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Groundwater & surface water: Double trouble from Twin Tunnels
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Go out by Costco in Manteca off the 120 Bypass at Airport Way and start digging.

You won’t go too far until you strike water.

Head toward Escalon and the water table drops by hundreds of feet.

The high groundwater in west Manteca as you move closer to the San Joaquin River has been the bane of construction firms that place sewer and water mains in the ground for years.

Go south of the 120 Bypass toward the confluence of the San Joaquin and Stanislaus rivers and you will find farmers that will tell you horror stories of increased salinity in the high water table that — just like the one near Costco — is fed by the “phantom Delta” that is kind of a subterranean mirror of what is visible above ground. Both are impacted by saltwater intrusion. The drought doesn’t bode well for either. The less fresh water flowing into and below the Delta, the more environmental havoc.

You don’t have to go back too many years to understand why increasing groundwater salinity is a stealth disaster in the making. It is an issue that parallels subsidence farther south in the San Joaquin Valley where in some places land such as that near Corcoran has dropped 13 inches in eight months due to the drought. While NASA pours over data from satellites to track subsidence to help sound the alarm, there is no high tech canary in place for saltwater intrusion.

Perhaps one reason that’s the case has everything to do with the areas impacted — essentially farmland and cities that surround the southern portion of the Delta where geology and water politics are a deadly mixture.

Saltwater intrusion is already a threat to deeper aquifers that Tracy and Lathrop rely on for domestic water. It is why surface water has become an essential component of the domestic supplies for the two cities and it’s not to accommodate just growth but to assure the viability of groundwater being tapped to serve the existing population.

Back in the 1991 drought, South San Joaquin Irrigation District board members took note of a serious trend that threatens not just the long-term viability of agriculture in the South County but water security for its cities as well. Salt water was detected for the first time in a well near Jack Tone Road down some 160 feet.

Too much salt in water used to irrigate crops can stunt growth and ultimately kill trees and plants. Long-term applying of water laden with higher levels of salinity can render soil sterile. Salt levels at certain point makes water unfit for human consumption.

The SSJID with its $14 million state-of-the-art pressurized delivery system in District 9 south of Manteca and west of Ripon has allowed farmers to wean themselves off brackish groundwater. It has also reduced air pollution by eliminating the need for diesel pumps to bring water to the surface. It has also reduced surface water consumption by more than 20,000 acre feet during the last three years.

It also has done something else that isn’t included very often — if at all — in the plus column. By reducing water pumping it has helped slow and possibly reverse the eastward drifting of saltwater intrusion to wells farther to the east. 

If you have a week or so to kill and have a super-sized container of Somnamax to keep you from doing a face plant while reading the endless documents analyzing the Twin Tunnels plan you won’t find too much attention paid to the serious consequences the plan to resurrect the Peripheral Canal as a phantom Delta bypass to satisfy the water needs of large corporate farmers and Southland cities would have on salinity of groundwater in areas along and near the southeast Delta.

Just like how fresh water runoff dropping in quantity allows salt water from the Bay Area to make its way farther east on the surface, the same is true for water tables below the Delta when the amount of fresh water that infiltrates through the soil from the main river channels and the endless sloughs is reduced.

The big dust up so far about saltwater intrusion issues for the Delta that the Twin Tunnels has been about the aboveground environment with nary a whisper about the water beneath the Delta. 

Drought year water reductions have made the Delta saltier with less fresh water flowing into the Delta. It has made salt water intrusion an issue numerous miles away from the last levee. Make a massive, permanent reduction in fresh water and it could easily lead to conditions rendering municipal wells in Lathrop and Manteca useless as well as seriously compromising the quality of well water to Escalon and beyond.





This column is the opinion of executive editor, Dennis Wyatt, and does not necessarily represent the opinion of The Bulletin or Morris Newspaper Corp. of CA.  He can be contacted at or 209.249.3519.