Confidential Residential Client
A homeowner experienced chronic wet basement conditions. Neither sump-pump installation nor a builder-paid treatment of the exterior foundation wall resolved the problem.
Purpose of Project
The owner initially engaged us to determine whether a defect existed that related to the hydrogeologic setting of the property. If so, the owner sought to understand whether the conditions was known at the time of the initial design and construction of the house and lot. The client was contemplating legal action against development and/or construction interests. This mandated a defensible and methodological approach.
Project Design & RECONNAISSANCE
Our initial research focused on the probable presence of on-site fill materials along and near the exteriors of the basement walls. Specifically, we sought to determine whether differential porosity and permeability between virgin soils and construction fill could cause or exacerbate seepage problems. Published information on the local geology and soils supported these theories, as did a visual reconnaissance of the site setting. During that site visit, we focused on uphill stormwater management measures.
ALWI made soil borings in both the fill proximal to the building, and in the surrounding undisturbed soil. We checked carefully for evidence of a seasonally high water table. Such evidence could have manifested as standing water in the borings, gray color tones or gleying, low chroma (i.e. muted colors), or mottling. We did not see such evidence.
Simulation of Rain Event
Next, we simulated typical lawn watering and heavy precipitation events. Specifically, we recreated a variety of natural weather conditions such as downpours during thundershowers. We introduced water-soluble fluorescent dye to trace the potential response of indoor water seepage to simulated, dyed rainwater.
For quality assurance, we carefully recorded antecedent conditions prior to the introduction of dyed water to the outdoor land surfaces. Specifically, we performed a preliminary visual assessment of both indoor and outdoor areas. The initial indoor assessment focused on observing the basement floors and walls for signs of existing moisture and dye unrelated to our test.
Observations and Findings
We verified the dryness of the indoor basement walls and floors before we began simulating lawn irrigation and precipitation events. We watched as these indoor surfaces began to get wet less than four hours after simulated rain events began.
No other source of water, natural or otherwise, explains these observations during this short time period. We concluded that emplacement and/or compaction of fill materials surrounding the residence increased the local likelihood for the seepage conditions.
We recommended the following remedial measures:
- Excavate soils adjacent to the foundation, as deep as the basement floor.
- Inspect the exterior foundation wall and its repair as necessary.
- Apply a waterproof foundation sealer to the exterior and interior walls.
- Install a deeply-trenched, sloping french drain system, with appropriately selected and graded backfill materials, to channelize it for safe down-gradient outfall.
- Delay basement improvement plans (to include vapor barriers, ventilation and inspection access) until the efficacy of remediation was monitored through at least one winter/spring season of normal or high precipitation.