Karst Terrain and Groundwater

 

The carbonate-rock aquifers are the predominate aquifer in the Valley and Ridge (V&R) of Virginia; however, there are areas in the Piedmont and Blue Ridge (P&BR) that also contain carbonate-rock aquifers. In total the carbonate rock aquifers underlie an area with a population of more than 40 million people in 10 states.

Where carbonate rocks are exposed at land surface or are overlain by only a thin layer of confining material they are easily dissolved by rain. As rain falls it absorbs some carbon dioxide from the atmosphere and from organic matter in soil. As the water percolates through the soil the weak carbonic acid water dissolves limestone and dolomite by enlarging pores between grains of limestone or fractures in the rock.

Over time these openings become larger as more of the acidic water moves through the aquifer; eventually the openings may be tens of feet in diameter. The end result of dissolution of carbonate rocks is a type of topography called karst- characterized by caves and sinkholes.

Water-supply wells drilled into the carbonate aquifers in karst terrain are generally more productive than wells that tap other rock types. The carbonate aquifers, due to the presence of dissolution channels, are very vulnerable to contamination from the surface. The carbonate aquifers are particularly vulnerable where sinkholes allow for the relatively rapid movement of contaminants into and through the aquifer. In some areas, the carbonate aquifers are locally isolated from the surface by thick layers of clay or shale that can impede the downward movement of water and contaminants.

The carbonate aquifers of the Appalachian Valley and Ridge Province, formed during Appalachian mountain building, have highly variable karst aquifer characteristics. The Valley and Ridge, Piedmont, and Blue Ridge Aquifers demonstrate karst features such as caves, sinkholes, sinking streams, and conduits. They are still used as a major drinking water supply for individuals and public supply, but without careful management these wells can become problematic.

The combined Valley and Ridge and Piedmont and Blue Ridge aquifers of all type rank second in the Nation as a source of groundwater for private domestic supply, providing about 470 million gallons per day (Arnold and others, 2016). The Valley and Ridge and Piedmont and Blue Ridge aquifers are also an important source of public supply, providing about 195 million gallons per day. Land use overlying the Valley and Ridge and Piedmont and Blue Ridge aquifers is mostly undeveloped (49 %), agricultural (35 %), and urban land (17 %).

Valley and Ridge and Piedmont and Blue Ridge aquifers in Virginia and were evaluated by the USGS National Water-Quality Assessment Project, which began in2012 and continued through 2021. Below are excerpts from that evaluation. The above information was taken from the USGS Groundwater Atlas of the United States.

Samples were analyzed for 34 trace elements and major and minor ions. Contaminants from this group were detected at high concentrations in about 10 % of the study area (at the depth zone used for public supply) and at moderate concentrations in about 5 %. Arsenic, manganese, and strontium were the only trace elements detected at high concentrations.

Samples were analyzed for eight radioactive contaminants, of which four have human-health benchmarks. Radioactive constituents were detected at high levels in about 3 % of the study area, but were not detected at moderate levels. Gross alpha activity was the only constituent detected at high concentrations.

Samples were analyzed for five nutrients, of which two have human-health benchmarks. Common sources of nutrients include fertilizer applied to crops and landscaping, seepage from septic systems, and human and animal waste. Nutrients were detected at high concentrations in about 2 % of the study area and at moderate concentrations in about 11 %. Nitrate was the only nutrient detected at high concentrations.

Some constituents affect the aesthetic properties of water, such as taste, color, and odor, or can create nuisance problems, such as staining and scaling. Samples were analyzed for 11 constituents that have SMCLs. One or more of these were present at high concentrations or values relative to the SMCL in about 15 % of the study area and at moderate concentrations in about 18 %.

Total dissolved solids (TDS) concentration is a measure of the salinity of the groundwater, and all water naturally contains TDS as a result of the weathering and dissolution of minerals in rocks and sediments. The TDS concentrations can be high because of natural factors or as a result of human activities, such as applications to the land surface of road salt, fertilizers, or other chemicals in urban or agricultural areas. The TDS concentrations were high in about 5 % of the study area.

Iron and manganese were both present at high concentrations relative to the SMCL in about 5 % of the study area. Sulfate was present at high concentrations in about 2 % of the study area. In a few samples, the pH of groundwater was not in the SMCL range of 6.5–8.5. In those cases, the pH was less than 6.5; such waters are considered acidic and potentially corrosive.

