WAC 173-351-490   The hydrogeologic report contents.  (1) The hydrogeologic report shall meet all of the following performance standards as follows:

     (a) Examine existing site conditions for compliance with groundwater and surface water location restrictions under WAC 173-351-130 and 173-351-140;

     (b) Determine existing or background groundwater quality conditions, including any groundwater contamination; and

     (c) Define a detection groundwater monitoring program capable of immediate and early warning detection for potential contamination as required in WAC 173-351-400 and the information required in subsection (2) of this section.

     (2) The hydrogeologic report contents shall include the following information:

     (a) A summary of local and regional geology and hydrology, including faults, zones of joint concentrations, unstable slopes and subsidence areas on site; areas of groundwater recharge and discharge; stratigraphy; erosional and depositional environments and facies interpretation(s);

     (b) A borehole program which identifies all performance criteria of WAC 173-351-405 including lithology, soil/bedrock types and properties, preferential groundwater flow paths or zones of higher hydraulic conductivity, the presence of confining unit(s) and geologic features such as fault zones, cross-cutting structures etc., and the target hydrostratigraphic unit(s) to be monitored.

     (i) A minimum of twenty subsurface borings is required for MSWLF sites which are 50 acres or less in aerial extent. For sites greater than fifty acres, twenty borings, plus three borings for each additional ten acres thereafter, is required. Soil borings shall be established in a grid pattern with a boring in each major geomorphic feature such as topographic divides and lowlands;

     (ii) Each boring will be of sufficient depth below the proposed grade of the bottom liner as to identify soil, bedrock and hydrostratigraphic unit(s) conditions as required in WAC 173-351-405.

     (iii) The jurisdictional health department and the department may approve alternate methods including geophysical techniques, either surface or downhole including electric logging, some sonic logging, nuclear logging, seismic profiling, electromagnetic profiling and resistivity profiling in lieu of some of the number of borings required in the subsurface borehole program of (b)(i) of this subsection, provided sufficient hydrogeological site characterization can be accomplished and prior approval is obtained.

     (iv) At each boring samples shall be collected from each lithologic unit and tested for all of the following:

     (A) Particle size distribution by both sieve and hydrometer analyses in accordance with approved ASTM methods (D422 and D1120);

     (B) Atterburg limits following approved ASTM methods (D4318); and

     (C) Classification under the unified soil classification system, following ASTM standard D2487-85.

     (iv) Each lithologic unit on site will be analyzed for:

     (A) Moisture content, following approved ASTM methods (D2216); and

     (B) Hydraulic conductivity by an in-situ field method or laboratory method approved by the jurisdictional health department and the department. All samples collected for the determination of permeability shall be collected by standard ASTM procedures.

     (v) All boring logs shall be submitted with the following information:

     (A) Soil and rock descriptions and classifications;

     (B) Method of sampling;

     (C) Sample depth;

     (D) Date of boring;

     (E) Water level measurements;

     (F) Soil test data;

     (G) Boring location; and

     (H) Standard penetration number of ASTM standard D1586-67.

     (vi) All borings not converted to monitoring wells or piezometers shall be carefully backfilled, plugged and recorded in accordance with WAC 173-160-420.

     (vii) During the borehole drilling program, any on-site drilling and lithologic unit identification must be performed by a hydrogeologist, geologist or other qualified groundwater scientist who is trained to sample and identify soils and bedrock lithology.

     (c) Depths to groundwater and hydrostratigraphic unit(s) including transmissive and confining units;

     (d) Potentiometric surface elevations and contour maps; direction and rate of horizontal and vertical groundwater flow;

     (e) A description of regional groundwater trends including vertical and horizontal flow directions and rates;

     (f) All elevations and top of well casings shall be related to the national geodetic vertical datum of 1929 (NGVD 29) and the horizontal datum shall be in accordance with chapter 58.20 RCW, Washington Coordinate System and as amended per chapter 332-130 WAC.

     (g) Quantity, location, and construction (where available) of private and public wells within a two thousand foot (six hundred ten meter) radius of site;

     (h) Tabulation of all water rights for groundwater and surface water within a two thousand foot (six hundred ten meter) radius of the site;

     (i) Identification and description of all surface waters within a one-mile (1.6 kilometer) radius of the site;

     (j) A summary of all previously collected groundwater and surface water analytical data, and for expanded facilities, identification of impacts of existing facility of the applicant to date upon ground and surface waters from landfill leachate discharges;

     (k) Calculation of a site water balance;

     (l) Conceptual design of a groundwater and surface water monitoring system, including proposed installation methods for these devices and where applicable a vadose zone monitoring plan, including well construction diagrams;

     (m) Land use in the area, including nearby residences; and

     (n) A topographic map of the site and drainage patterns; an outline of the waste management area and MSWLF units, property boundary, the proposed location of groundwater monitoring wells;

     (o) Geologic cross-sections.

     (3) Groundwater flow path analysis. The hydrogeologic report shall include a summary groundwater flow path analysis which includes all supportive documentation, and calculations of the performance criteria of WAC 173-351-405.



[Statutory Authority: Chapter 70.95 RCW and 40 CFR 258. 93-22-016, § 173-351-490, filed 10/26/93, effective 11/26/93.]