The site was three facilities in one: a styrene plant, a butadiene plant, and a synthetic rubber plant that combined their outputs into the ersatz rubber the war economy demanded. Multiple companies leased and operated the plants during the 1940s and early 1950s; Shell Chemical Company bought them outright in 1955 and continued operations independently. The industrial chemistry involved was effective at making rubber and also, as it turned out, effective at producing toxic waste. Benzene, ethylbenzene, naphthalene, chrysene — volatile aromatic hydrocarbons and polycyclic aromatic hydrocarbons that are, several of them, known human carcinogens. These compounds needed somewhere to go. The plants put them in pits.

At the southern end of the site, covering 3.7 acres, the rubber manufacturer dumped waste materials into six unlined pits and three or four unlined shallow ponds. Unlined means exactly what it sounds like: no clay barrier, no synthetic membrane, no engineering to keep what went in from going out. The waste seeped directly into the soil. From the soil it migrated into the shallow groundwater. From the shallow groundwater — the question that occupied regulators for decades — it threatened to migrate into the deeper aquifers from which people drew their drinking water. The pits were used for decades. When the plant closed and the land changed hands, the pits stayed. The waste in them stayed too.

The Environmental Protection Agency added Del Amo to the National Priorities List in 1997, approximately twenty-five years after the plant closed. Remediation efforts began in 1995 and are ongoing. They include capping the waste area, installing surface water controls, running a soil vapor extraction facility, and monitoring. Between 1982 and 1984, contaminated soil from one waste pit was excavated to 25 meters depth and hauled to an approved disposal facility. The hole was backfilled with clean soil. Later sampling found contaminated soil beneath the backfill. The cleanup, measured against the scale of what was deposited over three decades, is a process of generations. During the active remediation period, 55 of the nearest homes were bought out by the responsible parties.

The people who grew up near the Del Amo site did not know what was beneath the ground. Children played in and around the waste area before it was capped and fenced. They saw waste material on the surface without understanding what it was. A health study in the late 1980s found higher-than-expected rates of skin, eye, nose, and throat irritation among people who lived close to the site — along with earaches, dizziness, and fatigue. The same study found no elevated cancer rates. That finding was described as reassuring at the time, though the contamination has continued to evolve since. A more recent EPA review found volatile compounds migrating into groundwater reservoirs used for domestic water, a development that had not been anticipated in the original assessments.

The Del Amo site today is mostly an industrial park — warehouses, light manufacturing, the unremarkable built landscape of the Los Angeles Basin's working south end. Nothing in the streetscape announces what lies beneath it. The soil vapor extraction equipment runs quietly, pulling contaminated gas from the ground so it cannot seep into the buildings above. The monitoring continues. The neighboring Montrose Chemical Corporation Superfund site adds its own contamination plume to the groundwater picture. The work of containing what was made here — rubber for the war, poison for the future — is not finished and may not be finished in the lifetimes of anyone who remembers the plant's operation.