McKownville Improvement Association
McKownville groundwater in the Colonie Sand

Groundwater in McKownville
diagram of sand
      grains with pore spacesThe Colonie Sand, on which essentially all of McKownville is built is, like all unconsolidated sands, a porus material with about 25-30% void space between the sand grains. These pores in the material are connected around the sand grains, and so any fluid in the pores is able to flow in response to a pressure gradient; such material is said to be permeable to fluid flow.

water table
      diagram for sand
Beneath the surface at most times, the pores in the upper few feet of the sand contain mostly air but, at some depth, typically 6 to 9 ft or so below the surface in McKownville, the pores are filled with water. The water is there because much of the rain and snow melt percolates down through the pores in the sand and fills the sand up to an elevation where at any time a balance is reached between the amount infiltrating from the surface and the amount flowing slowly away, through the sand, to local streams. This top of the filled, or saturated zone is called the water table (or groundwater table).

Because the rate of supply from precipitation and infiltration rarely exactly equals the rate of outflow to local streams, the level of the water table changes with time, rising when the infiltration is more than the outflow, and falling when the outflow exceeds the local infiltration. In many places in temperate climate regions near-surface aquifers (geological layers in which groundwater flows) show a characteristic rise in the water table in winter months and a fall through the summer months, mainly because more of the rain evaporates, and is transpired from the soil by trees and other vegetation, and so less replenishes the aquifer during the summer interval. See this in the monitoring well record below.

diagram of
      water table and flow in unconfined sand aquiferThe flow in streams, like the Krum Kill, is at most times fed from the groundwater flow in the local near-surface aquifer; (other than brief intervals in and a few days after heavy rain storms or snow melt events where there is direct run-off of water from surfaces into the streams, or from storm drains fed to them). Flow times for a sample drop of water infiltrating near the upper end of recharge areas in such aquifers are typically several years to travel to the local stream.
The term water table is potentially a bit misleading, because it is not a flat surface, but (if not disturbed by pumping from wells) tends to follow and be a subdued copy of the local ground surface topography, as show in the diagram on the left. These differences in elevation of the water table create a natural pressure gradient which is the cause of the flow in the aquifer. The water table intersects the surface of running streams, and ponds and lakes if they are not lined with impervious (or impermeable) material, such as plastic sheet, or clay. It also intersects the ground surface at natural springs, which are commonly at the heads of streams in the area of the Colonie Sand.


Krumkill west branch
        stream at McKown Road, 26 Feb 1018
Krumkill west branch stream at McKown Road, 26 Feb 2018. Some modest quantity of precipitation (rain) had occurred in the week prior to this date, but non-flood flow in the stream as shown mostly comes from groundwater discharge out of the Colonie Sand, not from runoff.
for larger image, click here or on the image

      profile section for McKownville water table in the Colonie Sand
Geological profile section for groundwater in the Colonie Sand aquifer in McKownville. The vertical scale is enlarged relative to horizontal scale in order to show clearly the water table and its relation to the ground surface.
Location shown on map below

diargam of
      thickness of the Colonie Sand and Albany Clay
In McKownville (and in most of the larger area covered by the Colonie Sand), the water infiltrating the ground is unable to percolate to significant depths, because the geological layer of clay-rich material, the Albany Clay, underlies the Colonie Sand, and forms the base to the aquifer. [more information on the geology of McKownville]
The properties of clay, with very fine clay mineral particles packed closely together, do not allow fluids to flow through them, or only at such slow rates under natural pressure gradients that they are essentially a barrier to flow of water, or most other fluids. So water that enters the Colonie Sand stays in the sand layer, above the Albany Clay, flowing out only to local springs and stream channels at or above the elevation of the base of the Colonie Sand.

This borehole-based record (from the University at Albany campus, near Indian Pond) shows the elevations of the upper and lower surfaces of the Albany Clay as they are in McKownville. The upper surface of the Clay, the base of the Colonie Sand, is known (Dineen, 1982) generally to rise going north and west from here, being located up to or a bit higher than 250 ft above sea level in the area west of Route 155 near the NY Thruway. Flow patterns of groundwater in the Sand are probably affected by this significant change in elevation of its base. The top of the Sand in that area (the ground surface), is about 320 ft elevation outside the stream valleys, again with dunes up to 50 ft high on top.

site picture of
      USGS well A654water depth in USGS well A654 - 1 Nov 2018 to 1 Aug 2020
USGS water monitoring well A-654 located on the University at Albany campus. Water depth in the well is measured automatically every 15 minutes and the data transmitted via the satellite antenna on the pole.