VOCs were detected at moderate concentrations in 2 percent of the study area. The only VOC detected at moderate concentrations was chloroform.

Samples were analyzed for 227 pesticide compounds (pesticides and their breakdown products), of which 119 have human-health benchmarks. Pesticide compounds were not detected at high or moderate concentrations in the study area.

The Piedmont and Blue Ridge Groundwater

About half of the nation’s population relies on groundwater for drinking water. As the nation’s population grows, the need for high-quality drinking-water supplies becomes ever more urgent. The USGS has identified 68 principal aquifers in the United States, these are regionally extensive aquifers that are used as sources of drinking water.

Groundwater pumped from these primary aquifers provides nearly 50% of the nation’s drinking water. Twenty of these principal aquifers account for about three quarters of the nation’s groundwater pumped for public supply. These aquifers also provide 85 % of the groundwater pumped for domestic (private) supply. Three of these principal aquifers are in Virginia and were evaluated by the USGS National Water-Quality Assessment Project, which began in2012 and continued through 2021. Below are excerpts from the evaluation of the Piedmont and Blue Ridge aquifers and information taken from the USGS Groundwater Atlas of the United States.

The Piedmont and Blue Ridge crystalline-rock aquifers underlie an area with a population of more than 25 million people in 11 states (map). The Piedmont and Blue Ridge crystalline-rock aquifers, together with the other rock types in the Piedmont and Blue Ridge regions, rank second in the Nation as a source of groundwater for private domestic supply, providing about 360 million gallons per day (Arnold and others, 2017a).

These aquifers are also an important source of public supply, and about 92 million gallons per day are pumped for that use. Land use overlying the Piedmont and Blue Ridge crystalline-rock aquifers is mostly undeveloped (71 %) and agricultural (19 %). The cities of Atlanta, Georgia, and Charlotte, North Carolina, overlie the aquifers, as well as suburbs of Richmond, Virginia; Washington, D.C.; Baltimore, Maryland; and Philadelphia, Pennsylvania.

The Piedmont and Blue Ridge Provinces are underlain by three principal types of bedrock aquifers. In order of decreasing area, these are crystalline-rock and undifferentiated sedimentary-rock aquifers, aquifers in early Mesozoic basins, and carbonate-rock aquifers. Unconsolidated aquifers that are part of the surficial aquifer system overlie the bedrock aquifers locally in Pennsylvania and northern New Jersey.

Crystalline-Rock and Undifferentiated Sedimentary-Rock Aquifers are the most widespread aquifers in the Piedmont and Blue Ridge Provinces. These aquifers extend over about 49,000 square miles, or about 86 % of the area, of these provinces. Most of the rocks that make up crystalline-rock and undifferentiated sedimentary-rock aquifers are crystalline metamorphic and igneous rocks of many types. The main types of crystalline rocks are coarse-grained gneisses and schists of various mineral composition; however, fine-grained rocks, such as phyllite and metamorphosed volcanic rocks, are common in places.

Unconsolidated material called regolith overlies the crystalline-rock and undifferentiated sedimentary-rock aquifers almost everywhere. Because the regolith material varies greatly in thickness, composition, and grain size, its hydraulic properties also vary greatly. However, the regolith is more permeable than the underlying bedrock. Water in the bedrock is stored in and moves through fractures, which form the only effective porosity in the bedrock.

Early Mesozoic rift basins are spread out in the Piedmont Province and occupy about 9 % of the combined area of the Blue Ridge and the Piedmont Provinces. Aquifers in early Mesozoic basins are primarily in three major basins-the Newark Basin in New Jersey and Pennsylvania is the largest basin and the one from which the most ground water is withdrawn; second largest is the Gettysburg Basin of Pennsylvania and Maryland; and third is the Culpeper Basin of Virginia.

The Culpeper Basin of northern Virginia and Maryland is an elongate, fault-bounded trough that trends north-northeast from the southern border of Madison County, Va., about 90 miles to Frederick County, Md. All the formations in the basin are part of the Culpeper Group. The lower part of the group consists of sandstone, siltstone, and conglomerate of Late Triassic age; the upper part consists of Lower Jurassic sedimentary rocks and interbedded basaltic lava flows.

