Alex C. Blackburn and Lawrence Stipek

Loudoun County, located just west of Washington, D.C., began growing very rapidly in the mid-1980's. The county began improving its processes and its information base at that time so as to better manage the many problems associated with new development. A geology coverage was created in cooperation with the U.S. Geological Survey over a 5-year period. The new information, completed in 1992, was a refinement of earlier geologic mapping in the Triassic basin and included new, more detailed mapping in the Blue Ridge (western) portion of the county.

The initial purpose of the new geologic mapping was to serve as the foundation for a complete revision of the county's soil maps. The new, very large scale (1:2,400) soil maps were compiled from earlier maps, new field surveys, and the new geologic data. The new geologic information was also the framework for analysis and modeling of the county's ground-water data base. Developed and maintained from well logs, the data base was used to analyze the availability of ground water in the rapidly developing rural areas. The geology mapping was then used extensively in a landfill site selection study conducted for and by the county. This work culminated in the selection of a site, with net savings estimated to be $1,500,000 (U.S. Geological Survey Circular 1111, p. 36).

Today the county continues to use the refined geologic data. The data were incorporated into the county's geographic information system (GIS), and a new map produced that displayed both geology and the county's street centerline as a reference. The county has a policy of providing open access to its GIS and has distributed the geologic data to others for engineering purposes. The designers of the Dulles Greenway, a privately funded and constructed tollroad, used the county's flood-plain, parcel, and other data, together with geology, in the initial design phase of the project.

Perhaps more importantly, the public has direct access to the GIS at two public access terminals. The most common use of geologic information today is to make very important, personal decisions, such as purchasing property, analyzing the cost of making improvements such as a new fence or a foundation for a house, or estimating the yield of a new well. The latter is an important, almost daily activity at the Office of Mapping and Geographic Information public information counter and at the Virginia Tech Extension Office. Staff routinely help the public to search the geographic data base, display and access the well data, and compare it to the geologic map. Geology is an important component of the county's information base.

Thomas E. Carroll

Virginia's Mineral Mining Industry--Overview

• Approximately 84 million tons of nonfuel minerals were produced in Virginia in 1996, with a value in excess of one-half billion dollars. The majority, roughly 92 percent, was from the production of aggregates (crushed stone and sand and gravel) from 133 quarries and 270 sand and gravel mines.

• Virginia consistently ranks in the top 10 in the Nation in crushed stone production.
• Roughly 12 tons of aggregate are required annually for each Virginia citizen.

Exploration

• Unlike a shopping center, housing development, school, and so on, mining companies do not have the luxury of being able to locate mines and quarries where we want them to be. Minerals are where you find them--or where the Geological Surveys map them.
• Simplistic?--The reality is that geological maps are the base maps that generate interest and investment from the mineral industry. We use these maps as the fundamental building block in our exploration programs--whether to identify previously unknown geologic terrains and (or) geochemistry for precious metal deposits or something as simple as depth of weathering--what we in the aggregate business refer to as overburden.

Consumption/Growth

• Recall the aggregate consumption figure I gave you earlier? Virginia's population is projected to grow from 1994 to 2020 by roughly 30 percent or 1.9 million people.
• That means additional annual aggregate demand of roughly 23-25 million more tons of aggregate.
• A large percentage of this growth will come in Northern Virginia as part of the State's "golden crescent."

Role of Planning

• Local governments must plan ahead to ensure a continuous supply of locally available aggregates. If you truck this material over 20-30 miles, the cost of transportation can exceed the cost of the materials. This can and does significantly impact local government and private construction costs and the overall cost of living in an area when you consider that 95 percent of asphalt and approximately 85 percent of concrete consists of aggregates.
• Urban sprawl without any thought to future mineral development must cease.
• Approximately 1 year ago, Virginia took the first step in encouraging local governments to include the need for mineral resources as one of the elements to evaluate when developing and amending their comprehensive plans.
• This legislation will place an increased burden on the Geological Surveys to supply local government with this basic information. Unfortunately, it will take decades to complete the geologic mapping (over 100 years) and mineral resources mapping (over 17 years) at current staffing levels. Remember the issue identified by users of this information--it must be timely.

Conclusion

• In supplying geological information, the challenge to the Surveys is not only how quickly can the data be produced and published but also how must the data be repackaged to be less technical and more interpretive for the nongeologist (elected officials, land-use planners, and so on) to readily use. Through greater use, the public will understand the fundamental importance that geology plays in our everyday lives.
• Emphasis should be placed on publishing data electronically (GIS and so on) and on county and planning district boundary basis rather than on topographic quadrangle sheets.

A. David Martin

Geologic Mapping

This information is a basic unit of input for many Maryland State Highway Administration (SHA) activities in Project Planning, Design, and Maintenance. While our current concerns require that we focus on karst areas, we use geologic mapping for all our projects statewide. Rock cuts, coal mines, aggregate sources, blast design, surface- and ground-water contamination, landslide studies, and stormwater management are all examples of problems that we have to deal with where good geologic mapping is a basic tool. If mapping were not available, we would have to do it ourselves. The result would be a lesser product at more cost and time.

The economic benefit of accurate mapping is that we can clearly define the limits of our work, thus optimizing the scope of costly geotechnical exploration and design. On the other hand, modern mapping helps us conduct enough studies so that we do not miss geologic hazards. The cost to the State of even one sinkhole in the roadway or one small landslide is measured in millions of dollars. The cost to the State of an unexpected sinkhole on a construction site can easily run to hundreds of thousands. Mapping does not locate specific hazards, but it does guide the engineering geologist and geotechnical engineer in developing an adequate subsurface investigation.

Currently SHA is building a data base of geologic hazards on the highway system. This data base will include records of sinkholes, landslides, rockfall, and coal mines. The goal is to make the data base compatible with the geographic information system (GIS) being developed by a consultant. The value of current geologic mapping available through GIS will enhance our ability to understand and interpret the field observations that we make for ourselves.

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Last modified 15 April 1998
Maintained by John Watson and Kathie Watson