Sump/sewage pump size for run-off ground water discharge questions.

[ShinDiors]

Newly found this forum and want to seek some insights on this water problem I've been trying to solve for our recently bought old house (built in 50s).

House we bought a year ago had this strange setup. In order to accommodate the addition of a 2-car garage and the sunroom above at the rear of original house, they extended/carved the driveway into the original backyard, and now the driveway is downward, with the end of it enclosed by the retaining walls. The only route that the run off water from the driveway, and from neighboring lot, backyard is a grated channel with a 4 inch PVC pipe buried under garage floor connected to a sump pit at the corner of the garage. Currently I have a liberty LE50 sewage pump in the pit, which goes 8400 gph at 5ft, but the discharge tube that connects to it is half inch smaller than the pump's 2 inch port. That tubing is partially buried into the cinder block wall then goes underneath/around the house to the street side drain. Pump is hooked up to the backup generator, so the power failure was not too much of a concern. Here is the problem:

The inlet 4inch PVC is at a rather low height of the pit, along with some foundation draintile inlets at similar height. When no rain, the pit is almost dry with not much underground water coming in, the pump is not running. When it rains the pump is cycling at reasonable frequency, if raining more heavily, the pump runs for 10s every 30s, until the incoming water start to back up in the pit and water level rises higher than the inlet pipe, that's when things start to go bad （happens once or twice a year). Water will then backed up at the grated channel and eventually enter the garage. I got some advise from drainage company that because of the water backed up inside the pit first, then backed up at the grated channel, it means that the bottle neck is the discharging capability rather than the inlet 4 inch pipe. What I need is to increase the discharge rate, so that the incoming water can flow freely (without backed up water in the pit blocking) into the pit.

I have got quite a few opinions, which are rather costly to me, from digging another pit at different location with another wiring and pump, to adding another pump in addition to my current setup and replace the entire discharging port with large pipes (including break through the cinder block wall to locate and replace the 1.5inch pipe goes out into the side backyard. A few concerns/questions I have in order to really pick a valid solution

1. From my description, do you feel that the problem is the discharging speed? I understand better solution is to reduce incoming water, for example, repair/waterproof the retaining wall to reduce he water from neighboring yard. My neighbor has already built a french drain system behind the retaining wall which helped a little, but I still see water pouring out from the retaining wall when it rains heavily. All my gutters were discharged through other pipes to the curb side and storm drain, and no visible overflow from the gutter (had guttergaurds) to the driveway run off.

2. How do I know if a pump is enough, for example, this 1/2 hp liberty pump has rate of 8400 GPH at 5ft, but the 1hp pump I got only has 7250 gph at 4ft. (curves from manufacturers attached), but requires much higher current/power than the 1/2 hp pump. The 1hp pump seems to have higher head according to the curves though. How do I compare this two pumps, if the max rate (speed at 0ft head)matters, does it mean that my 1hp pump is not as strong as 1/2 pump i have right now (because of different brands)? I ask this because it looks like the failure prone portion of most pumps are the float switch, I was planning to use a Hydrocheck H6000 high-lo electric switch with the pump until I noticed that the switch is rated at 13.8A while this 1hp pump is 14.2A rated (3/4 hp ones would draw less than 12A which can be used with this switch). I attached the current Liberty pump 's curve and the new pump I just got (circled out the 1hp and 3/4 hp ones). If 3/4hp is what I need, then I would couple it with the electric switch no problem.

3. Another advise is to reduce the 90degree turns in the discharging pipes and use 2 inch pipes until it is connected to the 4inch gutter discharge pipe that is buried and eventually goes to the storm drain curbside. My estimate is that there is not too much 1.5 inch tube after it goes out the wall and joint with the gutter pipe (have a rough idea where the exit from wall is but have not confirmed by digging), would it help my situation if I replace the exposed portion of 1.5inch pipe with 2 inch pipe without breaking the wall? Again I understand it is ideal to replace everything 1.5 inch before it's connected to the gutter drain, just coming from cost-effective angle.

