Water Resources in Rockland - Planning in a Changing World

Water Quality and Arsenic

Arsenic in Rockland County's groundwater was in the news in 2007. Arsenic was detected slightly above regulatory limits in two wells which supply water to Rockland County. Click here for April 25, 2010 presentation on Preliminary Results from Arsenic Groundwater Survey.

Scientists at Columbia University’s Mailman School of Public Health and Lamont-Doherty Earth Observatory responded in part:

"The risk for the development of adverse health effects would... appear to be vanishingly small."
in a letter to the Rockland Journal News.


Sampling groundwater to test for arsenic (Winthrop, ME)
Sampling groundwater to test for arsenic (Winthrop, ME)


United Water Wells with Arsenic in Rockland County

Click here for complete testing results from 1996-2009. Note that only when the standard dropped from 50ppb to 10ppb in 2006 did any wells exceed the MCL. Between 1996 and 2005 only 7 out of 253 measurements were greater than or equal to 10ppb.

United Water Wells with Arsenic in Rockland County

This map shows Rockland Country and the watersheds within it (a watershed is an area in which all the rainwater drains to the same stream.). Also shown are the locations of the two United Water wells whose As measurements in 2006 exceeded the Maximum Contaminant Level (MCL) of 10ppb (view map). These wells were later shut down as a result of these As levels. Treatment has now been installed which reduced the As to undetectable levels, and the wells were approved by the NY State Dept. of Health for return to service. Complete As testing results from 1995 to 2007 show only six wells that have ever tested over 10ppb (see table). To understand the broader context it's helpful to look at other regions, including Bangladesh where over 50 million people are exposed to water >10ppb arsenic, and New England, where elevated arsenic is more prevalent than in Rockland.

A look at other regions puts Rockland County' arsenic exposure in perspective
  2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 1996
  ppb (micrograms/liter)   ppb* (micrograms/liter*)
    *converted from mg/liter by multiplying by 1000*
SW17 Spring Valley Well eff                     0.0 10.0
SW26 Tallman Well 3.5     4.2     5.6         10.0
SW53 Saddle River Well 4.4   5.2 5.2 5.8 5.6 5.5       10.0 0.0
SW 67 Grandview Well 0.5 11.0   9.0   12.0 0.0         10.0
SW 67 Grandview Well   12.0   9.0                
SW 67 Grandview Well   13.0                    
SW 67 Grandview Well   17.0                    
SW 67 Grandview Well   16.0                    
SW 67 Grandview Well FILTERED   16.0                    
SW 67 Grandview Well   13.0                    
SW72 Rustic Well 4.8   4.5 4.7 4.3   5.3       0.0 10.0
SW 78 Grandview Well   15.0   6.8     5.7       0.0 10.0
SW 78 Grandview Well   18.0                    
SW 78 Grandview Well   20.0                    
SW 78 Grandview Well Filtered   18.0                    
SW 78 Grandview Well   15.0                    
SW 78 Grandview Well 0.5 17.0                    

(Source: United Water) Download table in excel format.

What do we know about where the arsenic in Rockland County’s groundwater comes from?

We’re confident the arsenic in Rockland County’s groundwater is naturally occurring because the concentrations are consistent with those in groundwater with known naturally occurring arsenic in other locations, and because there are no known anthropogenic sources in Rockland County or the surrounding areas. The local geological history sets the stage for the natural occurrence of arsenic in the groundwater but we don’t currently know which of the possible sources is the actual one. It’s possible the arsenic comes from a single sedimentary layer in which groundwater is stored. It’s also possible the arsenic comes from different layers and that what controls where it occurs and where it doesn’t occur is something else, such as dissolved organic matter, iron concentration or groundwater residence time.


450 million years ago, this region was underneath an ocean, and sediments were deposited in horizontal layers. Subsequently, the region was compressed and folded, which transformed some of the sedimentary rocks into metamorphic rocks which can still be seen today. 250 million years ago the region was subject to extensional forces—in other words, it was stretched apart. This “stretching” allowed a basin to form, called the Newark basin, and sediment filled in that basin. This sediment is still the bedrock of much of Rockland County today. About 200 million years ago, magma (molten rock) flowed upwards and pushed two layers of the sediment deposited in the Newark basin apart. This volcanic rock formation is highly visible today as the Palisades sill—because it is harder to erode the Palisades sill than the surrounding sedimentary rocks, it appears as a cliff along the Hudson River.

Groundwater is stored primarily in the many sedimentary rock layers and the specific chemical composition of the rocks affects the chemical composition of the groundwater. Very small changes in the chemical composition of the rocks can have very large effects on the chemical composition of groundwater. Dissolved species including iron, manganese, and arsenic generally originate from the rocks in which the groundwater is stored.


