Inflatable "packers," recently installed deep in several contaminated wells in North Hollywood, have in some cases cut levels of pollutants in pumped water tenfold, allowing previously unusable wells to produce drinkable water again, according to city engineers.
The packers--rubber collars inflated inside the well casing--are designed to prevent contaminated water, which is mostly contained in shallow layers of sediment, from descending to the bottom of wells, where it would mix with and contaminate cleaner water from deeper layers.
The Los Angeles Department of Water and Power is installing the devices in 14 of 40 city wells in the San Fernando Valley that have been contaminated with two hazardous industrial solvents.
The custom-made packers, installed in 10 wells in the past eight weeks, have produced mixed results so far, said Gene Coufal, hydrologic engineer in charge of the project. But Coufal termed results in three wells "great," saying solvent concentrations had dropped well below state-set limits.
3 Back in Service
Those three wells, previously taken out of service, are now producing water that is being sent to customers, he said. When the technology is refined, the packers will restore a significant source of water to strained city supplies, he said.
Los Angeles draws about 15% of its water from a natural 112,000-acre reservoir of ground water beneath the suburban and industrial sprawl of the eastern Valley. The water flows at a snail's pace through layers of porous sand and gravel sediment laid down over many millennia.
The water is pumped from wells in and around North Hollywood and is piped over the Santa Monica Mountains to customers in Hollywood, the central city and East Los Angeles. Valley residents drink water brought to Los Angeles in aqueducts from the Owens Valley and the eastern Sierra.
Starting in 1980, high concentrations of a once-common industrial solvent called trichloroethylene, or TCE, were detected in water drawn from DWP wells in North Hollywood and wells supplying neighboring Burbank. Another solvent, perchloroethylene, or PCE, was also detected.
By 1986, almost half of the 80 wells in the area were found to be contaminated with excessive levels of the two solvents, both suspected carcinogens. According to DWP statistics, the contamination by TCE and PCE is still spreading, and each year an average of two new wells go over the state-set limits for these chemicals.
Half of the polluted DWP wells have been taken out of service because of the high concentrations of the solvents. The less severely contaminated wells have continued to operate, but water drawn from them has been blended with water from clean wells or aqueducts to bring solvent concentrations below state limits.
In 1985, Burbank abandoned almost all of its wells and began buying its water from the Metropolitan Water District.
The well packers constitute one of several temporary measures being taken to maintain a steady supply of ground water to supplement the water that Los Angeles imports by aqueduct from the eastern Sierra and that it buys from the Metropolitan Water District, Coufal said. It may be 10 to 15 years before the contaminated water can actually be cleaned up, he said.
Aeration Tower Planned
Along with installing the well packers, DWP is drilling 11 new wells north of the contaminated zone; is planning to construct an aeration tower meant to treat the contaminated water and keep it from spreading; and, under the direction of the Environmental Protection Agency, is conducting a study to determine where the contamination came from and to see if new sources of contamination are adding to the problem.
The highest concentrations of solvents seem to be confined primarily to three underground zones near the boundary between North Hollywood and Burbank. It is suspected that the solvents leaked over several decades from underground storage tanks and septic tanks in the industrial corridor along the Southern Pacific Railroad line that transects the Valley.
The wells that are being fitted with packers are located in the vicinity of the three zones. In this region, the aquifer--the underground lake locked in porous sand and gravel--is up to 1,200 feet deep.
When the wells were sunk--some are 60 years old--records were kept of the layers of sediment that were pierced during the drilling, Coufal said. It is thought that a 30-foot-thick layer of clay, found at a depth of 300 feet throughout much of the area, has acted as a barrier, confining most of the TCE and PCE to the shallower zone.
The wells, designed long before the pollution was detected, collect water from both the shallow part of the aquifer, above the clay layer, and the deep zone. Each well consists of a 20-inch-diameter perforated pipe that is sunk into the earth as deep as 800 feet. Within the outer casing is a second, narrower pipe fitted at its lower end with a powerful pump.
Casing Filters Water
Water from the surrounding gravel or sand pours through the holes in the outer casing, drops to the bottom of the well, and is pumped to the surface through the smaller pipe by the motor at its base.
In the modified wells, the small-diameter pipe is removed and fitted with a well packer. Once the pipe is reinserted in the well, the packer, like the cuff a doctor uses to check a patient's blood pressure, is inflated with pressurized air. The packer is placed in the well at the same 300-foot depth as the clay layer in the surrounding earth.
The bulging rubber packer prevents the shallow, contaminated water from pouring through the outer casing and cascading to the bottom of the well, where it would be pumped to the surface.
Instead, only water from the cleaner deep zone is pumped, Coufal said.
In the three working wells, TCE levels plummeted after the packers were inflated, Coufal said. All three had produced water with TCE concentrations of 50 parts per billion or more before the packers were installed. Since then, TCE levels from those wells have fallen to less than 2 parts per billion, well below the state-set limit of 5 ppb.
Water from these wells is being pumped into the distribution system and sent to the city's reservoirs, Coufal said. It is tested daily at the head of each well to ensure that concentrations of solvent remain low. As an added precaution, even if the concentrations remain below the state limit, the water is diluted with large amounts of water from supplies that are known to be clean, he said.
There are still substantial bugs to be worked out, Coufal said. Four of the packers installed so far have had mechanical failures, such as leaks, he said. And three do not seem to significantly affect pollution levels. That may be because they were placed at the wrong depth, away from the clay layer, or because the clay layer in that spot is not a continuous shield against the solvents.
Knowledge of the extent of the clay layer is scant, gathered only in spots where wells have been dug, said Henry Venegas, a DWP senior planning engineer. There may be gaps in the clay that would allow the solvents to sink farther than 300 feet.
The in-depth study of the ground-water basin, overseen by the EPA, should answer that question, he said.