The water in the Culpeper Basin is the least impacted by iron, manganese and sulfate in the region and of only moderate hardness. My home overlies a section of the Culpeper basin that runs through all but one small corner of northwestern Prince William County. I chose this area for the water. It requires no treatment.

Carbonate-Rock supports the largest aquifers in the Piedmont and Blue Ridge. Limestone, dolomite, and marble of Paleozoic and Precambrian age form carbonate-rock aquifers that extend over about 3 % of the Piedmont and the Blue Ridge Provinces. Although these carbonate rocks are of small extent, they are significant local sources of water. Carbonate-rock aquifers are in five areas of the Piedmont and the Blue Ridge Provinces. In addition to these areas, small, isolated elongate stringers of limestone and marble form minor aquifers locally, particularly in Virginia, and generally trend parallel to the Blue Ridge front.

Recharge is highly variable in the Blue Ridge and the Piedmont Provinces because it is determined by local precipitation and runoff, which are highly variable and are influenced by topographic relief, ground cover, compaction and the capacity of the land surface to accept infiltrating water. 

Most of the Piedmont and the Blue Ridge Provinces are covered by regolith. Compared to the Blue Ridge, the gentler topographic relief of the Piedmont and less precipitation make the Piedmont less subject to rapid denudation than the Blue Ridge and thus favor the accumulation of a thicker regolith. The combination of large areas of thin regolith and dense bedrock with minimal permeability in the Blue Ridge Province do not favor large amounts of ground-water recharge. These areas have a limited ability to provide water.

Almost all recharge is from precipitation that enters the aquifers through the porous regolith. Much of the recharge water moves laterally through the regolith and discharges to a nearby stream or depression during or shortly after a storm or precipitation event. Some of the water, however, moves downward through the regolith until it reaches the bedrock where it enters fractures in crystalline rocks and sandstones or solution openings in carbonate rocks.

The USGS Aquifer Studies were designed to evaluate groundwater used for public supply prior to any treatment. Groundwater quality was assessed by comparing contaminant concentrations to regulatory limits established for drinking water quality.  Trace elements and major and minor ions are naturally present in the minerals of rocks, soils and sediments, and in the water that comes into contact with those materials.

The USGS sampled 60 wells at depths that a used for public supply wells: 150-700 feet beneath grade. Samples were analyzed for 90 VOCs, of which 38 have human-health benchmarks. VOCs were detected at moderate concentrations in 5 percent of the study area but were not detected at high concentrations. Compounds detected at moderate concentrations were the disinfection byproduct chloroform and the solvent trichloroethylene (TCE).

Manganese was found to be present at high concentrations relative to the SMCL in about 15 % of the study wells. Iron was present at high concentrations relative to the SMCL in about 12 % of the wells.

Samples were analyzed for 227 pesticide compounds (pesticides and their breakdown products), of which 119 have human-health benchmarks. Pesticides were not detected at high or moderate concentrations in the study

In some areas, the pH of the groundwater was not in the SMCL range of 6.5 to 8.5. The pH did not meet the standard in 35 % of the study area, typically because it was less than 6.5, which is acidic and potentially corrosive.

The total dissolved solids (TDS) concentration is a usually considered a measure of the salinity of the groundwater, though all water naturally contains TDS as a result of the weathering and dissolution of minerals in rocks and sediments. Concentrations of TDS can be high because of natural factors or as a result of human activities such as applications of road salt, fertilizers, or other chemicals to the land surface in urban or agricultural areas. Concentrations of TDS were high in about 3 % of the study area. Chloride, fluoride, and sulfate—constituents that also contribute to TDS concentrations—were detected at moderate, but elevated concentrations.

Radioactivity is the release of energy or energetic particles during spontaneous decay of unstable atoms. Most of the radioactivity in groundwater comes from the decay of isotopes of uranium and thorium that are naturally present in minerals in aquifer materials. Samples were analyzed for eight radioactive constituents, of which four have human-health limits for drinking water. The USGS found radioactive constituents were present at high levels in about 30 % of the study area and at moderate levels in about 17 %. Radon (using the proposed alternative maximum contaminant level of 4,000 picocuries per liter) and gross-alpha activity were the only constituents that were present at high concentrations. Radium (combined concentration of Ra-226 and Ra-228 isotopes) was detected at moderate concentrations in 2% of the study area.

