Delaware River Basin NAWQA Study
DELAWARE RIVER BASIN NAWQA WORKPLAN
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Workplans on Study Design—May 1999
The National study design for groundwater focuses on water-quality conditions in major aquifers, with emphasis on recently recharged groundwater associated with present and recent human activities, by using study-unit surveys, land-use studies, and flow-path studies. In study-unit surveys and land-use studies, groundwater samples are analyzed for major ions, nutrients, pesticides, volatile organic compounds, and trace elements. Study-unit surveys are used to assess the quality of water in the major aquifer systems of each study unit. Typically, 30 existing domestic wells in each of two to three aquifer subunits are randomly selected for sampling. Land-use studies focus on recently recharged shallow aquifer systems to evaluate the influences of both natural conditions and land-use practices on groundwater quality. Typically, about 30 new observation wells are randomly located within each land-use and aquifer type. Results of the one or two land-use studies typically performed are compared with results of the general study-unit survey to determine the effect of particular land uses on groundwater quality. In flow-path studies, water samples are collected from groups of clustered, multilevel observation wells located along a flow transect. The purpose of this study is to characterize spatial and temporal variations in water quality, examine natural processes and human activities that cause changes in water quality along the flow path, and evaluate whether interactions between ground and surface water affect water quality.
For the Delaware Basin an analysis of the 9 subunits of our groundwater strata was conducted to determine where Study-unit surveys would occur. Strata were prioritized based on water use, population, how well they are characterized, impacts on human health, and NST needs. Based on this prioritization 3 strata were selected for Study-unit surveys: clastic rocks in the Piedmont, clastic rocks in the Valley and Ridge, and unconsolidated sediments in the Glacial Valleys of the Appalachian Plateau and the Valley and Ridge Provinces. A fourth survey is also being considered either in the metamorphic rocks of the Piedmont or the unconsolidated sediments of the Coastal Plain.
An urban land-use survey would most likely be conducted in the Philadelphia region of the Piedmont. The clastic rocks of the Piedmont are currently slated for an intensive fixed urban site. Thus we will try to nest a Study-unit survey and an urban land use survey in this strata as well. Before this survey can be conducted issues regarding the need for ancillary well-completion data (depth, open interval, etc.) need to be resolved. A schedule of proposed groundwater work is provided in the attached table.
Three study-unit surveys (SUSs) are planned during the initial high intensity phase of the Delaware Study Unit (SU). The strata to be investigated as part of these SUSs include the clastic rocks of the Piedmont, the clastic rocks of the Valley and Ridge, and the unconsolidated glaciofluvial valley-fill deposits in the Appalachian Plateau and the Valley and Ridge Physiographic Provinces. A fourth SUS in the metamorphic rocks of the Piedmont may be conducted if time and funding allow. For all Study-unit surveys 30 domestic wells will be randomly selected throughout the strata using a grid-based sampling approach described by Scott (1990). Wells will be sampled for field parameters, nutrients, major ions, trace elements, pesticides, VOCs, DOC, radon, bacteria, and selected wells for CFCs. (Groundwater sampling)
Piedmont Clastic Rocks SUS
The SUS for the clastic rocks of the Piedmont will be conducted in the summer of 1999. The location of this strata is shown in the attached figure. The rocks of this strata are mostly shale, sandstone, and conglomerates. Groundwater flow is predominantly through fractures. Groundwater quality is affected by urban and agricultural land-use activities and the resource is heavily used for domestic and public water supply. This area has been designated by the Delaware River Basin Commission as a `Groundwater protected area' to try and prevent overuse. We will attempt to nest an urban intensive fixed site in this strata.
Valley and Ridge Clastic Rock SUS
The SUS for the Valley and Ridge clastic rocks will be conducted in the summer and early fall of 1999. The location of this strata is shown in the attached figure. The rocks of this strata are mostly shale, slate, and sandstone with some limestone. Groundwater flow is predominantly through fractures. Groundwater quality is affected by agricultural land-use activities and the resource is heavily used for domestic water supply. An agricultural fixed site is nested in this strata.
Appalachian Plateau and Valley and Ridge Glaciofluvial Valley-fill Deposits SUS
The SUS for the glaciofluvial valley-fill deposits of the Appalachian Plateau and Valley and Ridge will be conducted in the summer and early fall of 2000. The location of this strata is shown in the attached figure. The deposits of this strata are a heterogeneous assortment of bedded clay, silt, sand, and gravel. Groundwater flow is predominantly through the highly permeable and porous sand and gravel outwash deposits. Some of the coarser and thicker deposits comprise the most productive aquifers in the entire Delaware River Basin. The Valley-fill Deposits are heavily used for public and domestic water supply. A high percentage of users also have septic systems. Very little water-quality data is available for this resource that is affected by agriculture and developed land-use activities.
* indicates unreliable data
Land Use Survey
One land-use survey (LUS) is planned for the first intensive phase for the Delaware study unit. NAWQA typically requires new wells to be drilled for a LUS. However, given the nature of the hard rock geology in the area, we anticipate that we will need to use existing wells for our land use study. Drilling new wells would be cost prohibitive. Because this study is designed to sample recently recharged water we must be sure that domestic well water is of recent age (about 10 years or younger). As part of our Piedmont SUS we are age dating about half our samples to determine if domestic wells will be adequate for a LUS. If the age dates of these samples is not too old we will proceed with our plans for the LUS. The other piece of information needed for successful completion of a LUS is adequate ancillary data for these wells (i.e. well depth, casing depth, open interval, aquifer type, etc.). If we cannot find sufficient ancillary information on the wells then the LUS will be cancelled.
If an urban LUS is conducted in the clastic rocks of the Piedmont Physiographic Province it will be conducted in the Summer of 2001. The rocks of this strata are mostly shale, sandstone, and conglomerates. The water table is a subdued reflection of the topography and groundwater flow is predominantly through fractures. Thirty domestic wells will be randomly selected throughout the strata using a grid-based sampling approach. The wells will be sampled for parameters listed in the attached table. Selection and use of wells will be simplified in part by use of the PaDEP ambient and fixed-site network of wells.
This LUS is of high priority in the study unit because it is the strata having the most newly urbanized land use, with the greatest change from agriculture and forest to residential and commercial land use. The LUS will be nested within the Delaware SUS of the same strata. The data collected by the PaDEP will augment the data collected as part of this SUS, and vice versa. Additionally, the data will augment, and provide regional information on water-quality trends for, the adjacent LSUS NAWQA LUS in a similar strata. Finally, part of the area was a type-area study (Mesozoic Basins) in the Appalachian Valleys-Piedmont Regional Aquifer-Systems Analysis program.
Flow Path Survey
A flow path survey is not planned as part of our groundwater assessment. Drilling in hard rock areas would be prohibitively expensive and there is no guarantee of useful results. The unconsolidated sediments of the Coastal Plain are a likely location for such a study, however they have problems with industrial contamination and induced recharge along the estuary. Also, they have been studied as part of the LINJ Urban Comprehensive Study. For these reasons we felt it would be more useful to expand the scope of other groundwater activities. This would allow us to cover more of the basin and fill in gaps in current understanding.