When Ed Thornton recently completed a study examining coastal erosion rates for the Monterey County coastline, he noted something strange. The data just didn’t line up as he’d expected. At least, not until Thornton, an oceanography professor at Naval Postgraduate School (NPS), began to focus his sights on a little-known sand-mining operation in Marina that may in fact be one of the largest sources of present-day coastal erosion on the Central Coast.

“[Especially] from the Marina to Sand City area, coastal erosion rates are not decreasing as they are in the southern part of the bay,” Thornton says. “One of the biggest reasons why is that mining operation.”

Situated between Marina State Beach and the Salinas River, the sand mining plant was purchased by the giant Mexican cement company CEMEX in March of 2005. When asked about Thornton’s assertion, CEMEX spokeswoman Jennifer Borgen says CEMEX “doesn’t comment on theories. We do know that we run a safe and environmentally-conscientious operation.”

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Thornton has spent much of his life attempting to understand coastal erosion, a process by which the sea steadily dwindles beachheads and knocks cliffs into the ocean. On the Peninsula, coastal erosion isn’t a theoretical exercise. Visitors at Del Monte Beach can witness sand dunes shrinking away from the water, revealing rusted pipes that had been buried for decades. Aerial photographs of the former Fort Ord show that the cliffs where Stillwell Hall used to sit are now buried underwater.

Most scientists agree that rising sea levels and violent storms—such as the 1997-1998 El Niño—are the two primary culprits behind eroding coastlines. But scientists like Thornton and Gary Griggs of the University of California at Santa Cruz (UCSC) also believe that several sand mining operations that took sand directly from county beaches in the past also played a factor in coastal erosion.

Thornton wanted to determine just how much of an impact they’ve had. So he measured erosion rates for a stretch of coastline from the Salinas River to Monterey. He examined erosion data from 1940-1984, when about six sand mining plants dotted the Central Coast and scooped out literally thousands of tons of beach sand each year to sell for industrial purposes, like cement mix.

By 1990, however, all of these beach-sand-mining plants shut down because scientists—including those at the US Army Corps of Engineers—suspected that the plants were quickening coastal erosion. State authorities concurred, and refused to renew the sand plants’ mining licenses in the late 1980s.

In his study, Thornton theorized that coastal erosion rates before 1990—when the beach-sand-mining plants were still operating—would be much higher than rates after 1990. It turns out he was right, but only partially.

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Erosion rates have slowed down significantly since 1990, Thornton found, but only at the coastline from Monterey to Sand City. From Sand City up to Marina, Thornton calculates that the coast is disappearing almost as quickly as in the years prior to 1990 (about eight feet per year at the former Fort Ord, for example).

The data presented Thornton with something of a problem until he turned his attention to the CEMEX sand and gravel operation located on the northern outskirts of Marina that has been operating for exactly 100 years.

While all the other beach-sand-mining operations in Monterey County closed by 1990, the state spared this one. Officials targeted only mines located directly on beaches, and this one didn’t fit the bill.

“CEMEX does not drag the coastline,” CEMEX’s Borgen stressed to the Weekly. “Our process is above the beach. We extract sand from a pond, not the coastline.”

While that’s true, Thornton and Griggs argue that as far as coastal erosion is concerned, it may not make much of a difference whether the plant extracts sand directly from the beach or from the pond.

 “It is clear that the sand in the pond is replenished by sand over-washing the [sand dune] berm by waves,” says Griggs, professor of earth sciences at UCSC. “So, in essence, they are still mining the beach.”

CEMEX officials report taking about 300,000 tons of sand from the mine each year.

According to Thornton, the Marina mining operation explains why coastal erosion rates from Sand City to Marina are still high. Sitting in his office at NPS, surrounded by maps and oceanography textbooks, Thornton calls an engineer to do the math. “Oh my, that’s a lot of sand,” the engineer says.

The CEMEX sand plant extracts about 180,000 cubic yards of densely packed sand from the pond every year. Before 1990, when the County had other beach-sand-mining plants in operation, these plants annually mined an estimated 250,000 cubic yards of sand combined.  

“To take out 180,000 cubic yards of sand in a year,” Thornton explains, “you need to have a standard dump truck leave their mine full of sand every 20 minutes, 24 hours a day, seven days a week.”

Griggs is likewise taken aback by the huge amount of sand. “This kind of blows [old erosion calculations] out of the water,” Griggs says. “This is clearly having a big effect.”

While she won’t comment on Griggs and Thornton’s allegations, Borgen stresses CEMEX’s commitment to environmental stewardship at the site.

“We believe in conducting business with the greatest possible care for the people, their communities, and the environment,” Borgen says. “We work with the Monterey County Health Department of Environmental Health and the California Fish and Game Department and many other local, state and federal groups to not only ensure our operations are continuously in compliance with regulations, but also so that we remain stewards of the land. We are planting dense native plant species on the site and of the approximately 400 acres we own, 80 percent is set aside as open-space habitat.”

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The CEMEX plant is a busy place. The way the operation works is that during high tides, large waves wash over sand dunes and fill up a pond with seawater. On the pond, a dredge boat operated by CEMEX sucks up the new granules of sand deposited by the waves and, through a large hose, delivers it to a sand plant located a few hundred yards further inland.

There, the sand is dried and packaged. The plant, which is surrounded by mounds of sand, can be plainly seen from the southbound lanes on Highway 1 as one nears Marina. Most days of the week, large trucks and trailers line up to load up hundreds of bags of sand and then drive out on Lapis Road to different destinations.

The sand extracted from the RMC CEMEX Plant isn’t run-of-the-mill sand, but a high-quality type. “There remains a constant demand for the sand we extract,” Borgen says. “Because of its type, it is [ideal] in the water-filtration process. We provide much of it to local municipalities in order to bring clean, safe drinking water to families, schools and hospitals in the area.”

Borgen adds that half of the extracted sand goes to the local area in the form of home foundations, sidewalks, roads and highways. The plant also employs 20 people and contributes at least $1.25 million annually to the city of Marina in payroll and taxes, Borgen says.

The state’s Mining and Geology Board, under the state’s Department of Conservation, is the primary jurisdiction overseeing the CEMEX plant.

Marina City Councilman Ken Gray meets monthly with a group looking at coastal erosion effects on the coast. “If the extraction of sand for a private business is having a negative impact down the coastline,” Gray says, “then that’s a big concern and it’s worth investigating.”

It’s unclear what, if anything, might happen next regarding the mining plant, which appears to abide by all existing rules. The biggest problem of all, Thornton says, is that until now, “there doesn’t seem to be anybody who worries about how much sand they are taking out.”