Spill Investigation, Remediation System Design, and Groundwater Monitoring, Uniondale, NY. A release of gasoline was discovered during the excavation of former fuel dispensing system at a cemetery operated by the Town of Hempstead. Floating product was observed on the groundwater within the excavation. Through a series of preliminary investigations, dissolved and free phase gasoline constituents were detected in the soil and groundwater surrounding the removed USTs. Walden completed further investigations to determine the impact of the spill to the soil and groundwater downgradient of the former tanks.

Walden developed and implemented a detailed soil gas/groundwater Geoprobe investigation utilizing an on-site laboratory to bound an offsite BTEX plume extending approximately one-half mile from the site. The investigation included the design and installation of an 8-well, offsite groundwater monitoring well network to track the migration of the plume. Walden conducted a Soil Vapor Extraction and Air Sparge (SVE/AS) pilot study to determine design parameters to support detailed design of a full scale SVE/AS remedial system. Walden designed and subcontracted out the SVE/AS system installation work. With the client utilizing its own work force for general construction items, the resulting installation savings was approximately 50 percent of the contractor’s quoted prices.

The original SVE/AS system consisted of seven Soil Vapor Extraction wells and four Air Sparge wells. In 2001, free product was detected in a monitoring well. Further investigations concluded that the free product had leaked from the diesel fuel filter. After removing the free product from the site, the SVE/AS system was upgraded to include an additional two Soil Vapor Extraction wells and seven Air Sparge wells.

The SVE/AS system continues to remediate the soil and groundwater on the site. A chemical oxidation system, utilizing ozone, was designed and recently installed, with NYSDEC approval to treat contamination detected offsite. Since the detection of the spill Walden continues to monitor the remedial efforts through monitoring wells on a quarterly basis. Quarterly monitoring reports are prepared and submitted to NYSDEC to track the effectiveness of the remedial system. Walden designed a new UST system for the site, managed the contractor bidding process, and provided field oversight during construction.