by William M. Kelly
Chapter 4: Sand and Gravel
Sand and gravel must surely have been among the first mineral resources extracted in New York. However, little was written about these materials in the nineteenth and early twentieth centuries except to disparage them for not making quality road surfaces. But sand and gravel were recognized as vitally important for sub-grade materials. Merrill (1897) cites 2,000 years of knowledge that the perfect road must have a hard, smooth, waterproof surface and a thoroughly dry foundation. He states, “The surface of a good road must have sufficient strength to resist the wear and tear of traffic, and smooth enough to prevent undue strain and wear on vehicles. In conjunction with this, the soil beneath must be made dry and kept dry” (emphasis in original). Sand and gravel made this latter condition possible. By the 1920s, the value and volume of sand and gravel deposits were recognized to be large. The large-scale production of these commodities was thought to be “merely a problem in extraction” (Nevin 1929).
Sand and gravel, like crushed stone, are fundamental to the construction industry. Unlike crushed stone, sand and gravel deposits are unconsolidated and hence do not require blasting to liberate the material from the earth. There are more mines for sand and gravel in New York than for any other commodity. They occur in all counties but New York, Bronx, Queens, Kings, Richmond, and Nassau. Sand and gravel deposits found in New York are the result of deposition of sediments by rivers and streams related to the melting of the late Pleistocene Wisconsinan ice sheet. Virtually all of the state was covered by 1 to 2 kilometers (0.6–1.2 miles) of ice. Material carried in the ice was generally deposited as till but where it was transported and winnowed by melt water, relatively clean sand and gravel were deposited. The glacial sand and gravel deposits generally take the form of kames, deltas, beaches, eskers, and outwash channel fill. The material in these deposits varies in size from sand to large cobbles with occasional large boulders. Post-glacial alluvial processes, particularly running water but also wind and freshwater and marine waves and currents, have also generated sand and gravel deposits.
The exception is a small area in southwestern New York in the vicinity of Allegheny State Park. Two Pleistocene ice lobes flowed around the higher land of the park area and created a triangular notch about 60 kilometers (37 miles) long and 27 kilometers (17 miles) deep in the roughly east–west margin of the Pleistocene glacial maximum. Known as the Salamanca re-entrant, this unglaciated area is roughly 725 square kilometers (280 square miles) in size, and is small compared to the glaciated area of the state. But in this area, ice contact deposits are absent and only the outwash deposits are present.
Products and Uses
Sand, as defined for construction use, consists of particles smaller than 4.76 mm (3/16 inch). Sand in this size range is dominantly quartz with variable amounts of feldspar, mica, silt, and clay. Gravel is material larger in grain size than sand and has more variable composition, often including rock fragments and reflecting the geological formations in the local area (Harben and Bates 1984). A commercially useful sand and gravel deposit should have a wide range of particle sizes so that several different final products can be extracted from it. Table 6 lists the typical sizes and uses for sand and gravel products quarried in New York. In 2006, 34,962,000 metric tons of sand and gravel were quarried in the state (USGS 2006).
Typical Size and Uses for Sand and Gravel Products Mined in New York. (Source: Harben and Bates 1984.)
While glacially derived sand and gravel are relatively widespread in New York, not all sand and gravel deposits can be developed for use as sources of construction aggregates. Some are not of sufficient quality to produce useful aggregates. Sand and gravel deposits should contain little fine silt or clay, organic matter, fissile shale, friable sandstone, or other easily disaggregated rock types. If fine particles are present, they must be removed by processing. The deposit should not contain excessive amounts of reactive chert or siliceous limestone to avoid alkali-aggregate reactivity which, if used in concrete mix, may cause the subsequent product to crack or blister (Harben and Bates 1984). Finally, the shape of the particles bears on the quality of the deposit. Flat or elongate particles, often derived from shale, siltstone, or low-grade micaceous metamorphic rocks are not desirable. Chert, siliceous limestone, shale, phyllite, and slate are rather widespread in certain parts of New York and contribute potentially deleterious materials to the sand and gravel. Quality issues constrain sand and gravel deposits that can be economically exploited.
