A Natural Resource Management Guide for the County of Morris A ...

Northwest The Territory
During the early eighties, having experienced drought conditions and wanting to plan for future dry spells,
the NJGS studied portions of the Pequannock and Upper Rockaway River Valley (upstream from Denville)
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watersheds. This area contains major water supplies serving Newark and Jersey City. Drainage from the
Pequannock River flows to the Charlotteburg Reservoir, from which water is conveyed to the Newark Water
Department. Downstream from Denville the Rockaway River flows to the Jersey City Reservoir at Boonton.
The local Precambrian gneisses and Paleozoic sedimentary rocks had been considered to be generally poor
water suppliers. Therefore, attention was focussed on the unconsolidated sands and gravel aquifers of the
buried valleys. Recognized as likely productive ground water sources, these aquifers were examined for
suitability as augmentation to surface water supply.
Buried valleys occurring in the Pequannock and Rockaway River Valleys are filled with glacial deposits
including tills, stratified sands and gravels, silts, and clays. Till, without silt or clay present, allows adequate
water supply for domestic use. However when fine sands, silts, clays, muck soils, and nonstratified till are
present, their lack of permeability takes them out of production well contention. Their porosity, on the other
hand, suits them well for slow and steady aquifer recharge.
Highly productive water-bearing zones were usually found in the deepest portion of filled valleys. These were
normally close to or directly beneath streams, lakes, wetlands or flood plains. As with the Central Passaic
River Basin, there were variations within the valleys resulting in differences in water production.
Within the study area, the floor of the Rockaway and its tributary valleys, are relatively flat in relief, and are
covered by very permeable granular soils. These conditions were conducive to excellent aquifer recharge
directly by rainfall. Additionally, runoff from the surrounding watershed area was found to contribute
considerable recharge both from surface flow and movement through fractures in the bedrock.
Although valuable in their water bearing capabilities, these valley fill aquifers also have their limitations:
size and depth, with bedrock walls restricting long-term yields; areas overlain by impermeable fine sand, silt,
and clay; medium-to-coarse grained sands and gravels with a fine-grained matrix impeding the flow of water;
unconfined or semi-confined conditions suggesting a greater vulnerability to contamination; and confined
conditions conducive to inter-valley impacts from pumping, due to connectivity.
Finally, the study concluded that ground water diversion for flow
augmentation is a consumptive use of groundwater and thus only suitable
as a temporary solution. The heavy reliance on the surface water supplies
necessitates careful assessment and consideration of historic, current, and
future land use and their respective impacts on ground water quality and
quantity in municipal long range planning.
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Ground Water