Hello all!

Been dealing with some major water retention in my yard and going to be wrapping up some final installs to get things situated. Looking for some suggestions on some of the nitty gritty details on this setup.

Here's what we have going on:

The property next door to me is a church. The church has a large parking lot that dumps quite a bit of rain water onto my back lot. There's a drain line that runs the entire length between my property and theirs, and dumps into the storm sewer at the street. It's a 200 ft run from the back of the property, to the storm sewer. There are a few inlet drains along the way, but they're not doing much good, as they're above grade. The church's downspouts are also tied into this line, which dumps a TON of water into the line. During heavy rains, the line maxes out, and overflows.

I have low spots (seen in orange waves on the diagram) in my back lot. When the water backs up, the parking lot and the lines that are backing up, fill this low spot. To help alleviate the water in these low spots, I tied in some collection basins (in gray). Once the main drain line finally clears, these basins will drain out the low spots into the main drain line. Sometimes it's slow, but it eventually makes it out.

The pitch on my back yard is VERY slow, so my next project is to bury my gutter downspouts and sump pump line, moving everything off my lawn and over to the side yard so they can flow into the main drain line. I currently already have them all tied together with black corrugated pipe, but it's simply all above ground for now.

The blue and green lines are showing where I'm going to be burying the lines.

Here are my main questions:

1. What's the safest way to run my sump line? I'm planning on putting a deck over this area, so I'd love to be able to come directly out of the pit from the side (underground) without coming up first above ground and then down into the ground at an angle. Is that feasible? I'm in Northwest Indiana, so I'm concerned with freezing. And yes, I'll be making a hatch on the deck to allow access to the pit.

2. I should run two separate lines, correct? One dedicated to the downspouts (corrugated), and one to the sump (1 1/2 schedule 40)? Or could I tie the sump right into the corrugated where they first intersect?

3. Where the sump discharge and the downspouts meet the collection basin area...how should I terminate these lines? Should I route them directly into the collection basin? Or should I pop them up to surface and let them find their way to the basin? I'm concerned that if the low spots fill and the collection basin(s) are completely full and covered, will this stop the movement of water from either the downspouts or sump?

Any suggestions on all of this would be GREATLY appreciated! Hoping to get this all done this week.

Thanks so much everyone!!