One other use, primarily for sand and generally derived from offshore, deserves mention. Coastal sediment is continually lost due to erosion, land subsidence, and sea-level rise. Loss or retreat of New York’s beaches, dunes, and barrier islands are serious problems. These geomorphic features provide important protection of the coast, infrastructure, commercial, and residential properties in coastal communities as population and development on the coast increases. The loss of sand and landforms endangers life, property, recreational opportunities, and sensitive environmental areas. Upland sand resources are, however, insufficient to provide the material necessary for restoration of lost sand. Beach nourishment from marine sources to mitigate the removal or submergence of coastal sand is a necessary and common practice on the south shore of Long Island. This method uses dredged sand from offshore, which is pumped on shore to widen and elevate the beach and dunes. This practice is often cost effective and environmentally acceptable and provides short-term (perhaps ten years) protection. The process can reduce the risk of storm damage and flooding, and improve degraded coastal ecosystems (Williams et al. 2009).
Other impediments exist to the development of the deposits. As crushed stone, sand and gravel are heavy materials of low unit value and cannot be transported economically far distances. They are used in large amounts in construction projects and therefore the source of the materials must be close to the point of use. Since most construction projects are in populated areas, the presence of a sand and gravel mine can be a source of contention. The issues include dust, noise, visibility, and truck traffic (Harben and Bates 1984). Perhaps the most difficult problem arises as the result of the location of sand and gravel deposits. Ice contact deposits such as kames are found on valley walls. Beaches and deltas are located at the transition between valley walls and valley bottoms. Outwash deposits form valley floors. These locations are sites of competition for other development. Well-drained, low-relief surfaces are desirable for dwellings, business establishments, roads, and municipal construction. Once a deposit has been overbuilt, it is generally no longer available for mining.
There are ways in which this conflict can be mitigated. In parts of California, the Surface Mining and Reclamation Act of 1975 (SMARA) and subsequent amendments resulted in the designation of “natural resource districts” wherein lands are reserved for mineral development. SMARA helps identify and protect mineral resources in areas in the state subject to urbanization or other irreversible land uses that preclude mineral extraction. Construction aggregates were selected as the first commodity targeted for protection due to its importance to society and its threat of loss by urban development (California SMARA 1975). In order that the lands not be permanently lost to the community, sequential land use is assumed (Harben and Bates 1984). For example, lands where aggregate resources are present are used first for sand and gravel extraction and then for residential development, recreation, or municipal facilities.
In Canada, Ontario’s Mineral Development Strategy provides methods to identify areas of high mineral potential based on economic and geologic factors. These results are then analyzed in conjunction with other land-use information that gives consideration to areas with mineral resources before final land-use decisions are made that might prohibit exploration or mining (Ontario Mines and Minerals Division 2009). Under the Provincial Policy Plan, as much of the available aggregate resources as possible is made available close to the market. In cognizance of future needs, regulations state that demonstration of immediate need for the resources is not required. Aggregate operations are protected from development or other activities that would preclude or hinder their expansion or continued use. In areas adjacent to or in known aggregate resources, developmentor activities that would preclude or hinder the establishment of new operations or access to the resources shall only be permitted under certain regulated conditions (Ontario Province 2005). This type of regional land-use planning would benefit New York.
