Building rainwater harvesting system. Anyone have some advise?

Hello everyone!

Im in Northern New Mexico. just moved in a few weeks ago and I'm getting our rainwater harvesting in place. What I have is a single story, double wide mobile home on a permentant foundation that is on a hill side. I just had seamless gutters installed and have three downspouts. Im looking for advise on a few issues in design.

1. Tank placement: Due to surroundings, I want to place the tanks downhill and use a solar powered on demand pump off the tanks to deliver water. We get nasty winds here and I need to place the tanks to help block wind for future development as well as not block any views (if possible) for resale value.
2. First flush diverter: Are these required? If so, is there a formula to determine tank capacity for it to be effective? I see people using 6' PVC pipe as "tanks" but I cant see getting enough volume to do any good in my situation.
3. Dry vs Wet piping. It freezes here during winter. Frost line is only 12" so going below the frost line to run pipes isnt an issue. Im concerned about freezing above ground though. Thoughts?

Details:
Total square foot of roof (Garage + House) is roughly 2800 square feet
Tank size 88"H X 142"D holds 4,995 gallons. There will be two for a total storage of 9990 gallons
Total annual rainfall is 15 inches a year
Gutter size is 6" seamless
3 Down spouts. 2 on the North side splitting the drainage roughly 75% and 25 %. South side 1 downspout for entire south side of house
Piping size: Thinking 3" for down spouts merging into a 6" underground to tanks then splitting back to 3" to each tank
I need to avoid digging over utilities as they are only 12" deep. I can place the tanks over the utilities, but I cant try to bury piping over them.
Contour lines represent 1 foot elevation change. Higher point is the East side of building (Bottom of pictures).
Gutter bottom to ground on west side of house is roughly 10 feet.
Gutter bottom to ground on downspout 1 (North side farthest up hill) is roughly 8 feet


Pictures:

Utility restrictions


Tank placement area. Lots of room to work with.


North Side with the two downspouts


South Side with one downspout


West side (where tanks will go) Mocked up an idea of tying south with north downspouts


Better shot of west side



Any feedback would be great. This move hasnt gone as planned and the tanks are showing up in a few weeks. I need to get this figured out so I can prep the site.

Thanks for reading,
Mav



* edited for addition details

Groundfous makes a brilliant 110v pump. No pressure tank. It uses the downstream pipe as the pressure tank. It also has a built in check valve. Pressure is better than many municipal water supplies.

I don't use a diverter, but I do have a device that sheds leaves. Its made for collection. It has hardware cloth at a 45 degree angle. As water drops down, leaves slide down the cloth.

Russ Keller wrote:
1. Tank placement: Due to surroundings, I want to place the tanks downhill and use a solar powered on demand pump off the tanks to deliver water. We get nasty winds here and I need to place the tanks to help block wind for future development as well as not block any views (if possible) for resale value.

Can you have a smaller holding tank uphill which you can fill with the pump during sunny times? That way you might get some help from gravity. Otherwise you'll need to pump to a pressure tank to distribute the water.
(unless you get that special pump!)

Russ Keller wrote:2. First flush diverter: Are these required? If so, is there a formula to determine tank capacity for it to be effective? I see people using 6' PVC pipe as "tanks" but I cant see getting enough volume to do any good in my situation.

As far as I can tell the diverter standpipe need only be slightly shorter than the height of the inlet into the tank.

Russ Keller wrote:3. Dry vs Wet piping. It freezes here during winter. Frost line is only 12" so going below the frost line to run pipes isnt an issue. Im concerned about freezing above ground though. Thoughts?

Make sure your first flush diverter and any other vulnerable pipes have a way to drain. An easy drain on the first flush diverter is a small hole at the base of the diverter pipe. This way it will drain even if you forget to unscrew the cleanout between rains.

Russ Keller wrote:Piping size: Thinking 3" for down spouts merging into a 6" underground to tanks then splitting back to 3" to each tank

I don't think you need such large pipe for the run down to the tanks. I think 3" should be plenty large enough.

There's an example of a cold climate rain harvesting system in the tour video on this page: http://vergepermaculture.ca/

I hope this helps a little!

Thanks for the responses.

The tanks arrived earlier than anticipated so I have been offline scrambling to get the ground prepped as well as find some help placing them. Needless to say, this old back is taking the morning off. Those tanks are a challenge to move with just two people!

Wayne,
Could you point out what pump exactly you are recommending? Im on Grundfos's site and Im not even sure what category I should be looking at. Im not knowledgeable in these things. My background is electronics and computers.

Thanks!

What is the distribution of rain in your area? For example, do you get most of your rain in 3 or 4 big events per year or are there numerous rainy days. If you are relying on a few big events, you might want to consider adding a few redundant downspouts because it would not be that hard to lose 1000+ gallons of water because one of the downspouts got clogged during a thunderstorm.

I changed what I had to say, here. 9000 gallons, that's a lot. If it freezes, then that is your main concern.

I know yo8ur setup doesn't have this, but for anyone who has composite shingles on their roof, manmade shingles, they are toxic and are breaking down all the time, and water collected off of a roof like that should only be used on landscape, not edible crops.

Groundfos mq-45