Contaminants found in north Stockton groundwater wells

STOCKTON — Investigators have discovered what appears to be a new plume of polluted groundwater in north Stockton, the culprit being a chemical commonly associated with dry cleaning businesses.

The area of concern is mostly between Thornton Road and Lower Sacramento Road, north of Hammer Lane and south of Paloma Avenue, officials said. Of 37 private domestic wells that have been sampled mostly in that area, concentrations of the chemical commonly known as PCE exceeded federal standards in 13 wells.

The problem should be of concern only to residents who rely on private wells for their drinking water. Homes served by the city of Stockton or San Joaquin County should be fine, officials with the State Water Resources Control Board said Monday, noting that one county well that did measure high levels of PCE was destroyed last year.

PCE plumes are not uncommon in the Central Valley, including Lodi and Stockton. The newly discovered contamination is less than a mile from a plume beneath Stockton’s Lincoln Center that has been known about for decades; a judge held a dry cleaning business liable for that problem, and treatment efforts are ongoing even today.

“We have quite a few of these going on in the Sacramento area and a few in Stockton,” said Stewart Black, who manages a cleanup program for the water board. “We feel like we’ve identified the significant problems that are out there.”

That’s why they were surprised earlier this summer to discover the “new” PCE problem while doing water quality testing for an entirely unrelated issue.

Officials noted Monday that they do not believe the new plume is related to the Lincoln Center pollution.

The state has, however, issued an order to the Parkwoods Cleaners dry-cleaning business on Hammer Lane and to the Sims-Grupe Management Co., which owns the property at the Parkwoods Shopping Center less than a quarter-mile away from some of the affected wells.

Dry cleaning operations began at the shopping center as early as 1960 and continue today, though at a different location within the center, the order says.

While they refer to the drycleaning business and property owners as “potentially responsible parties,” officials emphasized that they don’t know for certain where the pollution is coming from. The order requires the business to hand over documentation of current and past PCE use and how the chemical has been disposed of.

“We have to do some very specific investigation to identify the source of the contamination before we can tie it to one specific property,” Black said.

Representatives of both Parkwoods Cleaners and SimsGrupe could not be reached Monday afternoon.

Known formally as tetrachloroethene, PCE can get into the ground if it is spilled or leaked from a business.

Cleaning up the old sites can be costly. City of Lodi officials estimated in 2014 that cleaning up the five plumes beneath the central portion of the city could cost about $20 million.

And the health risks are real. Human exposure to PCE over a long period of time may cause liver problems and an increased risk of cancer, the state says.

In some wells, the chemical has spiked many times higher than the federal standard of 5 micrograms per cubic liter. Of the wells exceeding that limit, the state’s order says the detections have ranged from 9 micrograms to about 88 micrograms, or nearly 18 times higher than the standard.

Some wells in the area of the newly discovered plume have not yet been tested, and officials said residents are welcome to contact them to request sampling. Call Joe Mello at (916) 464-4661 or email Joe.Mello@waterboards.ca.gov.

“We’re trying to tell everyone that if you’re in that general vicinity to come to the meeting and talk with us and we’ll be happy to come sample your wells,” Black said.