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ESAEnvironmental environmental Ms.Margaret Lagorio Science March 9,2005 Page 2 Monitoring Well Construction Specifications Monitoring wells MW-2, MW-3, and MW-4 were installed in the parking lot area while MW-1 is located within the adjacent landscaped area(Figure 1, attached). Monitoring wells MW-1 through MW-4 were constructed using factory pre-packed wells installed within 2.5-inch borings. The wells were constructed of solid 0.75-inch diameter, schedule 40 PVC casing from 0 to 10 feet below ground surface(bgs)and 0.75- inch diameter schedule 40 PVC 0.010 well screen installed from 10 to 30 feet bgs. The pre-pack filter medium is constructed of 1.25-inch diameter schedule 40 PVC 0.010 well screen installed from 10 to 30 feet bgs containing number 2/12 sand filter pack material. The sanitary seal consists of bentonite pellets (transition seal)installed above the filter pack between 5 and 10 feet bgs. The annular seal consists of grout (neat cement) from 5 feet to 1 foot bgs within a six-inch bore hole. The first five feet of each monitoring well was hand-augured to achieve the monitoring well annulus diameter required by the SJCEHD. A 7-inch diameter traffic-rated well box with concrete collar and locking extension cap was placed over each well from 1-foot bgs to the surface. Refer to Attachment 1 for the schematic of the monitoring well construction. Monitoring Well Destruction Procedures ESA will contract a California-licensed well drilling company to destroy the four groundwater monitoring wells. At this time, it appears that Precision Sampling Inc. of Richmond, California(Precision)is the most appropriate drilling company to complete this work because it was Precision that installed the monitoring wells in 2001. Precision will initially remove the well cover, well box, and concrete collar/surface seal from each well. Monitoring wells MW-1,MW-2, MW-3, and MW-4 will be over-drilled from the ground surface to 30-feet, or maximum depth of the original soil boring, using a 6.5-inch outside diameter hollow stem auger.' The drillers will remove from the boring the monitoring well casing, sanitary seal (including bentonite), pre-pack filter medium, and well screen. As the augers are removed from the soil boring, the holes will be backfilled with Portland cement to approximately 5-inches from the surface(parking lot locations)and 1-foot from the surface at MW-1 in the landscaping. Grouting will be inspected by a SJCEHD field inspector. Finish repair of the parking lot locations will involve placing and adequately compacting cold-patch asphalt in the upper five inches to the existing parking lot surface. Topsoil will be placed in the upper one-foot of the backfilled boring in MW-1. Following the work,ESA will ensure the parking lot is clear of debris and that the finished holes do not settle to the extent that they represent a potential pedestrian safety hazard. To every extent feasible,ESA will endeavor to return the landscaping area to its original condition. Until recently, ESA proposed to destroy MW-1 in-place by pressure grouting due to its inaccessible location and potential safety hazard. Based on follow-up conversations,Precision Drilling Inc(Precision)revealed that it is not feasible to pressure grout 0.75-inch,pre pack groundwater wells. The only way to destroy these wells is to remove the well material,over-drill,and grout. ESA,with assistance from Precision,developed an alternate strategy to destroy MW-I. With concurrence from UOP,Precision will access MW-I through the landscaped area using rubber mats to protect the landscaping from drill rig damage. 225 Bush Street,Suite 1700 San Francisco,California 94104 (415)896-5900 fax 896-0332 email:esa.sf@esassoc.com