The garden is overseen by professionals, so it has likely had soil testing done, especially since they are growing produce. Manhattan is mostly an island of be

The garden is overseen by professionals, so it has likely had soil testing done, especially since they are growing produce. Manhattan is mostly an island of bedrock, and there is no manufacturing or industrial areas in Lower Manhattan that would contaminate the soil. The only concern would be protecting the garden from water running off the streets bordering the park, but those all have drainage and curbs installed.