Arsenic Drinking Water Standards

The 2007 arsenic readings above the Maximum Contaminant Level (MCL) of 10 ppb in two Rockland County wells need to be viewed in the context of an evolving set of standards. From the 1940s until 2006 the standard in the US was 50 ppb and that is still the standard today in Bangladesh and India. After proposing a standard of 5 ppb in 2000, EPA adopted the new standard of 10 ppb in 2001 (effective in 2006). The State of New Jersey adopted 5 ppb, effective also in 2006, the strictest standard in the nation. US standards always represent a balancing of health impacts, cost to remove the contaminant, and measurement technologies. The MCL for arsenic has been set at a level that represents an order of magnitude greater health risk than for a number of other drinking water contaminants.

Current Standards for Arsenic in Drinking Water (2008)
World Health Organization 10 ppb
US 10 ppb
Australia 7 ppb
Bangladesh 50 ppb
India 50 ppb
NJ 5 ppb

According to the [Second edition] of the WHO Guidelines for Drinking-Water Quality (1993) while, based on health criteria, the guideline value for arsenic in drinking-water would be less than 10 ppb, because the guideline value is restricted by measurement limitations, and 10 ppb is the realistic limit to measurement, this is termed a provisional guideline value. (Parts per billion (ppb) = micrograms/liter. Milligrams/liter x 1000 = ppb (micrograms/liter).)


What are the risks of arsenic exposure?

In Bangladesh, results indicated at least a doubling of lifetime mortality risk from liver, bladder, and lung cancers (230 vs. 104 per 100,000 population) in Bangladesh owing to arsenic in drinking water. (Chen & Ahsan, 2004)


drop in the pond



In acute doses, arsenic is lethal on the time scale of a few hours. Chronic low doses cause a range of serious health problems, including skin lesions, fatal skin cancer, gangrene, and a range of fatal organ cancers including those initiated in liver, kidney and lungs.

Photo at right shows J. Graziano and H. Ahsan in Bangladesh.

children in Bangladesh


Arsenic and Intellectual Function

graph of As effect on intellectual function

An investigation of the impact of water arsenic exposure on both 10 year olds and 6 year olds in Bangladesh shows that exposure to As from drinking water is associated with reduced intellectual function. The research on 6 year olds controlled for water manganese [Mn], blood lead levels and sociodemographic features that contribute to intellectual function. see larger figure


(Wasserman et al, 2004)


Thumbnail of risks chart 1

Risks from Arsenic at the Maximum Contaminant Level for Drinking Water

Risks from arsenic at the Maximum Contaminant Level (MCL) for drinking water are significantly higher than for other drinking water contaminants, at their MCL

see larger figure(s)/extended explanation


Arsenic exposure in perspective

map showing arsenic problems globally

Arsenic occurs in waters around the world, at a variety of concentrations. Most drinking waters with high enough arsenic concentrations to be of concern are groundwaters. In Bangladesh, Taiwan, Mongolia, Argentina, and Mexico, high arsenic in drinking waters may have affected public health. In the US, the largest affected urban water systems are those of Albequerque and Los Angeles. Geothermal (hot spring) inputs to drinking water are the source of arsenic in these cities. Closer to us here in Rockland County, certain areas of New England have somewhat elevated groundwater arsenic concentrations. No public health impact is expected from arsenic in New England drinking water, but in many locations the concentrations do exceed national standards. view fullsize map


Arsenic in New England

New England

Throughout New England, many municipalities and individuals rely on groundwater for drinking. Most of this groundwater contains arsenic concentrations less than the federal limit of 10 ppb, however, in some areas up to 30% of wells contain >10 ppb arsenic. These areas are primarily defined by the source of the groundwater which originates in particular geological formations (metasedimentary bedrock, which is sediment moderately metamorphosed by heat and pressure).

One region which has been studied in greater detail is the Augusta, Maine area. This area does largely draw groundwater from metasedimentary bedrock, meaning that somewhat elevated arsenic concentrations are expected. About 12,000 people (22% of the population) in the greater Augusta area consume groundwater with >10 ppb arsenic (Yang et al). It has recently been shown that the correlation between bedrock type and groundwater arsenic concentration is quite strong, and therefore knowledge of the underlying geology can be quite important for planning. In the Augusta region, as in Rockland county, the arsenic appears to be naturally-occurring. This region is somewhat analogous to Rockland County because here, as in the Augusta area, arsenic appears to be natural in origin. However, concentrations in the Augusta area are in general much higher, and elevated arsenic is more prevalent, than in Rockland.


Locations of wells and concentrations of arsenic in water from bedrock aquifer wells in New England. The concentration data are shown with circles sized by concentration ranges. Number of samples = 2470.
Ayotte, J. D., D. L. Montgomery, et al. (2003). "Arsenic in Groundwater in Eastern New England: Occurence, Controls, and Human Health Implications." Environmental Science & Technology 37(10): 2075-2083. (used with permission from the American Chemical Society)


Arsenic in Bangladesh

map showing As contamination

Bangladesh has a large population (year 2000 estimate = 128 million) living very close to sea level, mostly on the flood plain of the Brahmaputra and Ganges Rivers. The population density is about 900 people per km2, almost triple that of India and seven times that of China.

