WORK PLANS - Laserfiche WebLink

Home Browse Search

MEQNFATRIX As described in Section 2.1, the fingerprint of the petroleum hydrocarbon at the Dividend property is similar to that at the High i et/Monterosso parcel. Concentrations of TPH in soil range up to F 7,500 mg/kg on the Dividend property. BTEX was not detected in soil; however, low concentrations of polycyclic aromatic hydrocarbons (PAHs) were detected. A summary of soil data collected by Geo- matrix is included in Appendix B. 1 Groundwater at the Dividend property occurs at about 7 feet bgs and the gradient direction is Fnorth/northeasterly. Based on the results of the monitoring program, groundwater downgradient of the affected soil areas is not impacted by petroleum hydrocarbons. This demonstrates that the degraded Fpetroleum is not a source of dissolved constituents to groundwater and does not pose an environmental t threat. l . Human Health Risk Assessment A Screening Human Health Risk Assessment (Screening HRA) was conducted in accordance with the DTSC Preliminary Endangerment Assessment Manual (Geomatrix, I995). The Screening HRA evalu- ated the potential risk posed b the petroleum resent at the Dividend property - P p y p p p perry to future on-site resi- dents. The Screening HRA methodology assumes that affected soil is at the ground surface and that 6 : residents are exposed to the maximum concentration of chemicals detected in the soil. The conclusion of the Screening HRA was that the petroleum present in soil at the Dividend property did not pose a F. significant risk to future on-site residents; this conclusion was approved by DTSC in a memorandum to CPL dated 3 November 1995. F, 3.0 GROUNDWATER MONITORING PERFORMED BY GEOMATRIX Based on existing data, it appeared that groundwater at the Highiet/Monterosso parcel was not affected by petroleum hydrocarbons. At the request of the San Joaquin County Public Health Services Envi- ronmental Health Division (SJCEHD) and to confirm these data, field activities performed by Geo- matrix consisted of locating and repairing two groundwater monitoring wells, subcontracting an eleva- tion survey for all four monitoring wells, and performing two groundwater monitoring events in all four �R wells. These activities are described below. 3.1 Monitoring Well Location,Repair, and Survey Fj On 5 April 1996, Geomatrix mobilized to the site to perform groundwater monitoring. However, only . monitoring wells MW-3 and MW-4 could be located and sampled at that time; monitoring wells MW-I and MW-2 were covered by soil, debris, and/or vegetation. An attempt was made to locate both wells on 24 April 1996 using a front-end loader to remove soil, debris, and vegetation in the vicinity of the wells. Well MW-1 was located and repaired; well MW-2 was not located at that time. On 2 May 1996, F1 additional soil removal activities were performed and well MW-2 was located and repaired. Excavation services were provided by Kemp Grading and Excavation of Tuolumne, California. Fj 4 F