Groundwater Hydrology Lecture Notes II.
GROUNDWATER & SPRINGS. Lec. 20.
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Role of Groundwater in Water Cycle:
Groundwater aquifers act as hydrologic “shock absorbers” lessening impacts of
rainfall events and leveling out the flow in rivers.
The base flow of rivers is due to gradual groundwater discharge.
Big big volume:
Perhaps 200 times the total annual flow in all rivers is stored in fresh water
aquifers and there are saline and briny aquifers present at depth below many
freshwater aquifers.
Benefits:
Groundwater aquifers also act as filters to remove harmful organic matter,
bacteria, viruses etc from water.
Active Aquifers
However aquifer materials are not inert.
Aquifers in sedimentary deposits can have high concentrations of dissolved
substances some of which are innocuous, others are obnoxious or toxic.
Sandstone aquifers can add salts.
Examples:
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Well near Shiro, (H2S, Fe)
Arsenic in well water.
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Counter-example:
Perrier (France C02 also some benzene),
Ozarka (Moffat springs).
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Deep Concepts:
Once infiltration has replenished soil moisture and deep percolation has resulted in
groundwater recharge, the water may remain underground for days, weeks,
years, centuries or millennia.
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Older than Dirt:
Age of groundwater is determined by radioactive dating using tritium, carbon
14/12 and oxygen 18/16 isotope ratios.
Example: my backyard well water in Las Vegas fell as rain circa 12,000 years
ago.
Where does the tritium come from: nuclear weapons detonations in the
atmosphere?
Aquifer geologic settings:
Unconsolidated (porous) formations (most aquifer are unconsolidated alluvium).
Consolidated porous rocks (dissolution cavities, fractures also called secondary
porosity, rocks with primary porosity)
Consolidated impervious rocks and tight clays (aquitards, aquicludes, aquifuges and
bedrock).
Zones of the subsurface:
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Soil zone
perched aquifer
aquitard (clay layer)
capillary fridge
water table aquifer
aquitard or aquiclude
confined aquifer
bedrock (aquifuge)
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Sources of groundwater recharge:
Infiltration of water from precipitation
Influent streams (or lakes)
Recharge areas are often upland areas or swampy areas with permeable soils and
underlain by unconsolidated deposits (gravels and cobbles).
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Discharge:
Discharge can occur from springs, into the bed and banks of streams and lakes
and because of phreatophytes.
In arid areas there is little recharge (less than 1%) in most of U.S. recharge is
about 10% of precipitation.
Discharge accounts for about 40% of flow in streams in U.S.
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Balance of nature:
Discharge balances recharge except where man overdrafts an aquifer by
pumping.
Therefore a water balance can usually be worked out for a river basin.
Groundwater aquifers and river basins are not coincident:
Normally surface water basins and groundwater basins coincide but
unconformities can cause strange effects: Example Moapa River, NV.
Perched groundwater:
Often a shallow temporary saturated zone called perched groundwater exists
above a clay layer. It is called perched water since the soil below this layer is not
saturated.
Example: Yuma, Arizona area.
Water table aquifers:
Deeper is a true aquifer (water table aquifer)
The depth to this aquifer in a uniformly porous media is an indication of the
wetness of the climate:
Examples:
New Orleans, water table within a few feet of surface.
Unconfined & Confined aquifers:
In some areas the only aquifer is the unconfined (water table) aquifer but usually
one (as many as 16) other aquifers can occur under the initial aquifer trapped by
aquitards (retard flow) or even aquicludes (preclude flow).
These are confined aquifers.
Artesian conditions:
Conversely, a near-surface confined aquifer may well be under enough pressure
(head) to rise well above the level of its occurrence and even can flow freely
without the need to pump it (be artesian).
Named for Artois a region in France and Belgium.
No water down here:
Below the deepest of these aquifers is a zone of bedrock, an aquifuge and deeper
still is a place that is “hotter than Yuma”.
SPRINGS, Lec 21.
Springs:
• Most water seeps into beds of streams (or lakes or even the oceans).
• However, distinct springs (though accounting for minority of global water flow)
can be locally very important. Mecca and Jerusalem are holy cities partly because
they are the only major cities in arid areas due to the presence of abundant
springs.
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Significance:
Even in the U.S. springs can have an important influence: Examples: Huntsville,
Tex , Las Vegas, NV and NM and Balmorhea, TX.
Spring water is often more reliable than base flow water in terms of flow and
quality.
Types of springs:
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Contact springs
Fracture springs
Fault-controlled springs
Solution springs
Hot springs.
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Contact springs.
Usually located on a hill slope where there is a hallow. Flow is often low and
intermittent. Interflow is a temporary discharge from a contact type spring
location while continual seepage is a true spring.
Example: Deer Springs on Clark Peak, NV.
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Fracture springs:
follows fractures in massive rocks like granite or sandstones, can yield large flows
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of high quality water. If water in fracture is intercepted or earthquake occurs
spring can dry up.
Example: San Jose Springs, Ca
Fault Controlled Springs
If fault gauge is of low transmissivity (a measure of the water transmitting
capacity of a porous media) then water may back up along a fault zone creating a
series of springs:
Example: Palm Springs, CA.
Solution springs:
In a karst (limestone) geologic setting actual underground rivers (and lakes) may
exist. That causes water to collect and be discharged in large volumes with almost
constant temperature and flow:
Example: Merrimec River (a spring Branch) in Ozark Mountains of Missouri.
Hot springs:
• In hot springs gravity is not the only force acting on the water to cause it to
discharge the geothermal heat can cause water to be superheated and discharged
in large quantities at the surface: this can cause huge amounts of dissolved solids
(including valuable minerals) to precipitate and can also be a source of energy.
