DEPARTMENT OF ENVIRONMENTAL PROTECTION
BUREAU OF MINING AND RECLAMATION
|TITLE:||Liners - Impoundments, Stockpiles, and Coal Refuse Disposal Areas|
|EFFECTIVE DATE:||December 5, 1997|
|AUTHORITY:||25 Pa. Code Chapters 86-90 and 101|
The Department will ensure that impoundments, stockpiles, and coal refuse disposal areas at underground mines, surface mines, coal preparation plants, and coal refuse disposal sites are designedand constructed in a manner which prevents groundwater contamination.
The purpose of this guidance is to document the criteria and procedures which the Department will use in approving facility designs and as-built certifications regarding liners for impoundments, stockpiles, and coal refuse disposal areas.
This guidance applies to certain dams, impoundments, and storage areas at coal mining, coal preparation, and coal refuse disposal sites that are used for the storage or treatment of mine drainage, runoff contaminated by metals or sulfates, leachate from coal refuse disposal areas, and water from coal processing operations. It also applies to stockpile areas for coal, pollution-forming underground development waste, spoil and coal processing wastes, and to coal refuse disposal areas.
The policies and procedures outlined in this guidance document are intended to supplement existing requirements. Nothing in the policies or procedures shall affect regulatory requirements.
The policies and procedures herein are not an adjudication or a regulation. There is no intent on the part of the Department to give these rules that weight or deference. This document establishes the framework within which the Department shall exercise its administrative discretion in the future. The Department reserves the discretion to deviate from this policy statement if circumstances warrant.
PAGE LENGTH: 5 pages
LOCATION: Vol. 12, Tab 83 (BMR PGM Section II, Part 6, Subpart 56)
The Bureau of District Mining Operations (BDMO) issues permits for the construction and operation of impoundments, stockpiles, and coal refuse disposal areas that may be used to contain pollutive fluids and materials for extended periods of time. Many such facilities are located at underground mines, coal preparation plants, and coal refuse disposal areas which may have operating lives of ten years or more. If not properly constructed, these facilities may leak large quantities of contaminants to groundwater over time.
There are three regulatory requirements which pertain to the construction and performance of impoundments, stockpiles, and disposal areas. Chapter 89 (25 Pa. Code 89.58) requires that pollution-forming underground development waste and spoil be stored and placed on impermeable material. Chapter 101 (25 Pa. Code 101.3) requires that any activity which involves the impoundment, production, processing, transportation, storage, use, application, or disposal of pollutive substances must include measures to prevent such substances from entering the waters of the Commonwealth. Chapter 101 (25 Pa. Code 101.4) requires that all impoundments used for the production, processing, storage, treatment, or disposal of pollutive substances, must be impermeable. These regulatory requirements have been applied to require lining of stockpiles and coal refuse storage and disposal areas.
The following sections describe thickness standards, testing requirements, and related thresholds for proposed liner material. In instances where site-specific engineering factors result in a need to deviate from the outlined design criteria, the operator must demonstrate that any alternative liner design is at least as effective in protecting groundwater from pollutive discharges.
1. For Impoundments: All impoundments described in the applicability section of this guidance shall be equipped with liners capable of achieving specific discharge rates no greater than 1 x 10-7 cm/sec under operating conditions. Specific discharge is defined by the following equation:
where Ds = specific discharge (cm/sec) K = hydraulic conductivity of liner (cm/sec) I = hydraulic gradient (dimensionless) H = height of water above liner (length) L = thickness of liner (length)
2. For Stockpiles and Disposal Areas: All stockpiles and disposal areas, as outlined in the applicability section of this guidance, shall be equipped with liners having a hydraulic conductivity of 5 x 10-5 cm/sec or less.
B. Liner Thickness
For liners constructed of soil, clay, or bentonite-soil mixtures, the minimum thickness is 2 feet (0.61 m).
For liners constructed of synthetic membranes, the minimum thickness is 30 mils (0.76 mm).
