New Jersey Water Science Center
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Program to Maintain and Update Groundwater Models to Evaluate Continued WaterSupply Development in New Jersey
Project Title:NJ150 Program to Maintain and Update Groundwater Models to Evaluate Continued WaterSupply Development in New Jersey
Figure 1.—Location of the archived groundwater flow models constructed in the New Jersey Water Science Center. (click Image for larger version)
Through the Model Maintenance program, the U.S. Geological Survey (USGS), in cooperation with the NJ Department of Environmental Protection (NJDEP), is making available, to the public, model-input data for groundwater flow models that have been developed by the New Jersey Water Science Center (NJWSC). Since 1984, 25 models of groundwater flow in parts of New Jersey have been developed and are documented by USGS publications. Of these, 18 models are currently archived--13 of these have been developed in cooperation with NJDEP. Input data for 16 of the 18 models is currently available for download from the USGS NJWSC Model Maintenance website and eventually data for all 18 archived models will be available. Models range in size from 4.4 mi2 for the Picatinny model to 95,000 mi2 for the Regional RASA (Regional Aquifer-System Analysis) model (fig. 1). The models were developed to provide specific information on either a local or regional scale and cover diverse geology. In recent years, water management concerns have shifted from restricting withdrawals in deeper confined aquifers to determining the impact of withdrawals in areas of increasing use in unconfined aquifers or the lower producing aquifers. Water management concerns of the effects of withdrawals on the surface-water system have become more common. The use of existing models developed in the USGS NJWSC allows us to serve New Jersey water managers by providing hydrologic analysis in an efficient manner.
As water-supply development concerns evolve in the State of New Jersey, there is a need to revisit and update the groundwater flow models developed as part of previous water-resource investigations. New advanced analytical techniques may improve the analysis of previous studies, but the costs of building new models may be large. Water-resource planners benefit from the use of existing groundwater flow models to evaluate new water-use strategies.
The model maintenance program was started in 1995 to maintain existing groundwater flow models, use standardized procedures to archive the models, update models with recent data and analytical techniques, and re-evaluate the data network design of each model. This program provides water-resource planners and managers with the benefit of multiple uses of models in an efficient manner and at reduced costs.
EVALUATION OF WATER-SUPPLY ISSUES
Figure 2.—Simulated sources of water to the inactive Deptford Township withdrawal wells in the additional-withdrawal scenario. (click image for larger version)
The NJ Coastal Plain RASA (Regional Aquifer System Analysis) model (in this document referred to simply as “the RASA model”) is one of the most widely used models by hydrologists in the NJWSC. This model was developed as part of the RASA program, which was started in 1978 after a congressional mandate to develop quantitative appraisals of the major groundwater systems of the United States (Martin, 1998). In the 20 years since the RASA model was developed, it has been updated and modified to meet the needs of projects within the NJWSC and water managers. The model was updated in the late 1990’s to include water use from 1981 through 1998, rediscritized to a finer cell size, and modified to include spatially variable recharge rates based on recent studies (Voronin, 2004).
Figure 3.—Simulated potentiometric surfaces and pathlines from the 250-mg/L isochlor using the Cape May Atlantic City 800-foot sand model, (b) travel time of particles from the 250-milligram-per-liter isochlor to production wells, Atlantic City 800-foot sand, New Jersey. (click image for larger version)
Scenarios run using the RASA model also address concerns with increased withdrawals in the Potomac-Raritan-Magothy aquifer related to new housing developments in Woolwich Township, Gloucester County (Lois M. Voronin, U.S. Geological Survey, oral commun., 2006). The Picatinny model was used to provide information regarding a potential public-supply well installation near Picatinny Arsenal within the model boundary. The RASA model in conjunction with two other models—the Cape May-Atlantic County and New Jersey Coastal Plain Sharp models--address questions posed regarding eight new allocation permits within the 800-ft Sand Aquifer in Atlantic County. These models were used to simulate changes in water levels, identify the source supplying the increased groundwater flow, and quantify the effects on saltwater movement towards production wells in Cape May County as a result of the proposed increased withdrawals at proposed or existing wells (Pope, 2006). Simulated potentiometric surfaces and pathlines from the 250-milligram per liter isochlor under different withdrawal conditions using the Cape May Atlantic City model is shown in figure 3. The table indicates the times of travel for particles from the 250-milligram per liter isochlor to production wells tapping the Atlantic City 800-ft Sand.
The RASA model also was used to provide information to the NJDEP for the Water Supply Master Plan. Scenarios were run that evaluated the effects of increased withdrawals on water levels and water budgets within planning areas based on future population estimates (Gordon, 2007). Water managers incorporated this data into the State planning document. Simulations of groundwater flow from models provide valuable information that has helped shape the decisions of the water managers.
