It stays in ground months and can spread like wildfire. I'd close it post signs and say enter at own risk after 30 days.

We always treated with bleach when it happened in our yard..

Vet Approved Answer
According to Cornell’s vet school:
Do NOT bleach your grass, but you can bleach any surfaces that the dog may have pooped on
A combination of rain/watering down the lawn, along with sunlight will bring down the number of virus particles to acceptable in a few weeks.
Sunlight is a natural disinfectant and the best defense when it comes to outdoor.
Adult, fully vaccinated dogs, after diluting the area with water/rain should be okay but they may want to consider shutting down the park for 1 month, or just advise everyone what happened and let them use it at their own risk.
When using bleach on any surface, mix it 1 part bleach to approx 30 parts water
Any dog who is not vaccinated or is less than 18 months old, should NOT go to the park for the next month or so.
The goal of outdoor virus control is to limit the numbers of viral particles, you’ll never fully eradicate all of the virus, but the best option is to water down the area multiple times, and make sure all organic material (poop and potential vomit) is picked up.

And park can't be used for couple weeks

Once treated dogs will have to stay off of it for 30 days

Are you sure your pet park is to blame? Parvovirus can be brought into a home from one’s shoes who could have been infected anywhere? This is the first that I have heard of a community having this issue. If your park is infected then you will have to shut down for at least 7 months however it can be in your yard for at least 1 year