• Examples: Thermopolis Wy, Hot Creek, CA, Coso Hot Springs, CA, Hot Springs,
AR, Wirackie NZ.
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Other types of springs.
Anywhere where permeable rocks come into contact with impermeable rocks,
springs may form.
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Lec 22. The Geologic Setting of Aquifers.
Importance of geology:
Most groundwater hydrologists start out as geologists, because geology is quite
important to understanding the occurrence and behavior of water in the
subsurface.
What to look for in an aquifer:
The key factors that a hydrologist looks at with respect to any geologic formation
that may serve as an aquifer are:
Porosity
Hydraulic conductivity
Thickness
Uniformity
Stratigraphy
Porosity:
Porosity is the proportion of pore space. The more pores and the more pores of
uniform size, the better the aquifer will be. Unconsolidated rocks at depth can
have 5%-20% plus porosity while sandstones can range from almost zero to 10%
or more porosity.
Primary vs. Secondary Porosity:
There is primary porosity (intrinsic) and secondary (due to fractures). Crystalline
rocks have almost no primary porosity but can have 1-5% secondary.
Sometimes, it is possible to increase porosity of a formation by hydro-fracturing
and/or acidification.
Extreme example:
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Operation Plowshare.
Relationship between porosity and permeability:
High Porosity usually implies high permeability (and high HC) but if pores are
not connected this may not be the case.
HC is usually higher in horizontal direction than in vertical direction, why?
Characteristics of productive aquifers:
• Most groundwater occurs in unconsolidated materials. In some areas,
unconsolidated deposits extend to great depth (the Gulf of Mexico coastal plane is
the best example).
• Generally, groundwater extracted from aquifers shallower than 30 feet is likely to
be contaminated.
• Most aquifers are made up of alternating layers of water bearing and low
porosity formations:
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THICKNESS:
The thicker the aquifer the more water it can yield caterus paribus.
UNIFORMITY:
Geologic materials are never uniform, but the less uniform they are the more
difficult the job of the hydro-geologist. This is particularly true in areas like
complex alluvial environments (old stream channels) and glaciated areas.
Complexity:
• In this area (complex alluvial history) and in Ohio and Wisconsin (glaciated
areas) for example.
• If the layers are stratified in continuous horizontal beds (strata) then things are
easier, but if the beds are tilted twisted and warped and/or pinch-out, the
situation is complex and the aquifer likely to be less suitable.
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Stratigraphy:
Generally, a water table (unconfined) aquifer is less desirable as a source of
groundwater than the upper-most confined aquifer.
The water table aquifer can be easily contaminated; also it never rises above the
ground-surface (except at springs where it intersects the ground surface).
Ideal aquifers:
If the unconfined aquifer is thick and present in unconsolidated rocks then that is
an ideal situation. Most major water wells are completed in this type of
formation. Often with many screened intervals.
Where aquifers are found:
The most common situations where unconsolidated deposits are encountered in
the U.S. are:
Glaciated terrain.
Alluvial Valleys.
Ancient Alluvial Valleys.
Alluvial fill in tectonic Valleys.
Glaciated terrain:
• Glaciated valleys are complex aquifers.
• The porosity depends very much on what part of the glacial till, drift, outwash,
moraine etc you are drilling into. Some glacial till is clay with low porosity and
hydraulic conductivity.
• Outwash grades from coarse (good aquifer material) to fine (poor aquifer
material).
• Glacial features like buried valleys, eskers, terminal moraines, etc will cause
significant local differences.
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Examples:
In upper mid-west and Ohio there are many buried valleys with excellent high
quality confined aquifers in them.
As a result Ohio is “the groundwater hydrologist capital of the U.S.”
Alluvial Valleys:
Alluvial valleys are a complex environment.
Point bars and the river channel have coarse sediments and form good aquifer
materials.
Many communities extract water from under the beds of rivers, which are
actually in “hydraulic contact” with an aquifer.
Conversely, Oxbows, side channels, and other lacustrine environments deposit
fine silt and clay that makes for poor aquifer materials.
Most alluvial valleys make excellent aquifers.
Problems with alluvial valley aquifers:
Pumping water from an alluvial valley can often dry up the stream in the valley,
however.
Example: Jacko’s Creek.
Ancient alluvial valleys:
When the aquifer is adjacent to an existing river, figuring out the location and
characteristics of alluvial aquifers is easier.
But when rivers have been wandering all over a gently sloping coastal plane over
the millennia, it makes determining where to drill is an almost random exercise.
Alluvial fill in tectonic valleys:
• Where alluvium filled valleys have been uplifted, or where gravens have formed,
deep valleys form that have thick and often productive aquifers (Las Vegas is
more than 14,000 feet to bedrock). These conditions create some of the best
aquifers in the US.
• This tectonic activity traps water that would otherwise drain out, and since many
of these valleys are in the mountainous and semi-arid or very arid West, the
water stored in them is very important.
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Examples:
Include the eastern Sierra Nevada and the Las Vegas areas and other valleys in
the Basin and Range.
Frequently, the alluvium is both deep and quite coarse and snow melt helps
recharge these frequently closed basins via seepage through alluvial fans on the
mountain sides.
Lithified (consolidated aquifers):
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Sandstone
Karst
Coal and lignite
Sandstone:
Although consolidated sandstone can transmit or and store some water it often
produces highly mineralized water.
Typically water is only present in large quantities in fractures (Exception: the
Dakota formation).
Water will seep through sandstone and discharge from springs in the walls of
canyons or move down to aquicludes of low permeability (shales).
Most sandstone areas are not productive, but in of the Colorado Plateau this is
the only water source.
