ARCHIVED REPORTS_XR0007177 - Laserfiche WebLink

Home Browse Search

SVEIAS system was shut down Although residual petroleum hydrocarbon concentrations remain present beneath the site, the operation of the SVEIAS system resulted in the achievement of site remediation goals (13) Mass balance calculation of substance treated versus that remaining; Estimated mass balance calculations using TPHg data collected before the implementation of remedial action were previously submitted to the RWQCB in SECOR's Corrective Action Plan, dated September 8, 1998 According to assumptions outlined in the historical estimated mass calculations included in Appendix K, an estimated 24,355 pounds of residual TPHg was present in soil before remediation at depths ranging between 25 and 100 feet bgs Operation of the SVEIAS system from December 1999 through September 2003, and from June through November 2004 (Table 6) resulted in the estimated removal and treatment of approximately 38,894 2 pounds of TPHg, which exceeded the initial estimate by approximately 14,539 2 pounds Due to the limited amount of post-confirmation soil sampling data, petroleum hydrocarbon mass remaining in soil was estimated based on the assumptions outlined in Appendix K and the area over which pre-remediation concentrations were detected in soil borings in the vicinity of the source areas (in the vicinity of the USTs and pump islands) Based on these criteria, approximately 937 7 pounds of TPHg remain beneath the site Estimated TPHg mass in groundwater before and after remediation were calculated using assumptions outlined in Appendix K Based on these assumptions, approximately 37 84 pounds of petroleum hydrocarbon mass were present in groundwater before remediation Due to shrinkage of the dissolved plume beneath the site over time, with residual impacts currently centered in the area of well MW-1, the estimated area of impact used for post-remediation dissolved TPHg mass calculations is significantly smaller Based on these assumptions, approximately 35 14 pounds of TPHg remain within groundwater beneath the site This post- remediation mass estimate may be somewhat high due to the elevated average TPHg concentration used in the calculation (14) Assumptions, parameters, calculations and model used in risk assessments, and fate and transport modeling, Information pertaining to RBCA assessments previously performed at the site is included In SECOR's Corrective Action Plan dated September 8, 1998 (15) Rationale why conditions remaining at site will not adversely impact water quality, health, or other beneficial uses, and I Residual petroleum hydrocarbons in soil and groundwater beneath and in the vicinity of the site will not adversely impact water quality health or other beneficial uses based on the following o The majority of the source of petroleum hydrocarbons has been removed from beneath the site 0 Two municipal wells were found within a 2,000-foot radius of the site One well is located approximately 900 feet northeast (upgradient) Although the other well is located Time Oil Asmt&SCM doc 20 March 17,2005 1 770T 41 658 00 0015