Groundwater Extraction and Treatment

Management of Migration (MOM) Groundwater Remediation

This system is designed to extract contaminated groundwater, send it through a specifically designed treatment system, and inject it into wells or let it infiltrate from surface ponds back into the immediate aquifer without a net change in the groundwater levels (Boart Longyear). Details of the system are provided below.

Ground Water Extraction System

The extraction system utilizes “near-source” and “near-receptor” wells. Three near-source wells (wells within the contamination zone) are located in the western part of Parcel 2 near the Parcel 1/Parcel 2 boundary, while four near-receptor wells (wells closer to the boundary of the property) are located along the southeastern property boundary of Parcel 2. Extracted groundwater will be pumped to a new groundwater treatment system building located on Parcel 2, where it will be treated to the extent necessary for on-site discharge at the rapid infiltration basin (RIB), and injection well gallery (IWG).

The extraction system design is based on an operating influent flow rate of 130 gallons per minute (gpm), per the results of the MOM optimization analysis presented in the 30% Design. To allow for a potential increase in MOM pumping rates if needed and/or to allow for increased capacity during Parcel 1 source area remediation, treatment equipment is designed using an assumed maximum influent (i.e. peak) flow rate of 160 gpm. Design operating conditions assume extraction of 90 gpm from near-receptor wells, and 40 gpm from near-source wells. The maximum operating flow rate at any one single well is 40 gpm, which is consistent with the observable yield.

Groundwater Treatment System

The groundwater treatment system will be housed in a new building on Parcel 2. The system has been designed based on an average operating influent flow rate of 130 gpm and a maximum influent flow rate of 160 gpm. The groundwater treatment system will initially discharge treated effluent to both a RIB and IWG, and the treated effluent must meet the applicable groundwater discharge standards. Surface water discharge, i.e. directly into Kelley Brook, may be considered in the future if surface water discharge standards are determined to be achievable under the full scale operating conditions.

The treatment process includes metals removal (e.g. iron, manganese, and arsenic) via oxidation and filtration (Siemens) followed by organics removal via an advanced oxidation technology (AOT) system that oxidizes organics to carbon dioxide and water (APT Water). The metals removal system converts soluble (dissolved) metals to their insoluble (particulate) forms via the following steps: 1) oxidation of soluble iron and manganese via aeration within an equalization tank to insoluble metal hydroxides/oxides, and 2) addition of an oxidizer (sodium hypochlorite) within a 3,000 gallon reaction tank to oxidize any remaining soluble manganese. The removal mechanism for arsenic is via adsorption onto the naturally occurring iron in groundwater when it is oxidized.  If necessary, additional iron in the form of ferric chloride can be provided to enhance removal of arsenic. The addition of sodium hydroxide to increase pH will also be necessary to optimize oxidation of the metals, which is pH dependent. The insoluble metals are then filtered from the groundwater by a microfiltration membrane system. Following metals removal, the remaining organics are removed via the AOT system.

Based on the success at reducing 1,4-dioxane to low levels at similar sites, ozone/hydrogen peroxide (ozone/peroxide) based AOT was selected for the organics treatment process. In addition to its performance record, ozone/peroxide AOT is also preferable to ultra violet (UV)/peroxide treatment technology because UV systems require significantly greater energy and maintenance, mostly through the usage and frequent replacement of UV lamps.

Groundwater Treatment System

As with the groundwater extraction system, the groundwater discharge system is designed based on an average operating effluent flow rate of 130 gpm and a maximum effluent flow rate of 160 gpm. All effluent flow will be sent to Parcel 2 discharge locations, consisting of a RIB and IWG. Treated water will be discharged to the RIB and IWG simultaneously, with average operating discharge rates of 90 gpm and 40 gpm for the RIB and IWG, respectively. All wells in the IWG will be vented so that injection occurs under the force of gravity alone and is not under the pressure of the effluent distribution pipe.

Treatment System Operations

The treatment system is designed to be operated 24/7 until NH groundwater standards are met.  It is very difficult t o estimate how long the treatment will be required by the estimates range from 15-30 years.  It will be installed and then operated by a professional water treatment contractor (Weston Solutions).