Examples:
Navajo Reservation (Coconino Plateau)
Central Australia (Alice Springs).
Karst:
The Term Karst refers to limestones with dissolution cavities. This is a very
important and often bizarre type of aquifer. Underground rivers, sink holes that
swallow car dealers (or at least their cars), waterfalls, lakes, weird blind fish and
disappearing rivers all occur in Karst areas.
Good site for a whiskey still:
Karst areas often have productive springs with excellent water quality and
constant flow and temperature.
The natural acidity of water dissolves holes through Karst areas.
Problems:
Unfortunately, karst areas are vulnerable to surface water pollution getting down
into aquifers.
Also formation of sink-holes.
Locations:
Ozarks, Appalachians, some areas in the West and the Hill country of Texas is
Karst dominated.
Coal and lignite.
Coal and lignite can hold large quantities of water, but unfortunately coal also
has sulfides present that can degrade water quality. Grimes County (at least
around Carlos) has rotten water, since it is coming from a lignite aquifer.
Igneous & metamorphic rocks as aquifers:
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Volcanic Rocks
Fractured granites
Marble
Volcanic Rocks:
Basalts are most important igneous aquifer materials is not very porous but as it
cools it fractures deeply and it often is present in layers separated by
unconsolidated rocks hence it can make a good aquifer although surface water
will be rare in such an area:
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Examples:
Columbia River Plateau and Decan area in India. The discharge from such areas
is likely to be very uniform and the water quality excellent.
Other volcanics:
• Deep unconsolidated volcanic ash makes a good aquifer but the water quality will
not be as good as basalt areas. Examples include the Pallouse Plateau in
Washington State.
• Welded Ash (tuff) will not retain or transmit very much water.
• Porous lava such as present in Hawaii has high porosity but pores may not be
connected, Lava tubes can produce underground rivers much like karst areas.
Water is hard to obtain in such places.
Intrusive igneous rocks:
• Fractured granites: Do not hold much water in primary pores, but cracks can
hold and transmit some water.
• Since granite is very inert, such water will be of very good quality.
• Many famous springs for drinking water are in fractured granite: Such as
Arrowhead Springs in San Bernardino Mountains in CA.
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Problems with granitic aquifers:
The down side of granite is that fractures are vulnerable to up-gradient wells and
earthquakes,
Also granite can contain uranium so water in some areas like western
Pennsylvania contains radon gas.
Marble:
(which is metamorphic limestone) can also be dissolved (to a lesser extent) by
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acidic water and can form aquifers.
Marble Springs, Texas? A misnomer.
Generally, metamorphic rocks unless heavily fractured make poor aquifer
materials.
GROUNDWATER REGIONS OF THE USA.
12 regions in conterminous USA.
1.Western Mountain Region:
Narrow Alluvial valleys, shallow soils, limited aquifers, headwater areas for
many rivers.
2. Alluvial Basins:
Mountain bordered alluvial valleys.
Like:
Owens Valley,
Central Valley of California
Las Vegas Valley
San Gabriel Valley.
Large very important aquifers.
3. Volcanics.
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Fractured basalt,
Buried valleys productive in an otherwise arid area.
Eastern Oregon and Washington (Columbia Plateau) is largest area.
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4.Colorado Plateau and Wyoming Basin, Dakota Sandstone.:
Thin Soils and consolidated sedimentary rocks: poorest aquifers in USA in one of
the driest areas (hence lowest population density.
Many Indian Reservations (“Palefaces” didn’t want the land in 19th century)
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5. High Plains:
Thick Alluvial Deposits over sedimentary rocks:
Excellent aquifers but recharge is modest.
Ogallala is most famous aquifer in this region.
Also Dakota Sandstone.
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6. Non-glaciated central region:
Most of Texas is included, thin Regolith over sedimentary rocks (such as here in
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Huntsville).
Where carbonate rocks are present this area can provide good aquifers, also
ancient alluvium can be productive.
7. Glaciated Central Region:
Buried Valley aquifers of Upper Midwest.
8. Piedmont-Blue Ridge Mountains:
Thin regolith over crystalline rocks.
Valleys contain most productive aquifers where carbonate rocks are present can
have good aquifers.
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9.Northeast and superior uplands:
New England and Lake Superior area (surface water is abundant). Granite
shield rocks are pre-Cambrian.
Rocks are unproductive but gravel filled valleys can yield water.
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10. Atlantic and gulf coastal plain:
Starts here and extends to south.
Complex sequences of sand, silt clay and limestone.
Can provide very good to very poor aquifers.
Water quality is sometimes poor.
Saltwater intrusion and subsidence can be problems.
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11. Southeast coastal plain:
Thick sand silt and clay over limestone:
Good aquifer materials.
But sink holes, salt water intrusion and shallow groundwater can be a problem.
Mostly in Florida.
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Lec 23. WATER SUPPLY WELLS:
History of Wells
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Bamboo Drilled wells in china to 2,500 feet over 2,000 years ago.
Hand dug wells.
Ass powered wells.
ISSUES FOR ANY WELL.
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LOCATION.
DESIGN.
INSTALLATION
OPERATION
ABANDONMENT.
Water Well Location Do’s
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Tap productive aquifers.
locate near users
locate near power
drill as shallow as possible
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Water well location Don'ts
Avoid zones of surface water pollution related contamination
Avoid areas of sub-surface contamination
Avoid areas of subsidence
Avoid “superposition of cones of depression”. In other words stay well clear of
other wells.
Local examples:
• Around Huntsville this is the typical situation. Wells a few hundred feet apart
will have totally different properties: Some deliver large quantities of good water
others fill up with sand or have little yield of rotten water. It all depends on luck.
