[Code of Federal Regulations]
[Title 40, Volume 24]
[Revised as of July 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR258.51]

[Page 414-415]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 258_CRITERIA FOR MUNICIPAL SOLID WASTE LANDFILLS--Table of Contents
 
         Subpart E_Ground-Water Monitoring and Corrective Action
 
Sec. 258.51  Ground-water monitoring systems.

    (a) A ground-water monitoring system must be installed that consists 
of a sufficient number of wells, installed at appropriate locations and 
depths, to yield ground-water samples from the uppermost aquifer (as 
defined in Sec. 258.2) that:
    (1) Represent the quality of background ground water that has not 
been affected by leakage from a unit. A determination of background 
quality may include sampling of wells that are not hydraulically 
upgradient of the waste management area where:
    (i) Hydrogeologic conditions do not allow the owner or operator to 
determine what wells are hydraulically upgradient; or
    (ii) Sampling at other wells will provide an indication of 
background ground-water quality that is as representative or more 
representative than that provided by the upgradient wells; and
    (2) Represent the quality of ground water passing the relevant point 
of compliance specified by Director of an approved State under Sec. 
258.40(d) or at the waste management unit boundary in unapproved States. 
The down gradient monitoring system must be installed at the relevant 
point of compliance specified by the Director of an approved State under 
Sec. 258.40(d) or at the waste management unit boundary in unapproved 
States that ensures detection of ground-water contamination in the 
uppermost aquifer. When physical obstacles preclude installation of 
ground-water monitoring wells at the relevant point of compliance at 
existing units, the down-gradient monitoring system may be installed at 
the closest practicable distance hydraulically down-gradient from the 
relevant point of compliance specified by the Director of an approved 
State under Sec. 258.40 that ensure detection of groundwater 
contamination in the uppermost aquifer.
    (b) The Director of an approved State may approve a multiunit 
ground-water monitoring system instead of separate ground-water 
monitoring systems for each MSWLF unit when the facility has several 
units, provided the multi-unit ground-water monitoring system meets the 
requirement of Sec. 258.51(a) and will be as protective of human health 
and the environment as individual monitoring systems for each MSWLF 
unit, based on the following factors:
    (1) Number, spacing, and orientation of the MSWLF units;
    (2) Hydrogeologic setting;
    (3) Site history;
    (4) Engineering design of the MSWLF units, and
    (5) Type of waste accepted at the MSWLF units.
    (c) Monitoring wells must be cased in a manner that maintains the 
integrity of the monitoring well bore hole. This casing must be screened 
or perforated and packed with gravel or sand, where necessary, to enable 
collection of ground-water samples. The annular space (i.e., the space 
between the bore hole and well casing) above the sampling depth must be 
sealed to prevent contamination of samples and the ground water.
    (1) The owner or operator must notify the State Director that the 
design, installation, development, and decommission of any monitoring 
wells, piezo meters and other measurement, sampling, and analytical 
devices documentation has been placed in the operating record; and
    (2) The monitoring wells, piezometers, and other measurement, 
sampling, and analytical devices must be operated and maintained so that 
they perform to design specifications throughout the life of the 
monitoring program.
    (d) The number, spacing, and depths of monitoring systems shall be:
    (1) Determined based upon site-specific technical information that 
must include thorough characterization of:

[[Page 415]]

    (i) Aquifer thickness, ground-water flow rate, ground-water flow 
direction including seasonal and temporal fluctuations in ground-water 
flow; and
    (ii) 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.
    (2) Certified by a qualified ground-water scientist or approved by 
the Director of an approved State. Within 14 days of this certification, 
the owner or operator must notify the State Director that the 
certification has been placed in the operating record.