Section 8-704 Scope and Review of Groundwater Investigations
8-704.A. Preliminary Investigations.
8-704.A.1. A preliminary investigation shall determine if a project will encounter groundwater. Preliminary investigations must be certified by a professional engineer whose experience is sufficient to determine the location of the high water table and its relationship to a proposed structure.
8-704.A.2. A preliminary groundwater investigation must be of sufficient detail to determine the extent to which the proposed construction activity or final construction project will penetrate the water table. The method of investigation is at the applicant’s discretion; at a minimum, it shall consist of test pits, borings or other methods that can accurately characterize the location of the water table throughout the entire area to be excavated. The preliminary investigation may be conducted contemporaneously with a geotechnical site investigation.
8-704.A.3. The applicant must submit a written report of the results of the investigation along with three (3) sets of the proposed project’s sub surface construction plans. The report may be made a part of a geotechnical engineer’s report. If the investigation concludes that the construction activity and the final construction product will not penetrate the groundwater table, additional groundwater studies shall not be required.
8-704.B. Detailed Groundwater Investigations.
8-704.B.1. A detailed groundwater investigation is required when the preliminary investigation determines that the project will encounter groundwater or that the proposed construction or final construction project will penetrate the seasonal low water table. Typically, an expectation of pumping of groundwater on site during construction is enough to require this investigation. Detailed groundwater investigations must be completed and certified by a person whose education and experience qualify them to conduct such investigations. This shall include Colorado Licensed Professional Engineers, Hydrologists or Geologists with at least four (4) years experience in groundwater investigations.
8-704.B.2. The purpose of the investigation is to characterize the short term (construction period) impacts of the project on the groundwater system; and, if necessary, the applicant must characterize the long term impacts, as applicable, of the dewatering on wetlands, seeps and springs and/or adjacent structures. Long term impacts are expected when substantial water table intrusion is undertaken adjacent to or abutting existing structures, riparian habitats, and wetlands. The investigation must be of sufficient detail to:
a. Estimate the construction period drawdown adjacent to the site and provide an opinion of the impacts to the affected area.
b. Provide a mitigation plan to provide water to wetlands during construction whenever the construction period drawdown or dewatering is shown to remove a water source, either surface or ground water, that may affect the viability of the wetlands. Wetlands and riparian vegetation at the waters edge or along the river bank must remain intact, or shall be restored to a more natural or expanded state than that existing prior to undertaking the proposed dewatering activity.
c. Identify adverse impacts to adjacent structures during the construction period drawdown or dewatering and provide for mitigation measures to offset any adverse impacts.
8-704.B.3. The applicant must submit a written report addressing the above, along with three (3) sets of any revised sub surface construction plans.
8-704.C. Town Review of Groundwater Studies. The Town shall review submitted groundwater investigations for completeness and accuracy. Excepting single family and duplex home development in Zone 3, the Town reserves the discretion to employ an expert in the field, at the applicant’s expense, to review the adequacy of the investigations and findings. The reports and data shall be incorporated into the Town’s groundwater data base.
8-704.C.1. Preliminary Groundwater Investigations.
a. Determine if extent of the investigation is sufficient to characterize the entire site that may be excavated during construction activities.
b. Determine conclusively if the proposed construction activity and permanent structure will, or will not, penetrate the seasonal high water table.
8-704.C.2. Detailed Groundwater Investigations.
a. Determine if all required elements of the investigation have been completed.
b. Evaluate the adequacy of the investigation, anticipated impacts, and proposed mitigative actions. If in the opinion of the Town, or a consultant retained by the Town, additional investigation is required, it shall be conducted by the applicant.
8-704.C.3. Additional analyses may be required by the Town if, in the opinion of the Town Engineer, proposed construction creates a concentration or series of subsurface construction over an approximately one block diameter that has the potential to significantly disrupt groundwater flows in the Town. This analysis shall determine if the concentration of subsurface construction resulting from the proposed construction will cause a significant incremental increase in disruption of groundwater flows, and if the proposed construction that creates the disruption must be altered or avoided. Options for altering construction deemed to be potentially disruptive to groundwater flows include limiting subsurface construction at critical points, requesting a parking payment-in-lieu approval for a portion of required spaces, or seeking height variances.