Nutrients are naturally present at low concentrations in groundwater; high and moderate concentrations (relative to human-health benchmarks) generally result from human activities. Samples were analyzed for five nutrients, of which two have human health benchmarks. Common sources of nutrients, aside from soils, include fertilizer applied to crops and landscaping, seepage from septic systems, and human and animal waste. No nutrients were detected at high concentrations in the study area. Nitrate was detected at moderate concentrations in about 3% of the study area.

 

Groundwater Drought in Western Prince William

USGS monitoring well 49V1

It seemed that all of last week we had rain here in western Prince William County, my garden blooms and I am getting my garden in shape. As I was considering planting three trees that would need to be watered until they became established, I checked the water level in the U.S. Geological Survey (USGS) groundwater monitoring well up the road and was shocked at the water level. The median groundwater level for May based on 39 years of data is 9 feet below grade. The monitoring well’s groundwater level had fallen to just about 14 feet below grade. This was the lowest level of groundwater recorded for that well during May over the entire 39 years of data that had been recorded. The USGS maintains a group of 20 groundwater monitoring wells in Virginia that measure groundwater conditions daily and can be viewed online. One of the Virginia wells, 49V1 is just up the road from me in the same groundwater basin and serves as the proxy of the condition of my well.

The water level in a well usually fluctuates naturally during the year. Groundwater levels tend to be highest in the early spring in response to winter snowmelt and spring rainfall when the groundwater is recharged. Groundwater levels begin to fall in May and typically continue to decline during summer as plants and trees use the available shallow groundwater to grow and streamflow draws water. Natural groundwater levels usually reach their lowest point in late September or October when fall rains begin to recharge the groundwater again, though the lowest level ever recorded at the monitoring well up the road was in July 2011 at 15.38 feet below land surface. If the groundwater level in May is already this low, I am very worried about July and the general health of the aquifer. The natural fluctuations of groundwater levels are most pronounced in shallower wells like mine that are the most susceptible to drought.

The USGS has been using long-term groundwater monitoring data, combined with groundwater models, to improve our understanding of the storage and flow of groundwater. Whenever you pump water from a well it has to be balanced by a loss of water from storage in the groundwater aquifer. Groundwater is recharged from rain and surface infiltration from things like septic. If too much water is pumped, water tables can drop in unconfined aquifer like the one here in the Piedmont region of Virginia. The growing population and the effects of recent droughts have made the need for an updated status on the availability of the groundwater necessary and the USGS has been expanding their groundwater studies nationally.  I called the USGS Virginia Water Science Center in Richmond, Virginia and spoke to David Nelms the groundwater specialist. I happen to catch him right after the Drought Taskforce Meeting and so he was able to give me a well-considered opinion of what might be causing the low groundwater levels.

Mr. Nelms confirmed that this is the lowest groundwater level recorded in this region in May in 39 years. Though the Virginia Department of Environmental Quality, DEQ, has listed the groundwater conditions for Northern Virginia (including Prince William County) as normal, according to the USGS there is a small area in the Piedmont that just did not get enough rain last fall and over the winter to overcome the soil moisture deficit from the drought of 2012. According to Mr. Nelms this area of the Piedmont did not catch enough rainfall during the rains last fall even with Hurricane Sandy passing through. Though the water levels in the past couple of years have fallen to levels lower than recorded over the previous 39 years, the USGS did not think that anything other than a lack of rainfall was causing the low water levels. Mr. Nelms noted that the seasonal variation in groundwater levels seemed to be more extreme in recent years, and that the ownership of the property where the monitoring well is located had changed hands and could indicate a change in use could have impacted the apparent static pumping level by increasing the cone of depression if for instance the well had been used for irrigation or a sprinkler system. The USGS was not aware of any change in water use. As Mr. Nelms pointed the water level needs to be watched because it impacts not only the wells in western Prince William (including the Evergreen public water supply system), but also the surface water tributaries to the public water supply systems drawing from the Occoquan Reservoir and the Potomac River. Potomac River flow was also low for this time of year. Data from the National Weather Service’s Middle Atlantic River Forecast Center shows that the Potomac basin upstream of Washington, D.C. had a precipitation total which for the year to date is 1.5 inches below normal. We need to keep an eye on the water level and rainfall this summer.

