I wouldn't advise making compost filled holes. That will give you holes that are very porous surrounded by compacted soil, so all the water would tend to flow into those compost filled holes. Anything planted in the holes would get too much water.

What do you want to plant there? Do you want it to be lawn, vegetable garden, flower garden?

Since you think it might have been damaged by chemicals, you might want to avoid growing vegetables there until you find out for sure whether fire suppression chemicals were used, and if so, what they were.

One thing you might consider is creating a raised garden. A Lasagna garden would be a good way to create a bed where you could grow things and at the same time, provide a lot of organic matter so that the soil below it would loosen up. The lasagna garden concept is based on layers. You alternate layers of high carbon matter (tree leaves, shredded wood, paper, cardboard) and high nitrogen matter (coffee grounds, vegetable trimmings, grass clippings, manure). Pile it up in the fall and plant in it in the spring. I think you want to start with a pile that is about 3 feet deep int he fall. It will rot down quite a bit and probably be less than a foot deep in the spring. By next fall, it'll only be a few inches deep. Then you can start over again, or you can see whether it helped the underlying soil enough that it will support plants.

Organic matter does great things to the soil, but it continues to break down, so it needs to be added on a regular basis.

You can often get shredded trees for free from tree trimming companies. Depending on what was being shredded, there may be a fair amount of green matter, so it might be close to the mixture of C and N that you want without any additional N.

Starbucks has a corporate policy of making used coffee grounds available for free to anybody who asks for them. You can ask at other coffee shops and restaurants, but it's easy at Starbucks, because they have a "grounds for the garden" policy.

Some grocery stores will give you their spoiled fruits and vegetables and trimmings, but others are concerned about liability and won't. It doesn't hurt to ask, but don't get upset if they say no.

Start by contacting the local office of your state universities USDA Cooperative Extension Service about having a good, reliable soil test for base nutrient and soil pH levels and then dig in with these simple soil tests to see what that soil now has,

1. Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
to see what you need to do to make it into something good and healthy that will grow what you want.

I agree about the concern regarding fire suppression chemicals, if you are planning on growing something edible there. If it were me, I'd talk to the fire department and find out what they use, then google it to find out more information on the particular chemicals in the product. Assuming it's safe, lasagna is indeed a good way to go. I have two other alternatives to add:

1) Rent a rototiller and till in as much compost as you can. Under normal cicumstances I wouldn't ever recommend a tiller. I practice no-till techniques in my own gardens. But everything has its place in the world, even rototillers. There are some times (however rare) when using one makes sense. This might be one of those times. If you do rent one, make sure it's a BIG one. The biggest rear-tine tiller you can find, preferably hydraulic. Spread plenty of compost on the surface of the soil and then till it in. The only catch is that if you do this, you will have to keep adding compost or other OM periodically and avoid walking on it, because it will have a tendency to recompact.

2) Alternatively, you can spread a 1-2 inch layer of compost and then plant a cover crop. My favorite cover crop is winter rye. It has a VERY aggressive root system, and if anything can break up that hard soil, it will be winter rye. We have very hard soil in some spots too, and I tried this method as an experiment several years ago. I cut back the rye in the spring, then overseeded with finer grass seed, mulched with more compost, and it did fine.

-Diggity