Hundreds of mounds of leaves, dirt, tree stumps and construction debris are being illegally dumped on Caltrans property in San Mateo and Santa Clara counties.

The problem, which has grown considerably in the past few years statewide, cost the state transportation agency approximately $1 million to clean up in 2021 alone.

In San Mateo County, piles of debris litter the grassy areas adjacent to freeway exits and entrances along Interstate 280. At Sand Hill Road off the southbound side of 280, dozens of mounds of chipped wood, dirt piles and other landscaping detritus form hills. Along the entrance and exit to 280 at Alpine Road, it's much the same, with the addition of several large piles of gnarled tree stumps.

The problem increased dramatically more than a year ago when Caltrans was repairing the guardrails along 280 and repaving some of the exit ramps, some residents have reported. The sites most affected locally include the stretch along 280 from Woodside to Los Altos, spanning the two counties.

Other hotspots include Interstate 680 at Montague Expressway, U.S. Highway 101 at Montague, California State Route 237 at the "Golf Course" exit, Highway 101 at State Route 85, Highway 101 at Coyote Creek, Interstate 280 at Foothill Expressway, and 101 at State Route 25 in Gilroy, according to Alejandro Lopez, spokesman for Caltrans District 4, which oversees the nine Bay Area counties.

"We do see illegal dumping as a prevalent issue throughout the district," Lopez said.

At Alpine Road and 280, he said, the district estimated there are 75 piles, equaling approximately 150 tons, or roughly 210 cubic yards.

Caltrans is seeking the public's help to report the problem.

If the illegal dumping creates hazardous lane conditions or impedes sight-distance requirements, Caltrans responds immediately to clean up the site. But sometimes it's too large an area to have to clean up in its entirety.

"The crew that oversees the Sand Hill/Alpine area maintains roughly 1,100 lane miles including roadside vegetation, vista points and a Park & Ride. We have directed our crew to focus on this area and will request a heightened CHP presence when possible," Lopez said.

Illegal dumping has been prevalent for many years but has increased dramatically over the last two to three years, Lopez said. Caltrans doesn't know who is doing the dumping but the items are construction, demolition and landscape debris, he noted.

The price tag for properly disposing of these materials can be high, which likely explains the proliferation of dumping. The South Bay Recycling Center charges $49 per cubic yard for construction debris; $50 per cubic yard for yard trimmings; $119 per ton for dirt and concrete; $131 per ton for asphalt roofing and $50 per load for green waste and lumber, according to its online fee schedule.

The 210 cubic yards dumped at Alpine Road at minimum would cost upwards of $10,500 at the recycling center, if depositing just yard trimmings. Dumping the 8,500 cubic yards of materials that Caltrans had to clean up in 2021 on its properties "saved" the businesses at minimum $416,500, while the price tag to the agency was close to $1 million.

The costs for this illegal dumping are far higher when considering environmental factors, however.

In one recent notable case, the San Mateo County District Attorney's Office Consumer and Environmental Unit on Feb. 2 announced it obtained a judgment in a civil law enforcement action against a Livermore-based commercial contracting company. On-Site Commercial Services Inc. was illegally dumping harmful material in an area where it could pass into the state waterways.

On-Site Commercial Services performs contracting jobs throughout the Bay Area.

In January 2021, after dark, company employees drove a truck with an attached vacuum trailer of liquid slurry waste to a trail in the area of Whiskey Hill Road and Sand Hill Road in Menlo Park, according to a DA's office press release.

The dumping occurred up slope from Bear Creek, a habitat for steelhead trout, a federally threatened central California coast species. A representative of Stanford University's Jasper Ridge Biological Preserve, adjacent to where it occurred, spotted the dumped materials and notified authorities. Investigators collected mud samples in the area, which contained organic chemicals found in diesel and motor oil.

On-Site Commercial Services Inc. cooperated fully with the investigation, the DA's office said.

The company agreed to resolve the court complaint immediately, with no findings or admissions of liability. The judgment prohibits the company from polluting waterways and illegal dumping and requires a $28,927 payment in civil penalties and reimbursement of investigative and response costs.

To try to catch illicit dumpers, Caltrans is working with the Redwood City California Highway Patrol. Caltrans has also erected temporary no-dumping signage on barricades that ring the areas around Alpine Road and other locations as they remove the debris.

In a letter obtained by the Palo Alto Weekly, Caltrans maintenance program manager Parviz Lashai said the agency is evaluating the installation of permanent signage to deter illegal dumping. They are considering adding earthen berms around areas of concern but there are obstacles they must consider.

Caltrans also supplemented its routine litter and debris pickup efforts with a new program referred to as "litter blitz," with crews systematically working to clean from one major freeway corridor to the next. Workers began focusing on the Interstate 280 stretch from Woodside to Los Altos in mid-December. The area will be checked by maintenance supervisors on a weekly basis and activities will be scheduled twice a month for future clean ups or as needed.

The public can help. Lopez said illegal dumping or activities can be reported to the CHP or to the Caltrans Customer Service Request webpage at http://csr.dot.ca.gov/.