N.M. Code R. § 20.9.9.13
ASSESSMENT MONITORING.
C. The department may specifically approve an alternative frequency or subset of wells for repeated sampling for assessment monitoring during the active life and post-closure care period of the facility. In determining an alternative frequency or subset of wells, the department shall consider:
(1) lithology of the aquifer and unsaturated zone;
(2) hydraulic conductivity of the aquifer and unsaturated zone;
(3) ground water flow rate;
(4) minimum distance between the waste management unit boundary and downgradient monitoring well screen;
(5) resource value of the aquifer; and
(6) nature of any constituents detected.
D. After obtaining the results from the sampling required by Subsection B of this section, the owner or operator shall:
(1) within 14 days, notify the department in writing and document in the operating record any constituents that have been detected;
(2) within 90 days and at least semiannually, resample all wells and analyze for all constituents in Subsections A and C of 20.9.9.20 NMAC and any constituents in Subsection B of 20.9.9.20 NMAC or an approved alternate list that have been detected; the department may specify an alternate monitoring frequency in accordance with Subsection A of 20.9.9.11 NMAC, but all constituents in Subsection B of 20.9.9.20 NMAC shall be sampled no less frequently than once every five years during the active life and post-closure care period.
G. If one or more constituents in 20.9.9.20 NMAC is detected above the CALs in any sampling event, the owner or operator shall:
(1) within 14 days of this finding, notify the department and all appropriate local government officials in writing;
(2) install at least one additional monitoring well at the facility boundary in the direction of contaminant migration and sample this well in accordance with this section within six months; the department may approve an extension for this installation and sampling for good cause for up to an additional six months of the finding of the exceedance;
(3) characterize the nature and extent of the release by installing additional monitoring wells as necessary within one year of the finding of the exceedance;
(4) notify area residents and land owners in the same manner as described in Subsection B of 20.6.2.4108 NMAC; and
(5) initiate an assessment of corrective measures as required by 20.9.9.15 NMAC within 90 days; or
(6) the owner or operator may demonstrate that a source other than the facility caused the contamination, or that the increase resulted from error in sampling, analysis, statistical evaluation, or natural variation in ground water quality; a report documenting this demonstration shall be certified by a qualified ground water scientist and submitted to the department for review and approval; if a demonstration is specifically approved by the department, the owner or operator may return to detection monitoring; until a successful demonstration is made, the owner or operator shall comply with 20.9.9.12 - 20.9.9.20 NMAC, including initiating an assessment of corrective action.
H. Within 90 days after any AML exceedance, the owner or operator shall identify the ground water protection standard for each constituent in 20.9.9.20 NMAC that exceeded the AML in the ground water that was not identified pursuant to Subsection I of 20.9.9.10 NMAC. The owner or operator shall propose for department approval ground water protection standards for any constituent that exceeded the AML pursuant to Subsection B of this section and Paragraph (2) of Subsection D of this section that does not have an MCL or numeric standard in commission rules. The owner or operator shall make a demonstration that the proposed standard will be protective of the public health and the environment, in accordance with Subsection I of this section.
(1) The ground water protection standards for constituents shall be the more stringent of the MCL promulgated at 40 CFR 141, or the numeric standard established by commission rules.
(2) For hazardous constituents for which the background concentration is higher than the ground water protection standard, the background concentration shall be used as the ground water protection standard.
I. The secretary may establish an alternative ground water protection standard for constituents for which MCLs or commission standards have not been established. These ground water protection standards shall be appropriate health based levels that satisfy the following:
(1) the level is derived in a manner consistent with U.S. EPA guidelines for assessing the health risks of environmental pollutants;
(2) the level is based on scientifically valid studies conducted in accordance with the Toxic Substances Control Act good laboratory practice standards or equivalent;
(3) for carcinogens, the level represents a concentration associated with an excess lifetime cancer risk of more than one cancer per 100,000 exposed persons; and
(4) for systemic toxicants, the level represents a concentration to which the human population could be exposed on a daily basis that is likely to be without appreciable risk of deleterious effects during a lifetime; systemic toxicants include toxic chemicals that cause effects other than cancer or mutation.
J. In establishing ground water protection standards under Subsection I of this section, the secretary may consider the following:
(1) multiple contaminants in the ground water;
(2) exposure threats to sensitive environmental receptors; and
(3) other site specific exposure or potential exposure to ground water.
[20.9.9.13 NMAC - Rp, 20 NMAC 9.1.VIII.806, 8/2/2007]