by Rodney Harkness WATER TABLES ON A SHORE LINE Professional consulting is available. Over time, I have recognized two somewhat distinct classes of questions related to high level water tables: those of "highlanders" and those of "lowlanders", who are near a shore line. Highlanders are well away from or above a large body of water, or are on hilly ground. Lowlanders sit near a large body of water or on extensively flat land and/or are on sandy soil or any combinations thereof. The Lowlanders, the ones this article is written for, have elevated concerns about water that has, or may, enter their basement or crawl space being related to the large body of water. They may have additional concerns related to their particular soil type, or because their property is low or flat. The term "water table" and "high water table" are buzzwords (pseudo techno-babble). The water table term is widely used to mean different things, depending on to whom you are talking, and about what. The technical discussions of what various water tables are, is beyond the scope of this article However, for simplification a few things may be said: * A water table may exist where water gathers in a level body. * True water tables do not change much, outside of direct major human intervention. * Most true water tables are many feet down (usually 50 feet to hundreds of feet). * In developed locales where a true high level water table exists and is the result of a nearby large permanent body of water, a few more considerations are merited. The house was built about 90 years ago, and is near the coast. Our foundation is probably laid (ultimately) on sand. Buildings constructed near large bodies of water, with a basement, can be special cases especially if they are sitting on a mostly sandy or otherwise porous soil type. Being near the shoreline, or close to the water , or even almost level with the water is not the issue, the concern, in any case, is about whether the water line extends far enough into the surrounding soil and high enough to reach your building. This depends on soil type, overall landscape changes, or changes in the shoreline. In the case of a lake, changes in the water level of the lake if it has risen over time may have some effect. A second issue is are you now in the path of water migrating toward the lake or ocean even if you were not in such a path in prior years. To lay some ground work for this discussion, a few points should be covered. First, it is more likely that a true standing water table may exist in the ground close to the underside of your foundation floor if you are very near to and almost level with a large body of water. This water gathers in the highest soil level, the overburden, or soil above the bedrock, and forms one of the closest thing to a true high level underground water table. The level of this water table will under most circumstances be the same as the water line of the large body of water. As you travel away from the lake and/or into higher ground, being close to an underground water table this becomes less likely. Second, it must be recognized that water normally runs across land toward and into bodies of water. This is evident in creeks, streams and rivers. Often even a few feet from a river the ground is solid and not water laden. This is also true at the shore of many lakes. The nature of soil and water is they don't like to mix. Quite simply this is why there are rivers, lakes and oceans divided by land; otherwise the world would be one large mucky swamp. Anyone who has been around water knows that you can usually walk right up to and into the water on solid ground. Throw some dirt into the water and it sinks to the bottom and settles into itself. Water then migrates back into the soil only under hydrostatic pressure, or capillary action, unless the soil is very porous, such as highly sandy soil. Soil with a fair amount of clay is very resistant to water migration and penetration. Even sand resists water penetration. When rivers overrun their banks, often property damage is prevented by "sand-bagging" the bank to contain the water. Water gravitates toward water and soil gravitates toward soil, such is the action of nature. It is that very nature which predicates the conditions for rives and lakes to form. It normally takes centuries, without the intervention of human activity, for water to cut stream beds, gullies valleys and lakes; and it take time for water to penetrate sufficiently into the soil to form underground pools of water. Quite simply, if a hole can be dug and a basement built into it without it filling up with water before the basement is finished, it is almost certainly out of reach, or above a permanent water table of the type which can exist around a lake or bordering a river or ocean. There are four main exceptions to this: bogs, swamps and deltas, sandy soil (and rain and and high moon cycles), when the surroundings are changed by major construction or natural disaster (and surface characteristics change, and when the shoreline of a body of water rises in height --in other words the water becomes permanently deeper. None of these surface as common problems. Structures have been built on bogs and swamps or on drained bogs or swamps. These are the rarest of situations. Basic common sense and general rules of law minimize such applications. In the instance of intentional construction on wetlands, specially adapted practices are usually obvious. In the case of drained wetlands, the ongoing effort to keep the area permanently dry and drained are only as good as the constant work done to maintain the drainage systems. This is usually obvious as ditches, canals, and other structures and as a commonly encountered set of laws. Basements are therefore, of course, rare, not to mention nearly impossible. Even in-ground swimming pools suffer great restrictions and constant threat of all manner of damage. In the unusual case of a sizeable housing development