See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/225649123 Saltwater intrusion in coastal regions of North America Article in Hydrogeology Journal · February 2010 DOI: 10.1007/s10040-009-0514-3 CITATIONS READS 162 1,179 2 authors, including: Paul M. Barlow United States Geological Survey 29 PUBLICATIONS 856 CITATIONS SEE PROFILE All content following this page was uploaded by Paul M. Barlow on 17 December 2014. The user has requested enhancement of the downloaded file. Saltwater intrusion in coastal regions of North America Paul M. Barlow & Eric G. Reichard Abstract Saltwater has intruded into many of the coastal Keywords Saltwater intrusion . Coastal aquifers . aquifers of the United States, Mexico, and Canada, but the Groundwater management . Groundwater monitoring . extent of saltwater intrusion varies widely among local- North America ities and hydrogeologic settings. In many instances, the area contaminated by saltwater is limited to small parts of an aquifer and to specific wells and has had little or no effect on overall groundwater supplies; in other instances, Introduction saltwater contamination is of regional extent and has Groundwater is a vital resource for sustaining the resulted in the closure of many groundwater supply wells. ’ The variability of hydrogeologic settings, three-dimen- communities and economies of North America s coastal sional distribution of saline water, and history of ground- regions. Groundwater withdrawals for public supplies, water withdrawals and freshwater drainage has resulted in agriculture, industry, and other uses in the Atlantic and Pacific coastal regions of the United States alone exceeded a variety of modes of saltwater intrusion into coastal 3 aquifers. These include lateral intrusion from the ocean; 618 m /s (14.1 billion gallons per day) in 2000 (US upward intrusion from deeper, more saline zones of a Geological Survey 2004), and in many coastal commun- groundwater system; and downward intrusion from ities groundwater is the primary or sole source of drinking coastal waters. Saltwater contamination also has occurred water. As groundwater use in coastal areas has increased, along open boreholes and within abandoned, improperly so has the recognition that groundwater supplies are constructed, or corroded wells that provide pathways for vulnerable to overuse and contamination. Although vertical migration across interconnected aquifers. Com- groundwater overuse and contamination are not uncom- munities within the coastal regions of North America are mon, the proximity of coastal aquifers to saltwater creates taking actions to manage and prevent saltwater intrusion unique issues with respect to groundwater sustainability in to ensure a sustainable source of groundwater for the coastal regions. These issues are primarily those of future. These actions can be grouped broadly into saltwater intrusion into freshwater aquifers and changes scientific monitoring and assessment, engineering techni- in the amount and quality of fresh groundwater discharge ques, and regulatory approaches. to coastal saltwater systems. This paper focuses on the first of these issues—saltwater (or seawater) intrusion into coastal aquifers of North America, which was recognized as a problem in the United States as early as 1854 on Long Island, New York (Back and Freeze 1983). The objectives of this paper are threefold: to provide a summary of the extent and modes of saltwater intrusion along Received: 31 December 2008 /Accepted: 1 August 2009 coastal regions of the United States, Mexico, and Canada; to Published online: 17 September 2009 describe the many approaches and tools that are used to monitor and manage saltwater intrusion in these coastal * Springer-Verlag 2009 regions; and to provide a brief assessment of the prospects for addressing saltwater intrusion problems in the future. This P. M. Barlow ()) paper is limited in scope to the Atlantic and Pacificcoastsof US Geological Survey, Canada and the United States (excluding Alaska and Hawaii) 10 Bearfoot Road, 01532, Northborough, MA, USA and all of Mexico (Fig. 1). Previous reviews of saltwater e-mail: [email protected] Tel.: +1-508-4905070 intrusion in the United States have been done by Krieger et al. Fax: +1-508-4905068 (1957), Task Committee on Saltwater Intrusion (1969), and Konikow and Reilly (1999). Barlow (2003) provides a E. G. Reichard US Geological Survey, detailed review of saltwater intrusion along the Atlantic 4165 Spruance Road, Suite 200, 92101-0812, San Diego, CA, USA Coast of the United States, and Barlow and Wild (2002) e-mail: [email protected] provide an extensive bibliography of publications related to Hydrogeology Journal (2010) 18: 247–260 DOI 10.1007/s10040-009-0514-3 248 120˚W 100˚W 80˚W Hudson