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Water > Aquifers > Schenectady-Niskayuna Aquifer System

Schenectady-Niskayuna Aquifer System

Support Document Schenectady, Saratoga, and Albany Counties, New York December 1984

I. Introduction

• A. Statement of 1424(e)
• B. Receipt of Petition
• C. Area of Consideration

II. Hydrogeology

• A. Geologic Framework
• B. Geologic Setting
• C. Ground Water Hydrology
  • 1. Recharge
  • 2. Discharge
  • 3. Streamflow Source Zone
• D. Designated Areas
• E. Ground Water Use

III. Susceptibility to Contamination

IV. Alternative Sources of Drinking Water

V. Summary

VI. Selected References

VII. Tables

VIII. Figure

• Figure 1. Schenectady-Niskayuna Aquifer System Designated Area

I. Introduction

A. Statement of Section 1424 (e)

The Safe Drinking Water Act (SDWA), Public Law 93-523, of December 16, 1974 contains a provision in Section 1424(e), which states that:

If the Administrator determines, on his own initiative or upon petition, that an area has an aquifer which is the sole or principal drinking water source for the area and which, if contaminated, would create significant hazard to public health, he shall publish notice of that determination in the Federal Register. After the publication of any such notice, no commitment for Federal financial assistance (through a grant, contract, loan guarantee, or otherwise) may be entered into for any project which the Administrator determines may contaminate such aquifer through a recharge zone so as to create a significant hazard to public health, but a commitment for Federal financial assistance may, if authorized under another provision of law, be entered into to plan or design the project to assure that it will not so contaminate the aquifer.

This section allows for the specific designation of areas which are dependent upon ground water supplies. Following designation, the review process will ensure that federal agencies will not commit funds toward projects which may contaminate these ground water supplies.

B. Receipt of Petition

On August 29, 1982, Frank J. Duci, Mayor of the City of Schenectady, petitioned the U.S. Environmental Protection Agency (EPA) Administrator to declare the Schenectady Aquifer, as defined in the petition a sole source aquifer (SSA) under the provision of the SDWA.

On March 3, 1983, at a public hearing conducted by the Environmental Protection Agency to discuss the Schenectady petition, the Town Board of Niskayuna submitted a petition requesting that their wellfield be included as part of the Schenectady Aquifer for purposes of the sole source designation. For the purposes of this report, the two have been consolidated and treated as one.

The Schenectady-Niskayuna Aquifer System supplies water to ninemunicipalities which are entirely dependent on the aquifer for their water supply. In total, the Schenectady-Niskayuna Aquifer System supplies water to approximately eighty-four percent (84%) of the population of Schenectady County through municipal and private wells.

C. Area of Consideration

The Schenectady-Niskayuna Aquifer System is approximately twenty miles (20 mi.) long and underlies approximately thirty (30) square miles in the lowermost part of the Mohawk River drainage basin. The width of the aquifer is approximately one-half mile (1/2 mi) at its western edges and over five miles (5 mi.) at the City of Schenectady, its widest point. The water supply for Schenectady, Niskayuna, Charlton, Burnt Hills, Ballston and Rexford is derived from wells located in an exceptionally permeable coarse sand and gravel deposit which is up to two-hundred feet (200') thick at places and underlain by glacial till.

In 1980, an average of twenty-six point thirty-eight million gallons per day (26.38 MGD) was pumped from the aquifer. Figure 1 shows the population and pumpage from the Schenectady-Niskayuna Aquifer System for 1980.

II. Hydrogeology

A. Geologic Framework

The Schenectady-Niskayuna Aquifer System, which consists of a complex series of discontinuous coarse sand and gravel deposits, is underlain by glacial till. An extensive sand unit as much as thirty feet (30') thick separates the coarse sandy gravel unit from the till in much of the wellfield area. The coarse sandy gravel unit of the aquifer averages about thirty-five feet (35') in thickness at the Schenectady wellfield. It grades laterally into sand and thins rather abruptly to the south, east and west of the Schenectady wellfield. The average thickness of the aquifer between Lock Number 8 of the Mohawk River and the Rotterdam wellfield is estimated to be about one-hundred feet (100'). The aquifer is bounded on the west by the relatively impermeable till and bedrock of the valley wall. On the south, the aquifer thins rather abruptly and grades into a deposit of silty sand which ranges in thickness from thirty to fifty feet (30-50'). The permeability is significantly less than that of the underlying sandy gravel. The coarse sandy gravel unit of the aquifer averages about fifty feet (50') in thickness at the Niskayuna wellfield. The aquifer is bounded on the southwest and northeast by relatively impermeable till and bedrock of the valley wall. The aquifer continues for approximately three miles (3 mi.) to the east into the Towns of Clifton Park and Colonie.