Science has little to do with it since the stakes are not high enough to use seismic
or other subsurface mapping techniques. So it is hit or miss.
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Rule of thumb for well drillers in around here:
Where to drill a well in Walker County:
Drill “under a tree or on the shady side of a barn or next to an ice house with cold
beer on tap”….
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Typical design :
Gravel pack, screen, pump, casing, grout or cement and surface plug and cap and
pipe are typical set-up.
Water Well Design Variables:
Base diameter or expected demand and yield of aquifer.
Screen well in areas of greatest porosity and in zones of continuing production.
Use cased or uncased well depending on stability of aquifer materials.
Well characteristics:
The well diameter and screened interval and screen characteristics impose
maximum production limits.
Caterus paribus a larger diameter, slot size and longer screened interval produce
more water.
Over 30 inch diameter is not feasible
Pump selection:
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Select pump based on:
Desired yield,
Depth of well,
Need for accessibility,
Required durability and then cost.
Can be submersible, surface motor and impeller at depth or slicker rod.
Water Well Installation.
Wells can be augured, drilled, driven or jetted.
Augured wells are of limited depth and can only be used in unconsolidated
materials.
Driven wells can be in harder materials but limited depth
Jetted wells in unconsolidated materials.
Drilled wells can very deep and drilled in hard rock can be air rotary or reverse
rotary using a drilling mud.
Factors affecting choice of drilling method:
Choice depends on aquifer material and depth, also available money.
Jetted & augered are cheapest methods work only in shallow unconsolidated
materials.
Driven is next cheapest, works in shallow consolidated.
Drilled works in more difficult conditions.
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Variations on drilled wells.
Drilled wells use a rotary bit but the variations involve how cuttings are removed.
Can be air rotary or a mud system.
In a mud system a slurry of water and bentonite is used.
Method is also common one in oil and gas industry, where deeper wells are norm.
Depth of wells:
Most groundwater is obtained from wells less than 500 feet deep and almost all
wells are less than 2,000 feet deep.
Exceptions: arid and semiarid areas with large up-lift.
Well logs
As the well is being drilled a geologist should note the texture and other
characteristics of each layer and prepare a well log.
This is frequently required to be filed along with other information to a State
Engineer or water development board.
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Geophysical methods:
Also, various geophysical techniques can be used to get further information. These
include:
Neutron log: (looks for hydrogen) can be fooled by clay.
electric (resistively) log: wet soil is more conductive than dry soil.
Measure both water content and porosity. Each is fallible so both are combined.
Well loggers: the lonesome cowboys of the well business.
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Well tests:
Once a well is installed and developed it is typically tested.
Hydro-geologists spend a lot of their time in the field performing well tests.
The basic tests are pump tests.
There are also slug tests
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Pump Tests:
A graph of time pumping rate and time versus draw-down are developed to
estimate safe yield of the well. A monitoring well (or more than one) can be a very
useful part of this.
Give me a slug of that:
A slug test Can also be performed to estimate hydraulic properties of the
formation.
A known quantity of water is pumped into the well and the rise and fall in water
levels are recorded.
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Water Well Development:
Once a well has been drilled and casing set the well must be developed.
This is accomplished by pumping the well to remove silt and sediment inside the
casing then using a surge block or compressed air hose to push sediment out of the
slotted screen and into the gravel pack.
Water quality testing:
Water quality should be determined after the pump test is complete.
Some characteristics can be determined in the field some require laboratory
analysis.
Field parameters:
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Temperature,
Conductivity.
pH.
Dissolved oxygen
Also taste and odor.
Lab parameters:
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TDS,
Hardness,
Alkalinity,
pH.
D.O.,
General minerals: Na, Cl, Mg, Fe, Ca, Mn,
HCO3, H2CO3, SO4, SO2.
Advanced lab analysis:
required if contamination is suspected or for public water supply wells:
Many other tests can be conducted for trace elements, anthropogenic
contaminants, radioactivity and pathogenic organisms. These are expensive and
generally unnecessary.
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Water Well Operation:
Once installed water levels must be monitored to avoid too much draw-down. Or
reduced yield.
Water cannot be pumped continuously, so storage tanks are needed.
Also flow must be adjusted to required water delivery rate and pressure.
The more demand varies, the larger the tanks needed.
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Ongoing well operation requires::
Water may need to be analyzed at least quarterly for water quality.
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Water may need treatment after it is pumped out of the ground this includes:
Aeration, chlorination, softening, RO, and other treatment.
Water Well Maintenance
• If water has too much air in it may be cascading.
• Over aeration can promote growth of iron and manganese oxidizing bacteria that
form a slime that gunks up a well. Chlorination is needed,
• Well components may need to be oiled and cleaned periodically. Bearings and
impellers wear out.
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Well failures:
Casing can blow-out requiring pulling the casing and resetting it.
Wells can sand up or screen or gravel pack can get clogged (re-develop well).
Down hole Video now more common.
Insects (ants particularly) can get in wells.
If air bladder tank is used the bladder may need to be replaced.
Water system problems related to groundwater:
Hard water will cause scale, so softening and de-scaling with salfamic acid may
be needed.
Soft water corrodes pipes so silicon may be added.
Water Well Abandonment.
If a well is no longer needed it must be properly abandoned.
This requires pumping cement into the well or dropping bentonite grout down it.
The upper 10 feet of casing should be removed and a hole out at least 5 feet filled
with cement.
The location of the abandoned well should be recorded.
Improper abandonment of wells (particularly oil and gas) in a huge
environmental problem in Texas.
