Client project details
MVD - Production Well MVD-6
The Merrimack Village District (MVD) was forced to discontinue use of Production Well MVD-6 in 1988 after Volatile Organic Compounds (VOC) generated from a neighboring metals recycling facility contaminated the sand and gravel aquifer from which groundwater resources were pumped. A pump-and-treat remediation system subsequently was installed at the source of the contamination, limiting the ability of additional contamination to escape from the recycling facility property, and gradually reducing VOC concentrations in the aquifer. Because Well MVD-6 is capable of producing peak yields of nearly 1,500 gallons per minute (gpm), MVD wanted to determine the feasibility of returning it to service.
EGGI designed and carried out a 30-day pumping test of Well MVD-6. Purposes of this testing program included: 1) determining whether the well could be pumped at a lower targeted rate of 800 gpm (1.2 million gallons per day) without entraining additional VOCs from the contaminant source area; 2) determining whether VOC concentrations at the production well would exceed federal drinking water standards in response to sustained pumping; 3) delineating accurately the combined Wellhead Protection Area (WHPA) for MVD-6 and neighboring Production Wells MVD-7 and MVD-8, and 4) obtaining approval for use of the well as a public drinking water supply.
Throughout a monitoring period that lasted several months, EGGI measured water levels at more than 30 monitoring points, including monitoring wells, shallow piezometers, and surface water measuring points. Water samples for VOC analysis were collected from the pumping well and from a network of monitoring wells at intervals throughout the monitoring period. Using the results of the pumping test and information from well logs, EGGI constructed a numerical groundwater flow model which was used to delineate the WHPA and to make predictions about the effects of pumping on the residual VOC contaminant plume. EGGI then produced a report on the pumping test to support MVD’s application to the relevant state agencies for re-permitting Well MVD-6 as a public water supply.
The pumping test indicated that MVD-6 could be pumped at 800 gpm without entraining new contamination from the contaminant source and suggested that VOC concentrations would not exceed drinking water standards at the production well. MVD is considering whether to reinstate Well MVD-6 again as a possible source of water or to add other possible sources of supply to meet their existing and future water system demands.
EGGI then produced a report on the pumping test to support MVD’s application to the relevant state agencies for re-permitting Well MVD-6 as a public water supply."