In parts of New York, inland sources of sand and gravel are scarce, either due to the original paucity of deposits or land-use conflicts. This is particularly true in the lower Hudson Valley, the New York City Metropolitan Region, and on Long Island. Aggregate resources located offshore on the continental shelf offer a limited possible alternative. Most of the land controlled by New York under Lakes Erie and Ontario is authorized for sand and gravel extraction. Taking of material offshore Chautauqua County is prohibited (Public Lands Law Section 22.2.a), with minor exceptions near Walnut and Cattaraugus Creeks. To date, the New York State Office of General Services has not been approached about offshore mining in the Great Lakes. Apparently, upland sources are currently sufficient and more cost effective than these alternatives. Taking of sand and gravel from New York State land offshore Long Island is also prohibited except when, in the opinion of the U.S. Army Corps of Engineers, the removal of the material is necessary for navigational improvements (Public Lands Law Section 22.2.b). While offshore sand and gravel cannot be mined in New York waters (three miles from shore), for the past two decades the Federal Minerals Management Service has been aware of the interest in sand and gravel from the federal outer continental shelf as a source for aggregates for sale and coastal restoration. At present, these outer continental shelf deposits are not cost effective. Federal regulations are in place for competitive lease sales for offshore mineral resources. Since the late 1980s, the Minerals Management Service (MMS) has leased over 30 million cubic yards of outer continental shelf sand for twenty-three coastal restoration projects in five states. None of these projects were in New York, however (MMS 2009).
Beach nourishment is viewed for many developed coasts as a cost-effective and environmentally acceptable short-term (perhaps a decade of protection) method for mitigating coastal erosion, reducing storm and flooding risk, and restoring degraded coastal ecosystems. For beach nourishment to be successful, however, large volumes of high-quality sand are necessary. Federally sponsored beach nourishment projects in the past eighty years have consumed about 920 million cubic meters (≈1,200 million cubic yards) of sand (Bliss et al. 2009). For project benefits to exceed costs, the sand deposits must be located reasonably close to the beaches being considered for nourishment. Up to 8.1 billion cubic meters of sand may be available in New York waters off the south shore of Long Island for coastal restoration projects. This includes cape- and ridge-associated marine sand deposits as well as paleo-stream channels, blanket and outwash deposits, ebb-tidal shoals, and low sea-level stand deltas (Bliss et al. 2009). In the cape- and ridge-associated marine sand deposits on the inner continental shelf outboard of New York waters, there are probably 2,200 million cubic meters (≈2,900 million cubic yards) of sand. However, not all of this material will be available for extraction because of geographic, economic, environmental, geologic, and political factors, and preemptive use (Bliss et al. 2009).
There are currently 1,744 sand and gravel mines in New York. Of these, 1,499 operate above the water table as upland sources. Those operating below the water table number 245. The processes used to acquire the product are similar across New York. Information about companies that produce sand and gravel in New York is published by the New York State Department of Environmental Conservation, Division of Mineral Resources. Data organized by commodity is available in electronic format at http://www.dec.ny.gov/cfmx/extapps/MinedLand/standard/commodities. More specific information is available in a searchable mines database available at http://www.dec.ny.gov/cfmx/extapps/MinedLand/search/mines.
Upland, or dry-pit, sources of sand and gravel are those that operate generally above the water table. The process of mining sand and gravel from these sources is as follows. At a typical sand and gravel operation, wheeled equipment, such as front-end loaders with multiple yard bucket capacity, are used to extract the material from the mining face. Hydraulic shovels are infrequently used to load haul trucks to transport the material in the mine. Trucks or conveyors are used to transport the mined material to a permanent or portable processing plant. If haul distances are short or in small operations, a loader can be used to take the raw material directly to the processing plant.
The sand and gravel is passed over a grizzly, if necessary, to remove oversized material or the material may be fed to scalping screens. This removes deleterious materials such as roots, clay balls, and large rocks. The sand and gravel is then run over a multideck inclined set of screens, either reciprocating or vibratory, made of steel, rubber, or polyurethane for size separation. A typical set of screens would include opening sizes of 38 millimeters(1½ inch), 19 millimeters (¾ inch), 12 millimeters (½ inch), and 5 or 6 millimeters (¼ or 3/16 inch). An average screening plant has a capacity of between 100 and 300 tons per hour. If needed, water is sprayed at various rates onto the screens while in operation to suppress dust and wash the product.