4. If I put a more powerful pump in the pit (say the ihp pump listed above), how do I adjust the float switch to avoid over-cycling, especially when it only rains light to moderately heavy, which was handled alright with current pump) Should I let the pump turn on when water level is right below the inlet pipe since I notice that having water in the pit blocking the inlet seems to be reduce the inlet water speed quite a bit and cause water backup at the channel drain.
5. I'm restless about the pumping going bad for whatever reason, that's where the thoughts of more reliable non-moving electric switch came from. But other than that, do you think I need a secondary pump at all? Any other risk mitigation methods? Cheaper solution might be a utility pump with a flex tube either hooked up with the current discharge pipes somewhere or directly pump to street side? I will need to rewire another dedicated line from subpanel/backup generator for a 2nd pump too.

Sorry about such a lengthy post/repost, I'm trying the provide as complete information as possible for your suggestions. Thanks a lot

 

[cvg]

1 1/2 inch pipe can handle no more than about 60 - 70 gallons per minute (say about 4,000 gallons per hour). if you want to maximize the flow rate, you will need to upsize your discharge line to at least 2 inch diameter.

the photo seems to show about 50 gallons capacity in your sump which should take about 1 minute to pump out. however you say that the pump only runs for 10 seconds. 10 second run time every 30 seconds seems too short. seems like your sump may not be deep enough and during heavy rainfall, your pump discharge is inadequate.

 

[LittleInch]

Hmm, That's some pst alright and maybe not really one for a professional pump forum, but I'll give you a pass for today...

Any way a little more data if I can ask:

1) does your pump have a Non return valve incorporated in it?
2) What is the approx length of pipe before the pipe emerges into the open air?
3) When you get heavy rain does the pump run continuously? You mention 10 seconds every 30 then you start talking about the water level reaching the top of the pit?

Anyway I reckon your issue is the pipe, not the pump. The issue is head loss.
I think you have a static head of at least 8 ft from floor to where the pipe goes out the wall (does it go up any more from that last photo?)
With your current pump you only then have about 10 ft less for losses in the pipework. I reckon you're sitting about 60 gals/min

Those LE50 pumps appear to be very efficient compared to the other pumps you list which have less head and flow for the same input power.

But you're stuck with the issue of a realtively small sump and highly variable in flow which is very difficult to do with only one pump.

I think if you can increase your pipe size to maybe 3" then your existing pump will probably cope with a storm condition. 2" is better but still not great.

those pumps you show would be better because they are higher head but because of lower efficiency I don't think you'll get much more flow.

Or make the sump bigger to absorb the sudden downpour scenario....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ShinDiors]

@cvg, thanks for your reply.

One of the pix showed the inside of that pit, and as I mentioned in OP, I was a little concerned that the inlets of those pipes (the white pvc is the one catch water from the grated channel) plus the two black draintiles seemed to be low compared to other typical sump pit installation pix I've seen. When the pump cycles 10s every 30-40s, the water level in the pit is not too much over that inlet pipe, and would be discharged after the 10s cycle. If the water came in too fast compared to the discharging, I would start to see the water level rise above the inlet and pump would constantly running, that's when the grated channel area in front of the garage start to have water puddling. So I never really see the water level in that pit rise to over half of the height without having backed up at the channel and water start to enter the garage half way.

If it gets worse, the backed up water would enter the garage entirely, with 1 inch standing water, and the pit water level would maintain at high (rise slowly or maintain), until the rain gets lighter and water recedes. If keep getting worse, the water in pit would overflow and at that point, the standing water in the garage would be 2inch or higher.

My gut feeling of seeing this is that the sump pit's volume was not utilized efficiently (I think you want the inlet pipe higher up in the pit, so that the pump can have enough time to pump out water before it covers/blocks the inlet pipe, coz water flows into air is much faster than moving into a full tube of water) Did I understand the fluid mechanics correctly here?

I feel readjusting the pit seems to be a very costly project since the limited space there. But do you feel that I need to dig the pit deeper so that the relative height of the inlet pipes would be higher in the pit? Is it OK to have the edge of the sump pit/tub lower than the concrete inside that crawl space?