making its way onto such property, a constant set of challenges will prevail. Discussion of all of these rather uncommon applications are not intended to be included here. Each is a special case which would require on-site investigation. The only reason for including or even mentioning these exceptions is to emphasize how far from normal reality this is for most buildings with basements. Sandy soil is one of the most common special cases. One way of putting it is to say that sandy soil is much better at allowing water to pass through it than most other soils. Many sandy soils are found near the coast, near lakes and rivers, or in the remains of past lakes rivers and oceans. This combination or high porosity and nearby large (heavy ever present) body of water may allow an underground level body of water to form close to the level of the the water line of the nearby lake or ocean. As distance from the main body of water increases, or as height above the water line increases, the possibility of a nearby underlying water table decreases. The minimum acceptable depth of such a water table is about 5 to 6 feet (under the floor), more is better, I have seen as little as 3 feet in actual practice. (Three feet is really flirting with health and safety problems.) The point I wish to emphasize here is that 5 to 6 feet is usually not difficult to get. Moving away from the water also quickly reduces the possibility of a nearby water table. In moving away, there is no specific distance which works as a rule-of-thumb, however, I have seen 20 or 30 feet do the job, in a few situations of very dense clay soil, I have seen 10 feet work. Even with sandy soil next to the ocean, a few hundred feet usually works. Less distance can work. Again, if a general water table exists near the surface, placing a basement in such a place would be either hilarious entertainment, or a marvelous feat of misplaced engineering. In World War II, massive amounts of cargo was moved over the oceans on concrete boat hulls; they do a great job of floating. In the vast majority of situations,basements work or they don't. Water tables just do not accidentally show up. The last two main exceptions should be easy to understand. If major nearby construction has measurably altered the landscape, the flow of all ground water and the level of all soil moisture can change. When this happens, the changes are usually limited mainly to the surface and surface water control and surface water channeling. This is not a subject which can be easily discussed; each such case is a unique challenge. Of the many major construction sites I have walked, I have only observed this as being a cause of water problems in a few limited dwellings. Again, this example is more about what does not often cause a problem. When a lake water level rises it can also raise any connected water table. This happened to Lake Erie, bordering the USA and Canada on the eastern part of the continent. In the instance of Lake Erie, few houses were affected. In fact this has an irony, because the excessive construction of housing developments near the lake, caused considerable reduction of grassland and woodland (which absorbs water) and concomitant increase in pavement run off and roof/storm water disposal into the lake. The increase in the housing stock was the very cause of the rise in water level. This could also fall into the category of massive new construction that changes the landscape, rerouting surface water. In some areas around the lake, this change could also have lowered a water table by denying the soil its customary moisture input. the final statement here is that few of the houses near the lake have basements; those that do have basements sit on higher ground further away from the lake or any lake feed watershed. Weather, of course, always affects a near-surface water table, but does not necessarily raise it significantly. Flooding is a surface effect. If rains could so easily travel through the earth to a water table, flooding would be from the sub-soil up, not the other way around. Take graveyards for example, the real life nightmare of coffins surfacing happens only during extreme surface flooding, having one pop out of the ground because the water table has suddenly risen is unheard of. It takes extreme wet weather where disastrous surface flooding is out of control to cause this. More exceptions exist (in fact many), but are so rare and so specifically characteristic to a given area of the world and a given soil type and a given underlying strata type, that they are not normally found under heavily populated areas, represent unique situations, and need not be discussed here. Yet another issue here is the protection of an existing water table which for many reasons should not be contaminated with any form of waste, pollution, disease, chemicals, petroleum products, etc. Practices that put human habitation, commercial operations or industrial processes too close to a water table always has widespread significant negative repercussions. The concept of having a water table commonly touch upon (and therefore interface with) the bottom of any inhabited or trafficked structure would be such a potential threat to nature and infrastructure, that it commonly instigates the intervention of any number of major governing bodies, as well as any number of private eco-groups. At very high tides we are below sea level, thanks to a huge tidal range in excess of 40 feet? In the case of being below sea level at high tide, if this was a factor, the building would most likely be affected at every high tide, or at least often enough to make it unusable. Obviously, there is a significant land barrier between the building and the body of water. This barrier governs, and the immediate surrounding soil is the area to focus concern and logic. As an added commentary on being below sea level, this is a common scenario. It is not, in concept much different than being below a dam