field investigations ASBOG

API

unit of measurement of gamma rays
American Petroleum Institute

ASTM

american society for testing and materials
develops standards

borehole geophysics

recording and analyzing measurements of physical properties in wells or test holes

caliper log

well log that shows borehole diameter variations with depth
run before installing casing
use for grouting volume calcs and determine size imapcts on other logs

cone of depression

depression in potentiometric surface of gw. inverted cone chape
develops around a well that is withdrawing water. defines area of influence of a well

cone penetrometer

tool pushed into ground to record resistance to insertion
cone tip on steel rod

CPT

cone penetration test
measures resistance of cone to penetration and the friction on the rod
can have extra porewater pressure measurements (piezocone)
limted to

drawdown

amount the water level in a well is lowered due to withdrawal of water
rapid at first then slows down
helps calculate transmissivity, storativity, hydraulic cond.

dutch cone

specific type of cone penetrometer

gamma ray log

radioactivity log curve of intensity of natural gamma radiation emitted from rocks in a borehole
determines shale content of fms, bc radioactive elements concentrate in clays/shales
shale = high gamma
other sed rocks = lower gamma

gravity survey

measure variations in density of soil/rock
use gravimeter to evaluate gravitational pull
locate voids, caves, coal beds, mineral deposits, groundwater

ground penetrating radar

apply radar or radio waves to subsurface using radar impulse as source and receiver
signals reflected by subsurface conditions
as deep as 100ft
use low frequency for deeper depths, high frequency (better resolution) near the surface

InSAR

interferometric synthetic aperture radar
remote sensing method used to study ground deformation
subsidence, volcanic, fault studies, ice sheet movement
quick, big surveys at good resolution. errors from atm conditions.

invaded zone

transitional zone in borehold between flushed zone and uninvaded zone
transition from mud filtrate solution to in situ formation water saturation

LiDAR

light detection and ranging
remote sensing method using laser beams to record topographic changes
penetrates tree canopy (not water)
used for fault studies

lysimeter

device that collects water from pore spaces of soil to determine soluble constituents
samples water chem in vadose zone, measures deep percolation and ET

normal-resistivity log

log that makes measurements of resistivity of formations.
uses 4 electrodes in 16 (short normal) or 64 inch (long normal) spacing
used to determine water quality and find salt/fresh interface

neutron log

radioactivity log curve of intensity of radiation produced when rocks are bombarded by neutrons
indicates presence (hydrogen) but not type of fluid

packer test

aquifer test where 2 inflatable seals are set in open borehole to prevent movement of gw while determining permeability

percolation (perc) test

in-situ test that determines suitability of soil for a leachfield
dig hole, fill with water, measure time for water to infiltrate

piezometer

measures in situ pore water pressures.
often open standpipe to monitor water levels in permeable materials or enclosed pressure transducer in impermeable soils

pumping test

pump a well for a period of time and observe the change in hydraulic head in the aquifer

resistivity log

quantitative measurements of specific resistance R of a material to an electric current
high porosity or high salt = low R
ID water quality or fresh/salt water interface or hydrocarbon saturation

rippability

how easily a soil or rock can be excavated mechanically
based on seismic velocity, strength, weathering, spacing of discontinuities
most solid rocks rippable if seismic velocity = 3 to 8ish ft/secx1000

seismic reflection

survey method using travel times of seismic waves that are reflected back from deep formations
gives detailed picture of subsurface structures

seismic refraction

survey method using travel times of seismic waves that pass through materials of different densities
used to map layers

single-point resistivity log

log that measures resistivity using 2 electrodes
limited investigation area of 5-10x electrode diameter
used for making lithologic interpretations

slug test

aquifer test by pouring water into a well or removing water (bail-down) from the well
test hydraulic cond. and transmissivity

spontaneous potential SP log

log of difference in DC voltage between electrode in the well and electrode at the surface
result of electrochemical potentials that develop between different borehole and formation fluids
used to determine lithology, bed thickness, salinity

tensiometer

device to measure soil matric potential (soil water suction - drawing water into pore spaces)
used to determine irrigation needs and plants' water consumption

well efficiency W.E.

ratio in % of theoretical drawdown to actual measured well drawdown
max ~80%
realistic ~60%

stereo-paired low altitude photos

used in eng. geo to get clear view of faults and landslides
1:40,000 or larger
env. investigations use them to determine site's past uses and possible contaminant sources
take early/late on clear day to get helpful shadows. low cost

high altitude color infrared

show IR wavelengths reflected from ground surface. image in shades of red w/ higher contrast
used for vegetation health (healthy = red, stressed = pink/blue)
1:58,000 to 1:120,000

SLAR side looking airborne radar

beam microwave pulses at terrain obliquely to create light and dark images corresponding to reflectivity of earth's surface
can do in day or night. often USED IN CLOUD COVER AREAS

shuttle radar topography mision SRTM

data generate high resolution DEMs of earth's surface. show changes due to flooding, erosion, landslides, eqs, climate change.
military uses them for mission planning, modeling, simulation

high altitude landsat

visible, reflected IR, and thermal IR wavelengths
map soils, geology, effects of precip and evap on gw
open source imagery

SPOT

french satellite for visual/multispectral imaging. diff processing steps used for diff things (stereoplotting, radiometric studies, cartographic projection (DEMS))
expensive but quick turnaround. resolution down to 2.5m

uses for aerial photos

hist. uses of sites
landslide features and fault mapping
drainage and erosional characteristics
small-scale structural features to find petroleum traps
mapping joints/lineations
mapping soil patterns
determining lithology/structure for finding ore deposits
map surficial deposits for borrow areas

scale of aerial photographs

scale (like 1/12,000) = f/H
f=focal height ft
H=flying height ft

density and sonic logs

determine porosity of rocks

seismic refraction uses

depth to bedrock+rock type
locate faults/fractures
rippability surveys
mineral/petroleum exploration
depth to water table
haz waste site investigations.

