Ka’Boom: The Rising Cost of Removing Bedrock from Development Properties

November 20, 2010

While tourists flock to New Hampshire annually to hike the granite peaks and enjoy the craggy vistas, the price to remove that rocky resource during the development of properties underlain by shallow bedrock is potentially getting more expensive in the Granite State.

 

Given that more than 40 percent (%) of New Hampshire residents rely upon individual bedrock water supply wells for their source of potable water, and developers in the more populated areas of the state are beginning to use the more “undesirable” parcels of land, the proximity of rock blasting activities to private drinking water supply supplies is of concern. 

 

Based upon data compiled by the United States Geological Survey, New Hampshire’s use of explosives has increased six fold since the 1990s.  Commercial grade explosives used in the majority of blasting projects can be assigned to one of three groups:

  1. Ammonia nitrate/fuel oil (ANFO)
  2. Watergel/slurry; or
  3. Emulsions.  

 

These explosives all contain a relatively large percent of ammonium nitrate; however, they vary significantly in their reaction to water.  In general, the cost of a given explosive is proportional to its ability to dissolve in water.  The more water resistant the product, the higher the cost.  The most commonly used blasting agent (ANFO) is also reportedly the least expensive to manufacture hence it also has the greatest application.  Unfortunately, cost and application of the correct product are not always married on a development project.  Based upon its inherent physical properties, ANFO is not an applicable agent of choice when blasting bedrock that exhibits wet blast holes, artesian conditions, or rapid recharge of ground water.  The agent consists of a mixture of approximately 94% ammonium nitrate and 6% diesel fuel and results in a blast agent that is approximately 33% nitrogen by weight.  ANFO readily dissolves in water and as such has the ability to potentially release large quantities of nitrate into an aquifer. 

 

Evidence of ground water and surface water impacts resulting from blasting activities has been well documented at several recent high profile development projects in New Hampshire.  This has prompted the New Hampshire Department of Environmental Services (NHDES) to develop draft guidance documents in fall 2008 and summer 2009 to assist stakeholders with a basic understanding of the regulatory concerns and drivers associated with blasting projects.  The ultimate goal of the NHDES is to ensure that New Hampshire’s valuable water resources are adequately protected with respect to water quality and water yield.  To that end, the draft documents were written with examples of Best Management Practices for blasting projects and suggested baseline water quality monitoring programs; a concise summary of current legal authorities associated with many aspects of a blasting project from permitting to enforcement; and suggested minimum language for municipalities to use in their local blasting ordinances.

 

To date, the documented impacts to ground water and surface water have primarily included nitrate and to a lesser degree nitrite and perchlorate.  The potential health implications associated with the consumption of nitrate in particular is cause for concern and as such, one focus of the draft guidance was to promote the need for the creation of proactive blasting and monitoring plans. 

 

The NHDES initiative in disseminating information on blasting activities seeks to:

  • make sure measures are being implemented to protect water resources when blasting activities are taking place
  • implement monitoring when blasting is occurring near drinking water resources
  • ensure mitigation plans are developed prior to blasting when drinking water resources are nearby, and
  • identify legal approaches to protecting water resources when rock blasting and related activities are occurring.

 

Input from the NHDES Drinking Water and Groundwater Bureau (DWGB) is currently sought during review of Alteration of Terrain (AoT) applications to address water quality and quantity issues specifically during planned blasting projects in areas of known bedrock supply wells.  Ultimately, it is the intent of the NHDES to begin revisions to the AoT rules to incorporate many of the water quality concerns incorporated in the current draft blasting policy documents.  According to author Brandon Kernen, P.G., of the NHDES DWGB, the draft documents have met with mixed reviews from stakeholders.  While municipalities have in general appreciated the suggested ideas to incorporate into existing ordinances, industry representatives have viewed the documents as “too prescriptive.”  As a result, the NHDES is in the process of incorporating additional public comments into a new draft document that will primarily focus on providing stakeholders with suggested components to a comprehensive pre- and post-blast water quality monitoring program; will identify issues that should be addressed early in the blasting plan for a project; and that will provide additional key information to assist municipalities with amending their local ordinances to incorporate appropriate language such that potential receptors are adequately assessed, monitored, and protected during the permitting and performance of a blasting project.

 

Andrea W. Kenter, P.G.

awkenter@geoinc.com