How one municipality is engineering a solution with a reclaimed inactive site, tunnel blasting, and specialized drilling.
Frederick County has projected that the current public water demand of 6 million gallons a day for drinking water may double to almost 12 million gallons per day by 2035. This study has led the county to look at the Opequon Water Supply Plan (OWSP) and address facility needs as well as the water reserve to supplement the growing demand.
The overall project consists of replacing the existing water treatment plant with a newly designed facility to handle the larger volume of water and to create a reservoir to store that water. In addition to the current off stream storage such as the creeks and rivers, this project will utilize a nonactive rock quarry as a large reservoir. This rock quarry will store the off-stream flow and groundwater to be pumped from three intake shafts. The water will run from the shafts to the new treatment facility, Henry F. Sliwinski Water Treatment Plant just north, in the Stephenson area.
Quarry Intake Shaft Construction
Robert Royall Sr. of Royall Pump & Well Company out of Powhatan County, responded to the need for three, 23-inch large diameter wells to be drilled with an alignment accuracy down to five inches over 315 feet deep well. Construction began early summer of 2021 with shaft #2 that resulted in a 3 ½ inch drift. Shaft #1 was completed with a 3-inch drift and Shaft #3 was completed at the end of August with a 5 inch drift. Allowable drifts for each shaft were 38.7 inches over 315 feet in depth. The resulting tight construction generated 79% – 94% effective well diameters for the pump installation.
Each well began with a 13-inch pilot hole drilled to 315 feet. An alignment test is completed on the bore before moving onto the next hole. If the alignment is within the limits and ‘good’ then the bore hole is then filled with concrete to fill in voids and redrilled. The bore hole is then drilled with a 23-inch diameter bit to 53 feet while advancing steel casing and grouted to 50 feet. The rest of the bore hole is drilled with a 20 ½ inch diameter to a total depth of 323 feet.
While the drilling of the intake shafts is taking place, blasting and excavating for the connective tunnel is occurring 300 feet below. The intake shafts will be connected to the quarry by a nine feet wide diameter by 350 feet long tunnel from the bottom of the quarry to the bottom of the intake shafts. The water will then be transported from the intake shafts to the new water treatment plant.
July 2021 | VWWA Magazine | VAWaterWellAssociation.org