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‘Cone of depression’ is causing structural damage

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Posted: Saturday, October 6, 2012 12:00 am

A recent Record (AP) article, "Drought a boon for fix-it firms," addressed the serious problem of lack of water causing serious settling or "subsidence" damage to many homes. The article was from St. Louis, Mo., but could just as well been from Morada and San Joaquin County.

A large portion of San Joaquin County, including Linden and Morada, sits atop a vast void in our groundwater basin. This "cone of depression," or massive hole, is caused from groundwater depletion — a severe overdraft of our aquifer amounting to 200,000 acre-feet per year and growing. With little or no natural recharge or replenishment, and the continual overpumping by the city of Stockton, the cone of depression deepens.

The water table is 90 feet below sea level in our aquifer. When we developed our well in Morada in 1971, the water level was at 44 feet. When we replaced our pump in 2005, it was at 97 feet; a substantial decline of 53 feet in 31 years.

Any time large volumes of water are removed from the ground and not replenished, a void is created. If the void is small, surface effects are minimal. But if that void is large, like our cone of depression, major surface structure damage can occur.

The results of subsidence can be costly to repair, and often are not repairable. We can see the manifestation of severe subsidence in the cracking and separating of porches and stairs, patios and walkways, stem wall and slab foundations, basements and driveways, and brick work and mortar. We can also see it in dry-wall cracking and large gaps between fireplaces, ceilings and walls; also in doors and windows not fitting and opening properly.

We understood the challenge of building on Morada's adobe clay expansive soil, and sought advice from experienced local builders and took their advised precautions. Yet we have experienced an inordinate amount of the above-mentioned symptoms in the last few years. I do blame the city of Stockton's over-dependence and reliance on groundwater pumping in the past, and currently, for Morada's subsidence-caused property damage.

William Van Amber Fields


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