MTBE IMPACT TO DOMESTIC WELLS – INVESTIGATION, MODELING AND REMEDIATION

A development of homes within a beach community in Delaware has experienced potable water impact. Analysis of the wells indicated elevated levels of benzene and MtBE. Acceptable potable water was established immediately via carbon filtration. Lack of an aquitard, and the potential for salt-water intrusion, resulted in not pursuing the installation of deep potable wells. Based on what would better serve the public, an existing water line has been extended by the state to the area of impact but over 300 wells are present down-gradient.

A source area investigation is complicated by access and the presence of three gasoline retail facilities upgradient of the impacted development; two of which have been investigated (one a no further action letter and the other closure after remediation). To determine the potentially responsible parties (PRPs) the investigations included: direct push borings, geotechnical borings, and multi-level cluster wells (five per boring) to 90 feet below grade surface. The investigations have indicated that the two prior case file facilities to be the PRP’s for the impact.

With source areas now under remediation (mechanically remote pulsed air sparge soil vapor extraction and periodic high vacuum events) the link to the development is being assembled through modeling and a remediation plan for the dissolved phase plume is in the design phase. Options for this deep remediation include: continued pumping to prevent further impact, muti-level pulse ozone sparging, and bio-augmentation. Due to the large horizontal and vertical area of impact, multiple source areas, the down-gradient domestic wells, and the need to provide a corrective action plan (source and deep transport zones), the scope of this project is extensive. Ultimately, the project has moved forward based on legal, financial, and corrective action obligations and by choices and decisions of the PRPs and their consultants, the impacted residents, and the state.