The pine needles are not a problem in the soil. To get that soil into the good, healthy condition that grasses need to grow strong and healthy contact your county office of the Washington State University USDA Cooperative Extension Service about having a good, reliable soil test done so you know what that soils pH and base nutrient levels are and what to do to correct any problem areas adn also dig in with these simple soil tests, 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 se what else might need be done to make that soil into a good, healthy soil. Here is a link that might be useful: WSU CES

Digging it up is the only way I know besides poisons. You'll get it if you keep working at it. I wouldn't put it in an open pile without killing it first, which I would definitely do. You're going to earn that organic matter, it might as well be put to work. You could kill it in a plastic bin or bucket like a trash can, a trash bag, or even laying exposed on concrete or sheet metal to bake in the sun. After a point, it will definitely be dead, then you could put it in the compost to finish decomposing. It's not flowering and producing seeds is it? About the tiny roots, if you are able to smother the area with cardboard or newspaper after you are finished digging and leave that alone next summer, you should be able to be sure that any ivy that attempted to keep growing was smothered under that layer. Cover with mulch or leaves so it's not an eyesore and stays in place. Maybe set some potted plants there next summer. Then you are free to garden the area at will after that. If that's impractical, it should be fairly easy, assuming you've done a thorough job of removing the bulk of the roots, to spot-dig little pieces you might have missed that throw up new sprouts. They might be so loose you don't even need to dig, just pull. You'd want to check it often next spring.

Is this painted wood then? If they won't come off with a softer brush and soapy water, you may have no choice but to scrape or brush with wire brush, then sand, followed by prime and repaint.

I agree, you must spray it few times, run the mower over the dead ivy to scalp it, then mulch. If you want to plant over the area, beware the tangle of tough woody roots. Very daunting to remove by hand (Boy, do I know!). Maybe a BIG horse power rototiller might break them up, but you don't want to damage tree roots. If you are not in a hurry, it might be worth waiting till the roots rot a bit, and you can catch any stragglers. Good luck!