Category: Drinking Water
Check out this CNN video about the toll of the 2011 East Africa Drought
| May 5, 2013 | Posted by karmadsen under blog, Drinking Water, Drought, Videos |
Children were especially at risk during the the 2011 East Africa drought.
The National Groundwater Association’s New “Water Use Calculator” App
| March 29, 2013 | Posted by karmadsen under blog, Drinking Water |
The National Groundwater Association has a new Water Use Calculator, a free App for mobile devices available in the iTunes store. Pretty Awesome!
Biosand filters implemented in Socorro, Guatemala by Nora.jeanine530 (via Wikimedia Commons)
Conceptual Models of Saltwater Intrusion in Fractured Bedrock
| March 24, 2013 | Posted by karmadsen under blog, Conceptual Models, Drinking Water, Geology, Groundwater Contamination, Groundwater Pumping, Saltwater |
(Originally published on February 26, 2013)
Creating a conceptual model of a saltwater interface is complicated, even in simple sand and gravel aquifers. However, in fractured bedrock, understanding saltwater intrusion can get a lot more complicated. In these systems, saltwater intrusion is highly erratic and unpredictable based on preferential pathways, pump locations, and extraction rates.
Honeymoon Island State Park, Pinellas County, FL by Riverbanks Outdoor Store (Wikimedia Commons)
Honeymoon Island State Park, Pinellas County, FL by Riverbanks Outdoor Store (Wikimedia Commons)
In 2005, the USGS published a study of the highly heterogeneous aquifer providing water to the Eldridge-Wilde well field in West-Central Florida. Salinity has increased over time in the well field. Not only does the aquifer include layered rock aquifers with various degrees of fracture and primary porosity, but also, the mixing regime includes three different types of water: freshwater, saltwater (of ocean origin), and deepwater (salty water from deep in the aquifer).
In order to construct a conceptual model of the system, data was compiled from a variety of sources, including seismic-reflection surveys, and borehole geophysical surveys. Using these methods, the researchers were able to locate void-space connections within the rock matrix, and identify which rock units were associated with saltwater intrusion. These types of methods will be increasingly important in the future for managing well fields in fractured bedrock and for the placing of new wells.
Tihansky, A.B. (2005). Effects of Aquifer Heterogeneity on Ground-Water Flow and Chloride Concentrations, West-Central Florida. U.S. Geological Survey. Scientific Investigations Report 2004-5268.
Check out this video from CNN: Doc Hendley helps Syrian refugees access clean drinking water
| March 24, 2013 | Posted by karmadsen under blog, Drinking Water, Videos |
Saltwater Intrusion in the US – Part 2: Groundwater Models of NJ
| January 6, 2013 | Posted by karmadsen under blog, Drinking Water, Environmentalism, Groundwater and Surface Water, Groundwater Modeling, Groundwater Modeling Software, Groundwater Pumping, Models in Action |
This blog is part 2 of the saltwater intrusion in the US series. In this post, I will discuss two examples of ways that modeling has been used to study saltwater intrusion in Cape May County, NJ.
Cape May Water Budget Model
In 2002, the US Geological Survey and the New Jersey Department of Environmental Protection published an assessment of the water supply of Cape May County New Jersey, which included a water budget model of the significant aquifers in the region (US Department of the Interior, U.S. Geological Survey, 2002).
The population of the area exploded between 1900 and 2000, and by the early of the 21th Century the coastal neighborhoods on Cape May have become some of the highest priced real estate in the State of New Jersey. This growth has resulted in an increasingly unsustainable demand placed on the local aquifers and cones of depression have formed beneath densely populated areas, drawing the water table down tens of feet below sea level.
The region faces other challenges as well. The development of wetlands and canal modification has lowered the elevation of the water table in the surficial aquifer. Furthermore, precipitation that falls on the extensive salt water wetlands across the peninsula does not recharge the fresh water aquifer.
Although numerical models were not run as part of this assessment, previous groundwater flow models were reviewed to aid in the development of a groundwater flow interpretation. To calculate a detailed water budget for each of the significant aquifers, the researchers reviewed “precipitation, areal distribution of land types, areal distribution of aquifers, surface water discharge, calculations of evapotranspiration, estimated and measured flow into and out of the aquifers, and reported and estimated ground-water withdrawals.” They calculated flow direction from groundwater contour maps and used Darcy’s Law to estimate groundwater velocity.
During the course of their study they found that water levels had remained relatively constant in the Holly Beach water-bearing zone since the 1950s. However, significant cones of depression were found in most of the other aquifers, including the estuarine sand aquifer, the Cohansey aquifer, the Rio Grand water-bearing zone, and the Atlantic City 800-foot sand aquifer. Many of these cones of depression are between 10 and 20 feet below sea level. In the Atlantic City 800-foot sand aquifer, cones of depression are over 60 feet below sea level.
