N.M. Admin. Code § 20.9.9.9

Current through Register Vol. 35, No. 23, December 10, 2024

Section 20.9.9.9 - GROUND WATER MONITORING SYSTEMS AND GROUND WATER MONITORING SYSTEM PLANS

A. A ground water monitoring system shall consist of a sufficient number of wells, installed at appropriate locations and depths, to yield ground water samples from the uppermost aquifer that:

(1) represent the background quality of ground water that has not been affected by a release from the landfill as determined under 20.9.9.10 NMAC; and

(2) represent the quality of ground water passing the detection monitoring point which shall be at the waste management unit boundaries on land owned by the owner of the landfill:

(a) the downgradient monitoring system shall be installed at the detection monitoring point;

(b) when physical obstacles preclude installation of ground water monitoring wells immediately downgradient from an existing landfills, the secretary may approve a monitoring system plan that provides for an alternative detection monitoring point at the closest practicable distances hydraulically downgradient from the landfill that ensure detection of ground water contamination in the uppermost aquifer.

B. The ground water monitoring system plan shall comply with this section and shall include a detailed plan for all wells, piezometers or other measurement and sampling devices and an explanation of the purpose and placement of each (with maps). The ground water monitoring system plan shall be certified that it is in compliance with this section by a qualified ground water scientist on a form provided by the department.

C. The ground water monitoring plan shall include a description of the hydrogeologic characteristics of the site, a geologic cross-section of the site, a description of ground water sampling and analysis procedures, and a detection monitoring plan, and shall comply with 20.9.9 NMAC. The ground water monitoring plan shall be certified that it is in compliance with 20.9.9 NMAC by a qualified ground water scientist on a form provided by the department.

D. The owner or operator shall comply with the ground water monitoring system plan and ground water monitoring plan approved by the department throughout the active life and post-closure care period of each landfill subject to the requirements of 20.9.9 NMAC. The secretary may require monitoring for additional constituents, parameters and frequency as necessary to protect the public health, welfare and the environment. No change shall be made to the approved ground water monitoring system plan or ground water monitoring plan without a specific approval by the department.

E. Owners or operators shall not install or decommission any monitoring well, piezometer, or other ground water measurement, sampling, or analytical device unless it is in accordance with an approved ground water monitoring system plan. The owner or operator shall submit a written notice of intent to the department at least 14 days prior to the installation or decommissioning of any monitoring wells or piezometers. The notice shall include a statement, on a form provided by the department, that the installation or decommission of any monitoring well complies with this section and the approved ground water monitoring system plan.

F. The owner or operator shall submit an installation report to the department within 90 days after the installation of a monitoring well or piezometer. The report shall include the following documentation.

(1) A certification by a qualified ground water scientist that the monitoring device has been installed in compliance with the approved ground water monitoring system plan and 20.9.9 NMAC.

(2) A construction and lithologic log for each monitoring well or piezometer. The lithologic log shall be drawn to a scale of one inch equals ten feet, except if the boring is greater than 200 feet, then a scale of one-half inch equals ten feet may be used, graphically depicting the initial depth at which ground water was encountered and the soil or rock strata penetrated and describing each layer.

(a) If soil was encountered, the log should indicate the color, degree of compaction, moisture content plus any additional information necessary for an adequate visual description and classification of each stratum based on the unified soils classification system.

(b) If rock was encountered, the log should include a detailed lithologic description, including rock type, degree of induration, presence of fractures, fissility, and porosity (including vugs) plus any other information necessary for an adequate description. All field notes made by the qualified ground water scientist shall be made available on request of the department.

G. A copy of all construction and lithologic logs, and all sampling data from groundwater monitoring shall be placed in the operating record.

H. The secretary may approve an alternate detection monitoring point in the monitoring system plan if it is located 150 meters or less from the waste management unit boundary and it is located on land owned by the owner of the landfill. When approving an alternate detection monitoring point under this section, the secretary shall consider at least the following factors:

(1) the hydrogeologic characteristics of the facility and surrounding land;

(2) the volume and physical and chemical characteristics of the leachate;

(3) the quantity, quality, and direction of flow of the ground water;

(4) the proximity and withdrawal rate of the ground water users;

(5) the availability of alternative drinking water supplies;

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

(7) public health, safety, and welfare effects; and

(8) the practicable capability of the owner or operator.

I. The secretary may approve, in the ground water monitoring system plan or closure and post-closure care plan, a multiunit ground water monitoring system instead of separate systems for each landfill where the facility has several landfills, provided the multiunit system meets the appropriate requirements of this part and will be as protective of public health, welfare and the environment as individual monitoring systems for each landfill, based on the following factors:

(1) number, spacing, and orientation of the landfills;

(2) hydrogeologic setting;

(3) site history;

(4) engineering design of the landfills; and

(5) types of waste accepted at the landfills.

