Pipe seepage?

[Rockhound2015]

I am a civil engineer (sitting for PE in October) and I am building a new house. There is a 24" HDPE stormwater pipe that runs across my lot from upstream curb inlets in the road and outlets to a detention basin behind my lot. Besides the erosion control issues, lack of outlet rock protection and other observable problems, I have not observed any water coming from the pipe, even after rain events. I have noticed water bubbling up, (like a spring) from under the endwall. (see photo)

When I showed this to the developer, he said this is "common" in low flow situations. He also noted the pipes are not sealed at the curb inlets. I asked around the office and everyone here said this is not common.

Is this common? I think there may be pipe seepage here and the beginnings of a major problem. Any help would be appreciated.

 

[psmart]

From your photo it looks like the pipe might be perforated? The use of clean stone backfill also suggests this is intended to function as an infiltration structure. If this is the case, the open-ended pipe is only for overflow in larger events, and the seepage is an expected consequence of design. If the pipe really is perforated, it's going to make for a wet building site.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Rockhound2015]

It doesn't look to be perforated inside. (see photo)

Also, don't let the water lines let you think there has been water flowing through this pipe. This pipe was reused. The developer had to tear up the new road and all underground utilities and shift the road 50' west because they didn't include a overhead utility easement in their preliminary plan design. It was a costly mistake.

 

[Rockhound2015]

I just read the specs for the construction drawings. This pipe was supposed to be reinforced concrete(ODOT 706.02) and sealed(ODOT 603.06 {now 611.08}). Maybe that has something to do with the problem, since the HDPE pipe isn't sealed to the curb inlet structure.

 

[psmart]

I certainly looks like there is water seeping through the stone, presumably from the unsealed connection.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[CarlB]

Also if contractor was re-using pipe, perhaps the further upstream section is perforated.

It seems odd no water would discharge during a storm event, could there be another outfall to the system?

 

[cvg]

bedding or backfill of trench with open graded rock as seen in the photo will promote water seepage and flow through the rock. the water source may be horizontal groundwater flow, vertical seepage from the surface, from the catch basin inlet which is not sealed or even from leaking pipe joints. it may result in piping / internal erosion and then settlement of surrounding ground as well as the pipe. not generally a recommended method. it also appears that the pipe might have insufficient cover, only a few inches in the photo. I dont see any connection between the pipe and headwall.

 

[Rockhound2015]

psmart, Thanks for the feedback.

CarlB, There is another outlet pipe that drains another phase of the subdivision into the basin. This is the only one for this phase. There is a nice amount of water flowing from under the endwall. The lots are not graded yet to drain a lot of water to the street. The only flow to this pipe is from the street.

cvg, The cover increases further up, but I think the pipe is a little more exposed now than intended by the design (due to erosion). I didn't see any connection between the pipe and endwall either. See gap in photo?


I've asked the county engineer to look into this since it falls under their jurisdiction. I just want to make sure I don't get water in my basement because of the seepage.

 

[TerryScan]

It certainly looks to be poor construction all around. Besides water in your basemnent, I would be concerned with pipe/trench failure with more significant erosion or sinkholes that could compromise building foundations depending how far they are from the pipe. How far is the pipe from building setbacks?

If it fails further in the future, after buildings and lovely landscaping are in place, consider the impact of heavy equipment needed to repair the storm drain.

 

[Rockhound2015]

TerryScan, My house will be 25' from the side property line. The pipe is in a 10' easement running parallel along the side property line. The centerline of the pipe should be about 5' from the property line. So my house will be about 20' from the centerline of the pipe.

 

[gbam]

Not being familiar with those specifications, are the pipe joints supposed to be soil or water Tight? I know that our DOT standard specs have soil tight requirements and not water tight requirements. Just a thought

 

[Rockhound2015]

gbam, For what was specified (Reinforced concrete pipe), the seal can be:

[ul]
[li]bituminous pipe joint filler[/li]
[li]preformed flexible joint sealant[/li]
[li]or resilient and flexible gaskets[/li]
[/ul]

I think these are all water tight. If the pipe were for sanitary, it would need to be tested to infiltration/exfiltration.

But, since they installed HDPE and used no seal (per developer), I expect the water is seeping out at the connection.

