WAC 173-351-300   Design criteria.  (1) Applicability. Existing MSWLF units are not subject to this section. Waste placement in existing units must be consistent with past operating practices or modified practices to ensure good management, including operating plans approved under chapter 173-304 WAC.

     (2) New MSWLF units and lateral expansions shall be constructed:

     (a) For nonarid landfills, in accordance with a standard design as follows:

     (i) A composite liner as defined in (a)(ii) of this subsection and a leachate collection system that is designed and constructed to maintain less than a 1 foot (30 cm) depth of leachate over the liner.



Note: Leachate head in leachate pump sump areas, only, shall not be allowed to exceed two feet (60 cm).

     (ii) For purpose of this section, "composite liner" means a system consisting of two components; the upper component must consist of a minimum of 60 mil thickness high density polyethylene (HDPE) geomembrane. The lower component must consist of at least a two-foot (60 cm) layer of compacted soil with a hydraulic conductivity of no more than 1X10-7 cm/sec. The geomembrane must be installed in direct and uniform contact with the compacted soil component. Thinner geomembranes of other than high density polyethylene may be used provided that a demonstration can be made that the alternative has equivalent mechanical strength, permeability, chemical resistance and other factors under conditions of construction and use. Minimum thickness of geomembranes other than high density polyethylene shall be 30 mils.

     (iii) Equivalent liner designs and liner materials may be used provided a demonstration during the permitting process of WAC 173-351-700 can be made that the liner is equivalent to the composite liner design:

     (A) With respect to hydraulic effectiveness as shown by the use of the hydraulic evaluation of landfill performance (HELP) model or other approved models or methods;

     (B) With respect to mechanical strength;

     (C) With respect to chemical resistance;

     (D) With respect to potential physical damage during construction and operation;

     (E) With respect to attenuative capacity; and

     (F) And other factors identified by the jurisdictional health department and the department on a case-by-case basis.

     (b) For arid landfills, in accordance with a design that ensures that the maximum contaminant levels listed in Table 1 of this section will not be exceeded in the hydrostratigraphic unit(s) identified in the hydrogeologic characterization/report at the relevant point of compliance as specified during the permitting process in WAC 173-351-700. When approving a design that complies with the arid landfill design of (b) of this subsection, the jurisdictional health department shall consider at least the following factors:

     (i) The hydrogeologic characteristics of the facility and surrounding land;

     (ii) The climatic factors of the area; and

     (iii) The volume, physical and chemical characteristics of the leachate.


Note: When determining the need for a liner in arid settings and its ability to meet the performance standard of this section, considering (b)(i), (ii), and (iii) of this subsection, the owner or operator may use:


     (A) Existing information such as vadose zone, groundwater monitoring, or leachate characterization that has previously been conducted at the facility;

     (B) Contaminant transport modeling in accordance with the requirements of WAC 173-351-480; and/or

     (C) Other information determined as appropriate and relevant by the jurisdictional health department.

     (c) The relevant point of compliance approved during the permitting process in WAC 173-351-700, shall be no more than one hundred fifty meters (four hundred ninety-two feet) from the waste management unit boundary and shall be located on land owned by the owner of the MSWLF unit. In approving the relevant point of compliance the jurisdictional health department shall consider at least the following factors:

     (i) The hydrogeologic characteristics of the facility and surrounding land;

     (ii) The volume, and physical/chemical characteristics of the leachate;

     (iii) The quantity and quality, and direction, of flow of groundwater;

     (iv) The proximity and withdrawal rate of the groundwater users;

     (v) The availability of alternative drinking water supplies;

     (vi) The existing quality of the groundwater, including other sources of contamination and their cumulative impacts on the groundwater, and whether the groundwater is currently used or reasonably expected to be used for drinking water;

     (vii) Public health, safety, and welfare effects; and

     (viii) Practical capability of the owner or operator.


TABLE 1

CHEMICAL Maximum

Contaminant

Levels

(MCL (mg/l))
 
ARSENIC 0.00005
BARIUM 1.0
BENZENE 0.001
CADMIUM 0.01
CARBON TETRACHLORIDE 0.0003
CHROMIUM (HEXAVALENT) 0.05
2,4-DICHLOROPHENOXY ACETIC ACID 0.1
1,4-DICHLOROBENZENE 0.004
1,2-DICHLOROETHANE 0.0005
1,1 DICHLOROETHYLENE 0.007
ENDRIN 0.0002
FLUORIDE 4
LINDANE 0.00006
LEAD 0.05
MERCURY 0.002
METHOXYCHLOR 0.1
NITRATE 10
SELENIUM 0.01
SILVER 0.05
TOXAPHENE 0.00008
1,1,1-TRICHLOROETHANE 0.20
TRICHLOROETHYLENE 0.003
2,4,5-TRICHLOROPHENOXY ACETIC ACID 0.01
VINYL CHLORIDE 0.00002




[Statutory Authority: Chapter 70.95 RCW and 40 CFR 258. 93-22-016, § 173-351-300, filed 10/26/93, effective 11/26/93.]