Graph shows the depth to the water table measured in this well between November 2018 and July 2020; the decline seen during the summer months (May-October) and the recovery back up during the winter is a fairly consistent pattern for this well in the Colonie Sand aquifer.

Data, graph, photo and well description from USGS website.

location shown on map below

Views of groundwater in McKownville
Infiltration pond in
        Colonie Sand in construction next to Dutch Quad, University at
Infiltration pond in construction next to Dutch Quad, SUNY Albany
(no lining, this shows the water level (~245ft asl) of the water table in the Colonie Sand here on 5 December 2018)
location P on map below

  click here or on the image for larger version

excavation on Elmwood
        St to install new water main showing pump effluent from
        saturated sand of the top of the water tableexcavation on Elmwood
        St to install new water main showing saturated sand of the top
        of the water table
excavation on Elmwood St to install new water main showing effluent from pump in the excavation, and the source: saturated sand of the top of the water table ~ 5ft depth  (~221 ft asl) in the excavation, 29 November 2018
location E on map below

click here, or here, or on images for larger version

spring from base of
        Colonie Sand, 1257 Western Avenue
Spring of water from the Colonie Sand in the lot of 1257 Western Avenue, 19 March 2018. The darker and iron-stained area, indicated with the red arrow, is damp from the seepage, which is controlled here by the top of the Albany Clay at this elevation, 190 ft asl; location S on map below.
 click here or on the picture for larger version
The house formerly in this lot was plagued by water infiltration into its basement, and rapidly deteriorated after it passed in 1973 from owner occupancy to non-resident property; it was demolished in 2004. Later in the year this picture was taken, this lot was levelled and partly filled with gravel to support construction activities for new water mains and storm drains in nearby streets of McKownville. This fill has disguised the high water table here, but does nothing to remove the problem for future uses of the property.
Seepage and events of flooding of groundwater into basements of McKownville houses are a direct consequence of the often high level of the water table in the Colonie Sand. The Town Of Guilderland has a construction project funded and in progress since 2018 to replace old water main pipes and install a proper storm drain system in the area of McKownville north of Western Avenue in order to alleviate this situation. Completion of the project is scheduled to occur in 2021.

      map of McKownville with groundwater profile and photo locations
Map segment from USGS 7½' Albany quad,
 1953 base, purple additions to 1978.
Location of groundwater profile (above) - red line,
H- Hampton Inn
E- Elmwood St water line excavation photos
P - infiltration pond at Dutch quad photo
S - spring in 1257 Western Ave lot photo

The Colonie Sand contains in some places, far above its base on the Albany Clay, a thin (3-6 ft) clay layer which occurs at about 300 ft asl elevation in areas west of Rte 155 and, according to Dineen (1982), this persists to the east at least as far as the Adirondack Northway near its intersection with I-90. The elevation of this layer in the sand declines to the east down to about 250 ft asl. This layer appears to extend just into the northernmost part of McKownville west of Fuller Road, where it is probably responsible for the wetland north of Warren St and western Mercer St, whose ground surface is at 255 ft asl. Although thin, this clay layer is an aquiclude, sufficiently impermeable so that groundwater is ponded above it, a situation termed a "perched" water table, illustrated in the diagram below. The diversion of runoff from the SUNY Polytechnic Insitiute to a detention pond in this swampy area has likely raised the water table elevation in this part of McKownville and made more difficult the remediation of drainage here. Sending this runoff into the Patroon Creek groundwater and drainage area, where originally it would have gone if not diverted, would be helpful.
      section showing a perched water tabledetention pond for
        SUNY in larger wetland area north of Warren St
Detention pond in the eastern end of the swampy area north of Warren and western Mercer Streets, McKownville; houses on Warren St seen beyond the trees in the center. The pond receives runoff from SUNY Albany Freedom Quad and much more from the large built-over area of SUNY Poly. This swampy area in which this retention pond was placed is here because of a perched water table over the clay layer within the upper part of the lake sands of the Colonie Sand.

click here or on the image for a larger version

The origin of this persistent varved lake clay layer up in the Colonie sand is an intriguing geological question. Dineen (1982) thought that it was from deposition in a lagoon behind a sand barrier bar in Lake Albany, which would require it to be younger to the east, as the lake shore and the barrier bar migrated in that direction while the lake level was dropping slowly. Alternatively, if it is synchronous across the area, which its continuity as a single layer tends to suggest, an event temporarily interrupting the sand supply from the Iro-Mohawk river is implied, which could be a short-lived re-advance of the Laurentian ice front that for a brief interval of time dammed off the drainage down the Iro-Mohawk.

Dineen, R.L., 1982. The geology of the Pine Bush Aquifer, north-central Albany County, New York. New York State Museum Bulletin 449, iv +26pp.

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