You won't. Don't worry about it. It's just soap. We've been so dry, its not likely to sink more than a few inches...

Ok cool, Thanks I don’t use any harsh chemicals just regular car cleaning stuff

There’s plenty of dirt and sand that will filter out the soap before it reaches the watr table. If that wasn’t the case, people with leach fields off their septic tank would be in bad trouble.

Same situation with water so I only use environmentally friendly liquid dish soap on my car. Most chemicals are harsh.

As others have said here, in the amounts that you use water for washing a car it’s not gonna reach your ground water. What you use and what is being washed off of your car is more of a concern and it’s really only a concern for the microbial life in your soil and things like worms, insects, salamanders and frogs.

Dawn dish soap works very well as a car wash and it’s quite benign.

I use Sheiners concentrated car wash. It’s non-toxic and ph neutral.

If you're REALLY concerned they make stuff specifically for your concerns, but I wouldn't worry about it.

Go onto a farming sub and ask what they use to wash their shit. They obviously have a lot of reasons to not poison stuff.