Why abandonment is important:
Toddlers can fall into well
Well can be a conduit for movement of contaminants in surface into aquifers
(Ralph Grey Superfund site) Monitoring Well Location.
Lec.24 Groundwater Contamination
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Significance of groundwater contamination
Worldwide problem
Major issue at superfund sites, landfills and many other locations
Billions of dollars in costs
Thousands of suspected cancer deaths and birth defects.
Extent of groundwater pollution:
Over 1 million LUST sites.
Millions of anaerobic septic systems in poorly draining soils (a major problem in
Texas),
20,000 plus solid waste landfills, most not built in compliance with RCRA.
3,000 + hazardous waste sites, 1,200 on superfund list.
Sources of groundwater contamination
Hazardous waste sites
Landfills
LUST
Industrial facilities
Non-point source
Hazardous waste sites
Organic chemicals including cancer causing and highly toxic compounds seep
into groundwater from thousands of sites.
The number of uncontrolled hazardous waste sites is declining.
Old dumps/landfills a legacy of pollution.
Most of the 20,000 plus dumps existing in 1976 are now closed but their legacy
will continue for decades in form of groundwater pollution and wasted land.
Example: Henderson landfill
Can old dumps be reused: Yes for parks, golf courses and buildings.
Example: Cave Creek County Club.
LUST:
LUST stands for Leaking Underground Storage Tanks (also LUFT) with over 4
million tanks mostly holding fuel oil or gasoline many tanks or associated piping
have leaked(estimated at 1/3). Usually LUST is first a groundwater
contamination problem but due to discharge of aquifers this can get in surface
water.
Industrial facilities
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Many industrial facilities have contaminated groundwater.
Most contamination due to losses from pipes and tanks of chemicals, solvents and
hydrocarbons.
Oil refineries have the worst record.
Non-point source
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Agricultural use of pesticides can contaminate groundwater particularly in
shallow sand aquifers like Long Island.
Also nitrites derived from animal wastes is a major problem for rural wells near
feedlots.
Behavior of groundwater contaminants
Movement and dispersion
Behavior of “conservative” contaminants
Behavior of LNAPL’s
Behavior of DNAPLS
Other types of contaminants
Movement and dispersion
Contaminants move downward under force of gravity and spread down gradient
with groundwater flow.
As contaminants are transported they are spread-out dispersed and absorb on
soil materials to a greater or lesser extent.
Some contaminants can also volatilize.
Behavior of “conservative” contaminants
These contaminants such as chloride, nitrite or tritium (a radioactive substance)
move at the same rate and in the same direction as the groundwater,
Behavior of LNAPL’s
Light non-aqueous phase liquids like gasoline, benzene, jet fuel will float on the
water table.
The shape of the plume is a pancake.
A dissolved phase moves into the groundwater gradually.
Most of the gasoline is likely to be absorbed to the soil as a residual saturated
phase.
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Behavior of DNAPL’s
Dense non-aqueous phase liquids such as TCE and other chlorinated solvents will
sink rapidly.
They pass through the water table and settle on aquitards.
A portion of the plume dissolves into the water gradually.
Other types of contaminants
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Nitrites
Pesticides
Landfill leachate
Heavy metals
Radio-nuclides
Lec 25. Groundwater Contamination:
Monitoring and Remediation.
Well-head protection:
• This refers to a program of controlling landuse and remediation and survey of
contamination to safeguard wells. Frequently it is combined with an aquifer
vulnerability analysis.
• GIS is a useful technology
• Controlling landuse is difficult since serving as a recharge area does not generate
profits for the local landowner.
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How is groundwater protected:
Most groundwater protection is indirect (clean water act (CWA), & RCRA) but
Underground Injection Control Program (UIC) program provides direct
protection.
Shallow injection wells illegal.
Dumping liquid hazardous wastes in landfills is illegal.
LUST is controlled.
Monitoring Wells.
Designed to provide info on status of aquifers, not to supply water.
May or may not be capable of being pumped.
May be designed for monitoring of contamination or yield of aquifers or
sometimes for other purposes.
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Monitoring Well Location:
Locate to detect contamination.
Typically at least one up-gradient and three down- gradient. More for non-point
source.
Provide access for monitoring personnel
Try to monitor the potential source of contamination not con founding sources.
Access to other properties can be a problem.
Example: Henderson Landfill wells.
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Monitoring Well Design
Diameter usually narrow 1-4 inch
Depth should be down to aquiclude or lower for DNAPLs.
Screened above capillary fringe.
Can also monitor soil gas but soil moisture requires use of a suction lysimeter.
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Sampling a monitoring well:
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Usually have no pump.
Samples collected by bailer.
Or sometimes a surface peristaltic pump system
A “popper” or tape is used to determine depth to water (water level).
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Monitoring Well Installation.
Usually augured but can be driven for a temporary sampling event (Geoprobe).
Drill cuttings are a solid Hazardous waste
Pump and development water is a liquid haz waste.
Slug tests are common to avoid generating waste.
Cap must be locked and identify well.
Grouting is very important.
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Monitoring Well Development:
Monitoring wells are generally not developed.
If they become plugged compressed air is usual approach.
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Monitoring Well Operation.
A bailer is used to obtain a sample.
Since water in formation, not in well is desired three well volumes are pumped out
with an external pump or temporary submersible pump.
Water samples should be sealed as soon as possible.
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Pumped Monitoring Wells:
Flow through testing of EC, DO, pH Temp is possible.
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Other Monitoring methods:
TLC meter is easy and standard.
Down-hole video.
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Water Level Monitoring.
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Tape
Popper
Pressure transducer.
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Monitoring Well Maintenance.
Monitoring wells are only used occasionally (usually every 3 months) but they can
get slime like other wells so may need chlorination.
