Laserfiche WebLink
3 <br /> Slurry Wail. The construction of a 2-foot wide slurry wall around the contaminated <br /> zone was considered. To be effective, a slurry wall must be keyed into the impermeable <br /> base of the aquifer. The impermeable base of the aquifer below ARCO Station 434.is at a <br /> depth of at least 200 feet. While constructing a slurry wall to this depth is feasible, the <br /> cost is impractical for the project site. In addition, the slurry wall would have to extend <br /> off site to completely encapsulate the contaminated groundwater plume. <br /> Reverse Osmosis or Ultrafiltration. This method involves pumping the groundwater <br /> through a membrane capable of filtering out the hydrocarbon molecules. This method <br /> requires large amounts of energy to pump the groundwater through the membrane. In <br /> addition, the process would also filter out any other constituent in the groundwater, <br /> including the naturally occurring dissolved solids. This would necessitate a pretreatment <br /> process to the ultrafiltration or reverse osmosis process. This process is not considered <br /> feasible due to high capital and O&M costs. <br /> 1 J Ultraviolet Light and Ozone (Oxidation. This method invo.ves irradiating the BTX <br /> containing groundwater with ultraviolet (UV) light and contacting the BTX molecules with <br /> ozone. The UV radiation will break the benzene. ring carbon double bonds of the BTX <br /> .,J molecules. Once the carbon double bonds are broken, the ozone is capable of oxidizing the <br /> molecules to carbon dioxide and water. This process is high in capital and O&M costs. i„ <br /> 's <br /> addition,few applications of this+.ethnology on BTX compounds have been completed. <br /> Insitu Biological Degradation. Insitu biodegradation involves creating an environment in <br /> the aquifer capable of sustaining a microorganism population. The microorganisms would <br /> biologically oxidize the orgastic product to carbon dioxide and water. To create this <br /> i environment, oxygen, nutrients, and microorgaidsm cultures must be supplied to the <br /> aquifer. In this case, to maintain the optimum environment and monitor the results would <br /> require significant amounts of well drilling and pumping off site. In addition, the <br /> proximity of Municipal Well 12 increases the risk of introducing bacteria to the municipal <br /> water supply. <br /> ' Alternatives Selected for Evaluation <br /> ,# Brown and Caldwell his evaluated the following measures to remediate the problems at <br /> ARCO Station 434. The alternatives are divided into two categories; (1) remediation of <br /> contaminated soil and (2) remediation of contaminated groundwater. The remediation <br /> alternatives are discussed below. <br /> Contaminated Soil Remediation <br /> Four remediation alternatives were analyzed to determine the preferred methods for <br /> s removing the product from ti-e sail. <br /> y� Alternative AI--Excavatien and Off--Site Disposal. This method would remediate the <br /> problem in the shortest period of time. However, this method could cause the longest <br /> ----disruption---in--station--operations.----Due---to-the-type--of-.soil-(sand),-depth-_and__width---of_.-------- _--- -- -- <br /> rexcavation, and proximity of buildings, excavation of the contaminated area would be <br /> "t difficult. The contaminated soil is located on site in an area about 30 feet in diameter and <br /> 55 deep. To excavate the soil, a ramp to a depth of about 30 feet would be needed along <br /> x with sufficient shoring. <br /> k <br />