WORK PLANS - Laserfiche WebLink

Home Browse Search

Jeff Wong 40RION San Joaquin County Environmental Health Department 30 October 2019 Page 2 unacceptable safety hazard. On 18 September 2019, Pacific Coast Locators, Inc., of La Crescenta, California, marked underground utilities at the site using ground penetrating radar and electromagnetic locating instruments. Underground utilities were identified within 5 feet of 12 wells associated with the former East System (OS-57, OS-48, OS-47, OS-46, OS-45, OS-1613, OS-44, OS-15 B, OS-43, OS-13 B, OS-41, and OS-12 B). Of these wells, eight are screened within the shallowest water-bearing zone at the site (A-Zone) and four are screened within the underlying B-Zone. Photographs of the wells and respective utility markings are included in Attachment A. Due to the safety hazards associated with overdrilling near underground utilities, this method is not feasible for destruction of the 12 wells listed above. As an alternative, Orion evaluated the feasibility of grouting these wells by assessing (1) groundwater impacts in the vicinity of these wells, (2) the potential for degradation of the well seals over time, and (3) potential for cross-contamination of water-bearing zones at the site. Orion determined that well destruction by grouting is an acceptable method based on the following rationale: 1. The wells proposed for destruction are former ozone injection groundwater remediation wells. While petroleum hydrocarbon analytical data are not available from the ozone wells, it can be assumed that groundwater impacts in the direct vicinity of the ozone wells have decreased below cleanup objectives after approximately 8 years of ozone injection operation. 2. Groundwater analytical data from nearby monitoring wells indicate that concentrations near the ozone wells are generally below regulatory cleanup objectives. Recent groundwater data at nearby downgradient groundwater monitoring wells are summarized in the table below: Water- Petroleum Hydrocarbon Concentration ( /I)�') Bearing Date Well Zone Sampled TPHg TPHd Benzene MTBE Cleanup Objective ftll)lb) 100 100 1 13 AR/MW-21A 8/7/19 ND<100(`) 88 J« ND<0.5 ND<0.5 A PS/MW-18 8/7/19 ND<100 92 J ND<0.5 5.3 AR/MW-21 B 8/7/19 ND<100 107 ND<0.5 ND<0.5 B AR/MW-186 8/7/19 ND<100 114 ND<0.5 0.51 (a) Total petroleum hydrocarbons as gasoline(TPHg),total petroleum hydrocarbons as diesel(TPHd),benzene,and methyl tert-butyl ether(MTBE)reported in micrograms per liter(pg/1). (b) Cleanup objectives for benzene and MTBE are based on California maximum contaminant levels(MCLs). Because California MCLs have not been established for TPHg and TPHd,San Francisco RWQCB Environmental Screening Levels are included in this table for comparison. (c) Not detected(ND)above the reporting limit listed. (d) Laboratory qualifier 0): The identification of the analyte is acceptable;the reported value is an estimate. S:\Clients\52STTC\LTR\LTR002.docx 10/30/19