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Perched Aquifer --- Foundation Drainage

D

dartmouthrocks

Member
Joined
Aug 17, 2015
Messages
13
Location
boulder
Good evening:

Our house was built in the early 1980's. Our well report lists ground water table at below 65 feet (1983) A civil engineer used the term Perched Aquifer to describe the ground water table situation in the area of our home at this time, following a "1000 year flood" in our area a couple years ago.

The problem is that our historically dry cellar with dirt floor effuses water vapor. A few 20 inch deep holes in the cellar floor (one inch diameter) left overnight filled with water to 12 inches or so below the proposed built up new floor level base (mitigation efforts going forward are proposed to include drains to daylight, crushed rock, membrane, insulation, and rebar enforced floor above -- with associated shelf walls where needed for subjacent support (stepped foundation footers).

A home across the street required a mound septic system on account of soil wet at 3 feet and pooling water at about 5 feet. Reports from home construction in 1969 basically reported perc test pits as bone dry -- actually said the area had "no real ground water table" except at well drill depths.

We can really use help with a couple of questions:

With the IRC, does presence of water near bottom of footers require special reviews?

Does c!ose proximity to ground water preclude money shaving measures, such as treating it as a crawlspace with plastic placed down, without the drainage system described. (We do not want to kick the can down the road with mold issues to reappear again).

Last winter, we covered the entire cellar with plastic (to trap water vapor). Water condensed under the the plastic and then pooled, creating puddles both above and below the plastic (seams were overlapped but not fully taped).

Thank you for any direction that may be given.

Dartmouthrocks
 
Curious you mentioned NH. (Granite State.). House is surrounded by granite. My geology background makes me wonder if there is a depression of sorts in that material/local bedrock that has filled with water from the epic event.

I thought I saw somewhere that crawlsoaces can't be within a specified distance from groundwater -- given drainage requirements.
 
Good evening:Our house was built in the early 1980's. Our well report lists ground water table at below 65 feet (1983) A civil engineer used the term Perched Aquifer to describe the ground water table situation in the area of our home at this time, following a "1000 year flood" in our area a couple years ago.

The problem is that our historically dry cellar with dirt floor effuses water vapor. A few 20 inch deep holes in the cellar floor (one inch diameter) left overnight filled with water to 12 inches or so below the proposed built up new floor level base (mitigation efforts going forward are proposed to include drains to daylight, crushed rock, membrane, insulation, and rebar enforced floor above -- with associated shelf walls where needed for subjacent support (stepped foundation footers).

A home across the street required a mound septic system on account of soil wet at 3 feet and pooling water at about 5 feet. Reports from home construction in 1969 basically reported perc test pits as bone dry -- actually said the area had "no real ground water table" except at well drill depths.

We can really use help with a couple of questions:

With the IRC, does presence of water near bottom of footers require special reviews?

Does c!ose proximity to ground water preclude money shaving measures, such as treating it as a crawlspace with plastic placed down, without the drainage system described. (We do not want to kick the can down the road with mold issues to reappear again).

Last winter, we covered the entire cellar with plastic (to trap water vapor). Water condensed under the the plastic and then pooled, creating puddles both above and below the plastic (seams were overlapped but not fully taped).

Thank you for any direction that may be given.

Dartmouthrocks
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The IRC first print was 2000

Was this built in a city?

Or county

Do not no how Colorado works, just wondering If it was built to an adopted code, and if so which one and edition.

Some states if no state building code, you can sometimes build in county areas using no building code.

Plus what the code says today may not be the same when the your house was built.
 
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How badly do you want to stay at this location ?

IMO, ...this has "Money Pit" written all over it.

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Would maybe agree on money put, if gravity were not available to help move water along with proper trenching.

The issue really is how to respond to individuals without geotechnical backgrounds within admin entities who have likely never heard of a localized groundwater shift.

Just could use some direction on the question of whether minimal efforts typical for a crawlspace (6-10 mil plastic) ever is enough for instances where water is close.

Have fully engineering plans for the remedy, but some always will quibble.

A code base answer would help.
 
Thanks for the heads up. Great that irc available w/o purchase requirements. With the size of the project, new codes are being applied. Thx so much.
 
Also look at this, but still only pertains to new construction.

R408.6 Finished grade.

The finished grade of under-floor surface may be located at the bottom of the footings; however, where there is evidence that the groundwater table can rise to within 6 inches (152 mm) of the finished floor at the building perimeter or where there is evidence that the surface water does not readily drain from the building site, the grade in the under-floor space shall be as high as the outside finished grade, unless an approved drainage system is provided.
 
Thanks for the heads up. Great that irc available w/o purchase requirements. With the size of the project' date=' new codes are being applied. Thx so much.[/quote']So are you adding on to the house ??
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Actually -- our engineer drew up a drainage plan for use at cellar level. Not adding any square footage to home. Might be characterized as a comprehensive interior French drain system -- from footer to footer (or shelf wall as may be needed).
 
The IRC (and Residential Codes generally) provide two paths you can follow: Prescriptive and Engineered.

IF your project is within the scope (it is) and LIMITS (there's the rub) of the IRC then the Prescriptive path is available for use.

If on the other hand your project falls outside the limits for Prescriptive (and I feel your perched/induced high ground water may be doing just that), then an Engineered solution would be necessary.

The good news is that you have one already.

The bad news is you either have a Code Official who does not understand this OR a lack of sufficient detail (including calculations) from your Engineer. JMHO
 
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