WORK PLANS FILE 1 - Laserfiche WebLink

Home Browse Search

' The air sparging and vapor extraction pilot test will consist of the following: ' • We propose that a dedicated vapor extraction well be installed and used for the vapor extraction pilot test and use surrounding monitoring wells as vacuum pressure monitoring points. This well will be a 3-inch horizontal pipe, buried to a depth of 5 feet, and ' perforated for 20 feet. It will be located between SB-1 &MW-102. • The surrounding monitoring wells will be used to measure vacuum drawdown, which would allow the evaluation of the radius of influence of vapor extraction. The vacuum ' pressure measurements will be made in the surrounding monitoring wells and dedicated observation well using an electronic manometer with a resolution of 0.01 inches of water ' column vacuum pressure. • Four vapor extraction observation wells will be installed at two foot increments from the extraction trench well. ' • Two dedicated air-sparging wells will be installed to inject air for the purpose of assisting in volatile removal. These wells are proposed be installed into the sandy soil below 30 feet, one 3 feet to the north and one 2 feet to the south of the vapor extraction trench well. ' • A variety of vapor extraction and air-sparging flow rates will be used to evaluate the optimum configuration. • The air sparging/vapor extraction pilot test is expected to run approximately 6 to 8 hours ' during which up to 3 time-sequenced samples will be collected for analysis. The air samples will be tested for BTEX and TPH-gasoline at Air Toxics Limited in Sacramento (CA ELAP # 1149). Air samples collected during the pilot test can accompany the ' Authority to Construct (AtoC) Permit application to be filed with the San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD). • To ensure that the pilot test can be performed, we recommend that an asphalt cap be ' placed over the vapor extraction trench well and for 20 feet east and west of the well, and out to Durham Ferry Road to the north and to the building to the south. This will form the needed barrier to reduce short-circuiting of vapor extraction from the atmosphere. ' • The San Joaquin Valley Unified Air Pollution Control District and the Merced County Department of Environmental Health will be notified 48 hours prior to commencement of the pilot test. 2.2 General Design of Vapor Extraction Trenches ' Because of the relatively shallow depth to groundwater at this site a series of shallow vapor extraction trenches are proposed to address the contaminated zone within the site boundaries. The advantage of using trenches over wells is that trenches expose a larger surface area for ' treatment allowing higher volume airflows at a lower vacuum pressure. Operating the vapor extraction system at lower flow rates and higher vacuum pressure will limit the amount of groundwater mounding in response to the vacuum extraction. Groundwater mounding if not ' controlled can reduce the effectiveness of soil vapor extraction by hydraulically sealing off zones. ' We propose that the trenches will be installed in the area of the impacted soil. The trenches will be excavated to a depth of 5 feet. The trenches will be prepared for the installation of ' horizontal lengths of vanor extraction nines by first Dlacing a nea gravel filter Dack around