Also is increase the pump capacity (say getting a 1hp pump)+ maybe swap out all the exposed 1.5inch pipes right before it enters the wall, the easiest/cheapeast solution or i still need to pair it with a deeper pit?

 

[ShinDiors]

@littleinch, thanks for bearing with my lengthy posts and all. I've been battling this for the past year after several trials and errors, inherited this problem without the previous owner disclosing it.

To answer your questions, if the non-return valve is a checkvalve I'm not sure the pump has a built-in one, but i think there is one check valve(the black thingy) in the discharge pipe (vertical portion).

For 2), if you are referring to the vertical pipe from the pump till it makes the 90degree horizontal turn, I would say about 3-4 ft. That pit is just a standard size trash can with a lid, so not a big one. And the pipe goes horzontally out from the block wall but not higher. based on the surroundings, my guess is it goes out the wall and tap into the 4inch pvc gutter drain, and outside that wall is the higher point of my side backyard and I belive the gutter drain then use the gravity to carry water into the storm drain curbside.

For 3), when the pump cycles 10s every 30-40s, the water level in the pit is not too much over that inlet pipe, and would be discharged after the 10s cycle. If the water came in too fast compared to the discharging, I would start to see the water level rise above the inlet and pump would constantly running, that's when the grated channel area in front of the garage start to have water puddling. So I never really see the water level in that pit rise to over half of the height without having backed up at the channel and water start to enter the garage half way.

If it gets worse, the backed up water would enter the garage entirely, with 1 inch standing water, and the pit water level would maintain at high (rise slowly or maintain), until the rain gets lighter and water recedes. If keep getting worse, the water in pit would overflow and at that point, the standing water in the garage would be 2inch or higher. During the whole time, pump is running continuously. Also want to clarify, the pump currently in the pit is 1/2 hp LE50 (curve is the 2nd one), the cheap 1hp one I got has the curve in the first graph (I thought the 1hp one has more head than the LE50, but has less max rate,or I'm reading it wrong?). I was trying to trial and error to see if a larger pump would improve the situation, since that maybe the easiest thing to start with, I'm also trying to see which is the key point of the solution (pipe size, pump size or both). So thank you for suggesting the pipe size might be more important than having a larger pump in.

 

[cvg]

I think you understand clearly, the inlet is too low, the pit and the pump inlet is not very deep and the sump is not being fully utilized. making it deeper will be costly. installing a second sump tied to the first might be cheaper but still costly. Both options also require upsizing the discharge pipe improve the pumping rate. So start by upsizing to at least two inch diameter and cross your fingers that is enough to make the difference.

 

[ShinDiors]

@cvg Is the 1.5inch in/out the wall portion critical to change if I replace all the exposed pipes to 2-3 inch? If my estimate is right, the remaining 1.5 through the wall until getting tapped into the gutter drain, would be 2-3ft or less.

Also, if the pump has 2 inch port, would 3 inch pipe cause the slowdown of water and the deposition/potential clog of the particles in the water?

With the sump pit as is right now , I'm concerned about the cycling issue with larger pump given the volume (water below the inlet pipe from channel drain) that it needs to replenish is relatively small, the big pump may cycle way too often (it may only need to run 4-5s compared to the 10-15s the current pump runs) when it rains moderately. Is that an issue without readjusting the sump? Currently I think the pump was set to kick in not too high above inlet pipe, so when it runs normal, I would hear the water dripping sound fading and then the pump start to run for about 10-15s, until the next time water level covers up the inlet (depending on how fast water comes in). Should that be adjusted to kick in higher? I feel it works when moderately rain, but when incoming water is too much too fast, the pump is not gonna be able to get it out and I would probably see a lot more overflooding from the sump.

 

[LittleInch]

What are all those other pipes entering the pit??

More water from somewhere else?

what level does it start and stop at?

Can you sketch out a cross section view of this from the grating with some dimensions?

