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ekienvironment <br /> & water <br /> 2827 Spafford Street <br /> Davis,CA 95618 <br /> (530)341-2848 <br /> ekiconsult.com <br /> 13 July 2023 <br /> Greg Gibson <br /> City of Lathrop <br /> 390 Towne Centre Drive <br /> Lathrop, CA 95330 <br /> Subject: 2023 Spring Groundwater Monitoring Report <br /> City of Lathrop Consolidated Treatment Facility <br /> Waste Discharge Requirements Order No. R5-2018-0023, Monitoring and Reporting <br /> Program R5-2016-0028-03 Rev3 <br /> (EKI B90088.03) <br /> Dear Mr. Gibson: <br /> Please find enclosed the 2023 Spring Groundwater Monitoring Report, City of Lathrop Consolidated <br /> Treatment Facility, prepared on behalf of the City of Lathrop pursuant to the Waste Discharge <br /> Requirements (WDRs) of Regional Water Quality Control Board (RWQCB) Order No. 115-2018-0023, <br /> Monitoring and Reporting Program (MRP) R5-2016-0028-03 Rev3. The WDRs were rescinded by the <br /> RWQCB on 22 June 2023. <br /> This report describes the Spring monitoring event for 2023 (First Semiannual 2023)for the period January <br /> 2023 through June 2023.Water level gradients and directions beneath Mossdale,Central Lathrop Specific <br /> Plan (CLSP), River Islands, Consolidated Treatment Facility (CTF), and Pond S6 were typical of past <br /> monitoring events. Water levels in most monitoring wells increased due to the winter precipitation and <br /> associated increases in San Joaquin River levels. However, River Islands well MWR-12 continues to be dry, <br /> likely due to temporary construction dewatering in the vicinity. Hence,the gradient and azimuth beneath <br /> Land Application Area (LAA)A30 could not be calculated.Additionally,water level compliance well MWR- <br /> 9 was damaged during construction and the developer is formulating plans for proper abandonment. <br /> COMPLIANCE WELL EXCEEDANCES <br /> • Total coliform was detected above the groundwater limitation in three of the 17 compliance wells <br /> (MWR-28, CLSP-3, and MWM-19). Coliform counts in samples from MWR-28 and MWM-19 were <br /> within the historical range, however, counts in CLSP-3 were the highest recorded. As in the past, <br /> coliform bacteria are variable and erratic from well to well and between monitoring events. <br /> • Nitrate as Nitrogen (NO3-N) concentrations in CLSP-11 and KMW-10 exceed their respective <br /> groundwater limitations. The NO3-N concentration in CSLP-11 was within the historical range, <br /> however,the NO3-N concentration in KMW-10 was the highest recorded. <br /> • The Total Dissolved Solids (TDS) concentrations in the sample from MWR-32 exceeded the <br /> proposed groundwater limitation but was within the historical range. <br /> Daly City,CA•Irvine,CA•Marin,CA•Napa,CA•Oakland,CA•Roseville,CA <br /> Centennial,CO•Glastonbury,CT•Dedham,MA•Holyoke,MA <br />