DEWATERING SYSTEM NEEDED

E.  DEWATERING SYSTEM NEEDED:
If water from rising ground water or springs is expected in a basement or crawl space area (Fig. E1, Item A) a pickup system that collects and discharges the water may provide a suitable “solution.”  There are a variety of ways to install dewatering systems.  The most common dewatering systems consist of a perforated pipe around the inner circumference of the basement walls.  The piping is set beneath the slab and sloped so that entering water is generally fed into a collection pit (Fig. E1, Item B).  Under very severe conditions, additional tiles or pipes may be required at other areas under the slab (E1, Item C).  These “French Drain” systems are intended to intercept rising or seeping water before it can do any damage to furnishings within the basement.

The process of installing these systems is destructive, dirty, and expensive.  The concrete floor slab is usually broken through at the perimeter basement walls and a trench is dug out inside the footings.  A perforated pipe is laid in the trench, covered with gravel, and angled to a low point where a deeper hole accommodates the sump crock and pump combination.  The trenches are then cemented over.

The breaking of the slab itself is destructive from both a structural and waterproofing point of view.  The new cement, which is installed over the trench, will never be as watertight as the original.  The lack of solid blocking at the base of the foundation wall can allow the footings to slide inward (rarely occurs) if a heavy external load is pressing against them.  Sometimes holes are drilled through the foundation wall at the foundation/footing intersection.  These holes are intended to facilitate the passage of external water under hydrostatic pressure (which is the pressure that results from a standing column of water) to drain into the pick up system (Fig. E1, Item D).  This type of system and the “coving” systems (waterproof materials attached to the floor and wall area to “dam up” any seeping water and deliver it to a sump pit) usually work (Fig. E1, Item E). Often they can relieve severe seepage or flooding symptoms.

Their drawback is that they are expensive and add complications of their own.  They encourage water to seep through walls, causing high moisture conditions that can lead to mildew formation and water transpiration upward through the hollow concrete block walls. Footings can become undermined and settlement may occur if soil is removed or softened beneath them.

WHAT TO:  HOW TO:
If a dewatering system must be installed, it should be installed in such a way that it does the most good with the least amount of harmful side effects.  The best place for pickup or collection points may be external to the foundation, to minimize the likelihood of moist walls, undermined footings, or slab settlement.

Often, an existing exterior perimeter footing drain can be “rescued”, or made to function again by snaking and backflushing silt from it.  Digging strategic holes to intercept the drainpipe and using a plumber’s electric snake and water hose to unclog the old drain, usually removes silt from the drain and makes it functional.

Basement areaway entrance slabs are placed only a few inches above exterior perimeter drains such that breaking through the slabs and digging a bit may provide the easiest access.  These areas are often the sites for retrofitted sump pumps.

WARNING: BE CAREFUL WHEN HAVING WORK DONE: Many “waterproofing” companies employ sales people who have standard answers for any problems or symptoms relayed by homeowners.  Few really understand the dynamics of water within the ground or the effects of saturated soil against foundations.  Many companies have special dewatering systems that tend to be the only system their representatives want to sell.  According to them, their systems are the only solutions or remedies that will work.  Consult an architect, building analyst, professional engineer or soil scientist for a step-by-step prescription.

Many professional home inspectors and consumer affairs people believe that many water proofing companies routinely mislead and cheat consumers.