USGS Data for 49V1

Purchasing a Home with a Water Well-Caveat Emptor

In rural areas or here on the edge of nowhere private wells supply water to homes. If you are thinking about buying a home with a private water well you need to understand at a minimum the basics about groundwater, the local geology, water quality, how the well system works, how deep the well is and how old and what size pump it has. These are the factors that will impact water reliability, water quantity, and water quality.  It would be a real shame to discover after closing on home that the drinking water well does not supply enough water for you to do laundry in the summer, goes dry in a drought or that the water is contaminated or has an unpleasant taste or smell. It can be very expensive to replace a well or well components, engineer solutions to water supply problems and install and maintain a water treatment systems. A home inspection tells you nothing about the well or septic system.  

About 15% of households in the United States depend on private wells including over a million each in Virginia and Pennsylvania where I once lived. In its most basic sense a private water well is a hole in the ground that is drilled, driven, or hand dug to supply water for a household. Most wells today are drilled by a cable tool or by air-rotary drill. Hand-dug wells are usually very old but still exist; and are very susceptible to pollution from surface sources and may also present easy routes for surface contaminants to enter the aquifer. If considering purchasing a home with an old hand dug or driven well factor in the cost of replacing the well with a modern drilled well in the price and be aware that not all pieces of land have suitable aquifers to tap.

The aquifer is the groundwater. Aquifers may occur a few feet below the land surface, but useful aquifers are more commonly found at depths greater than 100 feet in Pennsylvania and 100-400 feet beneath the bedrock in Virginia. Some groundwater occurs in the pore spaces of solid rock, but most usable groundwater occurs in cracks and fractures in rock layers or between sand and gravel particles of unconsolidated layers. Except in Karst terrain which has its own special problem, groundwater normally occurs in small spaces within the geological layers and not as underground lakes or rivers.

 Geologic formations called aquitards are usually made of clay or dense solid rock. The aquidards inhibit groundwater infiltration, and restrict groundwater movement into and between aquifers. Aquitards located above and below an aquifer form a confined aquifer. If a well is drilled into a confined aquifer, artesian pressure forces the trapped water to rise in the well above the aquifer if the pressure is great enough, the water may even flow without pumping to the land surface creating an artesian well. The downside to a confined aquifer is that recharge is limited. The coastal plain in Virginia has a confined aquifer and is really only recharged at the “fall line.” A groundwater aquifer without an aquitard above it is an unconfined aquifer and more susceptible to contamination, but more easily recharged by precipitation. Without pumping, the water level in wells in unconfined aquifers is the same as the aquifer. The county department of health, the extension office, the local offices of the U.S. Geological survey are good places to find out about the local geological and groundwater conditions. You need to understand what type of aquifer you are dealing with to be aware of the factors that impact water quantity and quality. There are dry years and wet years and water availability will vary, though it is not always obvious. The groundwater aquifer tapped for water is not seen so you need to understand it to be aware of the water budget that you will have to live within before you run out of water.

In many locations private wells are not regulated or only minimally regulated. Virginia now has well drilling regulations and standards, but those only apply to wells drilled after 1992 and require a health department permit for drilling new wells and repairs of older wells.  If you buy a home with an existing well- buyer beware. It is your responsibility to make sure that you know what you are buying. The type of well, the well yield, the condition of the well and the quality of the water is your responsibility to determine before purchase. The type of well and the configuration will be determined by the age of the well and geology.  While there was a time when some wells were hand dug with a shovel or hand driven using connected pieces of pipe (as featured in Hallmark channel movies) most wells use equipment to drill, dig or drive pipe and by and large modern wells are drilled. Nonetheless, there are thousands of home supplied with water from older wells. Ask, look, investigate. Check driller’s logs filed with the health department.

The type of well is determined by geology and history. Sitting as my home does in the Culpeper groundwater basin above fractured rock and bedrock, drilled wells are predominant. When drilling a well, it is typical here and now in Prince William Virginia in the twenty-first century to drill the well through a first and second layer of groundwater. I have a second groundwater level I can drop my pump down to if need be in a drought.

