Centralized Impoundments for Storage of Wastewaters

1
Centralized Impoundments for Storage of
Wastewaters

• Design and Construction

2
Centralized Impoundments for Storage of
Wastewaters

• Service multiple well sites
• Regulated part of the well site
• Generally large capacity (10-15 million gallons)

3
Standards For Wastewater Impoundments

• Structural Standards
• Liner Systems
• Quality Assurance/Quality Control
• Leak Detection
• Action Leakage Rates
• Groundwater Monitoring

4
Distance Restrictions

• In the 100-year floodplain of waters of this
  Commonwealth.
• 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

5
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 3H1V are
  required
• Permanent vegetative ground covering must be
  established upon completion of dam construction.
• 2 of lined freeboard must be maintained at all
  times.

6
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.

7
Gradation Sheet
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
8
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.

9
Compaction

• 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.

10
Soil Placement and Compaction
11
Pad Rollers
12
Embankment Top Width Minimum 12
13
Take a closer look..
14
Failure to properly compact movement of the
embankment material
15
Failure to maintain 2 feet of lined freeboard
16
Centralized Impoundment Liner Components

• Sub-base
• Geo-textile Ventilation Layer
• Secondary Liner
• Leak Detection System
• Primary Liner

17
Failed liners (two separate locations)
18
Failed liner
19
Sub-base 6 Compacted Clay Particle Size lt0.75
1
3
Minimum Slope 3H1V
2 Slope
Leak Detection Trench
20
Sub-base Requirements

• Must cover bottom and sides
• Minimum thickness of 6
• Compacted to 90 standard proctor
• Coefficient of permeability lt 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
  material.
• Free of coarse rock fragments greater than 0.75
  in diameter.

21
Like This
Not Like This
22
Do not utilize organic matter in a subbase
23
The Decomposition of organic matter produces gas
and results in the potential for the liner to
burst or rupture!
24
Geotextile Fabric
2 Slope
Leak Detection Pipe Perforated, 4
Diameter Schedule 80 Minimum 2 Slope Minimum
Clean Stone
25
Geotextile

• The sub-base shall be covered with non-woven
  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.

26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
Secondary Liner Geo-Synthetic Membrane Thickness
40 mil
Anchor Trench
30
(No Transcript)
31
Secondary Liner Requirements

• Must cover bottom and sides
• Minimum thickness of 40 mil synthetic
  geo-membrane
• Coefficient of permeability lt 1 x 10-7 cm/s
• Liner compatibility shall satisfy EPA Method
  9090, Compatibility Test for Wastes and Membrane
  Liners
• Installed in accordance with QA/QC plan

32
Leak Detection kgt1 x 10-2
33
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.

34
Leak Detection Piping System Requirements

• 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.

35
Primary Liner Geo-Synthetic Membrane Thickness
40 mil
36
Primary Liner Requirements

• Must cover bottom and sides
• Minimum thickness of 40 mil synthetic
  geo-membrane
• Coefficient of permeability lt 1 x 10-7 cm/s
• Liner compatibility shall satisfy EPA Method
  9090, Compatibility Test for Wastes and Membrane
  Liners
• Installed in accordance with QA/QC plan

37
Action Leakage Rates
Fluid Height (ft) ALR (gallons/acre/day)
h 10 340
10 lt h 15 420
15 lt h 20 490
20 lt h 25 550
25 lt h 30 610
h gt 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 repaired
38
Groundwater Monitoring

• Minimum of 1 monitoring well located up-gradient
  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
• Chloride
• Sulfates
• pH
• Specific conductance

39
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 groundwater.

40
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 strength

41
Typical Monitoring Well
screen
42
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.

43
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.

44
Contact Information

• Joseph Adams, P.E.  Environmental Engineer
• Bureau of Oil and Gas Management
• Department of Environmental ProtectionRachel
  Carson State Office Building400 Market Street
   Harrisburg, PA 17101Phone [phone] 
  josepadams_at_state.pa.us