stormwater vault maintenance ideas??? 1

[jebbo2]

This stormwater vault is 22,800 sqft under the parking areas for 100yr floodplain compensation. The trouble is that it needs to be only 2.5 ft. deep which raises a flag about maintenance to everyone(not tall enough for someone to move freely around inside). I need some ingenious ideas about maintenance procedures and design(manholes etc.). Thanks!

Jeb

 

[Ginger]

One can argue that providing a structure which cannot be readily maintained is not good design. If you do not wish to lower the floor area over the entire area then reduce the plan area of the operating vault and make this section deeper such than maintenance staff can easily enter the void and work comfortably. Pipe flows from outlying areas of the car park to your void.

You should have a minimum of 2 access points for ventilating the area and for emergency escape routing.

 

[dellbs]

I agree with the first response, deeper would be better. Are you limited to the 2.5 foot depth due to the outlet invert? If you can't get deeper, you may need to consider surface storage. Does your jurisdiction allow using parking lots for surface storage during the 100 year storm event? Otherwise, some space may need to be used for a, I hate to say it, pond.

 

[dicksewerrat]

I agree that deeper is better. The difficulty with cleaning this type of facility is that all the solids will deposit in the "tank". It would be nearly impossible to clean them out. Unless it was done immediately after the storm event with jets and vac trucks. And we all know this will be cleaned about once every ten years. As soon as it is full of sediment. If it were at least deeper at one end and all the rest of the "tank' sloped to that end , cleaning would be simplified greatly. The sediments could be washed to the deep end and sucked out relavitely easily. It is nice to see a designer actually worrying about maintaining a facility instead of just saying" That's not my department. I won't think about it." If this will be an HDPE tank, they come with manholes built in. Call ADS Drainage Systems for their catalog.

 

[jebbo2]

I appreciatte the responses and I hope that they continue! Delbs, to answer your question and I think address Gingers, the problem like so many of us deal with down here in florida is that even if we go deeper the water table does not give you anymore room to store water. With the present design we are right on top of the seasonal high water table. We are already maxing out the height of the finished floor elevation because we can only slope the parking and driveways so much. So you see my delima! I am trying to brainstorm an idea which by design would allow access to the most pertinant spots in the vault for maintenance. Outa the box thinking here? Any ideas? Thanks!

 

[aspearin1]

I'm no civil engineer, but if things are of this great a concern, why not raise the parking surface? Would it be that much more expensive than digging deaper? Just a thought.

 

[jebbo2]

Raise the parking lot? Have you ever driven out of a parking area and the pavement at the end of the driveway looks like it has taken its toll on a few car bumpers. We are dealing with unique site.

 

[aspearin1]

Surely the suggestion isn't so absurd. If you need it deeper, and you can't dig down....?

 

[Ginger]

How about designing the parking lot as a series of small suspended slabs (narrow strips) seated on a grid of circular columns and support beams. Each slab can be lifted independantly for access into the undercroft. Your maintenance staff can lift say 2 or 3 adjacent panels in order to provide a sizeable plan working area at 2.5 feet deep. No manholes required as it will be similar to working in an open trench.

 

[bltseattle]

Removable top slabs/grates would be an option. While the area is quite large for grates, perhaps having alternating panels of grates and removable slabs would meet the need.

In terms of meeting the maintenance needs, consider:
1. Regular cleaning and sediment removal: plan enough removable grates that the areas between the grates can be pressure jetted, and construct the floor of the vault with some slope so that gunk can be jetted to sumps, which could be vactored.
2. Sumps & flow control risers: requires overhead access opening (standard 2' diameter manhole lid could work).
3a. Structural inspections: This would be tough with a low ceiling vault. Video survey might be the way to go
3b. Structural repairs: If settlement or damage to the structure could occur, then it might be necessary to repair the structure. This is where removable top slabs would be useful.

Talking and coordinating with the party responsible for maintenance should be part of the design.


BT

 

[pigdog]

jebbo2,
You know sometimes the result of the analysis is that because of time, money, space or other annoying elements of reality, the project won't work. Maybe in this case, the problem is keeping the mud out of the tank, rather than creating access to remove it once it is in there. How about one or more easily accessible settling ponds to collect sludge before overflowing the water into the tank area? If they are lined like swimming pools it really won't matter if they are poking down into the water table.
pigdog

 

[wolfhnd]

If you build the cells deep enough and don't use a floor you can have a large access point to get a bobcat into it. I like the idea of driving pilings to set the parking lot on. You may have to dig out a lot more than you would want but it would not be that big of a job.

 

[dicksewerrat]

I just talked to some people from HANCOR Products. they manufacture HDPE pipes and manholes. HDPE can be welded. you could use a series of pipes laid side by side with a sump manhole at the endof each pipe to collect the silts. then remove them throught a standard manhole cover. Connect all the pipes together to release the water to your storm drain system. Do you need all the 2.5 feet of depth and the entire 22,000 sq. feet of the lot?

 

[gibfrog]

Consider sumped inlet catch basins to trap some of the sediment inflow. For example, you have 24" minimum depth of sediment storage area below the lowest pipe invert of the catch basin. You could also slope the pipes to the inlet sumps and not the storage vault. The catch basin would have an open bottom (12" dia min) and then non-woven filter cloth and 12" of stone. The catch basins would have to be regularly maintained/cleaned. This is commonly used in southwest Florida, in the "poorly drained coastal lowlands" Clifford H Laubstein
FL Certified PE #58662

 

[KRSServices]

I had a similar problem while I was a Municipal Manager for a small community in south western BC. The parking lot, similar to yours, was constructed in a floodplain which had dynamic groundwater levels (5' to 8') depending on the time of year. The underlying soils were granular and therefore highly porous. Rather than a storage facility, I instead focused on a design which would allow exfiltration from large diameter pipe. The pipe itself would be utilized as temporary storage and the inverts set at the highest theoretical (average) groundwater elevation plus hydrgeological mounding. During winter chinooks, the surface water is efficiently disposed of and in summer, the capacity of the pipe plus the perculation rate of the soils ensures the efficiency. The system was designed for a 1:50 storm event and groundwater to 4'. Hope this helps.