A larger pump would only help a little bit because you're basically maxing out the practical flow in your 1 1/2" pipe. If you double the flow you need 4 times the pressure loss.

A larger pipe should allow you to flow more so velocity wouldn't be an issue here in terms of sediment. It's going to be going fast enough

Unless your remaining 1 1/2" pipe is less than 10% of the total length then your pipe size upgrade might not see much improvement.Try to do it all - It's much better.

Basically though as you improve that capability your pit will pump out even faster when on low water flows, burning your pump out.

Your pit is simply too small so its up to you as to how to make it bigger. Maybe another two or three of those plastic drums connected together at the base??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ShinDiors]

@LittleInch

The two black draintiles seem to be some kinda of foundation drain at the house's perimeter, I don't really see too much water from them. There is a smaller pvc seems to be the AC drain which is also minimum, the big PVC pipe is the 4inch tube that's buried under the garage concrete connecting the grated channel in front of garage. I think currently the concrete is grated to make this pvc pipe the lowest point.

Here I drew an illustration of the cross section, the tub is a 20" inner diameter around the top but narrows down a little towards the bottom, 39" deep. The center of that PVC inlet pipe is about 22" above the tub buttom, so roughly at the center height (higher than I thought). I can't tell the pump starting water level right now since it's only raining slightly, but judging from the sound (incoming water flowing down to hit the water inside the sump fading), I'd say it's set at about that inlet pipe level, around 20“-24”，it stops at maybe 2-3" where I can see the float sitting at the bottom out of the water.

The discharging pipe: 38"(from pump up)-elbow-19"(horizontal)-elbow-7"(down to ground level inside crawl space)-33"-elbow-9"-elbow-87"(45degree up)-45degree elbow-11"-right angle elbow (where it exits the cinder block wall), there are two right angles elbow from the pump up then back down to ground level(I think can be eliminated?) to give space for the lid

 

[cvg]

I estimate about 20 gallons or less is your useable volume, your sump is way too small. Cycling is currently a problem and increasing the pumping flow rate will not improve it. It will however allow your pump to keep up with higher storm flow to prevent flooding. the ultimate solution is to increase the useable volume of your sump

 

[ShinDiors]

@cvg, If the discharging speed improves with larger pipe, can I set the pump starting water level higher to improve the cycling issue? I don't know what normally a sump pump's kick in water level is though, is it higher or lower than inlet pipes? Another question is what a normal sump size is, I checked online and a lot places are listing 30" deep, 18-24" in diameter as a routine basin, for example

https://www.radonseal.com/pumps/articles/sizing-sump-pit.htm,

this pit I had seems already larger or at least on par, of coz, my application is different than a regular "sump pump", but is it really way too small (if paired with appropriate sized discharging pipes).

The crawl space is really tight to fit another sump, so to increase the usable volume, either dig it deeper and wider or maybe add another sump with/pump at another location? Don't know which one is more costly though, and it will be on top of replacing the discharging pipes.

One landscaper gave an idea to dig a sump inside the garage (the right front corner inside, view from the door), and then extend the channel drain and connect it with the new sump with some underground pipe, then discharging straight up and penetrating the cinder block wall and tap into the gutter drain right outside that wall (which I suppose is the same the drain that goes around the back and connect to the current pump discharging pipe on the other side). Easier way is to have an external sump+pump, but freezing could be an issue, especially if we want to pump straight up to meet the gutter drain.

 

[cvg]

If the discharging speed improves with larger pipe, can I set the pump starting water level higher to improve the cycling issue?

yes, that might allow the pump to run a little longer

what a normal sump size is

pumps are not normally sized to handle peak rainfall runoff rates for an entire driveway, they are usually for seeping groundwater and nuisance flows.

 

[LittleInch]

OK,

Interesting post and issues so here's what I make of this.

You are working with a very large range of flowrates of water here which is nearly impossible to do effectively with a single fixed speed pump and a very small pit relative to the flow rate / pump.

Having looked more at the details of your system as it is now I think you are more likely pumping at around the 90-100 gals/minute mark so have about 15ft of head losses (static and friction) when your pit is full. Even replacing the entire system in say 3" pipe won't get you much more flow ( say 120 gpm).

