Initial Yield to Depth Relation for Water Wells Drilled into Crystalline Bedrock—Pinardville Quadrangle, New Hampshire

Abstract

A model is proposed to explain the statistical relations between the mean initial water well yields from eight time increments from 1984 to 1998 for wells drilled into the crystalline bedrock aquifer system in the Pinardville area of southern New Hampshire and the type of bedrock, mean well depth, and mean well elevation. Statistical analyses show that the mean total yield of drilling increments is positively correlated with mean total well depth and mean well elevation. In addition, the mean total well yield varies with rock type from a minimum of 46.9 L/min (12.4 gpm) in the Damon Pond granite to a maximum of 74.5 L/min (19.7 gpm) in the Permian pegmatite and granite unit. Across the eight drilling increments that comprise 211 wells each, the percentages of very low-yield wells (1.9 L/min [0.5 gpm] or less) and high-yield wells (151.4 L/min [40 gpm] or more) increased, and those of intermediate-yield wells decreased. As housing development progressed during the 1984 to 1998 interval, the mean depth of the wells and their elevations increased, and the mix of percentages of the bedrock types drilled changed markedly. The proposed model uses a feed-forward mechanism to explain the interaction between the increasing mean elevation, mean well depth, and percentages of very low-yielding wells and the mean well yield. The increasing percentages of very low-yielding wells through time and the economics of the housing market may control the system that forces the mean well depths, percentages of high-yield wells, and mean well yields to increase. The reason for the increasing percentages of very low-yield wells is uncertain, but the explanation is believed to involve the complex structural geology and tectonic history of the Pinardville quadrangle.

A generalized 3-D geological and hydrogeological conceptual model of granite aquifers controlled by single or multiphase weathering

“…In highly foliated rocks (i.e., gneisses or schists) the orientation of the fissures can be also controlled by the rock structure (Pye, 1986;Sharma and Rajamani, 2000).The intensification of this horizontal fissuring at the top of the layer constitutes the overlying laminated layer. This layer mainly assumes the transmissive function of the global composite aquifer and is drawn from most of the wells drilled in hard-rock areas (Uhl and Sharma, 1978;White et al, 1988;Acworth, 1987;Houston and Lewis, 1988;Barker et al, 1992;BrizKishore, 1993;Drew et al, 2001;Gustafson and Krásný, 1994). However, the covering saprolite layer may have been partially or totally eroded, or unsaturated.…”

Introduction to the hydrogeology of hard rock

“…While Drew et al (2001) about 90 to 120 m and well yield increases up to approximately 130 m depth. That is, depth of drilling (DoD) is more where the yield from the top weathered zone is poor.…”

“…However, in general, the yield of shallow wells from weathered zone is around 1 lps (Clark, 1985) and mostly caters to local needs. In New Hampshire granitic terrain 2.5 lps well yield is considered high (Drew et al, 2001, Moore et al, 2002. Wells with 1 to 5 lps discharge can be considered as moderate-yielding and more than 5 lps as high-yielding.…”

Reply to the Comment on “Identification of the subsurface sulfide bodies responsible for acidity in Río Tinto source water, Spain” (Earth Planet. Sci. Lett. 391 (2014) 36–41)

“…In spite of the fact that productive water wells in crystalline rocks usually reach the maximum yield at shallower depths (up to ∼50 m), this does not mean that there is no groundwater at deeper depths, and many examples of the occurrence of groundwater in fractured aquifers at depths ranging from 50 to more than 100 m exist (e.g. Chandra et al, 2012;Drew et al, 2001).…”