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KOPPEL-STOCKTON TERMINAL MONITORING WELL ABANDONMENT AND CONSTRUCTION WORK PLAN At the request of the Water Board (Water Board,2010),CH2M HILL is submitting this Monitoring Well Abandonment and Construction Work Plan for the abandonment of four monitoring wells (Monitoring Well Pair KP-5S and KP-51)and Monitoring Wells KP-BG-1 and KP-10S)and the construction of two wells(Monitoring Well KP-10S-R and KP-4D).This report includes the following information: • Rationale for well abandonment and construction • Description of well drilling procedures • Description of well abandonment,construction and development • Schedule for installation and sampling 2.0 Rationale for Well Abandonment and Construction Since 2007,four wells have been inadvertently damaged or buried and potentially damaged at Koppel as a result of construction or industrial activities on adjacent properties.It is proposed that all four wells be abandoned in August 2010.These wells include Monitoring Well Pair KP-5S and KP-51)and Monitoring Wells KP-BG-1 and KP-10S.Well completion diagrams are included in Attachment 1. Furthermore,two wells are proposed for construction, a replacement well for Monitoring Well KP-10S and a deep well located adjacent to Monitoring Well KP-4(see Figure 1). 2.1 Monitoring Well Pair KP-5S and KP-51) Monitoring Well Pair KP-5S and KP-51) is a cross gradient shallow/deep well pair which was covered by a newly developed dirt access road on BNSF property.Since construction in 1999,ammonia has not been detected above 0.3 milligrams per liter(mg/L)in either monitoring well and nitrate has only been detected at Monitoring Well KP-5S,with concentrations relatively stable,ranging from 49 to 85.1 mg/L. Monitoring Well Pair KP-5S and KP-51) is in a high traffic area,and it is not recommended that replacement wells be constructed at this location. KP-5S is cross-gradient to the original poplar test grove and there are wells directly downgradient(TG-5 and KP-4)that show phytoremediation and natural attenuation are addressing nitrate concentrations. For these reasons,it is not recommended to replace KP-5S.However,installation of a deep well, Monitoring Well KP-41),adjacent to Monitoring Well KP-4 (a shallow well located furthest down gradient)is recommended.Previous monitoring has shown that there is a downward gradient at Koppel (CH2M HILL,2009),and this location would provide better monitoring of deep,downgradient nitrate concentrations than the original KP-51)location(see Figure 1). 2.2 Monitoring Well KP-10S Monitoring Well KP-IOS was one of three wells constructed in 2006 at the request of the Water Board to evaluate the direction of groundwater flow and to monitor nitrogen concentrations in the northern portion of the property (Water Board 2004). Monitoring Well KP-10S also replaced Cal Farm Supply's southernmost monitoring well (MW-6) that was inadvertently destroyed in 1999. Nitrate-nitrogen concentrations in MW-6 ranged from 216 to 367 mg/L(Karsyn Environmental,2004).These ranges of nitrate concentrations are similar to what has been detected in Monitoring Well KP-1 OS(145 to 400 mg/L). Data collected from Monitoring Wells KP-10S,KP-11S,KP-12S,and MW-6 indicates there is a RDW 02300006(CLR4507.DOCX) 2 EW V02283MDD