maximum contaminant level (MCL) for 1,2,3-TCP of 0.005 μg/L.

Statewide, 1,2,3-TCP was detected at concentrations above the MCL in 6.5% of 1,237 wells sampled by the U. S. Geological Survey (USGS). About 8% of domestic wells had a detection of 1,2,3-TCP, compared to 5% of public-supply wells. 1,2,3-TCP was detected at or above 0.005 μg/L in 5.5% of most recent samples from 7,787 public-supply well sources of the California State Water Resources Control Board Division of Drinking Water (DDW). Concentrations ranged from <0.005 to 2.7 μg/L.

Most of the detections occurred in the San Joaquin Valley, where 1,2,3-TCP was detected above the MCL in 16% of USGS sampled wells and 18% of DDW wells. In the San Joaquin Valley, 1,2,3-TCP occurrence and concentrations are related to legacy nonpoint source fumigant inputs and hydrogeologic factors. The highest concentrations of nonpoint-source 1,2,3-TCP are in young, shallow, oxic groundwater beneath primarily orchard/vineyard crops. These areas are in coarse-grained sediments that promote rapid recharge. 1,2,3-TCP frequently co-occurs with 1,2-dibromo-3-chloropropane (DBCP), 1,2-dichloropropane (1,2-DCP), simazine, and high nitrate concentrations. Analysis of groundwater age dates and temporal changes in 1,2,3-TCP indicate that 1,2,3-TCP is persistent throughout modern age groundwater, showing little evidence of degradation.

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