Installation, testing, and permitting two new gravel-packed production wells for the Town of Marlborough, New Hampshire’s water system

Nobis installed two new water supply wells to replace one of the Town of Marlborough’s previous wells in a more protected location on Town-owned property. Nobis worked closely with the Town, the Town’s general engineering consultant, USDA Rural Development (the funding agency), NHDES, and subcontracted well drillers. The two new, gravel-packed wells were drilled in 2011 by Nobis’ subcontracted well drilling firm, tested in 2012 to meet permitting requirements, and permitted in 2013. Nobis assisted the Town in obtaining a federal grant/loan funding package for the project.

Nobis performed the following for the Town of Marlborough:

  • Overall project coordination;
  • Assistance in obtaining federal grant/loan funding package;
  • Well drilling and well construction oversight;
  • Preparation of successful permit applications to NHDES for a Large Groundwater Withdrawal Permit and New Large Community Well Permits;
  • Extensive pumping tests that monitored groundwater, other supply wells, wetlands, residential wells, potential sources of contamination, and stream flow;
  • Preparation of Water Conservation Plan and a Wellhead Protection Plan; and
  • Technical support to Board of Selectmen at Public Hearings.

Additionally, Nobis assisted the Town with maintaining and upgrading the one remaining original well, in a different location, to provide operational flexibility for future water supply needs. This upgrade enabled the Town to meet increasing water needs of a commercial customer, who had proposed to drill their own well in the same aquifer as the Town’s new wells. This solution maintained the Town’s revenue stream and avoided a competing water withdrawal in a limited aquifer. Nobis continues to assist the Town of Marlborough with routine well maintenance and well operations consultation.

challenges

  • The area available for new wells on the Town-owned property was very limited due to accessibility, existing recreational and other land uses, wetlands, and varying geological subsurface conditions. Portions of the required Sanitary Protective Area (SPA) for the new wells were not within Town-owned property. Wetlands, streams, and private domestic drinking water wells were present on or adjacent to the site; assessment of potential impacts, due to pumping the wells, was required.
  • The project schedule was concurrent with the construction of a new public school on an adjacent property. This posed not only scheduling and logistical coordination challenges but also concerns that school construction activities could result in fuel releases that could contaminate the aquifer. The presence of gravity sewer main at the site posed a threat that pumping the wells could draw contaminants into the water system should there be a sewer main leak.
  • A former fuel leak at a gasoline station south of the site resulted in a small MtBE detection at the Town’s former well at the time of the leak and a groundwater plume that could possibly be drawn to the new wells under pumping conditions.

solutions

  • Nobis worked closely with the Town, other consultants, and NHDES to overcome the limited suitable well locations, multiple uses of Town-owned properties, concurrent construction schedules, and the presence of a gravity sewer main to successfully install and permit two new water supply wells.
  • Nobis worked with NHDES to ensure the proposed new well locations were permittable and would provide a greater degree of protection compared to an existing water supply well.
  • With Nobis’ assistance, the Town obtained easements from 3 of 4 private property owners within the SPA. Nobis obtained a waiver from NHDES for the 4th property.
  • Nobis coordinated directly with the school contractor to make sure best management practices were followed during school construction to protect the aquifer.
  • On Nobis’ recommendation, the Town double-lined and pressure-tested the sewer line through the property.
  • To evaluate potential leakage from the sewer main, Nobis collected groundwater samples from monitoring wells located between the main and the wells during a 5-day pumping test to evaluate potential leakage from the sewer main. These results confirmed there was no sewer leakage threatening the proposed supply well area. Monitoring is ongoing, as a permit condition.
  • Extensive monitoring of stream flow, stream stage, groundwater levels on the far side of the stream, wetland water levels, and homeowner wells indicated that pumping the wells caused very minor, non-adverse impacts on stream flow and wetlands and no appreciable impact on the homeowner wells.
  • Nobis communicated with the consultant who was monitoring the shrinking groundwater plume associated with the former gasoline leak south of the new well site. Nobis monitored selected monitoring wells associated with the gas station during the pumping test and showed that pumping the new wells did not draw the plume closer to the Town’s new wells and that the plume continued to shrink.
  • Nobis provided support to the Board of Selectmen during a public hearing and Town Meeting, answering the questions of project critics. The necessary warrant articles for the project passed at Town Meeting.

results

  • Two new gravel-packed water supply wells were successfully installed, tested, and permitted, allowing abandonment of one of the old wells that was in a threatened location, thus meeting NHDES requirements and improving the reliability of the Town’s water supply.
  • Ongoing monitoring, required as a permit condition, provides assurance that the new wells are not impacted by the sewer main.
  • The other previous well has been upgraded, providing a supplemental supply at a different location.