Laserfiche WebLink
} <br /> 4491 Durham Ferry <br /> Page 2 <br /> Contaminated groundwater was produced by the pumping of RW1 and was reportedly <br /> stored on site in a 21,000 gallon tank pending removal by a licensed hauler. The report <br /> indicated that over a period of 14.25 hours groundwater was extracted at a fiowrate of 5 <br /> gallons per minute which would generate approximately 4,300 gallons. Thank you for <br /> submittal of documentation for the disposal of this water; PHSIEHD questions how 7,000 <br /> gallons was generated for disposal. Please provide clarification, since the difference <br /> between 4,300 gallons and 7,000 gallons is significant. <br /> Soil Contamination <br /> The summary of contamination in the vadose zone failed to include the results of the soil <br /> borings drilled and sampled on December 14, 1987 prior to the tank removals, the soil <br /> samples collected on February 28, 1989 at the time of the tank removals, and the soil <br /> samples collected on August 28, 1991 during the installation of MW2 and MW3. Please <br /> update Table 1 Summary of Soil Sample Analytical Results. <br /> A function of the corrective action plan preparation process is an evaluation of the vertical <br /> and horizontal extent of contamination. PHSIEHD did not specifically request additional <br /> soil investigation in areas where the vertical migration of contamination may have been <br /> underestimated, however, you should be aware of this possibility. <br /> An accurate estimate of the mass of soil and groundwater contamination is important so <br /> that remediation systems may be accurately sized and to evaluate remediation <br /> effectiveness. A revision of the submitted estimate is required. <br /> Remedial Action Plan <br /> PHSIEHD concurs that the greatest costs for remedial actions are generally associated with <br /> treatment equipment and operation and maintenance time. As these costs are accrued on <br /> a monthly basis, the installation of additional extraction points can reduce the remediation <br /> time and therefore, overall costs for the remediation project. <br /> The remedial action plan (RAP) included vapor extraction using VW1, VW2, VW3, RW1 <br /> and a proposed RW2. The statement that the distribution should exert enough vacuum to <br /> cover the areal extent of soil contamination is not demonstrated by Figure 12. Since <br /> systems do not typically perform as theoretically predicted, PHSIEHD recommends that <br /> additional extraction wells be installed. <br /> Groundwater extraction wells for the purpose of dewaterring to enhance vapor extraction <br /> at least has the potential to remove significant contaminant mass more so than free <br /> product removal. The drawback to using groundwater extraction for free product removal <br /> is that product is smeared throughout the formation within the drawdown zone. Another <br /> drawback is the volume of waste water which is produced and which requires treatment <br /> and disposal. <br /> The groundwater extraction method which was proposed indicated that 7 gallon per minute <br /> pneumatic pumps would be placed approximately 2 feet off the bottom of the well (28 feet <br /> below grade) when groundwater depths range from approximately 8.5 to 17 feet below <br /> grade. The supplemental material which Clearwater supplied with correspondence dated <br /> June 5, 1996 referenced extraction methodology termed bioslurping and enhanced vacuum <br />