The NJDEP Well Head Protection program provides a regulatory framework for the evaluation and control of potential sources of contamination of public-supply wells. A critical element of such evaluations is the delineation of contributing areas for all public and non-community water supply wells in New Jersey. NJDEP allows for contributing areas to be delineated using a groundwater flow model in complex hydrogeologic settings (Pope and Watt, 2005). A version of the archived groundwater flow model developed by the USGS in the Pennsauken Township area, Camden County was used to delineate contributing areas to the Puchack well field. The contributing areas to this major well field, shown in figure 4, was determined by using particle-tracking analysis that calculates the travel times of water to wells (Pope and Watt, 2005). The Lamington model, in southwestern Morris County, also was used to determine groundwater flow patterns and areas contributing recharge to wells and streams under different withdrawal conditions for Randolph Township (Nicholson and Watt, 1998), as well as, for Morris County Municipal Utilities Authorities.
Figure 4. Simulated contributing area to individual wells in the Puchack well field, Pennsauken Township and vicinity, New Jersey. (click image for larger version)
Other models have been used to address different hydrologic issues such as saltwater intrusion or base-flow depletion. The Camden model was used to evaluate the vulnerability of production wells in the Potomac-Raritan-Magothy aquifer to saltwater intrusion from the Delaware River in Camden, Salem, and Gloucester Counties under different drought conditions (Navoy and others, 2005). Particle tracking was used to delineate the contributing area for the production wells and determine time-of-travel for saltwater intrusion. Several of the archived models describe and characterize the unconfined aquifer system and its interaction with the surface-water system in response to increased withdrawals. The Upper Maurice River basin model and Toms River-Metedeconk River model are two examples. Both of these models evaluated predevelopment, recent, and future withdrawal conditions and their relation to base-flow depletion.
SUPPORT OF THE NEW JERSEY WATER SCIENCE CENTER PROJECTS
Figure 5.—Example of nested models where larger more regional models provide boundary flows to smaller more local models. (click image for larger version)
The Model Maintenance Program also supports work done within the NJWSC. Existing groundwater flow models provide boundary flows for smaller more local models. For example, the Regional RASA model, which covers the entire North Atlantic Coastal Plain from Long Island, New York to South Carolina, provided the boundary flows for the RASA model. The Camden model, which is nested within the RASA model, uses boundary flows calculated using the RASA model. The Camden model is used to calculate boundary flows for the Pennsauken model located within the Camden model area (fig. 5). Larger regional models provide simulated groundwater flow to and from streams or between aquifer layers. This data is used for budget analyses in projects such as the surficial-aquifer studies. The models also are used in the quality assurance check of water-use data maintained by the NJWSC.
MODIFYING AND UPDATING MODELS
Figure 6.—Difference between model computed streamflow depletion and total monthly groundwater withdrawals from valley-fill aquifers, and storage inflow and outflow, upper Rockaway River drainage basin, new jersey. (click image for larger version)
Figure 7.—Trade-off curves in Upper and Middle Potomic-Raritan-Magothy aquifers for current 92003) and regularly spaced well locations in Critical Area 1, east-central New Jersey. (click image for larger version)
A continuing effort for this program includes the prioritization of models that need to be revised and updated to meet the ongoing needs of the NJDEP and the general public. Many models that have been completed have had additional uses and refinement besides simulation of different water-supply scenarios. The model of the upper Rockaway River Basin was developed as a steady-state model but later modified to a transient model with the capabilities to define time monthly. This was done to provide the model the capabilities to quantify the effects of variations of rates of withdrawals on the flow system of the valley-fill aquifer system and on the groundwater discharge to the Rockaway River especially during periods of low flow and drought. Figure 6 illustrates that groundwater withdrawals in the valley-fill aquifer are approximately equal to the decrease in groundwater discharge to the Rockaway River (Gordon, 2002). Seasonal changes in withdrawals and streamflow depletion and its effect on storage inflow and storage outflow over the period of the simulation also are shown in figure 6. The Lamington model has been updated to MODFLOW2000 and withdrawals have been updated to 2003. These updates provide the capabilities of addressing recent issues in development and their effect on the groundwater flow system. The RASA model continues to be updated and refined and new techniques and model codes utilized. An optimization module, GWM, which is part of the MODFLOW program, was used to evaluate how and where increased withdrawals would affect water levels within Critical Area 1 (Spitz and others, 2007). Figure 7 is an example of a trade-off curve produced to aid in quantifying the effects on varying groundwater constraints in the optimization analysis. The graph shows that as more drawdown is allowed in the system, the amount of available withdrawal increases. The curves on the graph are for two difference well configurations—the current well locations and regularly spaced well locations. Studies such as this one provide water managers with information needed to optimize withdrawals, including the relationship between the amount of withdrawals to the amount of expected drawdown.
Figure 8.—New Jersey RASA model outline and 2003 synoptic water levels in Piney Point aquifer which illustrates the need to expand the model grid further into Delaware. (click image for larger version)
The potentiometric surface of the Piney Point aquifer and the large cone of depression in Delaware resulting from increased withdrawals there is shown in figure 8. Current work on the RASA model includes extending the model into Delaware to better represent the relationship between the groundwater-flow systems in Delaware and southern New Jersey and the effects of withdrawals on regional water levels. More model layers representing aquifers and confining units are being added to refine the hydrogeologic framework. Simulated withdrawals are continually being updated with the most current water-use data collected by the NJDEP.