Without out knowing the fall or relative invert levels of your intake pipe it's not possible to say if you should raise the high level point on your pit or not but I can't see it making more than a couple of seconds difference so I would leave it as it is.

So I would think you should try

1) Replace what you can easily of the 1 1/2" pipe with 2 1/2" or 3" pipe and leave the rest as is. See if this is "good enough" for the 1-2 times/year when you get surface flooding.
2) If not then the next best thing is to install a second pit next to the first with a cross over at a high level (above the inlet level from the drain)so that it only works if the first pump is being overwhelmed or has broken. You might think about moving your current pump into this pit and installing a smaller pump to cope with the more "normal" flows to stop this intense stop/start action which will be reducing the life of your motor as we speak. You probably only need something which does 20-30 GPM at 10 ft head. Just run at least 2" pipe and preferably 3" pipe from this new pump to give it the best you can. Then with the smaller pump you will probably have around double your current flow capacity.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ShinDiors]

@cvg, thanks for the reply
@LittleInch Thanks for the reply and suggestions

You nailed the core of this problem, the wide range of flow rate vs single pump+smaller pit. Currently the 1/2 pump was put in with the mindset to deal with worst case scenario, but its on time each cycle probably was set too short to cope with the fastest incoming rate. I would probably see more flooding (both overflow from pit and water backed up and enter the garage) had I set the trigger level at higher water level.

I did a very coarse measurement, so the inlet 4inch pipe from the grated channel is roughly 23-24 ft, the height drop from entrance (at the channel) to exit (at the pit) is probably 20 inches or slightly less. I would see water pouring out fast when its raining heavily. I think the bottle neck might not be the incoming speed, but more with the water storage capacity and discharging speed.

I think there is some room for a 2nd pit in the crawl space (in front of the current pit) but could be very costly considering the narrow opening and hard to work condition. I would imagine you'd have to stand outside trying to operate a jackhammer then crouch/benddown to dig the hole.

Talked to at least four difference group of contractors (some are general contractors/handyman, some are landscaper/drainage/waterproof company), only a handful of original ideas but not once any measurement of the current capacity. There are currently two different proposed solutions at the table:
1. Adding a 2nd pit and pump, but originally it was brought up as an external pit/pump and discharging either with surface pipe to street side. But freezing could be a concern. This seems to be the least complicated/costly as it does not involve too much concrete breaking. (location is the yellow circle, it is the diagonal from the current pit) Variation of this solution is to put the pit inside the garage (red circled area) to avoid freezing risk, this would discharge straight up and penetrate the cinderblock wall and tap in the gutter drain right outside the wall at about ceiling level(should be the same gutter drain the current pump discharge pipe taps into as well. Shown in this pix).

I would like to have this pit to be the primary if that's the solution to go with, and leave the current sump and discharging pipe as is to save some cost. I have a spare 0.3 hp zoeller sump pump that I can put in the original pit, and use the Liberty 1/2 HP or the other 1hp pump in this new pit. One thing associated with this is how to divert the incoming water to this corner, since the channel drain and the concrete driveway is graded in a way that the PVC pipe in the channel drain is the low point for water to go. So the channel drain may need to be extended and regraded, which could be helpful to the garage door posts (currently both sides garage door posts are water damaged, and water flows along them from both sides, arrows shows the water flows direction).

2. Adding a second pump in the same pit, stack or parallel, with discharging pipes swapped to 3" pipe inside out. Two pumps will use the same 3" pipe (Y connected). There is only one drainage company mentioned dig another pit in the crawl space, simply because they thought the current tub may be too narrow for two pumps, not that they put in calculation of the current volume, pipe location, head loss etc like you guys helped me with here. This this also the company that tries to sell me the plan to spend 45k to replace the retaining wall and waterproof/drained behind the wall. Ultimately they are correct that the wall is failing and water from behind the wall (from neighboring yard) is contributing more than half of the incoming water especially when it's raining crazily heavy. Just don't have the fund to deal with that and also not sure if we would tear down and rebuild in the future (if rebuit, I would not want to have such a hefty retaining wall and lot height difference between mine and neighbor's, and will have space for a front load garage).