Bay 50˚N British Columbia Canada Prince Washington Edward Island Oregon Long Island, California United States New York Monterey New Bay area Jersey Los Angeles and surrounding areas Georgia Sonora Florida P a c Baja California n i Mexico Gulf of a f e ic Mexico c 20˚N O O Gulf of Yucatan Peninsula ce California Veracruz c a ti n n Sinaloa a tl Nayarit A Fig. 1 Map of study area showing some of the locations discussed in the text saltwater intrusion in that region. Surveys of saltwater square kilometers in areal extent. In many areas, unconfined intrusion on the Pacific Coast include California Department aquifers that lie close to land surface are underlain by one or of Water Resources (1958), Dion and Simioka (1984), and more confined aquifers that may be hydraulically separated Hanson et al. (2009). Cardoso (1993) provides an overview from the land surface by confining units. of saltwater intrusion in the 17 coastal states of Mexico. Groundwater flow systems along the coastal zones are characterized by flowpaths that range from a few kilo- meters to several hundred kilometers. The seaward limit of Extent and modes of saltwater intrusion freshwater in the coastal aquifers is controlled by a number of factors, including the amount of freshwater In order to manage saltwater intrusion, one must first flowing through each aquifer, the thickness and hydraulic understand the extent of the problem and the physical properties of each aquifer and adjacent confining units, the mechanisms (or modes) by which saltwater intrusion current geographic distribution of saline surface water, and occurs. This section briefly outlines what is known of the geologic history of global sea-level fluctuations. In the extent of saltwater intrusion in North America and some of the confined aquifers along the Atlantic Coast, gives examples of the many pathways by which saltwater relatively fresh groundwater has been found tens of intrusion has occurred. kilometers offshore; its presence has been attributed to The coastal regions of North America are characterized freshwater recharge that occurred over at least the past by a wide range of hydrogeologic settings. Although there 900,000 years during periods when sea levels were lower are numerous types of geologic formations in the coastal than at present (Meisler 1989). In other areas, such as regions, the most important water-bearing formations are southern Florida, confining conditions and sluggish unconsolidated and semiconsolidated silts, sands, and groundwater flow are thought to have contributed to the gravels of both marine and continental origin; and, among presence of large inland areas of residual seawater that consolidated rocks, carbonates (primarily limestones), sand- entered the aquifers during the Pleistocene when sea level stones, and fractured crystalline rocks such as granites. was higher than its current level (Sprinkle 1989). Inland Groundwater-flow systems within the coastal zones vary in areas of saline water also can be found near estuaries, size from single-layer aquifers that are a few square where saltwater carried up river channels by high tides has kilometers or less in areal extent to multilayer, regional- infiltrated into the adjoining freshwater aquifers. Examples scale aquifers that are from hundreds to tens of thousands of of this type of naturally occurring intrusion have been Hydrogeology Journal (2010) 18: 247–260 DOI 10.1007/s10040-009-0514-3 249 documented for fractured sandstones of Prince Edward Saltwater intrusion has been documented along the coasts Island, Canada (Carr 1969), and permeable deltaic sedi- of the United States for more than 150 years, but the literature ments near the Fraser River, British Columbia, Canada indicates that the extent of saltwater intrusion varies widely (Neilson-Welch and Smith 2001). among localities and hydrogeologic settings. In many The transition zone between freshwater and saltwater instances, the area contaminated by saltwater is limited to rangesfromlessthan30mthickinrelativelythinaquifersto small parts of an aquifer and to specific wells and has little or as much as 670 m thick and 60 km wide in thick, confined no effect on overall groundwater supplies. In Washington aquifers along the Northern Atlantic Coastal Plain where State, for example, no large water-supply systems that rely global sea-level fluctuations caused repeated advance and primarily on groundwater have been affected by saltwater retreat of the landward position of the freshwater-saltwater intrusion, although some wells and small community interface. In California coastal aquifers, where saltwater systems on Puget Sound shorelines have been affected, and intrusion tends to occur within coarse-grained layers of groundwater resources