Over 51 million people in Bangladesh have been chronically exposed to water with more than 10ppb arsenic, the current US and WHO standard, and over 25 Million people have been exposed to water with greater than 50ppb arsenic, the current Bangladesh standard. The source of the dissolved arsenic appears to be almost entirely natural.


map showing As contamination in Bangladesh
25 million people > 50µg/L (Bangladesh standard), 51 million people > 10µg/L (US/WHO standard).

BAMWSP (Bangladesh Arsenic Mitigation and Water Supply Program)

Bangladesh - History

Since the early 1970s, there has been an enormous effort in Bangladesh by UNICEF and other international donor organizations to install tube wells throughout much of Bangladesh, to reduce exposure of the population to infectious disease transmission via contaminated surface waters. As a result, there are now about 10 million shallow wells, accessed by hand pumps, located in many regions of the country. In some areas, which have saline water in the upper layers of groundwater, there are deeper wells that required much more extensive drilling operations to install.

From dissolved ion data in the major rivers reaching Bangladesh, there would be no reason to expect any particular problems with groundwater chemical compositions. But in fact, data (through Jan 1999) for dissolved arsenic [As] in 30,000 wells from many areas of Bangladesh indicate that the problem is widespread, but not uniform in geographical distribution. A band of several hundred kilometers width near the middle of the country has more than 20% of the wells with As levels greater than 50 ppb. Note that the field kits used to obtain this data do not have enough sensitivity to detect dissolved As below about 150 ppb. Thus it is likely that the extent of the problem of dissolved As is appreciably greater than indicated from this distribution of monitoring data. Monitoring data for dissolved As using other analytical methods, compiled by the British Geological Survey, also support the observation that elevated As is widespread in Bangladesh, and that deeper wells (> 200 meters below the surface) tend to have considerably lower As concentrations. The degree of spatial variation in dissolved As is extreme, even on a very local scale. Thus two wells within 10 meters of each other can have very different As concentrations, for reasons that are not fully understood at the present time.


Timeline for Bangladesh's As crisis

One of the great tragedies of the latter half of the 20th century is that the well-intentioned efforts of the international community and the Bangladesh government over a number of decades to improve health conditions through installation of shallow tube wells to access groundwater has now resulted in a massive episode of poisoning through dissolved As in drinking water.

Signs of As related disease were detected in the Bengal basin only in the mid 1980s. The detailed causes of elevated As in Bangladesh and West Bengal groundwaters remain unclear although the overall picture is generally agreed upon.

The most plausible explanation is that naturally-occurring arsenic from the sediments has become mobilized by the largely anoxic (ie no dissolved oxygen) groundwaters.

Within one region of Bangladesh, there is now a multi-year research program involving a number of researchers at Columbia University and other institutions, focused on documenting the effects of arsenic poisoning on the population of that region, as well as the geologic and hydrologic factors which tend to lead to high dissolved As and could potentially permit reduction in human exposure. The project is located in an area about 20 km east of the capital city of Dhaka in Arahaizar Thana. This effort involves faculty and staff from the School of Public Health, Lamont-Doherty Earth Observatory, Engineering School, School of International and Public Affairs, plus other units of the university and partners in Bangladesh.

  • Starting in 1960’s: Tube wells promoted by UNICEF to reduce infant mortality from water-borne diseases.
  • Mid-1980’s: First cases of arsenicosis reported in West Bengal, India.
  • Early 1990’s: First cases of arsenicosis reported in Bangladesh.
  • 1997: Survey of thousands of tube wells in Bangladesh by Depankra Chakraborti’s group in Calcutta. (Dhar et al)
  • 1999: Landmark compilation of existing and new data (British Geological Survey/Mott MacDonald)
  • June 2000: Launch of Columbia University Superfund/Basic Research Program, following pilot studies since January 1999.

Overview of remediation options in Bangladesh

boys pumping from well

In some locations, the aquifers are well separated and if not too large quantities of water are pumped, the deeper aquifer might provide an alternative source for low-As water. However, As is not low enough at depth in all locations. In areas with high spatially variable As concentrations, well switching might be a short-term remediation option. Most residents would not have to walk very far to obtain access to a "safe" well, but major cultural boundaries complicate this scenario. A small number of single-well treatment systems to remove arsenic have also been deployed. One system uses several plastic buckets, sand filters, and the addition of iron in tablet form to remove dissolved As. It appears difficult to create enough incentives for people to consistently use and maintain these systems.

The As problem poses major challenges to the scientific community to better understand the processes mobilizing As and the dose/response relationships of As, to develop feasible solutions, and to implement those solutions.
view remediation options figure


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