ground penetrating radar uses

locate subsurface features (UST, drums, utilities)
locate karst voids
map bedrock/stratigraphy/landfill boundaries
map re-bar to examine structural integrity
map GW table
profile lake and river bottoms

electrical resistivity survey uses

characterize hydrogeology (fresh water = high R, high TDS = low R)
map soil/gw contaminant plumes, bulk waste, buried utilities
estimate overburden/landfill thickness
map faults

magnetic survey uses

locate buried drums and tanks
ore bodies, igneous intrusions, abandoned mines
cheap, fast, easily interpreted

sand line and shale line (baseline)

sand line: line drawn through extreme negative (left) deflections on SP log = formation water is more saline than drilling mud
shale line: line drawn through extreme positive (right) deflections

interpreting SP and resistivity logs

lithologic contacts at inflection points
shales & clays have lowest SP (bulge right) and R
sandstone shows SP bulge to the left, moderate R
limestone has high deflection in R curve but not SP
fresh water positive SP (bulge right) high R
salt water negative SP (bulge left) low R

gamma ray log uses

can be used in cased wells
substitute for SP if saline mud or air-filled holes

neutron log uses

used with gamma ray log to distinguish INDIRECT POROSITY
petroleum/hydro investigations
or lithologic correlation. usually similar to R logs EXCEPT gypsum and coal have high left deflections which show higher porosity than really exists

Snell's Law

equation for refraction
v1/v2 = sin(a)/Sin(B)
alpha = angle of incidence
beta = angle of refraction

electrical resistivity surveys

measure bulk resistivity of subsurface
linear pattern of electrodes on ground surface then pass electrical current through them
further spacing = deeper penetration

annulus

space between pipe and borehole wall
ring-shape

blowout

uncontrolled flow of gas or fluids from a well

rotary drilling methods

holes deeper than 100ft or that enter bedrock
air, mud, reverse circulation (way more expensive)
can introduce fluids/foreign materials to gw/subsurface

cable tool drilling method

cable lifts and drop heavy drill hammer to break up subsurface materials which are then removed
slow and expensive, but no drilling fluids are used

sonic drilling method

vibrate rod and sampler to enable borehole advancement and continuous sampling
can drill at any angle, install well equipment, collect disturbed samples

other cone penetration tests

electrical conductivity cone (evaluate gw saturation and contaminants)
seismic (calculate soil shear wave velocities)
gamma (profile clay content or detect radioactive contamination)
hydraulic profiling (injects water to get profiles of permeability and soil strata)
ball penetration test (undrained shear stress of weak cohesive soils)

drilling fluid additives

bentonite (thickens fluid and reduces fluid losses)
polymer (thickens but cuttings drop out faster than bentonite)
CaCl or NaCl (adds weight or used in below freezing temps)
barite (adds density to fluids. prevents collapse or taking on fm water)

undisturbed piston samplers

less common than shelby tube bc lots of complicated parts
osterberg (hydraulic piston)
hvorslev (mechanical piston)
both for cohesionless sands and soft wet clays (below water table)

double tube samplers

pitcher barrel (anything except gravels)
denison (cohesive silts/sands/clays)

correcting SPT field blow counts by depth

Cn = 1/sqrt(effective overburden pressure)
Ncorrected = Cn*Nfield

rock joints

fractures along which there has been no relative movement of rock on either side

step-drawdown test

well is pumped at inc. higher pumping rates with measuring drawdown at each change used to get hydraulic conditions transmissivity, storage coefficient, optimum pumping rate and pump depth (well performance)

Theis equation

analytical solution for radial flow of gw in confined aquifer to a well
equations for transmissivity and storativity
assumes constant T, water is all from storage, negligible storage in well, homogeneous/isotropic materials

Theis curve

ideal curve (exponential decreasing) of drawdown vs time. has same shape as cone of depression
curves get less exponentially shaped for unconfined and leaky confined aquifers

Jacob-straight line method

draw straight line through drawdown vs time data points (ignore 1st few points)
use slope ds and intercept (t0 time where drawdown=0) to calculate aquifer parameters
can do a similar thing plotting drawdown vs distance (for multiple observation wells)

well efficiency from distance/drawdown graph

plot points and fit a straight line through them to the pumping well
intersection of the line with pumped well radius is theoretical drawdown

monitoring well standards

3 downgradient, 1 upgradient
small diameter
non-reactive sterile screens/casings
no drilling fluids
seal entire annular space

production water well standards

1 well
large diameter
usually steel casing
can be drilled with whatever best method
sanitary seal to 50 bgs
positive drainage away from wellhead

specific capacity

pumping rate gpm / drawdown ft

well screen material

depends on gw quality
corrosion from low pH, high TDS, high DO, high chloride
incrustation from high pH, high iron/Mn precip, low solubility CaCO3

iron bacteria

in gw with Fe/Mn, dissolved organics, bicarbonate, CO2
grows in pH < 3
bacteria make gelatinous slime that clogs pump+screen
remediate with chlorine, oxidizers, or acids

zone of contribution ZOC

area that receives recharge to the well

well-volume purging method

remove 3 well volumes of stagnant water above screened interval
not applicable to low yield wells, fractured rock, turbid wells

minimal drawdown low flow purging method

pump water from the screened interval until continuous gw indicator parameters are within acceptable variation
low flow is better for VOC sampling bc reduces agitation
need screen

water quality indicator stabilization

pH
specific electrical conductance SEC
redox potential ORP
dissolved oxygen DO
turbidity
(in order of stabilization)