SEPTIC SYSTEM INSPECTION, REPAIR AND RE-DESIGN
Convenience Store & Gas Station
Millstone, New Jersey

Project Description:

The on-site septic system at an existing convenience store and gas station in Millstone Township, New Jersey was under-sized and not designed to handle high customer volume associated with seasonal traffic from a large, nearby amusement park.

The site’s original septic system was designed to handle an average daily sewage volume of 1,828 gallons-per-day (gpd).  Sewage effluent volumes during months when the park was open were estimated to be 3,500 gpd.  This seasonal overload caused several outbreaks from the existing disposal field that resulted in health violations.  Whitestone was hired to evaluate and re-design the site’s sanitary sewage system to accommodate the excessive seasonal loading conditions and prevent future system failures.

Whitestone’s initial investigative efforts included invasive inspection of the existing septic system components, metering water consumption, and sampling effluent to determine strength prior discharge.  The initial septic system investigation and wastewater characterization study identified several key factors contributing to system failure including:

• excessive discharges associated with seasonal variations in business,
• elevated sewage effluent strengths, and
• water softener discharge.

Whitestone’s engineers re-designed the failing septic system to address these operating deficiencies and facilitate future store expansion.  The new on-site wastewater treatment and disposal system was sized to handle seasonal high effluent volumes and included separate discharges for water softener backwash, flow equalization capacity, a packaged aerobic treatment unit with denitrification to reduce effluent strength prior to discharge, and expansion of the existing disposal beds.

Because the new system’s design flow was greater than allowed in the site’s Wastewater Management Plan designation, Whitestone was required to obtain a Water Quality Management Plan (WQMP) Amendment from the New Jersey Department of Environmental Protection (NJDEP).  The WQMP amendment was secured despite local political resistance. 

New Jersey Pollution Discharge Elimination System (NJPDES) and Treatment Works Approval (TWA) permits also were required and obtained by Whitestone prior to new system construction.  The NJPDES permitting process included a hydrogeologic investigation with groundwater mounding analysis to verify site recharge conditions.

Whitestone managed the construction bid process and will provide construction phase inspection services for installation of the site’s new, state-of-the-art sewage treatment and discharge system in the Spring of 2009.

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