From Loudoun Water on December 5, 2011 (w/attachments):
Loudoun Water has completed its investigation into an event on August 9, 2011 when elevated turbidity was experienced in a portion of the system, resulting in a shutdown of Well F, a water well serving Raspberry Falls.
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. Emery & Garrett and Loudoun Water then conducted a series of pumping tests and water quality tests to further assess turbidity and bacteria to determine the cause of the elevated turbidity.
The investigation 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. Well F was found to have been intermittently pumped at a rate higher than the recommended rate of 100 gallons per minute during the period between July 7 and August 9, 2011, which ultimately resulted in the elevated turbidity.
The investigation also found that when Well F began pumping, it was immediately, but briefly, sent into an over-pumping state due to low backpressure in the pipeline. This is referred to by Emery & Garrett as a “hard start”.
Given the results of the investigation, Emery & Garrett made short-term and long-term recommendations to address the elevated turbidity. As a result of their recommendations, Loudoun Water submitted a response plan to the Virginia Department of Health. If the plan that was submitted is approved by VDH, Loudoun Water will do the following: 1) Install, in consultation with the Virginia Department of Health, an automatic flow control valve on the raw water main at the water treatment plant – this will eliminate the “hard start” conditions and allow us to prevent over-pumping; 2) bring Well F back online at a production rate of 75 gallons per minute (gpm) for a minimum of three months. After that period of time, the pumping rate may be increased to 100 gpm to meet demands; and 3) monitor water levels, flow rates and turbidity continuously for the next 12 months.
The results of the investigation confirm that Well F is an acceptable water source and should not experience high turbidity if the pumping is controlled. Following the implementation of the response plan and approval of the work by VDH, Well F will again be used to supply water to Raspberry Falls.
Attached are a statement from Loudoun Water about the results of the investigation and a list of Frequently Asked Questions about the investigation. The actual investigation report is too large to email so it will be posted, along with the attached documents, on the Raspberry Falls page of Loudoun Water’s website, www.loudounwater.org. Click on the Community Systems link on the homepage and then on Raspberry Falls.
Manager of Community Relations
44865 Loudoun Water Way
Ashburn, Virginia 20146