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Ms. Daisy Wei • -2- is 2 December 2011 <br /> years and currently range from 2 to 200 mg/kg nitrogen. Ammonium concentrations are less <br /> than 1 mg/kg. <br /> However, in two locations of the composite soil sampling (sites 3K and 4K), both within the <br /> bagging plant area, there has not been a noticeable decline in nitrogen at the four to six-foot <br /> depth. These elevated nitrogen concentrations range from 330 to 470 mg/kg, ammonium <br /> ranges from 6 to 475 mg/kg, and the pH of the soil is acidic, between pH 3.8 and 5.8. <br /> Also in the bagging plant area, Koppel obtained discrete soil samples to identify the source of <br /> the elevated concentrations of nitrogen observed in monitoring well KP-3. These discrete <br /> sampling results show that at the four to six-foot depth, nitrogen ranges from approximately <br /> 100 to 500 mg/kg. Grab groundwater samples obtained from these borings contained nitrogen <br /> ranging from approximately 300 mg/L to 1,000 mg/L. <br /> These high concentrations of nitrogen near the water table, which is approximately eight feet <br /> below ground surface, may be contributing to the groundwater nitrogen plateau of <br /> approximately 300 mg/L that is observed in the monitoring wells. Most ammonium appears to <br /> have been converted to nitrate, although some residual ammonium remains where pH is <br /> below 4.0. <br /> In the Ten Year Report, Koppel suspects that the low pH may be inhibiting strong plant root <br /> development and proposes to conduct additional plant root zone sampling to assess plant <br /> root health. <br /> Conclusion <br /> Central Valley Water Board staff concur with Koppel that the data show that in general, <br /> phytoremediation has been improving soil and groundwater quality, denitrification may be <br /> limited due to lack of electron donors, and acidity may be limiting the effectiveness of <br /> phytoremediation in the bagging plant area. <br /> By 24 February 2012, please provide a work plan to assess if amendments are needed to <br /> provide a healthy root zone environment at the bagging plant area. In the 2012 Annual <br /> Report, which is due 1 November 2012, please provide a strategy and implementation <br /> schedule to reduce nitrogen concentrations in the vicinity of KP-3 and improve the <br /> effectiveness of phytoremediation. <br /> Thank you for undertaking a comprehensive investigation into the source of rising nitrogen <br /> concentrations in KP-3. A video log of the well did not reveal anything unusual, but the <br /> composite and discrete sampling program did show where there may be inhibitors to healthy <br /> root development. <br /> If you have any questions, you may contact me by telephone at (916) 464-4680 or by email at <br /> aterrell@waterboards.c .gov. <br /> AMY ERRELL <br /> Private Sites Cleanup Unit <br /> Distribution List attached <br />