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Centralized Impoundments for Storage of Wastewaters

Centralized Impoundments for Storage of Wastewaters

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Centralized Impoundments for Storage of Wastewaters

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  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 3H:1V 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 compactmovement 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 <0.75” 1 3 Minimum Slope = 3H:1V 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 < 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. Secondary Liner Geo-Synthetic Membrane Thickness = 40 mil Anchor Trench

  27. Secondary Liner Requirements • Must cover bottom and sides • Minimum thickness of 40 mil synthetic geo-membrane • Coefficient of permeability < 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

  28. Leak Detection k>1 x 10-2

  29. 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.

  30. 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.

  31. Primary Liner Geo-Synthetic Membrane Thickness = 40 mil

  32. Primary Liner Requirements • Must cover bottom and sides • Minimum thickness of 40 mil synthetic geo-membrane • Coefficient of permeability < 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

  33. Action Leakage Rates 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

  34. 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

  35. 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.

  36. 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

  37. Typical Monitoring Well screen

  38. 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.

  39. 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.

  40. 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: 717.772.2199 | josepadams@state.pa.us