Water-bearing Zones in Fractured Bedrock Aquifers, Newark Basin ...

See examples of how water-bearing zones arecomposed of either single or multiple waterbearingfeaturesDemonstrate how the NJGS interprets, classifies,and catalogues information on water-bearingfeaturesHow we use this information to develop profilehydrogeological frameworks that reflectstratigraphic and structural controls on groundwaterflow, including measurable borehole crossflows

The identification and classification of water-bearingfeatures primarily relies upon the use of slim-linegeophysical tools to log the physical properties ofthe formation and the borehole fluids for the tappedinterval of the aquifer.Bedrock cores provide direct geological evidenceStraddle-packer tests provide measurements of thevolume yield of water from specific intervals (usually20’ sections)

Water-bearing features are identified and characterized primarily usingfour geophysical instruments:Fluid temperature and electrical conductivity (or resistivity) probe thatlogs changes in the fluid chemistry, usually associated with water-entryor exit points in the boreholeCaliper tool – measures the diameter of the borehole and indicatesintervals where the borehole is enlargedDigital Optical Televiewer (DOPTV)– provides direct visual inspection ofthe water-bearing feature and it’s 3D orientationHeat-pulse flow meter (HPFM) – measures the speed and direction offluids in a borehole

DOPTV also provides a record of the borehole geometry and is used tomeasured and categorize the various bedrock structures

The heat-pulse flow meter is one type of flow meter that provides a directmeasure of the fluid speed and direction of flow in the borehole

The HPFM is lowered into the borehole into a stationary position at specified depthswhere it is allowed to stabilize with respect to the fluid moving around and through it.A heat-pulse is fired to create a warmed fluid front that is carried to either the upper orlower thermistor by fluids moving in the borehole.Fluid speed is calculated from the arrivaltime of a heat pulse using a simplelogarithmic formulae programmed into thedata acquisition software.Fluid speed is multiplied by a boreholeconstant to obtain the volume flow atvarious depths in the borehole.

The volume and direction of water flow is measured and recorded at multipledepths and combined with other geophysical logs to create a profileinterpretation of the aquifer framework.

Bedrock aquifer studies where water-bearing features have been analyzed arecatalogued by the NJGS using a HTML based interface

Catalogued data are also compiled by aquifer, County and Municipality

Catalog entries include an index map showing the well locations on a base map,and an interactive list of catalog entries including geophysical log summaries,histogram and stereonet structural analyses summarizing feature orientations,and sometimes a profile interpretation of the hydrogeolgoical framework

Brunswick aquiferWatchungzoneupperredzonemiddlegrayzonelowerredzonePrimary aquifers in thedatabase include theStockton, Lockatong, andBrunswickThe Brunswick aquifer issubdivided into five zonesbased on the distributionof red gray, and blacklithologic colorslowergrayzoneLockatongaquiferStocktonaquiferThese zones are used forexamining the ability ofdifferent bedrock units tostore and transmit waterand to evaluate waterquality as a function ofstratigraphic controlPaul Olsen and Others, Lamont-Doherty Geological Observatory and Roy Schlische, Rutgers University

Water-bearing zones (WBZs) consist of a single or multiple water bearingfeatures (WBFs) that are effectively porous and hydraulically conductiveWBFs are either related to stratigraphic layering or fractures other thanlayeringWBFs related to stratigraphic layering are categorized as mechanical(fracture) partings between beds or compositional layers or layers havingeffective matrix porosityWBFs related to fracturing are categorized as either tectonic fractures or otherfractures stemming from all other processes including weathering,exhumation, erosion, unloading, etc.A third category of WBFs consists of intersections of layering and fractures

Layered WBFs related to mechanical (fracture) layering often occur at thecontacts between beds of varying grain sizePassaic conglomeratic sandstoneRidgewood Boro, Bergen CountyPassaic conglomerate and sandstoneBedminster Twp., Somerset CountyPassaic Fm. mudstone and shale,Hopewell Twp., Mercer County

Fracture partings along mechanical layers provide pathways for aquifer recharge

Layered WBFs also occur where networks of conductivepores occur in specific sedimentary bedsStained pores in Stockton sandstoneEwingville Twp., Mercer CountyPores in desiccated Passaic Fm. mudstoneand siltstone, Pennington Boro, Mercer CountyPores in Passaic Fm. sandstoneRidgewood Boro, Bergen County

This class of layered WBF includes gypsic soils where accumulations of secondaryauthegenic minerals have been dissolved and removedSCALE: 1/12\NJGS_Data_Catalog\Geology\Bedrock\Aquifer_investigations\Stony_Brook_Millstone_GWI\SB6_optvdata.jpg