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Monitoring Well Abandonment
Since monitoring wells are in locations that may be contaminated abandonment is
even more important than for other types of wells.
Groundwater remediation
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Assessment
Modeling
Design and installation
Operation
Monitoring
Closure.
Assessment
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Assessment is an initial step includes using aerial photography, land-use history
and other documents to assess type and magnitude of contamination.
Existing wells and springs may be sampled.
Shallow soil cores and soil gas samples may be taken.
Monitoring
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Involves installation of dedicated monitoring wells.
Logging cores and analysis of deeper cores
Periodic sampling of wells following pumping to assess aquifer conditions
May also involve slug or pump tests
Modeling
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Requires data from soils, recharge, depth, aquifer transmissivity and any
boundary conditions to be known.
Type of contaminant, magnitude of release, source and duration of release.
Model used is finite difference or finite element of stochastic.
3D visualization is now more common.
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Design and installation
Once extent and transport of contaminant and character of aquifer is know a
remedial design can be made.
Requires installation of treatment system and frequently wells dedicated to
pumping contaminated groundwater to treatment system
System must be monitored and modeled.
Operation
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System may need to be operated for years or decades with periodic monitoring
and revision to simulation models to reflect observed changes in contaminant
plume.
Some sites can be definitively cleaned some may need to have long term
monitoring following active clean-up.
Closure.
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If monitoring reveals that plume has been abated then site may be “closed” with
no further action required.
Many sites that remain “open” still can be used for other activities but access to
treatment systems or monitoring wells must be maintained.
Remediation methods
Monitoring/natural attenuation
Pump and dispose
Pump and treat by air stripping
Pump and treat by aqueous carbon filtration
Air sparging/bio-venting
In-situ enhanced bio-remediation
Use a 57 chevy…
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Monitoring/natural attenuation
Least costly alternative merely monitor and model plume and show that due to
dispersion, absorption and bioremediation the concentration of contaminants will
be diminished below action levels prior to reaching wells, springs, etc.
Mostly limited to LUST sites in some “industry friendly” states.
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Pump and dispose
Install sufficient pumping wells to intercept plume and remove plume at source.
Pump contaminated groundwater to surface and store and test.
Either haul away with tanker truck
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Or dispose to sanitary sewer (requires NPDES) permit and permission.
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Pump and treat by air stripping
Send extracted water to tower where volatile components are separated.
Volatile components may then be burned or absorbed on activated carbon.
Limited to solvents like TCE
Requires permits for possible air emissions.
Pump and treat by aqueous carbon filtration
• Pump contaminated water to a series of 3 or more drums that contain activated
carbon.
• Drums are placed in series, flow of contaminants from 1st drum n series is tested
for when contaminants seep from 1str drum it is replaced by 2nd and a clean
drum added at end.
• Works well for small volumes of highly contaminated water
• Limited to gasoline, spent carbon is shipped to be recycled.
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Air sparging/bio-venting
Air is bubbled down into well or pumped into contaminated soil.
This flushes volatile contaminant up through and out of the aquifer.
Works for TCE near surface and for residual gasoline contamination of soil
Creates air pollution possible explosion hazard,
Works badly in clay soil, well in sand,
In-situ enhanced bio-remediation
Aerated water, nutrients such as P and N and sometimes selected microorganisms
are pumped into contaminated groundwater.
Slow process, works well for jet fuel and diesel.
Works badly for TCE, benzene.
Works well in sandy soil, poorly in clay soils.
Use a 57 chevy…
Pump contaminated groundwater to surface
Separate volatile fraction pipe to a running internal combustion engine. Vapors
supplement gasoline running engine, burn off and go through exhaust system of
car.
Works for recent shallow gasoline contamination.
At refineries slurped gasoline is just sent back to be re-refined.
Lec 26 Groundwater Flow & Darcy’s Law
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Heads:
Head refers to a height above some reference level.
Head differences are the driving force causing groundwater flow.
Water flows from higher to lower head.
Driving Force:
Since elevated things have more potential energy than lower ones, head relates to
the gravitational potential energy which is a driving force for flow.
In a water table aquifer, the head is the elevation of the water surface above sea
level.
Heads above the rest:
The difference between the top of the water table at one point and at another
point is a head difference in a water table aquifer.
In confined aquifers, pressure differences rather than the elevation differences
are what cause head differences.
Gradients:
The head difference divided by the distance between the measuring points (“rise
over run”) is a slope called a
Gradient.
All water tables have a slope, usually a small one.
Flow is Down Gradient:
Groundwater will flow from an area of higher head to an area of lower head (just
as surface water flows downhill).
The steeper the slope, the faster the flow.
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Hydraulic Conductivity:
Aquifers transmit water. The speed at which water flows in an aquifer is the
hydraulic conductivity.
Since hydraulic conductivity is a velocity, its units are distance divided by time.
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Units of HC:
The most common units for HC are CM/SEC. Also M/day, Ft/Day.
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Ranges for HC:
• Highly permeable formations may have HC as high as 10-2 cm/sec or several
hundred feet per day while typical numbers are on the order of 10 -5 cm/sec and
can be as low as 10 -10 cm/sec or less.
• The higher the HC, the faster water will flow through the formation and Caterus
Paribus the more water the formation can yield to a well in a given period of
pumping.
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Tortuosity…
A measure of how much torture devices hurt you…
This material is torture:
Groundwater does not flow in a straight line; it follows a twisting tortuous path
around particles.
The property of the porous media that causes this complex path is the tortuosity.
A clay aquitard has a higher tortuosity than a sand aquifer.
Get out of here…
Dispersion is the process where by flow through porous media is spread out.