Drilled wells penetrate about 100-400 feet into the bedrock. To continually supply water, a drilled well must intersect bedrock fractures containing ground water. The art of well drilling is having a feel for what a fracture looks like at the surface- knowing where the water is. A trained and experienced hydro-geologist can generally find the fractured rock zones, or the intersection of two fractured rock zones using aerial photography and the fracture trace technique. It can be expensive to hire a professional hydro geologist, but the cost is worthwhile for difficult areas.  Where I live in the Piedmont region of Virginia the local geology is a fractured rock system that is water rich with more than one groundwater layer, so using hydro geologists is not common, but I do know of a couple of instances where several wells were drilled before obtaining adequate water flow and it might have been more cost effective to locate water before the house was built or to design a different well system. The Piedmont tends to be so water rich that alternatives are not in common use. In some regions low production wells are common.

If a property has a low producing well, there are ways to deal with it. First is water conservation and the second is to increase water storage within the system. Water conservation involves changing water–use behavior such as taking shorter showers, but usually involves installing water saving devices like a front-loading washer (saves 20 gallons of water for each load),low flush toilets, flow restricting faucets and shower heads. Installing watersaving appliances can reduce household water use by up to 30%. Water conservation may solve the problem of a 5 gallon a minute well, but increasing water storage can make a reliable 1 gallon a minute well viable for a modern household. An intermediate storage system consisting of a storage tank ,reservoir or cistern that can be installed between the well and pressurized distribution system. The reservoir serves as the primary source of supply for the pressure pump supplying peak demand. Ideally, the storage tank or cistern should be able to hold at least a day’s water supply and be regulated by a float switch or water level sensor. A 1 gallon a minute well can pump 1,440 gallons per day more than adequate for a household of almost any size.  The rule of thumb is to size a storage tank or cistern at 100 gallons per person in the household. It is much cheaper to installed intermediate storage than keep drilling wells.   

Once you have determined that the water supply is adequate, the water quality should be checked. The quality of the groundwater is a characteristic of the aquifer and the ability of your local geology to protect or impact your aquifer. The most common sources of pollution to groundwater supplies come from two categories; naturally occurring ones and those caused by human activities. Naturally occurring contamination are produced from the underlying soil and rock geology. Microorganisms in the soil can travel into groundwater supplies through cracks, fissures, and other pathways. Nitrates and nitrites from the nitrogen compounds in the soil can also enter the groundwater. From the underlying rocks radionuclides and heavy metals can enter the groundwater. There are areas with natural occurring arsenic, cadmium, chromium, lead, selenium and fluoride. While many natural contaminants such as iron, sulfate, and manganese are not considered serious health hazards, they can give drinking water an unpleasant taste, odor, or color.

Human activities can also introduce contaminants into thegroundwater. Bacteria and nitrates can be caused by human and animal waste. Improperly constructed and sealed wells can allow surface contamination to enter the well. Improperly maintained septic systems containing human waste and any chemical you flush down the drain, horses, and backyard poultry can contaminate the groundwater. Leaks from underground storage tanks, surface disposal of solvents, motor oil, paint, paint thinner, termite treatment or nearby or historic landfills or industrial operations can contaminate groundwater. A confining geological layer can protect groundwater from surface contaminants more effectively than a fractured rock system, and there is extremely limited natural protection in karst terrain. Though it is cost prohibitive to test for every potential contaminant, a broad baseline analysis should be performed before purchasing a home (and every few years). A bacteria test is not enough. The cheapest way to do this is a commercial product aimed at the private homeowner. One product I have used is the WaterCheck with Pesticides. This product covers 15 heavy metals, 5 inorganic chemicals, 5 physical factors (like hardness and pH), 4 trihalo methanes, 43 volatile organic chemicals (solvents), and 20 pesticides, herbicides and PCB’s. The analysis takes two weeks and so the contingency period must allow for that or a more expensive analysis must be used. Whatever analysis you use, make sure you use an EPA certified laboratory that is also certified in the State where the property is located.

All private wells should be have as a water-tight, vermin-proof well cap and a cement or bentonite grout seal between the borehole and the well casing to prevent surface contamination and bacteria from entering the well. In coal or gas country, a well should include a vent. Well water should be tested annually to ensure a safe drinking water supply for your family. The supply of water should be adequate. In our modern world household water demand is not spread evenly over the day. There are peak usage times driven by washing machines, dish washers, showers. An adequate water system must be able to yield enough water to satisfy peak demand. Look for a minimum of 10 gallons a minute from a modern drilled well to supply a household or a system with intermediate storage (remember in some instances the well itself can provide storage). To live comfortably with your well, your water system has to be able to deliver an entire day’s worth of clear uncontaminated water within a 90 minute window.