The presence of large amounts of ice in the soils and underlying materials of the Planning Area makes mineral materials difficult to use. When heated, ice-rich silts slump, collapse, and liquefy. Sand and gravel in permafrost areas may contain ice, but still provide substantial strength upon thawing. Gravels are found specifically in floodplains and low terraces.

Alluvium, which consists of deposits of fine to medium sand, silty sand, gravel, and gravelly sand, is probably no more than 15 ft thick along modern channels and it includes floodplain and alluvial terrace deposits up to 24 ft above modern streams. Terrace drainage is generally poor and subject to flooding between 18 and 24 ft above low water in some streams. The entire area is in a zone of continuous permafrost except for an unfrozen area 6 to 18 ft thick beneath larger channels and lakes. It is typical for deposits to be frozen 1.5 ft beneath the active layer during the summer months, while the lower depth of permafrost is measured in hundreds of feet. The value of construction materials is related to the levels of organics and silts and the amount of water frozen in the deposit. The materials in channel and bar areas, where alluvium is composed of medium to coarse sand gravelly sands gravel, provide good foundation stability. Areas with low silt content may be suitable for fill.

Deposits in the ACP (Map 28 ), or northern portion of the Planning Area, are composed of marine sands and silts 20 to 180 ft deep. The marine deposits are two types of silts and clays, or sand over silts and clay, both with high ice content. Beach deposits contain gravelly sand and sand with areas of high organic content (wood and peat) that may be well drained when found along low beach ridges. Active ice wedges are well developed and fossil ice wedges occur locally at depths of a few feet.

Interstitial ice content exceeding natural voids produces settlement upon thawing. Similar deposits near Barrow are supersaturated with ice to about 18 to 24 ft, with ice content of 75 percent by volume at a depth of 3 ft, exclusive of wedge ice. The sediments are highly frost susceptible and not suitable for foundations because of excessive differential settlement of ice-rich permafrost, with the silt having a high liquefaction potential when thawed. Sands may be suitable for fill, base source, or surfacing if silt content is low and stable.

Thaw-lake deposits vary, depending upon the underlying lithology. For example, lakes underlain by marine silts and clays have silt and clay deposits; lakes underlain by eolian sands have fine sand deposits. These materials are generally unsuitable for construction because of their high organic and silt content. The alluvium deposits found along the major rivers contain fine to medium sand and silty sand with some organic materials in areas such as abandoned river channels. Fluvial-lacustrine deposits are undifferentiated alluvial and lacustrine sands and silty sands, which are ice-rich and poorly drained. Eolian sands cover a large portion of the Planning Area. For example, eolian sands cover approximately the southern half of the Teshekpuk quadrangle. These sands are a few feet to more than 100 ft thick and they are underlain by permafrost. The sands may be adequate for natural foundations but require stabilization for use as a surface material or fill. Sand dune ridges can reach 100 ft and they are generally well drained, making excavation relatively easy.

The surficial deposits of the AFP (Map 28 ), or southern portion of the Planning Area, are composed of eolian sand and upland silts and undifferentiated bedrock of sandstones, shales, and conglomerates. As in the coastal plain, alluvium is found along the river systems. Eolian sand and upland silts (also wind-blown) are the most widespread unconsolidated sediments in the entire NPR-A. A band of upland silt stretches from east to west across the NPR-A. The material may contain a high amount of interstitial ice and may not be suitable for construction use except as binder material. The material is not suitable for foundations because of excessive differential settlement when ice-rich permafrost thaws. Locally, the deposits may liquefy when thawed.

There was concern that sand and gravel resources would become scarce in certain areas of the ACP as early as 1974 (U.S. Army Corps of Engineers, 1974:123). This concern is reflected in the 1976 National Petroleum Reserve Production Act (NPRPA). Because sand and gravel have economic value, BLM regulates the sale of mineral materials (43 Code of Federal Regulations [CFR] 3600), defined generally as common varieties of sand, stone, gravel, clay, etc.

Sand and gravel in the NPR-A are treated as subsurface-mineral resources. Unlike other states, Alaska's mineral-material resources are not conveyed with the surface lands. Until the recent transfers of subsurface estate, specifically Nuiqsut subsurface to ASRC, the Federal Government controlled all mineral materials in the NPR-A. The BLM issued mineral-material permits to the four villages or cities of the NSB for dredging sand and gravel as part of the Borough's Capital Improvement Projects (CIP) in the 1980's. Nuiqsut dredged material from the Colville River bottom, while Atqasuk used material from the Meade River and the bottom of an adjacent lake. Materials from rivers, ocean beaches, and reserve pits were used in the 1970's and 1980's for well site pad, road, and airfield construction.

The 1975-1982 NPR-A exploration program involved not only oil and gas exploration, but also engineering research related to construction in the NPR-A. This period reflected an interest in cold regions mineral development worldwide. New techniques currently offer alternatives and supplements to the use of sand and gravel. These techniques include the use of pilings, insulated pads, geotextiles, elevated or reinforced pads, ice pads, and roads. The latter part of the NPR-A exploration program used reduced gravel in conjunction with insulation in pads, ice-reinforced silt pads, and ice roads and airstrips (Kachadoorian, Reuben, and Crory, 1988, as cited in Gryc, 1988). The U.S. Army Cold Regions Research Laboratory, an early engineering contributor and researcher, continues to monitor sites in the NPR-A for long-term changes.

Generally, the high cost of obtaining aggregates (sand and gravel) in the arctic makes them useful for permanent facilities, whereas other less expensive options, such as ice techniques, are used for temporary or seasonal needs. Whether to use ice, sand and gravel transported over long distances, or enhanced local materials as construction materials is a decision driven by economics. Mineral materials along beaches were used in the past and, depending upon the specific needs and location, materials extraction may occur with minimal concern. In some instances, mineral materials found in relation to streams and rivers could use the flowing water to recharge extracted material. Materials might be found elevated on ridges and hillsides in the middle to southern section of the NPR-A. If material is removed from ridges or hillsides, possible debris flow and thawing of ice-rich materials becomes a consideration. Development of gravel roads on the ACP may affect habitat. This requires a good understanding of road-tundra interactions and well-devised mitigating measures to minimize future impacts.

Pits are difficult to fill because water in a pit or the removal of the natural insulating vegetative mat can cause the pit to deepen over time. As the ice melts, the volume of the material removed from the pit shrinks, so it may take much more material to fill the pit than the amount extracted. Experience suggests it is better to design the pit to conform to natural features, reclaim the material that is available, and allow the pit to remain.

All of the NPR-A is underlain by permafrost, thus all of the engineering and geotechnical problems associated with sand and gravel excavation and use in construction have the potential of disturbing the thermal regime of the ground surface, thus impacting the environment.