Some of the impacts of these declines are mtigated by water flowing from the fresh surficial aquifer into the lower aquifers. However, 10 public supply-wells, 100 domestic-supply wells, and 3 industrial-supply wells were decommissioned due to salt water intrusion between 1960 and 1990 (US Department of the Interior, U.S. Geological Survey, 2002).
A parent American Oystercatcher with chicks in Atlantic coast, New Jersey, USA. By Bear Golden Retriever (via Wikimedia Commons)
Calculated the velocity of the freshwater/saltwater interface
In 1996, the USGS and the New Jersey Department of Environmental Protection calculated the speed that the freshwater/saltwater interface was moving inland (Voronin et al, 1996). Using coupled regional and subregional groundwater flow models, the researchers estimated that the travel time needed for the interface to reach the public supply wells was on the order of hundreds of years. The modeling effort was based on particle tracking and estimating the rate of flow from regions of high salinity to the public supply well. The work was based on 1991 withdrawal rates.
The researchers embedded a subregional MODFLOW model into a larger regional model. The use of MODFLOW in this manner was considered valid, because it was only used to model freshwater flow in the Atlantic City 800-foot sand aquifer. The code for the regional model was developed as part of a separate USGS effort to simulate groundwater flow throughout the larger coastal plain aquifer system (Martin, 1998). The regional model, which was also used to simulate the freshwater/saltwater interface, accounted for differences in density between freshwater and saltwater. Both models were quasi-three-dimensional finite-difference codes.
The researchers stated that they had assumed homogeneous hydraulic conductivity throughout the study area and that zones of higher conductivity might increase travel time (Voronin et al, 1996).
Martin, M. (1998). Ground-water flow in the New Jersey Coastal Plain: U.S. Geological Survey Professional Paper 1404-H, 146 p.
US Department of the Interior, U.S. Geological Survey. (2002). Hydrogeologic Framework, Availability of Water Supplies, and Saltwater Intrusion, Cape May County, New Jersey. Water-Resources Investigations Report 01-4246. Available at: http://pubs.usgs.gov/wri/wri014246/pdf/wrir01-4246.pdf.
Voronin, L.M., Spitz, F.J., McAuley, S.D. (1996). Evaluation of Saltwater Intrusion and Travel Time in the Atlantic City 800-Foot Sand, Cape May County, New Jersey, 1992, by Use of a Coupled-Model Approach and Flow-Path Analysis. U.S. Geological Survey. Water-Resources Investigations Report 95-4280. Prepared in Cooperation with the New Jersey Department of Environmental Protection. Available at: http://pubs.usgs.gov/wri/1995/4280/report.pdf.
Saltwater Intrusion in the US – Part 1: Southeaster NJ
Saltwater Intrusion in the US – Part 1: Southeaster NJ
| January 3, 2013 | Posted by karmadsen under blog, Drinking Water, Drought, Environmentalism, Groundwater and Surface Water, Groundwater Pumping, Groundwater Regulation |
This post is the first of a multi-post series on salt water intrusion in the United States, which will focus on 1.) regions of the United States where salt water intrusion threatens the drinking water supply, 2.) models of salt water intrusion, and 3.) the affects of climate change on salt water intrusion.
Today, I will look at problems associated with salt water intrusion in Southeastern New Jersey. Salt water intrusion is a major danger across the lower part of the state, where much of the drinking water comes from the Kirkwood-Cohansey aquifer, a massive reservoir of high-quality fresh water with a shallow water table and high conductivity. It extends westerly from the coast, and pinches out near the Delaware River (Montgomery & Juelg, 2004). During the 2002 drought, record low water levels were observed in the Kirkwood-Cohansey aquifer (New Jersey Department of Environmental Protection, 2003).
Population growth is another threat to the water supply. The population is expected to increase significantly in some of the most threatened areas, including Atlantic County and the Cape May watershed.
New Jersey Pine Barrens by Jim Lukach (via Wikimedia Commons)
In response to the 2002 drought and water supply emergency, a New Jersey Executive Order asked the Department of Environmental Protection to review the security of the water supply in Atlantic County. As part of this review, the DEP calculated the safe extraction rate that could be drawn without inducing salt water intrusion or damage stream ecosystems. The studied aquifers included the Kirkwood-Cohansey aquifer, the underlying Atlantic City aquifer, and local sand aquifers; All of these aquifers are somewhat hydraulically connected. The DEP determined that, due to population growth, the safe rate of extraction would match water demand by 2050 (New Jersey Department of Environmental Protection, 2003).
The Cape May Peninsula at the lower tip of New Jersey is surrounded by the ocean on three sides, and its population is expected to increase by 68% by 2040. The highest point on the swampy peninsula is only 54 feet above sea level and while the population depends on groundwater for water supply, the water will have to be tightly managed in the coming decades to avoid salt water intrusion (State of New Jersey, 2011).
