SUFFOLK, VA – HRSD recently discovered an exceedance in the maximum contaminant limit (MCL) for nitrite in 11 of 15 samples of SWIFT Water used to recharge the Potomac Aquifer from early June through June 21. The exceedance occurred while biomass in the biological filters was still developing during initial startup and is no longer an issue.
Nitrite is converted to harmless compounds through natural processes in the groundwater environment, with nitrite dropping below detection limits after 30 days in the ground. This has been confirmed through ongoing soil testing being conducted at the SWIFT Research Center.
In an abundance of caution and in demonstration of HRSD's ability to withdraw SWIFT Water from the aquifer, HRSD is clearing the aquifer of the SWIFT Water with elevated nitrite levels. An estimated 4.8 million gallons of SWIFT Water exceeded the MCL. Removal of SWIFT Water from the aquifer will continue until the water being removed tests at half of the MCL, and withdrawal will continue for an additional seven days beyond that time to ensure all SWIFT Water not meeting specifications has been withdrawn. The total amount being withdrawn is estimated at 20 million gallons and the total time to remove the water is estimated to take 10 to 14 days. For additional treatment process controls, a nitrite analyzer is being added as another critical control point and lab reporting systems have been modified to highlight results that approach or exceed an established limit.
SWIFT Water entering the aquifer travels slowly - initially moving at a rate of speed of approximately 50 feet over three days' time and slowing significantly as the water moves further away from the recharge well. With the nearest drinking water well more than one mile (5,280 feet) away from the SWIFT Research Center replenishment well, the instability of nitrite in the groundwater environment, and the slow travel speed of SWIFT Water, at no time was there any risk of elevated nitrite groundwater reaching any drinking water well.
In addition, the tasting system at the SWIFT Research Center was not impacted by this issue. Free chlorine is added to SWIFT Water used for tasting in order to achieve the required drinking water chlorine residual. The addition of chlorine oxidizes the nitrite, eliminating it and ensuring that the SWIFT Water available for tasting meets drinking water requirements.
The SWIFT Research Center, located on the grounds of HRSD's Nansemond Treatment Plant in Suffolk, VA, began operations on May 15 as a learning facility that will inform the development of future full-scale SWIFT facilities for aquifer replenishment.
HRSD's mission is to protect public health and the waters of Hampton Roads by treating wastewater effectively. A political subdivision of the Commonwealth of Virginia, HRSD was created by public referendum in 1940 and currently serves 18 cities and counties in southeast Virginia - an area with a population of 1.7 million.
HRSD Vision: Future Generations will inherit clean waterways and be able to keep them clean.
Should you have any questions or comments, you may contact:
Leila Rice, APR - 757.460.7056
Director of Communications