H2M was responsible for the professional engineering services associated with the design of two new identical wellhead treatment systems for volatile organic compound (VOC) removal at three pump stations servicing four wells. This project was noted as the highest priority project in the WAWNC Master Plan. A fourth pump station, servicing five booster pumps and one well, was also designed to be rehabilitated under this project. This four site, five well project is currently being constructed in three one year phases.
VOC concentrations above the NYS Maximum Contaminant Level for VOCs. The fourth well, also impacted by VOCs, has been available for only the summer peak pumping season through use of temporary granular activated carbon vessels. When in operation, these wells feed directly into a 4.7 MG ground storage tank. The WAWNC has been unable to utilize the maximum storage capacity of the tank due to lack of acceptable water quality from the three wells. Restoring the capacity of these wells would provide the WAWNC with 5.55 MGD of much needed reserve capacity.
H2M conducted a comprehensive engineering study which led to the preparation of design documents detailing the construction of two 27 foot tall air stripping towers, operating in series, for every two VOC impacted wells. Additionally, tower air discharge vents were specified to comply with NYS Department of Environmental Conservation (NYSDEC) air emission guidelines, as required by Nassau County Department of Health (NCDH). For system versatility, one treatment facility was designed with the option of pumping directly to the distribution system or to the 4.7 MG storage tank. Three separate chemical bulk storage systems for sodium hypochlorite, zinc orthophosphate, and sodium hydroxide were also detailed in accordance with NYSDEC and NCDH regulations.
In addition to the capital upgrades for treatment, the WAWNC also chose to rehabilitate a fourth pump station within this wellhead treatment project. The fourth pump station required the reactivation of one groundwater well, and rehabilitation of five booster pumps that pump from the 4.7 MG storage tank to the distribution system. This groundwater well has been out of service for several years due to elevated nitrate levels. H2M redesigned the existing site piping system to blend the water from this well with the treated water from the aforementioned wells to reduce nitrate concentrations and improve the WAWNC system capacity. The scope of work included in the construction documents is generally described below:
- Select site demolition across four sites
- Rehabilitation/reactivation of well and booster pumps
- Conversion of submersible well pumps to vertical well pumps
- Installation of four 27 foot tall air stripping towers with below grade clearwells
- Installation of transfer pumps and finished water pumps
- Installation of chemical bulk storage tanks and chemical feed systems
- Construction and/or rehabilitation of new and existing buildings
- Installation of generators
- Installation of motor control centers and power distribution
- Site piping and grading modifications
- Installation of new fences, gate operator, driveway, curbs and sidewalk
H2M is administering the construction of this multi-year project, including on-site inspection, shop drawing review, contractor and owner coordination, start-up operations, and regulatory approvals. Completion of the three phases will upgrade the entire group of stations and make them invaluable operating systems.
