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EDMUND G.BROWN JR. <br /> QJ GOVERNOR <br /> .rky <br /> C A l I F O A N I A MA—EW RODRIGUEZ <br /> SE RO <br /> Water Boards ENVIRONMENTAL FROT'e CTION <br /> Central Valley Regional Water Quality Control Board <br /> 10 October 2014 <br /> Mr. Brian Duggan <br /> Environmental Manager <br /> Crop Production Services, Inc. <br /> 3005 Rocky Mountain Ave. <br /> Loveland, Colorado 80538-9001 <br /> CONDITIONAL CONCURRENCE WITH SITE INVESTIGATION WORKPLAN, CROP <br /> PRODUCTION SERVICES, VERNALIS, 35100 S. HIGHWAY 33, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the 31 July 2014 Site Investigation Work Plan (Work Plan), and the <br /> 28 April 2014 2014 First Semi-Annual Groundwater Monitoring and Sampling Report <br /> (Monitoring Report), both prepared by Rubik Environmental, Inc. Crop Production Services <br /> (CPS) is investigating current nitrate and ammonium conditions in soil at the former tank farm. <br /> The Work Plan proposes collecting soil samples from 9 soil borings within the unpaved area of <br /> the former tank farm in order to compare current soil conditions to previously identified <br /> conditions. In addition, a shallow monitoring well (MW-8) is proposed for the right-of-way on <br /> Welty Road to define groundwater quality downgradient of the former tank farm. <br /> Soil Sampling <br /> Samples from each boring are proposed to be obtained from 5 feet, 10 feet, 15 feet and 20 feet <br /> below ground surface (bgs). In 1990 and 1995, soil samples were also obtained at multiple <br /> depths at the former tank farm, as presented in the 18 June 2013 Conceptual Site Model <br /> prepared by Rubik. In order to correlate the new sample results with the older results, the <br /> sampling depths should be similar. The highest density of laboratory-analyzed soil samples <br /> from 1995 was from the 1-3 foot interval. Other sampling depths were from about 5 feet, 8 feet, <br /> and 16 feet bgs. Therefore, CPS should adjust the soil sample depths to more closely match <br /> the historical sampling depths. <br /> The Monitoring Report shows that groundwater at the former tank farm does not consistently <br /> contain either 1,2-DCP nor 1,2,3-TCP, as shown by data from MW-3. Therefore, at the present <br /> time, nitrogen is the only constituent of concern at the former tank farm. <br /> Monitoring Well <br /> The proposed downgradient monitoring well, MW-8, will be installed with a 20-foot screen <br /> extending from about 25 feet to 45 feet below ground surface. This is comparable to the other <br /> monitoring well screen intervals and depths. Central Valley Water Board concur with the <br /> monitoring well placement and design. <br /> KARL E. LONGLEY SCD, P.E.,CHAIR I PAMELA C. CREEDON P.E., BCEE, EXECUTIVE OFFICER <br /> 1102D Sun Center Drive#200.Rancho Cordova,CA 95670 1 www.waterboards.ca.gov/centralvalley <br /> C,RECYCLED PAPER <br />