 

[Rockhound2015]

I just received this email from the county engineer:

"I’m not sure who you spoke with from the development team, but when they say that the pipe isn’t “sealed”, that isn’t completely accurate. ADS N-12 pipe contains a factory installed gasket within the spigot end of the pipe to meet the requirements of 611.08. For type C conduit, we do not exclusively require RCP, despite what the drawings may say. Outside of the pavement sections, we allow HDPE pipe for storm applications, as does pretty much every other agency that I know of in Ohio and beyond. In fact, some agencies (ODOT, Delaware County and others) have approved the use of HDPE product under the roadway in a multitude of scenarios.

In terms of the water bubbling under the endwall, I wouldn’t go as far as to say this is a common occurence, but I don’t believe it’s a reason for panic. The pipe trench consists of granular backfill, and when compared with consolidated clay adjacent to the trench, groundwater will choose the path of least resistance (i.e. the trench). Being that the inlet to pond is at the most downstream end of the system, the presence of groundwater within that trench would be expected. Hope that answers your questions."

I still don't think this explains the lack of water coming from the pipe itself, but at least I have this documented now.

 

[cvg]

"the pipes are not sealed at the curb inlets."

611.10 Drainage Structure Construction. part b

After placing the conduit, grout all openings less than 4 inches (100 mm) between the pipe
and structure with mortar. Grout all openings greater than 4 inches (100 mm) between the pipe
and structure with non-shrink mortar.

 

[Twinkie]

Dude .... all good comments above .... now add to that .... do you really want to buy a house from a builder who had to rip out and move a road 50 feet?

 

[cvg]

ADS N-12 comes in several types, watertight and not watertight. joints may be leaking water if any water gets into the pipe.

http://www.ads-pipe.com/en/product.asp?page=n_12

I think your problem is at the curb inlet where the catch basin is not connected to the pipe or another possibility is that temporary SWPPP has blocked the curb inlet to prevent sediment leaving the construction site

 

[Rockhound2015]

Twinkie, The home builders (there are 2 for this subdivision) didn't rip out and move the road. The developer did. (There are a lot of problems from this developer).

cvg, Thank you for this information. I think if there is a leak anywhere it will be at the curb inlet connection. I will look at this and take a photo.

 

[Spartan5]

Leaky joints aren't going to make a 24" pipe full's worth of water just disappear. What drains to that pipe?

Is that pipe permanent? Or was it part of a temporary sediment control basin that no longer has contributing drainage? Not that it looks like erosion and sediment control is a high priority out there.

For what it's worth, in my neck of the woods if it's in the right-of-way, it's Class IV reinforced concrete pipe with gasketed joints and someone would be getting smacked for the lack of site stabilization.

Who's responsible for operating and maintaining the pond? It's going to need to be dredged before the development is built out.

 

[Rockhound2015]

Spartan5, There are about 10 acres that drain to this pipe. There are about 25 lots and one main road (about 1000'). There are several curb inlets along the road and a few yard drains. Homes are in the process of being constructed, so a lot of the runoff doesn't make it to the piping yet. There is water heading to the piping, I've seen and heard it at the curb inlet, just not the outlet.

The pipe is permanent. Erosion Control is a high priority here, but it took getting the Ohio EPA involved to light a fire under this developer. I expect Erosion Control measures will be enacted this week (or fines will result).

The County Engineer let them get by with the HDPE (about 25' in ROW, rest on private property with easement) although the plans specified RCP.

Currently the Developer is responsible for the "dry" basin (not supposed to have that much water in it). Eventually, it will become responsibility of HOA. I'm hoping things get fixed before then.

I really believe there is a leak/break/etc in the piping somewhere between the curb inlet and the outlet endwall. I'm waiting until a rain event (maybe this weekend) to take pictures to confirm.

 

[Spartan5]

Really ballpark number, that's about 10 cfs (5,000 gpm) in the one year storm. That's a big leak into a sizable reservoir to just disappear like that. Think about the size of the pipe vs. the size of the opening that would have to exist to make all that disappear.

Is that an "offline" pond with a splitter structure (diverts everything above the "first flush" to a different outfall)? Oftentimes if there is a splitter structure leading to a pond or other stormwater management facility, they will require the pond feed to be blocked until the site is stabilized to prevent the facility from getting overrun with construction sediment.