Notice from Loudoun Water dated May 15, 2012:
VDH-Approved Plan to Address Turbidity Issue Completed
Ashburn, Virginia – May 15, 2012: Loudoun Water is pleased to announce it has completed implementing its Virginia Department of Health-approved plan to address the August 2011 turbidity incident that resulted in a temporary shutdown of Well F in the Raspberry Falls community. As a result, following a visual inspection by VDH and several rounds of performance testing reviewed by VDH, Loudoun Water is returning the well to service this afternoon. (NOTE: Because the August 2011 event did not cause any permit violation or contamination and because the modifications did not directly impact water treatment, quality or capacity, formal VDH approval was not required prior to restart.)
On August 9, 2011, elevated turbidity was observed in a portion of the system during routine monitoring. Following the incident, Loudoun Water enlisted Emery & Garrett Groundwater, Inc., a company with a significant, positive track record of work in Loudoun County, to conduct an investigation into the incident. In consultation with VDH, Emery & Garrett and Loudoun Water then conducted a series of pumping tests and water quality tests to further assess turbidity to determine the cause of the elevated turbidity.
Most importantly, the investigation confirmed that Well F is an acceptable water source and should not experience high turbidity if the pumping rate of water is controlled. It revealed that the event was caused by unforeseen hydraulic transients in the raw water main. These transients – which, in this case, were rapid fluctuations in flow and pressure – allowed the well pump to operate at higher discharge rates than it was designed to maintain.
The investigation also found that when Well F began pumping, it was immediately, but briefly, pumping at higher than anticipated rates due to low backpressure in the pipeline. This was referred to by Emery & Garrett as a “hard start”. Water levels in Well F were also found to rapidly fluctuate by one foot or more during some pumping intervals. These fluctuations confirmed that unstable (and variable) pumping rates were occurring, agitating water within with well casing, and increasing the turbidity in the well.
Based on the results of the investigation, Loudoun Water submitted a response plan to VDH to address the issues and return Well F into service. The plan was approved by VDH in February completed this spring and is attached to this release. The plan included:
- Modifying the current set-up of the raw water pipeline between Well F and the water storage tank in the treatment plant to prevent over-pumping of Well F. The modification involved the installation of a flow control valve at the water treatment plant. The valve controls the start-up of pumping and prevents “hard starts”, reducing the potential for elevated turbidity.
- Placing Well F online at the production rate of 75 gallons per minute for a minimum period of three months. After that period of time, the pumping rate may be increased to the permitted level of 100 gallons per minute to meet demands.
- Monitoring water levels, flow rates, and turbidity continuously for the next 12 months as Well F is in operation.
A comprehensive list of Frequently Asked Questions is attached to help explain the incident and our work to return the well to service. The results of the Emery & Garrett investigation can be found on the Raspberry Falls page of our website, www.loudounwater.org. Click on the Community Systems link on our homepage then Raspberry Falls.