J. Unless otherwise approved by the department in the ground water monitoring system plan or by specific approval, monitoring wells shall be constructed in such a manner that the integrity of the bore-hole and well is maintained and is in accordance with American society of testing materials method D-5092 or the following requirements:

(1) the bore-hole shall be drilled a minimum of 4 inches larger than the casing diameter to allow for the emplacement of sand and sealant;

(2) care shall be taken not to introduce contamination to the well;

(3) the well shall be developed so that ground water flows freely through the screen and to decrease turbidity, and that all sediment is removed from the well;

(4) the casing shall, unless otherwise approved by the secretary, consist of schedule 40 or heavier threaded PVC pipe of not less than 2 inches diameter;

(a) the casing shall extend from the top of the screen to at least one foot above ground surface;

(b) the casing top shall be protected by a cap and a locking shroud shall protect the exposed casing; and

(c) the shroud shall be large enough to allow easy access for removal of the plastic cap;

(5) the screen shall be at least a 20-foot section of machine slotted or other manufactured screen; a slot size of 0.01-inch generally is adequate for most installations; no on-site or hack-saw slotting is permitted;

(6) if the uppermost aquifer is unconfined; the top of the screen shall be 5 feet above the water table to allow for seasonal fluctuations;

(7) if the uppermost aquifer is confined, the top of the screen shall be at the location of the geologic boundary between the top of the aquifer and the bottom of the confining unit;

(8) centralizers shall be placed at the top and the bottom of the screen;

(9) an annular space from 2 feet below to 2 feet above the screen shall be packed with sand;

(a) the sand shall be clean and medium to coarse grained;

(b) the sand shall be properly sized to prevent fines from entering the well; and

(c) a tremmie pipe shall be used for sand placement in deeper wells when appropriate;

(10) the annular space for at least 2 feet above the sand pack shall be grouted or sealed;

(a) pressure grouting with bentonite or cement using a tremmie pipe is preferred; or

(b) alternatively, a bentonite seal may be installed using bentonite pellets, 1/4 or 1/2 inch in size;

(11) the annular space above the seal shall be fully sealed using grout or bentonite to within 3 feet of the ground surface;

(12) the annular space above the cuttings shall be filled with bentonite-cement grout to within 3 feet of the ground surface;

(13) the remaining 3 feet shall be filled with concrete (expanding cement); and

(14) a concrete slab with a minimum 2-foot radius and a 4-inch thickness shall be poured around the shroud; the pad shall be sloped so that rainfall and run-off flows away from the shroud.

K. The casing of each well or wells that will be used to monitor ground water shall be surveyed, referenced to a standard grid, and subsequently mapped by a licensed surveyor. The location of the well shall be determined within one-tenth of a foot, and the height above sea level at the top of the casing shall be determined within one-hundredth of a foot. This information shall be submitted to the department with the installation report required in Subsection F of 20.9.9.9 NMAC.

L. The monitoring wells, piezometers, and other measurement, sampling, and analytical devices shall be operated and maintained so that they perform to design specifications throughout the life of the monitoring plan.

M. The number, spacing, and depths of monitoring systems shall be based upon site-specific technical information that includes thorough characterization of:

(1) aquifer thickness, ground water flow rate, and flow direction, including seasonal and temporal fluctuations in ground water flow; and

(2) saturated and unsaturated geologic units and fill materials overlying the uppermost aquifer, materials comprising the uppermost aquifer; and materials comprising the confining unit defining the lower boundary of the uppermost aquifer; including, but not limited to: thicknesses, stratigraphy, lithology, hydraulic conductivities, porosities, and effective porosities.

N. Vadose zone monitoring or leak detection systems, if required by the secretary pursuant to Subsections C or F of 20.9.9.8 NMAC, shall include:

(1) direct and indirect monitoring techniques such as:

(a) permanent monitoring stations such as those which utilize access tubes for neutron moderation instrumentation, time domain reflectometry (TDR) probes, capacitance probes or other permanently installed devices;

(b) nested piezometers when used for monitoring perched water or locally saturated portions of the vadose zone;

(c) soil gas measurements;

(d) lysimeters;

(e) electronic leak detectors; and

(f) other devices or methods as approved in the permit ;

(2) an adequate frequency of testing and a sufficient number of sampling points at appropriate locations and depths to determine a change in soil characteristics; and

(3) an action plan that addresses potential vadose zone contamination and the sources of the contamination.

O. Amendments to an approved groundwater monitoring system plan shall be by specific approval.

N.M. Admin. Code § 20.9.9.9

20.9.9.9 NMAC - Rp, 20 NMAC 9.1.VIII.802, 8/2/2007