How to build a cutoff drain sump pump pit?

[kn_ll]

I am planning to install approx 35 meters of aggie pipe drain with a sump pump pit for lowering the water table. The pit needs to be 1500mm deep. For the pit I am looking at installing Everhard 600 x 600 x 600d pit with three Everhard 600 x 600 x 300d riser stacked on top making the total depth 1500mm. It is unlikely that any vehicles would run over this pit. Are there any issues with the narrower pit and is there other pits in the market that does a similar job? Further what size sump pump would be required? Note no direct rain water would be collected except what is absorbed from the surface into the ground. The ground is medium dense clayey sand, so the vertical surface collection area into the scoria would be 35m long by 1 m deep one side only, the other side of the trench would be lined with polythene.

[MitchellMc]

Welcome to the Bunnings Workshop community @kn_ll. It's sensational to have you join us, and many thanks for your question about installing drainage.

You might like to post a diagram of your setup so our members can better understand what you're planning. That way, they'd be better informed and able to offer great suggestions. Let me know if you need a hand uploading images.

Depending on your expectations for water collection, you could get away with a 450mm pit. We can Special order the 450mm risers for you. It sounds like you are installing the agline and pit particularly deep, to capture subsurface water as well. If you are successful in your endeavours, that could be an immense amount of water. Out of interest, why are you trying to capture the subsurface water? Is it heading into an area you don't want it to be? Remember, if this subsurface water is running from adjacent properties, it could well exceed the capabilities of your system, and I wouldn't have thought a lowering of the water table is particularly practical or possible.

I'm keen to hear more about your project, especially the issue you are trying to resolve.

Please let me know if you have any questions.

Mitchell

[kn_ll]

Thanks @MitchellMc 

Very rough sketch below.  Thankyou for advising the Everhard 450 series  (450 pit plus three risers) would be suffice for my needs.  I did my own calculations on water flow as follows:

permeability of clayey soil from search of internet 5.6 x 10-6 m/s x 35 metre length x 1 metre deep = 0.0002 cu m/s = 0.196 l /s = 11.76 l /min.  The pit itself would be installed such that minimal surface water/rain water would not drain into it. The surrounding ground would be graded such that surface/rain water will collect into the existing storm water system.

Bunnings pump https://www.bunnings.com.au/claytech-ecosub-7-clean-and-dirty-water-drainage-pump_p4819842 = 140 l /min should suffice - do you have further comment/recommendations?

[EricL]

Hello @kn_ll 

Your plan looks very sound, my only other recommendation is to make sure that the connection of the agi pipe to the pit is very secure. I recommend using an Everhard EasyDRAIN Pit Boss Connector in conjunction with Selleys 290ml Grey Storm Waterproof Gutter And Roof Sealant to provide a good seal for the pit boss connector. Please make sure to use screws to secure the pit boss to the pit.

In order to get a good cut on the pit, I suggest having a look at the Hole Saw Kits in the tool shop. 

If you have any other questions we can help with, please let us know.

Eric

[kn_ll]

Thanks @EricL. The sealant in my case is probably not required as I require the ground water to seep into the pit and any  rainwater will or should be pumped out and not increase the ground water table significantly.  I have further queries  - how reliable are the lower end pumps like  https://www.bunnings.com.au/ozito-350w-dirty-water-submersible-water-pump_p4816179. Are there other manufacturers products similar to the Everhard pit and riser?

[EricL]

Hi @kn_ll 

Between the two, the Clay Tech pumps have been around for a long time and have a very good reputation. 

I'm currently not aware of any other pit that will do the same work as the Everhard pits. About the only other way to replicate the pit function is to build it out of bricks and concrete.

If you need further assistance, please let me know. 

Eric

[kn_ll]

Thanks EricL

A few more queries:

With either pump how high above the base is the inlet?

With the pit cover does Everhard produce a fully covered plate like a checkered plate?

I am not planning to fit a Pit Boss Connector as there is no need for a completely sealed pit - from Everharde Installation manual it states of possible movement of the pipe - do you know of have any experience with movement?.

Everhard Installation instructions state "450 x 450 pits should no be deeper than 600mm to outlet invert"  - my pump would be installed at bottom of 1500mm deep pit and I understand that "the pump can be fully submerged up to a depth of five metres for efficient water removal".

[EricL]

Hi @kn_ll 

According to the Ozito brochure the minimum suction depth is 50mm the gap seems to be the same for the Clay Tech unit. However, I'll double check that for you when I get a chance. But the Clay Tech unit has one feature that the Ozito unit doesn't have and that is low level suction up to 10mm when manually operated.

To my knowledge they only do the solid checker plate cover for the 300mm pits. However, they do make a polymer cover in 450mm which would be suitable for your needs. Here is the link to the cover's technical details - 450x450 Everhard Polymer cover.

Movement occurs when water enters under the bottom of the pit. This causes the soil to soften up and "movement" occurs when the water drains away causing the pit to settle.

The outlet invert refers to the bottom of the outlet pipe and the pit must be no deeper than 600mm from this point. I'll have to doublecheck with Everhard regarding the position of your Agi pipe and how deep you plan on using it. As soon as I have more information, I'll get back to you.

Eric

[kn_ll]

Thanks @EricL 

I have a further query regarding float level for on/off.  Refer attached sketch (NTS) - Can the float be set such that it switches on when it reaches 300mm above water level - I don't want water siting above the sand layer, The float switch turn off when its below 100mm.  If the float is difficult to set then what is the minimum depth where it turn on?  Further its noted that the minimum area is 500x500mm.  Is this a concern if it's installed in a 450 x 450mm pit?

[EricL]

Hello @kn_ll 

My apologies for the late reply, I spoke to Everhard's technical team about the proposed depth of the pit. I explained to them what you were planning, and they mentioned that they can't predict what will happen or how the pit will behave when it is buried that deep. Their warranty only covers the pit and the first riser at standard depth, any deeper than that or any additional risers will void the warranty of the product.

In regards to activation, I'm afraid you'll need to tie a rope to the float switch to manually activate it if you want the water to be less than 100mm. The float switch is sealed and can't be adjusted, so when the tank reaches 100mm it will stop pumping and when it goes above 100mm it will start pumping.

Now that I've had time to think of it, the narrow shape of the pit might not be ideal for the pump to operate in. It is clearly stated that an area of 500mm x 500mm must be provided for the pump to operate properly. If the float switch should get caught up in the corner of the plastic pit, it will burn the motor out.

As a possible alternative, I propose building the pit out of bricks, rendering it and then covering the surface with Gripset Betta 1L Waterproofing Membrane Bitumen Rubber. 

If you have any other questions we can help with, please let us know.

Eric