Mr. Britt McMillan, a privately employed hydrologist who is based in Virginia Beach, was invited by Supervisor Wanda Thornton to provide a briefing to citizens of Chincoteague Island regarding the groundwater of the Eastern Shore. He delivered his briefing in the Chincoteague Community Center on Monday, October 15 at 7:30 p.m.
His presentation described the Shore's ground water system of aquifers, their depths and locations relative to both bay and sea shores, and the impact that pumping levels have had (data source is USGS sample observation wells) over time since the 1950's.
There is a big spike in the test data in the early 1970's, when Tyson & Purdue developed their respective operations here. Mr. McMillan, spoke of the risks of 'up-coning' and salt water intrusion, relative to over pumping. Up-coning is when the silt & clay layer (called a 'confining unit') which separates the vertical aquifers 'cones up,' and prevents water from being extracted from the Yorktown Aquifer, which is just below the water-table or Columbia Aquifer, and is where pumping occurs here on the Shore. Mr. McMillan said the risk of salt water incursion is very real here, and he said that it will happen, but he did not speculate as to when this might occur.
Mr. McMillan offered the following hydrological facts about groundwater on the Easter Shore:
• During a 'normal' year on the Eastern Shore 44 inches (mean average data), of rain water falls on the surface
• Only 6 inches of this reaches the Columbia Aquifer, which is about 20 feet below the ground,
• Only .05 inches of the 44 inches ultimately reaches the Yorktown or confinement aquifer, where pumping occurs.
• 84% of the precipitation is lost to evaporation,
• 15% of the precipitation is retained in surface water streams and ponds.
• Only 1% of the 44 inches of annual rainfall reaches the confinement aquifer for pumping use.
Permitted groundwater in Accomack County over 20 years has increased by 80% due to Tyson and Purdue. Purdue is permitted to pump up to 1.8 MGD (million gallons per day). Tysons is permitted to pump up to 1.0 MGD
DEQ and irrigation stakeholders met recently to discuss use of holding ponds in lieu of pumping, for re-usable farm irrigation. Agriculture accounts for 40% of permits in Accomack Co. Mr. McMillan also said that most agricultural irrigation already comes from surface water (ponds, etc.).
DEQ stochastic models are currently in development to test for water quality and volume over wider areas on the Eastern Shore. Mr. McMillan said that most fresh water is located in aquifers along the 're-charge spine' which basically tracks with Rt. 13 down the center of the peninsula. Locations nearer to the bay and ocean, as well as very deep aquifers, are brackish or salty.
During the Q&A session following the presentation, Mr. McMillan said that a waste water sewage treatment plant using a water injection system (as was done in FL and CA), is not feasible for the Shore, due to the small land area here. He said such a system would corrupt existing wells here, and that the result would be sewage would be pumped back out in wells due to incursion into the water table via the injection process. He cited new de-salination processes via 'membrane treatment' as a promising cost-effective future option for municipalities and even for commercial and private dwellings.
Notes by Victoria Weiskopf
N.B. These notes do not constitute the public record of this meeting. The information contained herein is offered in good faith, is presented as accurately as possible, is thought to be a complete account of the proceedings. These notes are intended to be a public service devoid of political commentary for those who are interested in following the civic affairs of Chincoteague Island. Notes of the meeting are recorded, transcribed and distributed by volunteers who receive no financial compensation for their efforts.