B. Geologic Setting

Bedrock underlying the Mohawk Valley in the Schenectady area is flat lying shale with some interbedded siltstone. During the last glaciation period, glaciers modified the regional topography by smoothing off hilltops, scouring out some valleys and filling in others and then leaving a mantle of unconsolidated material over the land surface nearly everywhere in the area.

Till, silt and sand overlie bedrock throughout most of the area. The till is exposed in the upland areas surrounding the Schenectady-Niskayuna Aquifer System. Sand, silt and clay carried by glacial meltwater were deposited in a large temporary glacial lake, now termed Lake Albany, which covered much of the mid-Hudson valley, including the Schenectady-Niskayuna area. These find sediments are found in the surrounding valley or interlayered in some places with the coarse aquifer gravels. The aquifer gravels are found primarily within the center of the channel near the Schenectady wellfield and comprise most of the channel near the Niskayuna wellfield. Most of the glacially derived deposits are now covered by sand and silt that form the modern floodplain.

In the northern side of the middle portion of the aquifer, kames consisting of highly permeable sand and gravel were deposited by meltwater streams at ice margins. Although the kames subsequently became partly buried by lake sand and silt of Lake Albany, a layer of sand and gravel that once formed the kames now extends sediments to the main valley of the Mohawk River. This occurs east of the Schenectady wellfield west of the Niskayuna wellfield.

The areas of the aquifer containing the Schenectady and Niskayuna wellfields are part of the same unique sequence of depositional conditions. The gravel layers forming the aquifer were deposited at the same time by the same glacial meltwater river flowing into glacial Lake Albany. The two wellfields are not directly connected by a continuous hydrologic unit,since they are separated by a north-south trending bedrock high. Both wellfields, however, operate on the same principle of wells drawing ground water from the sand and gravel aquifer that is recharged from precipitation and infiltration from the Mohawk River.

C. Ground Water Hydrology

Aquifer recharge occurs from precipitation directly on the land, by seepage from the tributary streams flowing across the aquifer, by subsurface flow from the till on the sides of the valley and by seepage from bedrock and deposits of low permeability underlying the aquifer. In addition, recharge from streams may be induced by nearby large-capacity pumping wells.

Ground water levels closely reflect the level of the Mohawk River. Within the flood plain, depth to water is generally less than thirty feet (30') but at higher elevations may be as much as seventy feet (70'). Springs discharge at the base of some slopes. The water table extends up into the till and bedrock adjacent to the aquifer, water levels are generally less than twenty-five feet (25') below land surface but may be as deep as fifty feet (50') in places adjacent to small down cut stream valleys.

Defining the exact boundaries of the area of influence of the Schenectady and Niskayuna wellfields is difficult because of the complex nature of the influences. Since the Schenectady-Niskayuna Aquifer System extends over many square miles of the Mohawk Valley, the area immediately surrounding the Schenectady and Niskayuna wellfields is not the only area through which potential contaminants can enter the water system. When one considers the overall water supply system, a much larger area, the "Extended Areas of Influence", must be included in the study. For the Schenectady and Niskayuna wellfields, the critical area is the "cone of depression" around the wells. Since contaminants from elsewhere could travel laterally and vertically to the protected area, the study includes the aquifer recharge zone and the streamflow source which is the watershed area tributary to the recharge area. These areas, as outlined in the C.T. Male Aquifer Preservation Study and Report, represent the geographic components of the areas of the water system, that is the area of influence.

The wellhead protection area has a radius of two-hundred feet (200') from the well and extends to include the well's "cone of depression" which is a depression, roughly conical in shape, produced as a result of ground waterpumpage. In the Schenectady Aquifer System area, water may enter from the river or from any point on land over the aquifer. Along with this water, any soluble or liquid material may also be drawn into the aquifer and travel through it to the wellfield. As municipalities, such as the City of Schenectady and the Town of Niskayuna, use their wells, more water is drawn into the aquifer. As water is removed by pumping, ground water slowly flows into the cone of depression and is pumped out. Pure water and any contaminant entering the ground near the cone of depression may travel to the well and enter the water supply. This zone is therefore critical and requires careful consideration.

1. Recharge

The aquifer recharge zone is the land mass where precipitation percolates directly through the ground to the aquifer. Part of the recharge area for the Niskayuna wellfield lies within the Towns of Clifton Park and Colonie. The aquifer's ability to filter out many types of organic and chemical impurities as the water percolates down and travels underground is an important asset not found in surface reservoir systems. Since the aquifer is recharged from both the Mohawk River and percolation through the surface, the absorption of toxic substances is also possible. In fact, serious ground water contamination has occurred in the past and has resulted in the closing of many public wells in many parts of New York State.

2. Discharge

Discharge from the aquifer system occurs as seepage into streams or lakes, evapotranspiration and as flow to pumping wells.