Layered WBF identified as dissolution zones in gypsic soils have been mappedin the subsurface for distances of a couple of kilometersOBS-2SB3~ 10M SB6 ~ 10MSB1~2KMHopewell Borough, Mercer CountyStony Brook - Millstone Watershed Preserve, Hopewell Twp., Mercer County

Orange Mt. Basalt, West Orange Twp., Essex CountyLayered WBFs in basalt and diabase often relate toprimary compositional layering

Layered WBFs in diabase locally show mineral staining indicating flowLambertville Sill diabase, Lambertville, Hunterdon County

WBFs identified as tectonic fractures occur in both sedimentary and igneous rocks andcan be seen in outcrop, in rock cores, and in DOPTV recordsPassaic Fm. red beds, Somerset County, Bedminster Twp.

Water-bearing tectonic fractures in sedimentary bedrockStockton Fm. sandstonePrinceton Boro., Mercer CountyLockatong Fm. argilliteLawrence Twp., Mercer CountyPassaic Fm. MudstoneHopewell Twp., Hunterdon CountyPassaic Fm. conglomerateBedminster Twp., Somerset County

Water-bearing tectonic fractures in sedimentary bedrockPassaic Fm. Mudstone (-277’)Hopewell Boro., Mercer CountyStockton Fm. Sandstone (-198’)Ewing Twp., Mercer CountyPassaic Fm. mudstoneEast Amwell Twp., Hunterdon County

Lambertville Sill diabase, Lambertville, Hunterdon CountyWater-bearing tectonic fractures in diabase

Orange Mt. Basalt, West Orange Twp., Essex CountyWater-bearing tectonic fractures in basalt

Water-bearing conduits also occur along the intersections of layering and fracturesStockton Fm. SandstonePrinceton Borough, Mercer CountyLockatong Fm. argilliteRaritan Twp., Hunterdon CountyPassaic Fm. mudstoneEast Amwell Twp., Hunterdon County

The different types of WBFs are tabulated together with the range of values for thevarious sets of geophysical logs collected in each water well

A summary of the types of WBFs mapped in the various aquifers shows thatlayered WBFs are most common in sedimentary red beds (55%) whereas fracture-relatedWBFs are more common (65%) in sedimentary units composed of gray and black beds.An unexpected result stemming from this research is that half of the WBFs identified inbasalt and diabase stem from compositional layering.

Another significant result of this research is that non-pumping (ambient) cross flowsmeasured in boreholes can be directly the differential erosion of layered sedimentarystrata as illustrated in profile hydrogeological frameworksBorehole cross flows of opposite direction are locally found to occur in closely spaced wells

The direction and relative volume of cross flow directly relates to elevation differencesbetween inflow and outflow zones tapped by the different wells~ 0.1 to 2 GPM ~ 5 to 8 GPM

Conclusions:The NJGS uses caliper logs, FT&C/R, DOPTV, and a HPFMto identify and characterize water-bearing zones tapped by water wellsWBZs are composed of a single or multiple WBFs that are classifiedas stratigraphic layering, fractures other than layering, andintersections of layer and fracturesLayered WB features include fractured partings along stratigraphicbeds, igneous layering, and strata containing effective porosityincluding highly transmissive mudstone and siltstone related to theaccumulation and dissolution of secondary, authegenic, minerals suchas gypsumWB fractures are categorized as steeply dipping tectonic extensionfractures and other moderately to gently inclined fractures of variableorigins

Most conductive fractures were also once filled with secondaryauthegenic minerals that are now locally dissolved and removed in thesubsurfaceMost WB zones in ‘red’ sedimentary units are gently-dipping layeredfeatures (55% to 80%) whereas most most WB features occurring in‘gray’ sedimentary units are moderate- to steeply dipping fractures(55% to 75%), although all types of WBFs are found in all bedrockaquifers.Ambient cross flows measured in water wells tapping layered, semiconfinedbedrock aquifers stem from the differential erosion of thesedimentary strataAmbient flow volumes measured in water wells in the NB rangeupward from no measurable flow to ~ 15 gpm in the Stockton Fm,~ 8 gpm in the Brunswick aquifer, ~ 1 gpm in the Lockatong Fm., and~ 0.5 gpm in diabase and basalt.

HydrogeologicalFramework;Stratigraphic &Structural ControlsGypsic soils andangular unconformitiesin ‘rider blocks’

Drake and others, 1996, Bedrock geological map of northern New Jersey, US Geological Survey

NEHydrogeologicalFramework;Stratigraphic &Structural ControlsGypsic soils andangular unconformitiesNW

Hydrogeological Framework; Stratigraphic & Structural ControlsGypsic soils and angular unconformities