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FAQs:
Geology
1) Why won't
my pumping and/or injection wells maintain their design flow
rate?
Many times
extraction or injection wells at pump and treat sites experience
a relatively quick deterioration within the first year of
operation. The major cause of this is usually biofouling and
this is often compounded by either poor drilling or development
techniques. Many of the sites lack an Operation & Maintenance
(O & M) plan for the wells and try to rely on the plant operator
who has a poor understanding of wells and their problems.
Biofouling or the fact that the effluent from the plant is
geochemically incompatible with the water in the aquifer may
cause the injection well problems. The CX is currently
developing guidance for O & M of extraction and injection wells
at EM CX sites.
2) What can I
do to restore my pumping or injection wells to their design flow
rate?
When wells are
clogged, site data needs to be assessed to determine if it is a
biological or chemical problem. This can include performing
reactivity tests and video camera surveys of the wells. If
biofouling is the problem, there are only a few methods that
have been shown to be effective for rehabilitating these wells.
There are also several commonly used methods that have limited
effectiveness when applied to EM CX wells. The CX is currently
developing guidance for Operation & Maintenance of extraction
and injection wells at EM CX sites.
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Geotechnical Engineering
1) What are
the benefits of HDPE liner materials for landfill covers/liners?
HDPE geomembranes
are well suited for both landfill liner and cover systems. The
primary benefits are excellent chemical resistance and long term
performance characteristics, and established installation
techniques. Although other materials (e.g. LLDPE, PVC) have
been used routinely for landfill cover systems, HDPE has been
the primary choice for landfill liner systems.
2) What are
some design considerations for a landfill cover system drainage
layer?
One of the
primary causes of landfill cover system failure is an inadequate
drainage layer resulting in seepage induced instability. When
designing a drainage layer, factors such as slope angle, slope
length, interface friction angles, climate, cover soil types,
drainage layer material, and outlet drain requirements must all
be considered together. It is recommended that Geosynthetics
Research Institute Report # 19, "The Design of Drainage Systems
Over Geosynthetically Lined Slopes" be used for all designs of
granular or geosynthetic drainage systems placed over
geosynthetically lined slopes.
3) What are my
options to control/collect landfill gas?
The methods used
to control landfill gas migration are either a passive gas
venting system or an active system. A passive system allows
landfill gas to be vented through vertical wells, trench
systems, or granular layers to the atmosphere. An active system
mechanically withdraws landfill gas by means of blower systems.
Usually the collected gas is flared. The decision to use either
a passive or an active system depends on the type of waste
materials, age of the waste, size of the landfill, proximity of
off-site receptors, and final cover configuration.
4) How should
a site be monitored for off-site migration of landfill gas?
All gas venting
systems must be monitored at the site perimeter for off-site
migration, usually around 10% of the Lower Explosive Limit (LEL)
for methane. Monitoring is done with gas monitoring probes,
consisting of small diameter perforated pipes located around the
landfill at a minimum of 1000 feet on center.
5) What are
"Alternative Cover Systems"?
The term
"Alternative Cover Systems" refers to cover systems that rely on
natural processes to reduce or minimize infiltration into
underlying waste materials. These cover systems are usually
constructed primarily of soil materials with no or minimal
geosynthetic layers. By balancing precipitation, runoff,
evapotranspiration, and water holding capacity of soils,
infiltration can be minimized. Often, alternative covers are
quite feasible in semi-arid to arid environments. The primary
benefit of an alternative cover is lower costs than a
conventional geosynthetic cover system, with comparable
performance.
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Process
Engineering
1) What are safe practices for handling recovered
flammable liquids, especially JP-4 and JP-8?
Fire hazards are present whenever petroleum products are
leaked or spilled. Flammable vapors can accumulate in enclosed
spaces. Ignition can occur in pipelines, pumps and tanks from
an accumulation of static electricity or an external ignition
source. Air Force jet fuel Grade JP-4 requires added
precautions in handling because of its relatively low vapor
pressure range and poor electrical conductivity. It forms
explosive vapors in the space above the liquid in storage tanks
in the range of minus 10o F and to plus 80o F; these are temperatures usually encountered in storage and
handling of fuels.
In addition, JP-4 is more subject to buildup of static
electric charge than other gasoline products. When liquids flow
through closed metal pipes, static electricity is not a hazard.
