"Dewatering" shall mean lowering the water level in a wet pit by pumping water from the pit, regardless of the purpose of the pumping. Water generated from dewatering activities must be beneficially used and discharged on-site. Pumps systems used to dewater the wet pits shall be powered by electricity (i.e., through connection to power lines) or solar power. This ordinance does not permit water generated from dewatering activities to be used or discharged off-site. No off-channel excavation shall use dewatering as a part of surface mining operations, unless site-specific technical analysis performed by a qualified Professional Engineer or Professional Geologist with experience in hydrogeology demonstrates that the proposed dewatering will not adversely affect off-site wells with respect to groundwater level and quality. The Professional Engineer or Professional Geologist shall demonstrate, using appropriate hydrogeologic analysis (i.e., using data-supported empirical, analytical, and/or numerical investigative tools), that the proposed dewatering activity will not adversely impact active off-site wells or other water resources (e.g., creeks and wetlands) within one thousand (1000) feet of the proposed dewatering pit boundary. Average historic low groundwater levels in the subject well shall be used for the analysis. Site-specific aquifer testing shall be conducted, if needed, to determine aquifer properties for the analysis. Consistent with the OCMP EIR, an effect shall be considered adverse if the reduction in simulated groundwater levels exceeds two (2') feet at any well located within one thousand (1000) feet of the pit boundary or results in well failure.
The hydrogeologic analysis shall be submitted to the County for review and approval prior to implementation of any dewatering activities. If an adverse impact is identified by the analysis (either impacts to existing wells or other water resources, including creeks and wetlands), dewatering activities will be modified to eliminate any adverse impacts, and/or the applicant shall otherwise mitigate adverse impacts to the satisfaction of the County.
Prior to and for the duration of dewatering activities, the applicant shall: 1) monitor water levels in the wet pit(s) and nearby monitoring wells on a quarterly basis; and 2) quantify the amount of water pumped from and returned to the wet pit(s). This monitoring data shall be reviewed by the applicant's Professional Engineer or Professional Geologist to determine whether any adverse impacts are occurring. Documentation of the monitoring and data evaluation shall be submitted to the County annually. If adverse impacts are found to be occurring, dewatering activities will be modified to eliminate adverse impacts, or the applicant shall otherwise mitigate impacts to the satisfaction of the County. Any measures designed to mitigate adverse impacts identified after implementation of dewatering activities shall be approved by the Planning Commission at a regularly scheduled meeting, with written notice of the adverse impact and proposed mitigation measures given by mail to all property owners within 1,000 feet of the pit boundary in addition to any notice otherwise required by law.
For purposes of this section, mitigation measures of adverse impacts may include, but are not limited to, well modification, well relocation, compensation of well owners for increased pumping cost, or providing an alternative water supply. Such mitigation measures shall be paid for by the mining operator, with sufficient financial security to ensure completion of the measures.
Pumping of water from the wet pit in lieu of pumping of groundwater from a well shall not require predictive impact analysis in addition to analysis provided in the approved, site-specific CEQA document, unless the total annual water demand, as set forth in the CEQA document, is exceeded. This does not remove the requirement for monitoring and reporting activities described above.
(§ 1, Ord. 1190, eff. September 5, 1996; as amended by § 2, Ord. 1487, eff. April 6, 2017; as amended by Ord. 1518, eff. February 13, 2020)