With all the additional info, do you guys have more suggestions which solution would be my best compromise? You both pointed out to swap the existing discharging pipes with larger (2 or 3 inch) and leave the rest (including the 1/2 hp pump?) as is and see how it goes. If this is not enough, I will have to use solution 2 right? Otherwise, I will basically spend entire cost of solution 2 plus maybe half of solution 1 (I think the pipe replacement might be more than half, coz it invloves digging and conrete breaking) all together. Also in my case, I'd probably really need a 2nd pump as a backup, although I have backup generator to mitigate power outage, can't help if the pump itself goes bad. A side-note, is it possible to leave a twist open inlet on the discharging pipe that I can drop a pump inside the pit in the case of emergency and discharge it with the existing pipe? Or maybe I should just go ahead put in a 2nd pump while at it? Any thoughts on the two pump configuration (I have a 0.3hp zoeller sump pump at hand (1.5" discharge port), 1/2 hp Liberty, 1hp off brand (both 2" ports). I read that if do parallel, two pumps need to be similar size/power, I then probably want to buy another liberty. What if stack layout, should I put big pump up or down?

Any advice?

P.S: We just confirmed and located the exit out of the brick wall for the 1.5" pipe at the backyard.

 

[LittleInch]

Yeh, a world of pain and cost you're in there.

What's under that concrete slab in the top photo where the two black wires are? Can't understand why you don't saw cut the slab and then dig out a hole for the second pit?? why do you need to break it out?

Or could you not break out a hole in the floor of your garage on the line of the inlet pipe and insert a pit which you can grate over or drive over and insert your little 1/3 hp pump. Then when that overflows it flows into your existing pit which you've improved by making the pipes a bit bigger? So your red pit circle but in a different place. Far better than trying to dig up your gutter.

Getting two pumps in parallel is never easy and even "identical" pumps, one will be 60 to 65% of the total unless you're very fortunate.

I terms of existing capacity can you do some tests? Just open the top and when you drain a hose into it slowly measure the level it kicks off the pumps, level it stops at and accurately measure the time taken to reduce the level.

work out the volume then divide by the fraction of a minute it took to get GPM.

Do that a few times to get some consistent readings then come back and tell us. At least then you'll have some idea of what flow you might get from a properly designed pumping system

for option 1 just replace the pipes you can get at without digging or excavating - that's a days work if that. Best if you could replace the lot, but you're into diminishing returns there.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ShinDiors]

@littleInch, thanks for the follow-up. The space you referred to actually is the room for a possible 2nd pit, it's just that the opening to enter that little crawl space is pretty small and low (it's a square cut out from the brick wall, with bottom edge 5inches off the ground, one pix in my OP showed that entrance) so any adult person would either have to sit/crouch outside and operate the tools to remove the concrete. Sorry for my ignorance, I thought to remove concrete you only use jackhammer so not sure saw is an option.

As for the location of "red circled", we picked that corner because of the ease of tap the discharge line (initially it was proposed outside the garage, but it evolves into the yellow circle inside for the freezing risk. There is a gutter drain accessible at ceiling level).

Also putting it in that corner has little interference to the normal use of the garage. On the other side of the garage, the only possible location outside the crawlspace is the corner where the lawn mower is (shown in the op's pix), but it's not on the line of inlet pipe which was place not parallel to the sidewall but with an angle), there is a door, part of the staircase in the way for pipe routing too.