Figure 9.—Englishtown aquifer system (a) potentiometric surfaces along section A-A', 1988-2003; (b) withdrawals in the developed zone of Critical Area 1, 1980-2003 in Critical Area 1, east-central New Jersey, 1988-2003. (click image for larger version)
Future work on the RASA model will include further rediscritization of model parameters, adding particle-tracking capabilities, and additional calibration to 2008 synoptic water-level measurements.The USGS, in cooperation with the NJDEP, has documented the water levels in the confined aquifers of the New Jersey Coastal Plain every five years since 1978. USGS personnel measure water levels in approximately 750 wells over a 4- to 5-month period in the fall to assess the status of the regional water levels. Results of these studies have been used by NJDEP to develop withdrawal regulations and to establish the Water-Supply Critical Areas. These water-level measurements also are a necessary part in calibration of the RASA model. Many of the groundwater models use this data to determine the relation between groundwater withdrawals and water levels. Figure 9 shows potentiometric water levels through a cross section of Critical Area 1 collected during the synoptics in 1988, 1993, 1998, and 2003 and the corresponding graph of water use.
MODEL MAINTENANCE WEBSITE
Figure 10.—Example of mini-summary page for each model on the New Jersey Water Science Center web page. (click image for larger version)
Web pages that document the Model Maintenance program and the models that have been completed in New Jersey since 1984 have been added to the NJWSC website. Twenty-five models have been completed since 1984; of these, 18 models are currently archived. Input data for 16 of these models is currently available for download from the USGS NJWSC website and eventually data for all 18 archived models will be available. These Web pages serve to standardize the archiving process and documentation of models for the release to the public. Information on the Model Maintenance program, as well as, user and computer requirements needed to run the models are listed. The Web pages provided a summary sheet of each archived model—model code used and year, type of simulations available, size of model, minimum grid spacing, and grid dimensions are listed (fig. 10). The report abstract is also available and a link to the USGS publication warehouse. Users can request model-input data for each of the models available.
Seven non-archived models are listed on the Web pages. These models typically are older models with little to no computer files or models with a limited extent. For these models, a link to the published report on the USGS publication warehouse website is available.
Since the Model Maintenance program was started, the existing models in the NJWSC have been archived to a central location and have been made available to the public. Care has been taken to standardize each model and to update and revise models when needed. Many of the models have been used to address issues regarding a variety of public supply issues throughout the State. Periodically, the models are evaluated to see what updates or revisions might more fully benefit water managers. This way the models that were developed for a single project may be used multiple times providing manager with efficient use of the models at reduced cost. As more models are completed in the NJWSC, the standardized method of archiving and releasing these models to the public makes them a valuable resource. The continuing use of the models provides important data in guiding future water-supply issues.
Gordon, A.D., 2002, Simulation of transient groundwater flow in the valley-fill aquifers of the upper Rockaway River basin, Morris County, New Jersey: U.S. Geological Survey Water-Resources Investigations Report 01-4174, 47 p.
Martin, Mary, 1998, Groundwater flow in the New Jersey Coastal Plain: U.S. Geological Survey Professional Paper 1404-H, 146 p.
Navoy, A.S., Voronin, L.M., and Edward Modica, 2005, Vulnerability of production wells in the Potomac-Raritan-Magothy aquifer system to saltwater intrusion from the Delaware River in Camden, Gloucester, and Salem Counties, New Jersey: Scientific Investigations Report 2004-5096, 35 p.
Nicholson, R.S. and Watt, M.K., 1998, Simulation of groundwater flow patterns and areas contributing recharge to streams and water-supply wells in a valley-fill and carbonate-rock aquifer system, southwestern Morris County, New Jersey: U.S. Geological Survey Water-Resources Investigations Report 97-4216, 40 p.
Pope, D.A., 2006, Simulation of proposed increases in groundwater withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain: U.S. Geological Survey Scientific Investigations Report 2006-5114, 17 p.
Pope, D.A. and Watt, M.K., 2005, Use of a groundwater flow model to delineate contributing areas to the Puchack well field, Pennsauken Township and vicinity, Camden County, New Jersey: Scientific Investigations Report 2004-5101, 47 p.
Spitz, F.J., Watt, M.K., dePaul, V.T., 2007, Recovery of groundwater levels from 1988 to 2003 and analysis of potential water-supply management options in Critical Area 1, east-central New Jersey: U.S. Geological Survey Scientific Investigations Report 2007-5193, xx p.
Voronin, L.M., 2003, Documentation of revision to the Regional Aquifer System Analysis Model of the New Jersey Coastal Plain: U.S. Geological Survey Water-Resources Investigations Report 03-4268,
Watt, M.K., 2006, Sources of water to wells in updip areas of the Wenonah-Mount Laurel aquifer, Gloucester and Camden Counties, New Jersey: Scientific Investigations Report 2005-5250, 34 p.
Zapecza, O.S., 1989, Hydrogeologic framework of the New Jersey Coastal Plain: U.S. Geological Survey Professional Paper 1404-B, 49 p., 24 pl.
FOR MORE INFORMATION
For more information about this study, please contact:
Mary Chepiga, , (609) 771-3955