Cold patch asphalt is commonly used to effect minor, short term repairs of permanent asphalt such as potholes, temporary curbs and gutters, driveways, access roads, etc.
Cold patch does not cure and harden like hot asphalt because is has diesel oil added to keep is soft and pliable which makes it easier to remove when a more permanent repair is to be completed or temporary fixtures are not needed any longer.
Because of the diesel oil additive, stockpiles of cold patch need to be kept covered and protected from rain as rain will wash some of the diesel off and allow it to run off, possibly into a storm drainage system.
Any petroleum product that washes into storm water is regulated and laboratory-tested as a total petroleum hydrocarbon (TPH).
The easiest way to tell if there is TPH is the water is by looking for a sheen, which is the petroleum product floating on the water.
A sheen is recognizable by the rainbow effect it produces.
You have seen this in parking lots when rain washes off oil that has dripped from cars. The petroleum-caused sheen is visible in this video.