Oversized material is reduced in jaw, gyratory (cone), or impact crushers to the desired size. This also produces a more angular product from the originally rounded, water-worn coarse gravel and cobbles. Impact crushers are more costly to operate but are being used to achieve desired particle shapes and remove less sound material. Sand products, after being separated on a screen deck, may travel to a classifier where they are washed and sized. The sands are then dewatered with screw-type equipment and placed in stockpiles. Transportation to stockpile areas is via fixed conveyor system, a radial stacker, or an extendable belt conveyor system. A radial stacker is a conveyor system that rotates from a fixed pivot point, and stores the conveyed material in an arc-shaped stockpile. The extendable belt conveyor system has the capability of lengthening or shortening itself by moving the head section. The head section is mounted on wheels, and moves on rails, which allows the conveyor to supply several stockpiles, hoppers, or silos.
Below Water Table Sources
Sand and gravel deposits that are in areas of low relief can be mined below the water table with dredging equipment. Mining is often started with an excavator that creates a pond of sufficient size for a dredge. Dredging equipment is usually of a suction type with a rotary cutter head. The cutter head is especially necessary in deposits which contain higher concentrations of gravel. Occasionally, clam-shell equipment or a dragline is used. Dredges are usually in the range of 500 to 1,000 horsepower. Mined material is transported as a pumped slurry at 6,000 to 7,000 gallons per minute via pipeline to the processing plant. The material can be pumped directly to the plant or to a sump in order to separate sand and gravel from the water. From this point, processing of the material is the same as for sand and gravel from upland sources.
Currently, one operator, based in New Jersey, recovers sand and gravel from the Ambrose Channel under permit for navigational improvements and sells into the aggregate New York market. Westward-directed longshore drift along the south shore of Long Island brings sand and gravel into the shipping channel used for the approach to New York Harbor. This material is roughly 92 percent coarse to fine sand and 8 percent gravel. The materials are recovered by the dredge Sandy Hook, a trailing-arm suction hopper vessel, propelled by the tug Sand Miner, which is dedicated to sand mining (Figure 20). The dredge unloads its cargo in South Amboy, New Jersey, where the sand and gravel are drained, processed, and washed. The finished product is then loaded onto barges, commonly of 611 cubic meters (800 cubic yards) capacity, and delivered to a market area that stretches from Atlantic City, New Jersey, to New Haven, Connecticut.
Trailing-arm suction hopper dredge Sandy Hook operates in lower New York Harbor to extract construction sand and gravel.
There may be potential to expand this activity. Several countries, including the United Kingdom, Japan, and Germany, derive significant portions of their construction aggregates, in the form of sand and gravel, from offshore deposits. In 2005, marine sand and gravel accounted for 19 percent of total sand and gravel in England and 46 percent in Wales. Some metropolitan regions are almost entirely dependent on marine resources for construction aggregates. Eighty percent of total aggregate used in the City of London originates offshore (British Geological Survey 2007). It should be noted that most of the sediment on the continental shelf south of Long Island is fine to medium sand, with 10 percent or less gravel (Cochet al. 1997a, 1997b; Harsch et al. 1997; Williams et al. 2003). Most aggregates require medium- to coarse-grained sand, so only a small percentage of channel maintenance sand has value as construction material. Offshore sand mining is cost effective and practicable in the general New York City area for two reasons: (1) shortages of upland sources have led to elevated costs of concrete sand and other sand products in this market area—concrete sand that sold for approximately $8/ton in upstate New York sells for up to $25/ton in the New York City area (Griggs, pers. comm. 2010); and (2) many end users have established infrastructure to receive aggregate by water. In general, offshore sand mining costs significantly more than upland sand mining and would only be feasible where the construction material costs are elevated and suitable and where specialized docking facilities exist.