or a set of dykes. The great salt flats of the western USA are all below sea level, as are many large areas around the world. In the great salt flats, you couldn't find a much dryer place, even underground water is nearly unreachable. Further, fluctuating sea levels due to tides ultimately average out in an underground water table, such that the underground water table (if it even exists above the bedrock), fluctuates much less widely. Except in certain specific unique circumstances, this fluctuation would measure in inches or fractions of an inch of change, not feet. In fact it is more likely that such a water table would rise due to long term local rain (here we are talking about weeks of steady medium to heavy rain, the same as would produce surface flooding). To what extent would the level of dampness in the walls vary with factors such as the season as it affects the level of the water table, which presumably fluctuates significantly where we are? Another unusual but occasional situation is when the extreme limits of safety have been challenged and an uncommon event aggravates the natural status quo. This can happen when there are long periods of medium-heavy rain, perhaps enhanced by an unusually strong pull from the moon. Stronger that average effects from the moon (which controls tides) sometimes happens when one or more planets line up with the moon on its high tide cycle. Were are really stretching the imagination here, as even this does not change a water table in any great degree. Again, the emphasis here is on rarity. Above all, the main point is that a wet basement (or crawl space) in combination with sandy soil, and shore line situations which do involve basements, are rare. Basic considerations should, still, always be the first and most direct approaches to remedy such uncommon problems. All the while focusing on he immediate surroundings and circumstances first. We have not been heating the whole house continuously. Do we need a background level of warmth to prevent build-up of moisture in the walls. To what extent would the internal temperature (or perhaps the temperature differential between inside and outside) affect the moisture levels in the house walls? Inside moisture level is affected powerfully by the temperatures maintained, both in terms of absolute temperature and in terms of temperature relative to the outside temperature. The inside temperature should never be less than 55 degrees Fahrenheit in temperate climates. Allowing it to go below 32 degrees Fahrenheit, in addition to freezing pipes, is often and absolute disaster to the foundation, structure and finishes of the building. This is a major control factor and could be a big part of any moisture or dampness problem. There have been situations where a problem of paint peeling, plaster bubbling/loosening, wood warping or delaminating, was solved just by raising the temperature. For the purpose of recommending damp proofing or water proofing procedures, I generally assume that homes are kept at a constant temperature above 55 degrees Fahrenheit. Relative temperature should always be kept higher than the outside, up to about 90 degrees "F". The most accurate moisture level readings in construction materials are taken or obtained with an even, normal (65-70 degrees F, or higher), stable temperature throughout the home. The effects of relative temperature, interior and exterior, would open a whole new subject of discussion, which in itself can fill volumes. Suffice it to say moisture follows changes in temperature, and the state of ambient moisture changes when temperature changes. The best and only policy is to maintain inside temperatures above outside temperatures until the outside temperatures rise to uncomfortable levels (about 80-90 degrees Fahrenheit). When temperatures rise to an uncomfortably high range (assuming that people or animals are there), then inside temperatures may be allowed to remain close to outside temperatures, but not much lower. If heat and humidity become a comfort problem, then mechanical cooling with air conditioning as a common solution should also not lower the inside of the building more than 10 to 15 degrees Fahrenheit below what is outside. (If you have ever been a building which is over-cooled you may have felt damp of chilled.) Remember an air conditioner is primarily a big dehumidifier. Comfort, again is another subject concept. Comfortable temperature and moisture levels(humidity) adds another variable to the challenge of overall building moisture control, which is unlikely to need to be discussed here, where we are considering moisture control in construction materials. Lowering temperatures below 55'F, is poor economy. In areas of extremely high utility cost for heating and air conditioning, there are many ingenious methods (often using automatic timers or temperature sensitive actuators to operate fans) for controlling and maintaining temperature. These sometimes bring down naturally heated attic air to circulate through the lower areas of building. Again, "solar" and alternative heating and cooling is yet another immense subject area. The point of even mentioning this is to emphasize the extent of thought and effort that is put into inside temperature maintenance. Keeping the inside of any building above 55'F is generally considered an assumed necessity. If there is anything true about water tables it is that the concept is poorly understood, confusing and the term is overworked. In real life its best to focus on keeping things simple, on the surface, and let common sense rule. [ JUMP TO TOP ] [ HOME PAGE] [ PLACE ORDER ] [ RETURN TO MENU OF ARTICLES [ INSPECTION RELATED LINKS ] [ COST GUIDE ] If you have special questions We are available for professional consulting. For professional service, call (412) 241-1980. RETURN TO MENU OF ARTICLES     Or, if you wish to go back to where you were, click your back button. watshor:970307-0324,980510,990526,20080923.