My general contractor (who renovated my house and put in the liberty for me) would come for something else, I would ask him to swap out the pipes first if he can do it. Digging a 2nd sump definitely is not his thing though. He should be able to put in the 2nd pump in the pit, that's why I was trying to seek advice if the pumps I currently have can be repurposed while he is dealing with the pipes already. Again, we could swap the pipes first and see how it goes, but I definitely would need some advice on any backup plans if we are still in a single pit/pump situation. Prior to posting this, my plan was to have him put the 1hp offbrand with existing setup and trial/error, but then started to worry about pump failure/mitigation plan. It's almost freezing temp outside, but would rain in a couple of days, I will try to take a few timed measurements then and update back. Based on @cvg's estimate in post above, the usable volume is around 20gallon or less (pump is on when water rise at the inlet pipe level, so less than half of that 50gallon tub, minus the volume leftover when pump turned off), and about 10-15s tops, the pump would stop, so we are roughly talking about ~70-90gallon per minute currently. I'd probably need to observe (with almost freaking out mind) at the crazy rainstorm event to see the worst case's incoming flow rate. I agree that the sump is maybe too small for those events (when it start to backed up), say, if it only takes 10s or less for the pit to be filled to the inlet pipe level, then pump then has to be on 10s to remove it for the next fill up (ideally, I'd think the water level in the pit should be at an equilibrium at inlet pipe for any sump? Otherwise water flow is seriously blocked by the water body), increasing the pump power would only make it cycled even shorter which is worse.

I'd be interested to know what a "optimal" triggered on water level should be? Is it right below the inlet pipe (to avoid incoming water backed up at fastest rate/bad storm). But again, cvg got a valid point that "sump pump" is not speced to do this type of run-off water discharging, but more for the seeping/slower underground water.

I want to thank you both again, LittleInch and CVG for offering your insights. How much I wish that there could be a company/contractor that would really have the expertise to carefully evaluate the capacity and nail the core, offer and deliver solutions (or maybe I should've not gone to landscapers/waterproofing co/drainage co but some other specialty?)！ None of the people I talked to pointed out that the sump size might be a problem. Only one backed his diagnosis with my described symptoms that the discharging rate is the cause of my water backed up, but not really talked about potential cycling issue if I improve the discharge but with the same capacity sump.

 

[miningman]

A few more observations and comments. I was going to ask if occasional flooding of the garage floor was a serious concern but then I see the man door access, which I'm guessing leads into the house. So yes occasional flooding is serious and unacceptable.

Almost any modifications to the retaining wall would be extremely expensive. This might be self evident but fundamentally the ideal solution would to be to minimise the volume of water. I mention this for two reasons. Whatever your mental budget is, you may need to increase this $$ amount in order to avoid even evaluating modifications to this wall. Dont perform a half ar***ed job in the garage and still have to deal with water in the house. One of your photos appears to show downspouts from the roof feeding into a 4 inch pipe. Does this pipe lead to the sump?? If so, surely you could redirect this roof drainage away from the garage. You appear to have at least 7 feet of elevation to work with, so even 200 feet of drainage pipe affixed to the retaining wall should work.

You acknowledge that concrete removal is not one of your strengths. I agree with Littleinch that cutting out say a 30 inch square within the garage would not be expensive. The contractors who do this very often will do concrete coring as well. It appears to me that where your existing pipe comes thru out of the garage, you could easily core out a 3 , or even 4 inch hole in the wall, say about 30 inches above grade. Then replumb your 2 inch pipe with at least 3 inch pipe, or even 4 inch if future design confirms Littleinche's suspicion that 3 inches might be marginal. Install all the necessary Wyes etc at this stage to give you flexibility in the future. Dont worry about the cost of excavating a second sump at this stage..... you will only have to incur this cost if all the other preparatory work proves inadequate.

I might be failing to recognize some of your logistical difficulties here, but hopefully this gives to more to work with. And dont even think about two pumps in series... two in parallel might have some problems , but two in series will provide virtually zero increase in flow rates. A four inch discharge system should be able to deal with a 3 HP pump , giving additional flexibility going forward

 

[ShinDiors]

Thank you, miningman for you reply.

Let me attach a sketch of the cross-section (view from the backyard). The sunroom and garage were addition added together, that downspout pvc you see goes underneath the deck at about the ceiling height (of the garage) then making a turn connected to the downspout on the other side, eventually goes to the curb storm drain. I have located the 1.5inch pump discharging pipe exit at that side of backyard and 99% sure that it taps into this gutter drain pipe (not sure how long it extends out from the wall though, hopefully not long). It is about 10inches deep at the backyard level, right outside that sunroom side wall/window.

