Laserfiche WebLink
amec— <br /> M-26C2). <br /> Groundwater samples from lower aquifer zone wells M-81D and M-41 D plot <br /> farthest to the right within the Group 3 area, where chloride concentrations in the Q3 <br /> samples were 280 and 320 mg/L, respectively, exceeding the drinking water standard <br /> of 250 mg/L. Potential sources of salinity to groundwater in the Ripon area include <br /> recharge from the WWTP, discharge of water containing elevated total dissolved salts <br /> (TDS) at former Neenah Paper Company and predecessor companies (collectively <br /> referred to as NP hereafter), and irrigation return. Chloride concentrations were highest <br /> in lower aquifer wells M-81D and M-41 D, which is inconsistent with deeper background <br /> major ion composition reported in the USGS study, indicating that vertical conduits <br /> such as idle supply wells associated with NP could provide a likely explanation for TDS <br /> impacts at M-81D and M-41 D. <br /> Our evaluation of the study results indicates that ongoing shallow sources of anthropogenic <br /> salinity appear to enter the deeper aquifer zones via conduit wells. This same pathway is <br /> known to exist for COCs and is likely the primary mechanism by which COCs entered the <br /> intermediate and lower aquifer zones. CDCs detected in groundwater samples from wells TH- <br /> 10, M-31 C and M-17C have been associated with historical discharges of untreated industrial <br /> wastewater at the WWTP. The major ion composition of groundwater from these wells does <br /> not strongly indicate the influence of anthropogenic discharge, perhaps due to the long <br /> timeframe since untreated wastewater was discharged (and prior to lining of the primary <br /> treatment lagoons approximately 10 years ago), or because of a conduit type mechanism for <br /> COC transport to deeper aquifer zones. <br /> 3.1.2 Minor Ions <br /> Nitrate, iron and boron comprise the minor ions analyzed during this study. Nitrate and iron are <br /> both redox-sensitive; their importance in understanding redox conditions is described in <br /> Section 3.3. This section focuses on nitrate and boron as these constituents can be indicative <br /> of industrial wastewater discharges, municipal wastewater discharges and agricultural <br /> activities (fertilizers) (Standley et al, 2008, Robertson and Blowes, 1995, Bundschuh et al., <br /> 1993), and therefore may also provide an indication of groundwater movement because the <br /> WWTP is a known area of industrial and municipal wastewater discharge. Although nitrate <br /> concentrations are influenced by strongly reducing conditions, dissolved boron exists as a <br /> borate salt in groundwater. As this form, boron (as borate) is a conservative groundwater <br /> tracer (i.e. borates are not considered to be biodegradable and do not adsorb to aquifer <br /> sediments to an appreciable extent; Bundschuh et al., 1993). Groundwater samples collected <br /> during a recent State-funded water quality study of the Eastern San Joaquin Subbasin <br /> generally had low boron concentrations (typically less than 0.05 mg/L; Bennett et al., 2010), <br /> suggesting that boron concentrations are expected to be low in groundwater absent <br /> anthropogenic impacts. In the same study, nitrate concentrations were generally less than the <br /> California Maximum Contaminant Level (MCL) of 10 mg/L as nitrogen. <br /> AMEC Geomatrix, Inc. <br /> \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.4\Attach B-4.docx 134-6 <br />