Dispersion is important, since it is what causes contaminants to spread out into a
plume as they are carried along with water through an aquifer.
The larger the tortuosity the greater the dispersion.
Groundwater Flow-Nets:
In an entire aquifer, the complex pattern of flow gets equalized and flow can be
assumed to follow straight paths, perpendicular to the contours of the
groundwater table elevation.
Stream-lines:
The reason these flow lines are perpendicular to the groundwater elevation
contours is that the elevation is a measure of the force (gravity) that is driving the
flow.
So if one can draw a groundwater contour map, one can determine the direction
of groundwater flow.
Groundwater Flow & Topography.
Often information to draw groundwater contours is absent.
A single well allows a point to be drawn, two a line, three a plane, so at least four
wells are needed for contours.
However, groundwater is recharged from infiltrating soil moisture and from
streams and lakes.
Implications:
So areas with higher elevations have higher groundwater tables. Also, streams
and ponds are usually in contact with the water table, at least during base flow
conditions.
So if depth to groundwater is known, topography can be used to estimate (map)
groundwater contours.
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Groundwater Velocity (Darcy’s Law)
The rate at which groundwater will flow through an aquifer is the hydraulic
conductivity it is estimated by use of the single most important equation in
groundwater hydrology
Fortunately Darcy’s law is a simple one.
Darcy’s Development:
Darcy’s law was developed in the 1850's by a French engineer experimenting
with flow of water through sand filled pipes (an early water purification
technique).
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Factors effecting Darcian velocity.
Three factors determined the rate (velocity) of flow.
1) The slope of the pipe,
2) The diameter of the pipe,
3) The permeability of the sand.
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More about these factors:
In an aquifer the slope is the hydraulic gradient (slope of the water table). ).
In an aquifer the cross-sectional area is the equivalent of the diameter in a pipe.
In an aquifer the hydraulic conductivity is the measure of permeability.
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So…
In an aquifer flow is equal to the hydraulic conductivity times the hydraulic
gradient times the cross-sectional area.
Some (ugh) Math:
Mathematically, Darcy’s law is:
Q = KIA
Where Q = rate of flow
K = Hydraulic Conductivity
I = Slope
A = Cross sectional area.
Units for Darcy’s law:
If Q = cubic meters per second, then K must be in meters per second, A in square
meters (I is a unitless quantity: a 1% slope would be .01).
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Transmissivity:
Hydraulic conductivity is a measure of how much flow in a small part of an
aquifer.
However, aquifers are not of uniform, they have variable HC, gradients and cross
sectional area.
A more useful measure for a real aquifer is Transmissivity.
Definition of Transmissivity:
This is the quantity of water that a given aquifer can transmit. It is the average
hydraulic conductivity times the average thickness of the aquifer.
Estimating transmissivity:
The transmissivity of a given length of an aquifer can be measured by dividing
the flow from that portion of the aquifer by the width of the aquifer times the
slope (gradient of the aquifer)
Even more math (double ugh)
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Mathematically this is:
T = Q/W*I
Where T is Transmissivity, W is the width of the aquifer, Q is flow and I is the
hydraulic gradient.
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Groundwater Flow Systems:
Groundwater systems consist of a number of components. Groundwater aquifers
exist in appropriate geologic settings but rarely have sharp boundaries.
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Recharge my batteries:
There are recharge areas that are generally where porous rock, sand or soils
outcrop or areas where streams and ponds and wetlands are present.
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Out of there:
There are discharge areas where springs appear, where streams are fed by
exfluent flow and also the ocean.
The other main discharge area is the well or well field.
Go with the flow:
Groundwater flows from recharge to discharge areas at a rate determined by
Darcy’s law and in quantities determined by the transmissivity of the aquifer.
Importance:
Estimating these flow parameters is essential to understanding the quantity of
water that an aquifer can produce and the direction and speed of the flow of
groundwater and contaminants.
Storage Coefficient:
• The storage coefficient is a measure of how much water can be gotten out of an
aquifer.
• Specifically, it is the drop in head per unit surface area for a given quantity of
water that has been pumped out.
• The more transmissive the aquifer, the less the head will fall for a given flow of
water being pumped out.
Cone of Depression:
What sitting through more boring lectures on groundwater will drive you into…
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Cone of Depression:
A funnel shaped lowering of the water table produced by pumping a well faster
than water can replenish the well.
This is not undesirable, rather it is the increasing slope of the water table that
draws water into the well to continue to feed the pump.
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Steep & Deep:
In a highly transmissive aquifer, the steepness cone of depression will be gentle.
In an impermeable aquifer the cone of depression will be very steep.
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Contours:
Groundwater contours around a well will form concentric circles. In a uniform
aquifer the circles would be perfect, but usually they are eccentric.
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Super-position.
Two (or more wells) in close proximity will
Have cones of depression that overlap.
The result is an additive potentiation (increase) in the total draw-down over the
area.
Thus many wells in a limited area cause over-draft.
Lec 27 Groundwater Resources Management I.
Management of well fields:
• Multiple wells are put in, because production from a single well can be limited
and because distribution facilities are costly and recharge sources, aquifers, etc
may have multiple locations that can have great local differences.
• The challenge is to operate the wells so as to produce the most water with the
least cost.
• Large draw-down = higher costs. Why?
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Whose on top?
Determine super-position of cones of depression to determine interference of
multiple wells with each other.
Sometimes this comes up in law suits from adjacent property owners.
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Well monitoring:
Wells should be checked periodically to determine:
Depth to groundwater,
Water quality,
Production rate,
Time/draw-down.
Down-hole video is now common.