3. Streamflow Source Zone

The streamflow source zone represents the watershed area tributary to the recharge zone. Contaminants may be carried by the water from this zone that replenishes the recharge area. This zone was mapped by geographically locating the watershed area based on existing contours and stream drainage patterns that may contribute runoff to the recharge area. The geographic extent of this area, which has influence on the water system, extends about four miles (4 mi.) upstream from the Schenectady wellfield. Part of the streamflow source zone for the Niskayuna portion of the aquifer system lies within the Town of Colonie. The watershed area upstream of the recharge zone contributes runoff directly to the MohawkRiver which may travel downstream and enter the aquifer system. This is a secondary zone and the potential for contamination would depend on the type and amount of the contaminant.

D. Designated Areas

The area that has been designated as the Sole Source Aquifer is defined as the stratified drift and glacial outwash within the valleys. This area is coincident with that identified as a Primary Water Supply Aquifer by New York State Department of Health (1981) and New York State Department of Environmental Conservation (1987). The aquifer service area is the same as the aquifer area. Figure 1 shows the location and boundaries of the designated area.

E. Ground Water Use

Table 1 shows the population served and the amount of water withdrawn by public water suppliers within the Schenectady-Niskayuna Aquifer System.

III. Susceptibility to Contamination

The SchenectadyNiskayuna Aquifer System is highly vulnerable to contamination, from many various and diverse sources. Potential sources of contamination are as follows:

Transportation Routes and Facilities

The New York State Thruway, three railroads, several state highways and the New York State Barge Canal all pass through the aquifer area. The potential exists for an accidental spill on the land overlying the aquifer or into the Mohawk River which could result in serious contamination of the water supply. Thousands of tons of petroleum products and industrial and agricultural chemicals are carried through the area each year, and minor spills are not uncommon.

Landfills

Several active and inactive landfill sites are located at or near the aquifer. Runoff and leachates from these landfills may pose a problem.

OnSite Septic Disposal

Very little of the aquifer area is served by municipal sewers therefore, mostdevelopment depends upon onsite septic systems. The effect of these systems, depending on the design and soil conditions, may lead to the contamination of ground water systems.

Mohawk River

Since this river is the primary aquifer recharge source, it may convey upstream contaminants into the aquifer. The possibility of spills along the barge route poses a great potential for contamination.

Storm Water Runoff

Rain and snowmelt runoff can contain various potential contaminants as it enters the aquifer. These include deicing salts, animal excrement, pesticides, fertilizers, petroleum products, bacteria and particulates from air pollutants.

Commercial and Industrial Facilities

There are various commercial, industrial and military facilities located at or near the aquifer system border. Several of these facilities make, use or store chemicals and substances that could be hazardous if allowed to enter the ground water system. A common example is the storage of heating oil and gasoline, often in underground tanks. Leakage and spills from the storage tanks is not uncommon.

Miscellaneous

Dense commercial, industrial or residential development may also pose a potential source of contamination to the aquifer.

IV. Alternative Sources of Drinking Water

The only alternate source of drinking water for the Schenectady-Niskayuna Aquifer System is the Mohawk River, however, without treatment, water taken from the Mohawk River would not be of the same quality as that derived from the Schenectady-Niskayuna Aquifer System. The utilization of the Mohawk River as a potential source of drinking water would, therefore, entail significant capital expenditures to build treatment and distribution facilities.

V. Summary

Based upon the information presented, the SchenectadyNiskayuna Aquifer System meets the technical requirements for SSA designation. More than fifty percent (50%) of the drinking water for the aquifer service area is supplied by the Schenectady-Niskayuna Aquifer System. It is therefore recommended that the Schenectady-Niskayuna Aquifer System be designated a SSA. Designation will provide an additional review of those projects for which Federal financial assistance is requested, and will ensure ground water protection measures, incorporating state and local measures whenever possible, are built into the projects.

VI. Selected References

1. C.T. Male Associated, "Master Water Plan, Town of Niskayuna, 1983".

2. Dunn Geoscience Corporation, Schenectady Sole Source Aquifer Map 10/10/83.

3. The LA Partnership, "Water Supply and Aquifer Protection Study-City of Schenectady, New York", March 8, 1982.

4. Schenectady County Planning Department and Schenectady County Environmental Advisory Council, "Schenectady County Aquifer Preservation Strategy Program-Final Report", August 1980.

5. U.S. Geological Survey, Walter, R.M., and Finch, A.J., 1982, Atlas of Eleven Selected Aquifers in New York State: U.S. Geological Survey Open-File Report 82-553, 225 p.

VII. Table

Table 1. Community Water Suppliers and Population Within Schenectady-Niskayuna Aquifer System

* Water Supplies with home use of one-hundred (100) gallons per person is assumed.

VIII. Figure

Figure 1. Schenectady-Niskayuna Aquifer System Designated Area

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