Salt water intrusion not only threatens drinking water supply, it also threatens the local ecosystems. The Pine Barrens is a 1 million acre area of undeveloped forest along the southern coastal plain, and is considered one of the most important ecological resources in New Jersey. The local Kirkwood-Cohansey aquifer supplies fresh water to streams and wetlands, and the unique characteristics of the aquifer are responsible for the complex ecosystem present in the Pine Barrens. Many of its species exist within very narrow environmental conditions, and any change to the aquifer threatens their continued existence (Montgomery & Juelg, 2004).
A pine barrens tree frog by R. Tuck (via Wikimedia Commons)
Saltwater Intrusion in the US – Part 2: Groundwater Models of NJ
New Jersey Department of Environmental Protection. (2003). Status of the Water Supply of Southeatern New Jersey. Executive Summary. State of New Jersey. Land Use Management. Available at: http://www.nj.gov/dep/watershedmgt/DOCS/pdfs/SEWSexecsum.pdf
State of New Jersey. (2011). State Hazard Mitigation Plan. Appendix E Background of the State of New Jersey: Watershed Management Area 16 – Cape May. New Jersey Office of Emergency Management. Available at: http://www.state.nj.us/njoem/programs/pdf/mitigation2012/mit2012_appendixe.pdf
Montgomery, C. & Juelg, R. (2004). The Pine Barrens: Up Close & Natural. A Guide for Teachers. The Pinelands Preservation Alliance. Available at: http://www.pinelandsalliance.org/downloads/pinelandsalliance_665.pdf
1.)
CNN: Reports on water contamination in a VA hospital
| December 21, 2012 | Posted by karmadsen under blog, Drinking Water, Videos |
This VA hospital’s water distribution system is contaminated with Legionella, a dangerous bacteria.
The math behind the SWI – MODFLOW package, Part 3
| December 7, 2012 | Posted by karmadsen under blog, Drinking Water, Groundwater and Surface Water, Groundwater Modeling, Groundwater Modeling Software |
In SWI, the continuity of flow equation can be expressed like this:
∂i[σ1∂ih1] = S(∂h1/∂t) – ɣ +R1 (Continuity of total flow in the aquifer)
δp∂i[σp∂iζp]=n(∂ζp/∂t) – ɣp +Rp (Continuity of flow below surface p)
- σn =comprehensive transmissivity below surface n
- hn = groundwater head
- S = storativity
- t = time
- ɣ = a source term
- R coefficients = pseudo-source terms. Their value depends on whether flow is stratified or variable density
- δn = the measure of the variation of the density between zones
- ζp = the elevation of surface n
From thee user’s manual, “The groundwater is discretized vertically into N zones. Zones and surfaces are numbered from the top down; zone n is bounded on top by surface n.”
Bakker M. 2005. The Sea Water Intrusion (SWI) Package Manual Part I. Theory, User Manual, and Examples. Version 1.2. Department of Biological and Agricultural Engineering University of Georgia.
Southern Ocean by LeeAnne Adams (wikimedia commons)
The math behind the SWI – MODFLOW package, Part 1
| December 4, 2012 | Posted by karmadsen under blog, Drinking Water, Groundwater and Surface Water, Groundwater Modeling, Groundwater Modeling Software |
The SWI package for MODFLOW allows for the creation of salt water interface models in MODFLOW. It’s main advantage over SEAWAT is that it may be easier for MODFLOW users to apply. Because it is a package within MOFLOW, the only additional requirement is the exception of the SWI input file. Indeed, an existing model can be modified with the addition of a single file. The formula in SEAWAT is based on the concept of equivalent fresh water, which I have discussed before here. By contrast, SWI is based on a non-dispersive, continuity-of-flow method to simulate multiple-density iso-surfaces (Langevin et al 2006).
To modify an existing MODFLOW model into a SWI model, the only requirements are that a SWI input file be developed and specified in the NAME file, along with an output file for the final density distribution.
SWI relies on several simplifying assumptions, including:
- The Dupuit approximation is adopted, which means that there is no resistance to flow in the vertical direction.
- Dispersion and diffusion are ignored.
- More dense water (i.e. salt water) can never be present above less dense water.
The SWI file describes the initial density distribution in the aquifer and the parameters needed to model the distribution as it evolves. Each aquifer is split vertically into zones bounded by curved planes. These zones are used to define density variation across the aquifer (Bakker 2005).
Bakker M. 2005. The Sea Water Intrusion (SWI) Package Manual Part I. Theory, User Manual, and Examples. Version 1.2. Department of Biological and Agricultural Engineering University of Georgia.
Langevin CD & Guo W. 2006. MODFLOW/MT3DMS–Based Simulation of Variable-Density Ground Water Flow and Transport. Ground Water. 44(3): 339-351.
Beach, Saint John NB by Cusack5239 (wikimedia commons)
Another hurricane threat: dirty water
| November 10, 2012 | Posted by karmadsen under blog, Drinking Water, Environmentalism, Groundwater in the News, Storm Water |
CNN discusses some of the water contamination dangers associated hurricane flooding.