| boring must be presented in the form of a log that contains, at a minimum, the boring number; surface elevation and location coordinates; and a columnar section with text showing the elevation of all contacts between soil and rock layers, description of each layer using the unified soil classification, color, degree of compaction, and moisture content. A key explaining the symbols used on the boring logs and the classification terminology for soil type, consistency, and structure must be provided. The boring plan, including locations and depths of all proposed borings, shall be approved by the executive director prior to initiation of the work. (A) A sufficient number of borings shall be performed to establish subsurface stratigraphy and to determine geotechnical properties of the soils and rocks beneath the facility. Other types of samples may also be taken to provide geologic and geotechnical data. The number of borings necessary can only be determined after the general characteristics of a site are analyzed and will vary depending on the heterogeneity of subsurface materials. Locations with stratigraphic complexities such as non-uniform beds that pinch out, vary significantly in thickness, coalesce, or grade into other units, will require a significantly greater degree of subsurface investigation than areas with simple geologic frameworks. (B) Borings shall be sufficiently deep enough to allow identification of the uppermost aquifer and underlying hydraulically interconnected aquifers. Borings shall penetrate the uppermost aquifer and all deeper hydraulically interconnected aquifers and be deep enough to identify the aquiclude at the lower boundary. All the borings shall be at least five feet deeper than the elevation of the deepest excavation. In addition, at least the number of borings shown on the Table of Borings shall be drilled to a depth at least 30 feet below the deepest excavation planned at the waste management unit, unless the executive director approves a different depth. If no aquifers exist within 50 feet of the elevation of the deepest excavation, at least one test hole shall be drilled to the top of the first perennial aquifer beneath the site, if sufficient data does not exist to accurately locate it. The executive director may accept data equivalent to a deep boring on the site to determine information for aquifers more than 50 feet below the site. Aquifers more than 300 feet below the lowest excavation and where the estimated travel times for constituents to the aquifer are in excess of 30 years plus the estimated life of the site need not be identified through borings. Attached Graphic (C) All borings shall be conducted in accordance with established field exploration methods. The hollow-stem auger boring method is recommended for softer materials; coring may be required for harder rocks. Other methods shall be used as necessary to obtain adequate samples for soil testing required in this paragraph. Investigation procedures shall be discussed in the report. (D) Installation, abandonment, and plugging of the borings in accordance with the rules of the commission. (E) Both the number and depth of borings may be modified because of site conditions with approval of the executive director. (F) Geophysical methods, such as electrical resistivity, may be used with authorization of the executive director to reduce the number of borings that may be necessary or to provide additional information between borings. (G) Cross-sections must be prepared from the borings depicting the generalized strata at the facility. For small waste management units, two perpendicular cross-sections will normally suffice. (H) A narrative that describes the investigator's interpretations of the subsurface stratigraphy based upon the field investigation shall be provided; (5) geotechnical data that describes the geotechnical properties of the subsurface soil materials and a discussion with conclusions about the suitability of the soils and strata for the uses for which they are intended. All geotechnical tests shall be performed in accordance with industry practice and recognized procedures such as described below. A brief discussion of geotechnical test procedures including: (A) a laboratory report of soil characteristics determined from at least one sample from each soil layer or stratum that will form the bottom and side of the proposed excavation and from those that are less than 30 feet below the lowest elevation of the proposed excavation. Additional tests shall be performed, as necessary, to provide a typical profile of soil stratification within the site. No laboratory work need be performed on highly permeable soil layers such as sand or gravel. The samples shall be tested by a competent independent third-party soils laboratory; (B) permeability tests performed according to one of the following standards on undisturbed soil samples. Permeability tests shall be performed using tap water or .05 Normal solution of calcium sulfate (CaSO 4 ), and not distilled water, as the permeant. Those undisturbed samples that represent the sidewall of any proposed cell, pit, or excavation shall be tested for the coefficient of permeability on the sample's in-situ horizontal axis; all others shall be tested on the in-situ vertical axis. All test results shall indicate the type of tests used and the orientation of each tested sample. All calculations for the final coefficient of permeability tests result for each sample tested shall be included in the report: (i) constant head with back pressure per Appendix VII of Corps of Engineers Manual EM1110-2-1906, "Laboratory Soils Testing;" American Society for Testing and Materials (ASTM) D5084 "Saturated Porous Materials Using a Flexible Wall Permeameter"; (ii) falling head per Appendix VII of Corps of Engineers Manual EM1110-2-1906, "Laboratory Soils Testing"; (iii) sieve analysis for the 200, and less than 200 fraction per ASTM D1140; (iv) Atterberg limits per ASTM D4318; and (v) moisture content per ASTM D2216; (C) the depth at which groundwater was encountered and records of after-equilibrium measurements in all borings. The cross-sections prepared in response to paragraph (4)(G) of this subsection must be annotated to note the level at which groundwater was first encountered and the level of groundwater after equilibrium is reached or just prior to plugging, whichever is later. This water-level information must also be presented on all borings required by paragraph (4) of this subsection and presented in a table format in the report; (D) records of water-level measurements in monitoring wells. Historic water-level measurements made during any previous groundwater monitoring shall be presented in a table for each well; (E) a tabulation of all relevant groundwater monitoring data from wells on site or on adjacent MSW landfill unit(s); and (F) identification of the uppermost aquifer and any lower aquifers that are hydraulically connected to it beneath the facility, including groundwater flow direction and rate, and the basis for such identification (i.e., the information obtained from hydrogeologic investigations of the facility area); (6) for owners and operators seeking an arid exemption for their landfill unit designs, a groundwater certification process must be used for meeting the provisions for groundwater certification of the arid exemption, as described in §330.5(b) of this title: (A) locate and plot the facility accurately on a topographic map (7.5-minute or 15-minute United States Geological Survey quadrangle). Draw a line to enclose all of the area within one mile of the facility boundary; (B) visit the facility and locate by physical inspection water wells and springs in the facility area. Determine the locations and plot them on the topographic map: (i) if no wells or springs exist within the facility area, refer to subparagraph (I) of this paragraph. Otherwise, refer to clause (ii) of this subparagraph; and (ii) determine from appropriate records (for example, water-well drillers, pump installers, city records, underground water conservation district, Texas Water Development Board, Texas Commission on Environmental Quality, United States Geological Survey, etc.) which of the wells are completed in the shallowest aquifer. If no wells are completed in the shallowest aquifer or if the shallowest aquifer is more than 150 feet below the land surface at the facility, refer to subparagraph (I) of this paragraph. Otherwise, refer to subparagraph (C) of this paragraph; (C) determine the groundwater gradient of the shallowest aquifer in the vicinity of the facility. This can be done by measuring stabilized water levels in wells completed in the shallowest aquifer in the facility area (from subparagraph (B)(ii) of this paragraph) or from previous hydrogeologic studies using contemporaneous stabilized water-level measurements. Care should be taken to measure water levels when nearby high-volume wells, such as irrigation wells, have not been pumped for a long enough period to allow the water level to stabilize. Where no data exist or cannot be determined, the regional gradient can be used; Cont'd... |