C. Information Required in Permit Applications
1. Basic information required for all types of liners:
a) Drawings showing the location, dimensions (including water levels for impoundments), and construction of each facility to be lined. Include type and thickness of liner and depth to groundwater.
b) A description (analysis, if available) of the fluid or material to be retained by the liner, including a statement concerning the potential presence of oil, grease, solvents, etc. Include a statement regarding the compatibility of the liner and the waste type.
c) The specific discharge rate (Ds) for the liner (as designed).
d) A description of the potential impacts of subsidence due to underground mining(impoundments only).
e) A description of the equipment and procedures which will be used to install the liner, including a construction quality assurance plan. For earthen liners, address type of compaction, lift thickness, methods of tying lifts together, installation on sloping surfaces, scarifications, etc. For concrete and synthetic liners, address the method to be used to seal or seam the joints.
f) A description of marker layers or other measures which will be used to protect the liner when excavating materials at storage sites or cleaning impoundments.
g) In cases where the subgrade must be prepared prior to liner placement, a description of the procedures and testing methods to be used.
h) A description of the method which will be used to test the liner prior to putting it into service.
2. Additional information for liners constructed of soil or clay.
a) A detailed description of the borrow area(s) which will serve as the source of the lining material.
b) Test results for liner material including:
i. Liner material density/moisture content relationship.
ii. Hydraulic conductivity.
iii. Sieve analysis showing that fifty (50) percent of soils proposed for use as liners or liner material pass a 200-mesh sieve. (This is consistent with the various soil classification systems which designate soils passing a 200-mesh sieve as fine grained soils (silts and clays). The fifty (50) percent of the soil particles retained on a 200-mesh sieve are classifiedas sands or gravels. Soils proposed for use as liner material must not exceed one inch (2.54 cm) in diameter. This top-size requirement is recommended to avoid concentrations of coarse soil fragments which can jeopardize liner material.)
iv. Atterberg limits - Soils proposed for use as liners or liner material must have a Plasticity Index of at least 10. (Engineering soil classification systems use this value as a basis for classifying fine grained soils. This is necessary to stay within the range considered for a clay and limit the use of silty soils for liner material.)
c) Soil Material Processing Procedures (if needed).
3. Additional information for liners constructed of admixed materials.
a) A copy of the manufacturer’s recommended construction specifications for the liner material to be used.
NOTE: Materials contained under the heading "admixed" include asphalt-concrete and bentonite-soil mixtures. Each material, depending on parent material and mix ratio, mustbe compacted during placement to varying densities. Therefore, it is important to rely on manufacturer’s specifications in order to attain the desired permeability. Additional guidelines regarding these materials may be found in the federal publication, "Lining of Waste Contaminant and Other Impoundment Facilities" (PB89-129670).
4. Information requirements for liners constructed of concrete:
a) A description of the design strength of the liner, i.e., how will the liner stand up under loading of material and equipment.
D. Special As-built Testing and Certification Requirements
As part of the facility certification, newly installed liners will be subject to in-place testing. Facilities relying on alternative liner designs or modified testing protocols may be subject to additional in-place testing.
1. All liners constructed of soil, clay, or a bentonite-soil mixture must be tested by a density survey over the constructed liner, e.g., one test/acre/lift.
2. Concrete and asphalt-concrete liners will generally not require testing.
3. Synthetic liners need only be tested if installed as part of an impoundment. The testing must be done by one of the following methods:
a) Procedures recommended by manufacturer; or
b) Filling the structure with water and determining the leakage rate over a period of at least five (5) days with corrections for precipitation and evaporation.
E. Waiver of Lining Requirements
Lining requirements may be waived for transitory impoundments and stockpile areas such as those associated with certain surface mining operations.
Liner requirements for other types of facilities may be waived if a demonstration can be made that there is no potential for a pollutive discharge from the impounded or stockpiled material. The decision whether or not to require a liner should be based on site-specific conditions, such as the nature of the stored or impounded material, background groundwater and surface water quality, and the projected "life" of the facility.