Centralized Impoundments

Centralized Impoundments for
Storage of Wastewaters
Design and Construction
Centralized Impoundments for
Storage of Wastewaters
multiple well sites
►Regulated part of the well site
►Generally large capacity (10-15 million
Standards For Wastewater
► Structural
► Liner Systems
 Quality Assurance/Quality Control
 Leak Detection
 Action Leakage Rates
► Groundwater
Distance Restrictions
In the 100-year floodplain of waters of this
In or within 100 feet of a wetland.
Within 200 feet from an occupied dwelling
Within 100 feet of a perennial stream.
Within 200 feet of a private water source.
Within 1,000 feet upgradient, and within 300
feet downgradient, of a public water source
Embankment Design Criteria
Maximum Particle Size = 6”
Bottom must be at least 20” above seasonal high
groundwater table
Must meet specific soil type and compaction standards
Minimum embankment top width of 12’ is required
Minimum inside & outside side slopes of 3H:1V are
Permanent vegetative ground covering must be
established upon completion of dam construction.
2’ of lined freeboard must be maintained at all times.
Embankment Construction
► Soils
to be used for dam embankment
construction must be classified in
accordance with ASTMD-2487. A minimum
of three samples must be classified.
► Soils acceptable for dam embankment
construction are limited to GC, GM, SC, SM,
CL or ML.
► Soils must contain a minimum of 20% of
Plus No. 200 sieve materials.
GC- Clayey gravels
GM- Silty gravels
SC- Clayey sands
SM- Silty sands
CL- Inorganic clays low to
medium plasticity
ML- Inorganic silts and fine
sand, slight plasticity
Site Preparation
Foundation of dam embankment must be stripped and
grubbed to a depth of two feet prior to any placement &
compaction of earthfill.
Any springs encountered in the foundation area should be
drained to the outside/downstream toe of the embankment
with a drain section two foot by two foot in dimension
consisting of PennDOT Type A sand, compacted by hand
tamper. No geotextiles to be used around sand. The last
three feet of this drain at the outside/downstream slope
should be AASHTO #8 material.
 20” Separation must be maintained.
All compaction for embankments must be done with a
sheepsfoot or pad roller.
Loose lift thickness must be 9” or less.
A minimum of 5 passes of the compaction equipment over
the entire surface of each lift is required.
Compaction to visible non-movement of the embankment
material is required.
Soil Placement and Compaction
Pad Rollers
Embankment Top Width
Minimum 12’
Take a closer look…..
Failure to properly compact
movement of the embankment material
Failure to maintain 2 feet of lined
Centralized Impoundment Liner
► Sub-base
► Geo-textile
Ventilation Layer
► Secondary Liner
► Leak Detection System
► Primary Liner
Failed liners
(two separate locations)
Failed liner
6” Compacted Clay
Particle Size <0.75”
Minimum Slope =
2% Slope
Leak Detection
Sub-base Requirements
Must cover bottom and sides
Minimum thickness of 6”
Compacted to 90% standard proctor
Coefficient of permeability < 1 x 10-6 cm/s
Compaction and permeability testing must be
conducted once per 2,500 ft2
Hard, uniform, smooth and free of debris, rock
fragments, plant materials and other foreign
► Free of coarse rock fragments greater than 0.75”
in diameter.
Like This
Not Like This
Do not utilize organic matter in a
The Decomposition of organic matter
produces gas and results in the potential for
the liner to burst or rupture!
Geotextile Fabric
2% Slope
Leak Detection Pipe
Perforated, 4” Diameter
Schedule 80 Minimum
2% Slope Minimum
Clean Stone
The sub-base shall be covered with nonwoven geotextile fabric to cushion the
secondary liner and allow for adequate
venting between the secondary liner and
sub-base to prevent entrapment of gases
beneath the liner system.
Secondary Liner
Geo-Synthetic Membrane
Thickness = 40 mil
Anchor Trench
Secondary Liner Requirements
Must cover bottom and sides
Minimum thickness of 40 mil synthetic
Coefficient of permeability < 1 x 10 cm/s
Liner compatibility shall satisfy EPA
Method 9090, Compatibility Test for
Wastes and Membrane Liners
Installed in accordance with QA/QC plan
Leak Detection
k>1 x 10-2
Leak Detection System Requirements
Coefficient of permeability of 1.0 x 10-2 cm/sec or greater
Uses a perforated piping system capable of detecting and
intercepting liquid within the leak detection zone and conveying the
liquid to a collection sump.
