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Orange Well Net - Background Information

Observation Well Network Presentation

Groundwater is the sole source of water for approximately 40 percent of the citizens of Orange County.  Orange County has a history of proactive measures regarding the investigation and protection of surface water and groundwater resources.  The County cooperated with the United States Geological Survey (USGS) on the production of three technical publications regarding groundwater quantity and quality issues in Orange County.  A Water Resources Committee was first organized in the county in early 1992.  The Water Resources Committee issued the Report of the Water Resources Committee which was later adopted by the BOCC on March 27, 2001.  In this report, the Water Resources Committee “recommends that the county institute a long-term program of well measurements that can provide information as to the effects of land use changes and climatic changes on the availability of ground water.  The USGS data (the reports mentioned above) gives us a base line of information that can be useful into the future with the addition of a good monitoring program.”

Subsequently, the Orange County Commission for the Environment produced the Water Resources Initiative in early 2005.  This report was adopted by the BOCC in May 2005 and included areas for further investigation.  The first goal in the Droughts and Floods section of the Water Resources Initiative was: “Planning and creation of an observation well network to increase available knowledge and data about the impact on ground water supplies from drought.”  The first goal included in the Ground-Water Contamination section of the Water Resources Initiative was: “Further research on elevated radon findings in some ground water samples from the United States Geological Survey studies of 1996/2001.” 

The observation well network that is now being planned for the County will address these issues as well as others including recent work exploring the relationship between bedrock lithology (geology) and arsenic content in groundwater.


The stated goals of the Observation Well Network, consistent with the Water Resources Initiative which was adopted by the BOCC in 2005, are as follows:

1.  Monitor impact of drought on groundwater levels across the county, i.e., to work as an “early warning system” and permit monitoring of groundwater quantity county-wide.

2.  Conduct further delineation of groundwater base flow, which is the contribution of groundwater to streams.  This would provide useful information regarding the amount of groundwater which feeds surface water  reservoirs in the county.

3.Enable further research into groundwater quality issues, including elevated radon and arsenic concentrations detected in groundwater during previous investigations in the county.  Elevated radon concentrations were detected by Cunningham and Daniel in their 2001 report entitled Investigation of Ground-Water Availability and Quality in Orange County, North Carolina.  This report documented radon activity in groundwater ranging from 38 to 4,462 pico Curies per liter (pCi/L), and a median groundwater concentration of 405 pCi/L in Orange County.  The proposed Federal MCL (maximum contaminant level) for radon is 300 pCi/L if no statewide or local EPA approved multimedia mitigation program exists, with an alternative proposed MCL of 4,000 pCi/L if an approved multimedia mitigation program is in place.  The 2001 report of Cunningham and Daniel also identified some correlation between bedrock lithology and radon concentration.

Arsenic concentrations in groundwater in this area of the Piedmont have been documented by several researchers, and Phil Bradley with the North Carolina Geological Survey has recently worked to establish links between arsenic concentrations and certain bedrock lithologies in Orange County. 

A groundwater level measurement program as described above is only possible with a dedicated groundwater observation well network.  Periodic sampling of observation wells in identified areas to research radon and arsenic content in groundwater, as well as other groundwater quality issues, will also be possible.  Partnerships in the development and utilizations of the network are possible with local Federal and State agencies.  Collaboration with local scientists interested in exploring aspects of groundwater quality and quantity issues in the county is also anticipated as a result of the establishment of the Observation Well Network.