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Groundwater Laws Requiring Monitoring:
Safe Drinking Water Act SDWA requires yearly tests for most municipal wells.
Wells specifically for monitoring the quality or quantity of groundwater are
called monitoring wells.
Resource Conservation and Recovery Act (RCRA) requires monitoring wells at all
haz-waste and solid waste disposal facilities
How groundwater is monitored:
At least 4, sometimes several hundred wells are installed.
Monitoring is usually quarterly.
Monitoring for depth to water is done with tape, electric line, popper or TLC
meter.
Samples are obtained with a bailer or pump.
Well-head protection:
• This refers to a program of controlling landuse and remediation and survey of
contamination to safeguard wells. Frequently it is combined with an aquifer
vulnerability analysis.
• GIS is a useful technology
• Controlling landuse is difficult since serving as a recharge area does not generate
profits for the local landowner.
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How is groundwater protected:
Most groundwater protection is indirect (clean water act (CWA), & RCRA) but
Underground Injection Control Program (UIC) program provides direct
protection.
Shallow injection wells illegal.
Dumping liquid hazardous wastes in landfills is illegal.
LUST is controlled.
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Case Studies: Edwards Aquifer
CHARACTERISTICS:
Karst topology, recharge in Edwards Plateau
Main source of Guadalupe River (endangered species) & San Marcos springs.
Crucial for San Antonio
Vulnerable to overdraft.
Home of Satan’s catfish and other weird, wonderful and white creatures.
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Edwards Aquifer Management:
Edwards Aquifer Conservation District.
Saline Water line monitoring network.
Control of pollution in recharge area (DRASTIC) analysis.
An underground River?
Edwards Aquifer Research Institute.
The most hated Farmer in Texas??
Sierra Club to the rescue??
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Ogallala aquifer: Characteristics
High plains of Texas, Nebraska, Eastern Colorado, Oklahoma and Kansas.
Sole supply for many areas that are highly productive for agriculture.
Ancient deposition.
Variable thickness
Slow rate of replenishment.
Fossil water.
Some contamination, pesticides and PANTEX
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Ogallala Management:
• Protected in Nebraska Kansas and Colorado but not very well in Texas where it
is most threatened
• Overdraft is concern, especially in Texas.
Robertson County a water colony?
• Long term, likely depopulation of area with loss of agriculture.
• Alternatives: conjunctive use, injection, trans-basin water projects, etc.
Santa Barbara County:
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Story of 6 aquifers:
Santa Barbara
Goleta
Santa Maria
Lompoc
San Antonio Creek
Cayuma Valley.
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Santa Barbara:
Small aquifer provides 30% of water for city of 100,000.
Supplemented by rain fed reservoirs in the mountains.
Contaminated by TCE
Overdrafted, but protected by fault from salt water intrusion.
During drought strange things happened:
Well permits (bring your lawyer)
Goleta.
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40% of water for 100,000 people.
Separated from Santa Barbara by a low range of hills.
Not protected from Salt Water Intrusion.
Building moratorium 1972-1992.
Worst municipal water in California.
The $2 million well.
No well permits, most existing wells for agriculture so “farmers” live in million $
mansions.
Santa Maria
Sandy alluvial plateau, easy recharge easy contamination.
Twitchell Dam and conjunctive use of surface water
Contamination from oil and gas and hazardous waste dump.
Agricultural conversion, growth center of county.
Lompoc:
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Flower seed capital of U.S.
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Salinization of groundwater
Abundance of municipal water from agricultural conversion
Groundwater unfit for sewage treatment plant.
San Antonio Creek Aquifer:
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Contaminated by VAFB.
Endangered species in Barka Slough.
Indian village sites
Air Force vs. State and County Gov.
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Cayuma Valley.
The wells are the biggest things around.
Thick water table aquifer.
400 feet of draw-down.
No subsidence.
Groundwater “mining”: 50,000 years of accumulation gone in 50 years.
Bunny Love carrots gone, now emus and ostriches…no development since 1952.
County Water agency controls permits.
Lec. 28: Groundwater Resources Management & Mismanagement.
Overdraft Examples:
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Examples:
San Jose area, CA.
FT. Stockton, TX.
More impacts of over-draft:
2) Water that formally flowed in streams and surface water features may be
drawn into the aquifer and the well.
Thus over-drafting a well can dry up not only the aquifer but streams flowing
over the area underlain by the aquifer.
Salt water intrusion
Subsidence
• Subsidence is due to dewatering aquifers that contain collapsible clays.
• When the water pressure in the aquifer is reduced the pressure holding the clay
layers apart is also reduced and the clays are compressed by the weight of
overlying sediments.
• Subsidence of as much as 60 feet is possible.
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Examples of subsidence:
Eastern San Joaquin Valley, CA.
Arizona.
Brownwood and other areas along ship channel in Houston area, Jersey Village
& north-west Harris County
Venice, Italy
Mexico City.
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Las Vegas Groundwater management
Use of both surface and groundwater
Conservation program
Groundwater injection program
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Well fields:
To exploit groundwater, frequently more than one well will be placed into an
aquifer.
Contamination at Nellis AFB Nevada
900,000 gallons of jet fuel floating on water table, off-site migration of
contamination, on-base wells contaminated.
Order from State “monitor, replace contaminated wells, let natural attenuation
work…”
What is the difference between these two sites…
Henderson Landfill, Nevada
Landfill opened in 1957, closed in 1976.
Received mix of wastes including wastes from Basic Industries chemical complex.
Located in stream-channel, homes built on top of waste piles.
Seepage of toxins into stream, monitoring wells contaminated with PAH, cyanide,
arsenic, DDT, BTEX, radio-nuclides etc