The collection sump shall be equipped with a sump pump with an
automatic switch.
Discharge from the sump pump shall be directed back into the
impoundment or other suitable containment.
The pump and sump shall be of sufficient size and capacity to
convey any leak that may occur without a discharge.
The leak detection zone and sump shall be designed to allow the
operator to monitor and record leakage rates.
The leak detection zone shall have a minimum bottom slope of 2%.
Contain non-carbonate stones or aggregate with no sharp edges.
The operator shall monitor the leak detection zone weekly to
determine whether liquid is flowing from the zone.
Leak Detection Piping System
The slope, size and spacing of the piping system
shall assure that liquids drain from the leak
detection zone.
► The pipes shall be installed primarily
perpendicular to the flow and shall have a
minimum post-settlement grade of at least 2%.
► The minimum diameter of the perforated pipe
shall be 4 inches with a wall thickness of
Schedule-80 or greater.
Primary Liner
Geo-Synthetic Membrane
Thickness = 40 mil
Primary Liner Requirements
Must cover bottom and sides
Minimum thickness of 40 mil synthetic
Coefficient of permeability < 1 x 10 cm/s
Liner compatibility shall satisfy EPA Method
9090, Compatibility Test for Wastes and
Membrane Liners
Installed in accordance with QA/QC plan
Action Leakage Rates
Fluid Height (ft)
h ≤ 10
10 < h ≤ 15
15 < h ≤ 20
20 < h ≤ 25
25 < h ≤ 30
h > 30
case by case
Allowable leakage rates shall be determined based upon the maximum depth of the
impounded fluid as specified in the table below. The area shall be calculated as the area
of the liner in contact with the impounded fluid.
In the event that the flow rate of leakage through the primary liner, as collected in the
leak detection sump, exceeds the value above for a given fluid depth, the impoundment
shall be drained to the extent necessary and the leak or leaks shall be located and
Groundwater Monitoring
Minimum of 1 monitoring well located upgradient and 3 down-gradient
Must be within 200 feet of the impoundment
and at least 100 feet closer than the nearest
drinking water well
Quarterly monitoring for (as a minimum):
Total dissolved solids
Specific conductance
Monitoring Well Construction
The minimum casing diameter shall be 4 inches unless
otherwise approved by the Department in writing.
The well shall be equipped with a factory-made screen
designed to maximize open area and minimize entrance
velocities and allow rapid sample recovery.
The well shall be filter-packed with chemically inert clean
quartz sand, silica or glass beads. The material shall be
well rounded and dimensionally stable.
The casing shall be clearly visible and protrude at least 1
foot above the ground.
The annular space above the sampling depth shall be
sealed to prevent contamination of samples and the
Monitoring Well Casings
Must Be of sufficient strength to protect the well from
damage by heavy equipment and vandalism.
Must Be installed for at least the upper 10 feet of the
monitoring well, as measured from the well cap, with a
maximum stick up of 3 feet.
Be grouted and placed with a concrete collar at least 3
feet deep to hold it firmly in position.
Be numbered for identification with a label capable of
withstanding field conditions and painted in a highly
visible color.
Have a locked cap.
Be made of steel or another material of equivalent
Monitoring Well
Engineer Certification
Design plans for centralized
impoundments must be developed and
sealed by a registered professional
engineer in Pennsylvania.
The design engineer shall provide
oversight for all aspects of construction to
ensure that construction is completed in
accordance with the design and quality
assurance and quality control plan.
Engineer Certification
Upon completion, a facility completion and final certification report must be
submitted to the Department. The report must be completed and sealed by the
licensed professional engineer who provided oversight for construction and
contain the following items:
 A statement that the engineer provided oversight for all aspects of
construction and that the impoundment was constructed as designed and
in accordance with these requirements and the quality assurance and
quality control plan
 Soils classification testing results for the embankments
 Soil compaction testing results for the sub-base
 As-built drawings noting any deviation from the original plans submitted to
the Department
 Quarry tickets for drain material
 Quality assurance and quality control test results
 Color photographs
► The impoundment shall not be filled until the facility completion and final
certification report is received and approved by the Department.
Contact Information
Joseph Adams, P.E. | Environmental Engineer
Bureau of Oil and Gas Management
Department of Environmental Protection
Rachel Carson State Office Building
400 Market Street | Harrisburg, PA 17101
Phone: 717.772.2199 | josepadams@state.pa.us