It may become a hazard, however, when liquids are pumped into
tanks. Charges produced in the liquid during pumping can
accumulate on the surface of the liquid and cause sparking
between the liquid surface and the tank or a projection in the
tank. This static spark has enough energy to ignite a flammable
atmosphere of JP-4. Although the pipe and the tank should be
grounded, the grounding does not necessarily eliminate this
danger for poorly conductive flammable liquids such as JP-4.
Filters in pipelines greatly increase the generation of
static electricity. In one in aircraft fueling test it was
reported that the charge development was 10 to 200 times more
with a filter than without one.
Also, settling out of a conductive phase through a
non-conductive phase, such as water through fuel, greatly
increases the hazards of generation of static electricity.
Thus, handling an emulsion could be more hazardous than handling
a single-phase system. OSHA regulations (40 CFR 1910.106)
require fill pipes to terminate within 6 inches of the bottom of
a tank.
In addition, all sampling probes and containers should
preferably be non-conductive; a lost conductive object floating
in a tank could cause sparking when it approaches the tank wall.
JP-4 is very flammable and dangerous to work with. It is
difficult to always eliminate two of the three legs of the fire
triangle (Fuel, Air, and ignition source). The Air Force
eliminates ignition sources by adding a static dissipater
additive to the fuel, controlling the pumping rate to minimize
static generation, grounding and bonding, using non-sparking
materials of construction in the tank openings/tools, and using
well-trained people to handle fuel.
Although JP-8 is less volatile and safer to handle than JP-4,
the Air Force uses the same precautions in handling both fuels.
Trucks, piping, sampling equipment, and storage tanks are all
grounded and bonded.
JP-4 fuel is being phased out by the Air Force, however,
remediation of past spills will continue into the future. JP-4
floating on the top of the groundwater table will have to be
pumped to the surface, along with some entrained water, for
treatment and disposal.
Caution must be exercised when specifying air operated pumps
for handling flammable liquids. Some vendors may claim to have
intrinsically safe air-operated pumps on the market that are in
fact not appropriate for handling flammable liquids. Pumps that
use compressed air to directly contact and "push" the fluid from
the pump should not be used for transferring flammable liquids.
However, there are a number of pumps on the market that are
capable of transferring combustible liquids without using
compressed air as the means of transfer. Also, some companies
offer a bellows or bladder pump that isolates the compressed air
from the fluid pumped.
The following authorities have rulings concerning the use of
air pressure in the transfer of flammable liquids: 29 CFR 106
(d) (4) (iii) prohibits transfer of combustible liquids using
compressed air; ER 385-1-1 09.B.28b also prohibits transfer of
flammable or combustible liquids by means of air pressure; and
NFPA 30 Flammable and Combustible Liquid Code, 1990 Edition,
paragraph 5-4.1.1 prohibits transfer of a flammable liquid using
air.
2) What are good practices to use in remediating sites
containing spilled JP-4, JP-8 or other flammable/combustible
liquids?
- Insure that the system is designed
operated in accordance UFC 3-460-01, 16 Jan 04, Petroleum Fuel Facilities.
- Do not use conductive sampling or test
equipment inside an enclosed space or tank, which might draw
a spark and create an explosion.
- Ground and bond the tank, piping,
pumps, and sampling equipment. Refer to API Recommended
Practices 2003 "Protection Against Ignitions Arising Out of
Static, Lightning, and Stray Currents".
- Test the vapor space of the recovery
container or tank for flammability with an oxygen analyzer
and a combustible gas analyzer. Whenever 20% of the
explosive limit is detected, the receiving tank should be
purged with an inert gas such as nitrogen until the oxygen
level is reduced below the minimum oxygen for combustion (MOC).
Refer to NFPA 69. The MOC for petroleum fuels is 11.5%.
- Test the conductivity of the recovered
liquid. Conductivity Meter Model 1152, available from EMCEE
Electronics, Inc., may be used which measures electrical
conductivity of fluids in conductivity units (CU), of
picosiemens per meter (pS/m). Refer to ASTM D 2624, Standard
Test Methods for Electrical Conductivity of Aviation and
Distillate Fuels. Air Force MIL-T-5624 N specifies a range
of 150-600 pS/m for the safe handling of JP-4.
- Use an anti-static additive as
required to maintain the recovered fuel in the safe
conductivity range. There are at least two suppliers of
Static Dissipater Additive (SDA)/ conductivity additives.
One is Stadis ™ 450 supplied by Octel America, Inc., and the
other is ASA-3 supplied by the Shell Oil Company.
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