07.09.09
Sometimes the Easiest Solution is Best
I would like to share a somewhat success story or, at least one in the making. I am currently involved with a shopping center that was developed from an assemblage of properties that once included two gas stations. It was later discovered that that these gas stations combined, had released thousands of gallons of gasoline during their operational history and, subsequently, created a large phase separated plume; basically, a large area of gasoline floating on the water-table beneath the shopping center property. By the time I became involved, the property owners had gone through three consultants and spent millions dollars in remediation costs over a ten year period.
Briefly, Consultant 1 recommended pump and treat whereby recovery wells were installed, large volumes of water pumped, and treated on site before discharging to the sanitary sewer. This was later deemed ineffective by the State, fines incurred for improper discharge, and another consultant was hired. Consultant 2 came up with this elaborate pump and treat system, enhanced by vapor extraction, using horizontal wells: a series of horizontal wells were installed below the plume (25 feet deep) along the main axis (400 feet long) to dewater the aquifer; another series of wells were installed above the water table to extract the vapors; and then everything was directed to on onsite compound (oil water separator to air stripper to charcoal cells, and finishing with a thermal oxidizer). However, after 3 pump replacements and a broken compressor, the system was shut down after 3 years. Consultant 3 opted to use mobile, multi-phased extraction (MME) treatment method (aka, enhanced fluid-vapor recovery or EFR). After eight of these 8-hour treatments over a two year period, and removing 10-15 gallons of gasoline per event, this method also proved ineffective, I was brought on board. My collaborative solution was not to aggressively attack the problem, but to let gravity do its job. What the previous consultants failed to recognize was that the formation materials consists of fine grained silts, clay and sand sized weathered bedrock. The storage capacity of the formation may be high, but its ability to transmit water is very low; therefore, attempts to pull large volumes of water along with the gasoline, is not going to be effective. Instead, we I opted was to use product-only recovery pumps. These pumps are fitted with a hydrophobic membrane that only lets the gasoline into the pump (ie, keeps water out) and eliminates any costs associated with onsite treatment. The pumps are also, pneumatic (hooked up to an air compressor) that only run when they are full (saves energy and wear-and-tear); the pumps initially ran once a week for 3 hours and, after five weeks, we collected 65 gallons of gas. I think the easiest solution is the most cost effective and productive in this case.