I think my difficulty is maybe trying to find a contractor to do the whole project (from digging a hole to replace pipe and install pump), and several contractor we discussed in detail onsite ghosted on me afterwards without a quote.

My reading comprehension might be off, so when you said " Dont worry about the cost of excavating a second sump at this stage" were you also suggesting the need of a 2nd sump pit on top of the discharging pipe up-sizing, but not a 2nd pump (but how would the water be discharged out in the overflow pit)? Or you meant no need to go with solution 2 in my post，putting a pit at the other corner with a 2nd pump tap into the gutter drain? My thinking is that it may be easier (hence cheaper) for contractor to dig a hole in the open, compared to having to work their tool in that tiny opening of the crawlspace where the current pit is (my pix shows that opening), if either way I can't get away from having to get a 2nd pit (and a 2nd pump), I may save the cost of current pipe up-size (if the new pit on the other side being the primary with bigger pump and 2-3inch pipe), since I can use a smaller pump (for example, the 0.3hp zoeller i have as spare, which has 1.5inch port only), and use that original setup as the backup/overflow setup. From cvg and LittleInch's posts, it seems that my current pit setup has too little of usable volume (~20gallon), so even at my not-optimal discharging pipe, 1/2 hp pump cycles on too short. But if the incoming water is not much (only overflow level), I can afford to have a smaller pump for longer cycling on time.

If it's not crazily expensive to swap the discharge pipes, it will certainly be better to swap it still, giving me flexibility of using a larger pump in that original pit.
Looking at my record, I got quote of $3,600 to up-size all 1.5inch pipe and install a 2nd pump in the same pit.　And they were saying this was the lower end price (if the digging is not too much in the backyard).

 

[keyepitts]

A couple of other obvious things to check- make sure all the existing pipes are clear of debris, a partially clogged discharge pipe could be why your pump is unable to keep up with the extreme flow scenario. Hopefully this was already checked, just making sure. Check the pipe from the driveway grate to the sump pit also while you're at it, this should probably be a yearly maintenance item to keep the pipes clear of sediment and debris. Also as others have mentioned, there appears to be a second pipe draining into the sump, any idea what this is connected to? Have you ever seen water pouring out of it? If so, possibly this flow can be redirected elsewhere easily. I agree with everyone else that it sounds like a larger sump capacity is required, and probably larger discharge piping also.

 

[ShinDiors]

Thank you keyepitts. All checked no obvious blockage, also other pipes do not contribute too much water if any.

@LittleInch Just want to follow up on the overflow sump adjacent to the current sump idea. You mentioned that the cross over should be above the current inlet pipe, I assume that this crossover pipe should sit relatively higher in the new sump pit unlike my current one right? So the new pit, (if I can still house a same 50gallon one) should sit relatively lower compare to the current pit (not higher as you mentioned), coz we want to use more volume in the pit before having to cycle on the new pump? Also I should be the larger pump in the overflow and use a smaller size one in the old pit? Since the discharge rate is improved, the current 0.5hp pump probably only need to cycle on shorter time to discharge this fixed volume of water, which is worse to the pump. Can I set the trigger level higher than the inlet pipe (but I'm concerend that it would cause water to backed up in the inlet pipe). Can you clarify a little more?

$all, another smaller reason I was leaning towards having the new sump in that corner (if I have to get another sump and pump) is that : related to this water problem, the run-off water from both front and back would always flow towards the garage door posts (shown in my pix above with arrows), so they are already water damaged. One solution of fixing that is to extend the channel drain (let it become a U shape) to cover the door poss/brick session) so that water would fall into the channel instead of hit the door post. Building the sump in that corner would probably need this extension of grated trench in order to channel it into the pit. It seems that this project (extension of channel drain) was too small for a lot contractors they don't even bother to respond. It may be a stupid logic here, please feel free to call it out.