Existing well deepening, hydrofracturing, and pumping tests to assess and increase yield and manage pumping schedules to address water supply crisis

The Pillsbury Lake District in Webster, New Hampshire provides water to over 100 residential customers and is served by 4 bedrock wells. The system experienced water supply shortfalls in 2010 and 2011, requiring the District to purchase truckloads of water delivered to its storage tank. The District needed a resolution to its short-term crisis and assumed that a new well would be needed in 2012.

Nobis assisted the District to address its water supply crisis and meet Corrective Action Plan (CAP) requirements set by NHDES during the crisis. Nobis obtained accurate yield estimates for three of its four existing bedrock wells (the fourth well already had a satisfactory yield estimate); deepened and hydrofractured two of its wells; and performed pumping tests on the two deepened wells and a third well that had not been adequately tested in the past. Nobis submitted required reports and information to the NHDES for permitting the deepened wells. The District worked to locate and repair water main leaks. NHDES subsequently notified the District that its water supply shortfalls were corrected and CAP conditions had been met without the expected expense of drilling, testing, and permitting a new well.

challenges

  • The Pillsbury Lake District was experiencing a water supply crisis when Nobis began work in 2011.
  • System issues included declining well yields; well interference that was not understood, documented, or quantified; lack of hydrogeologic testing data and permits; and water main leaks that required the District to purchase truckloads of water to be delivered to its storage tanks.
  • Emergency orders and requirements were imposed by NHDES and had to be satisfied according to a CAP.
  • Two of the existing wells are on a peninsula in Pillsbury Lake and are very close to the water’s edge. Preventing discharge of drill cuttings and drilling water to the lake during well deepening posed a significant challenge.

solutions

  • Nobis oversaw deepening and hydrofracturing of two wells to increase their yield and storage. Subsequently, Nobis conducted pumping tests on the two modified wells to determine sustainable yields, recommend pumps and pump depths, and assess interference effects between wells to optimize pumping schedules and increase the overall water yield available for the system.
  • Nobis worked closely with NHDES to complete missing permitting information and document the sustainable well yields when pumping individually and in combination. Work was performed to satisfy both NHDES permitting and CAP requirements and address NHDES concerns that the District had insufficient water supply.
  • Nobis worked closely with the District and local contractors to mitigate impacts of airlifting water and drill cuttings from test wells adjacent to Pillsbury Lake, using hay bales and drain hoses to construct temporary water basins to store airlifted water and drill cuttings until it could be hauled offsite. The drilling and airlifting was completed with no discharge of water or sediment into Pillsbury Lake.
  • Nobis’ work, combined with the District’s efforts to repair water main leaks, eliminated the District’s need to drill, test, permit, and connect a new well to their water system, which resulted in significant cost savings for the District.

results

  • Individual well yields were assessed and optimized and pumping schedules were recommended to minimize well interference.
  • NHDES sustainable yield requirements were met and wells were appropriately permitted.
  • CAP conditions were satisfied.
  • The District addressed its water supply crisis, increased its total available well yield, and reduced water loss due to leakage without drilling a new well, thereby saving significant costs.