HARGIS + ASSOCIATES, INC. HYDROGEOLOGY ENGINEERING

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1 HARGIS + ASSOCIATES, INC. HYDROGEOLOGY ENGINEERING La Jolla Gateway 9171 Towne Centre Drive, Suite 375 San Diego, CA Phone: Fax: February 5, 2018 VIA Mr. David P. Bolin, CHG Principal Hydrogeologist ORANGE COUNTY WATER DISTRICT Ward Street Fountain Valley, CA Re: South Basin Groundwater Protection Project, Additional Groundwater Assessment Field Sampling Plan Addendum 1 Dear Mr. Bolin: Hargis + Associates, Inc. (H+A), on behalf of the Orange County Water District (OCWD), prepared the Additional Groundwater Assessment Field Sampling Plan and Quality Assurance Project Plan Addendum (FSP) as part of the South Basin Groundwater Protection Project (SBGPP) (H+A, 2017a). The FSP described additional assessment activities to be conducted in support of the Remedial Investigation and Feasibility Study that is being conducted in the cities of Santa Ana, Irvine, and Tustin, California (the Study Area). Specifically, the FSP described additional groundwater assessment activities that are and will be conducted to further characterize the hydrogeology and extent of contamination in areas of the SBGPP that have been identified as having key data gaps; and provide data to support the development of appropriate remedial actions. H+A prepared an analysis of data gaps that described the process of identifying the key data gaps and a summary of the results of the analysis (H+A, 2017b). The analysis of data gaps identified seven areas where additional monitor well clusters were recommended. Installation, sampling, and aquifer testing at six of the proposed monitor well clusters commenced in mid-2017 and is on-going (SAM-7 thru SAM-11; SAM-13) (Figure 1). Construction of one of the seven monitor well clusters was deferred (SAM-12) and the recommended activities to complete the data gaps analysis at this location were revised in October 2017 (H+A, 2017c). The revised proposed activities include installation, sampling, and testing of two new deeper monitor wells; and sampling and testing of the closest accessible existing Former Service Chemical Facility shallow monitor well (MW-42B or MW-43B). With the exception of SAM-12, the new monitor well clusters being installed and sampled as part of the FSP are located within2 and near the downgradient portions of the SBGPP (H+A, 2017a). More than 500 monitoring wells have been installed as part of contaminant investigation programs at source sites located within and near the SBGPP source areas. In general, samples collected from the source site monitor wells are shallow (up to 70 feet below land surface) and analyzed for a limited suite of analytes. The wells installed as part of the FSP are being sampled and analyzed for Contaminants of Concern (COC) and an expanded suite of analytes to evaluate potential remedial technologies in the Feasibility Study (Table 1). In order to characterize the groundwater quality in the areas downgradient of relatively high COC concentrations it is recommended that groundwater samples be collected and analyzed for the expanded suite of analytes from select existing accessible source site shallow monitor wells that are not on source properties (Figure 1; Table 2). The recommended locations include: Other Offices: Folsom, CA Mesa, AZ Tucson, AZ

2 HARGIS + ASSOCIATES, INC. Mr. David P. Bolin, CHG February 5, 2018 Page 2 Holchem/Former Service Chemical monitor well MW-42B or MW-43B in the vicinity of SAM-12 as previously proposed in the vicinity of SAM-12 (H+A, 2017c); GE Plastics monitor wells MW-8A and MW-8B; Bell Industries monitor wells OW-1A and OW-1B. It is anticipated that the groundwater samples could be collected by OCWD during an upcoming monitoring event conducted by the respective potentially responsible party in the next several months. In the case where an upcoming event is not planned in this time frame or the respective party does not want to provide samples to OCWD, then OCWD would collect the samples using methods outlined in the FSP. If you have any questions or require additional discussion, please contact us. Sincerely, HARGIS + ASSOCIATES, INC. Christopher G.A. Ross, PG 4594, CHG 221 Principal Hydrogeologist Kevin L. Coons, PE Senior Engineer CGAR/KLC/jak

3 HARGIS + ASSOCIATES, INC. Mr. David P. Bolin, CHG February 5, 2018 Page 3 Enclosures Figure 1. Table 1. Table 2. Groundwater Sampling Locations Handling Protocol for Initial Groundwater Samples Proposed Existing Monitor Well Sampling Locations and Recent Contaminants of Concern in Groundwater cc w/encl: Mr. Roy L. Herndon, RG CHG, District Hydrogeologist, Orange County Water District Mr. William Hunt, Executive Director Operations, Orange County Water District REFERENCES CITED Hargis + Associates, Inc., 2017a. South Basin Groundwater Protection Project, Additional Groundwater Assessment Field Sampling Plan and Quality Assurance Project Plan Addendum, Version 2.0. Orange County Water District, Orange County, California. May 9, 2017., 2017b. Letter to David P. Bolin of Orange County Water District Re: Summary of Data Gaps Evaluation and Basis of Proposed Additional Groundwater Assessment Well Locations. June 12, 2017., 2017c. Letter to David P. Bolin of Orange County Water District Re: South Basin Groundwater Protection Project Remedial Investigation, Data Gaps, Groundwater Assessment Well Location SAM-12. October 31, _A01_01_FSPAddm1.docx

4 W EDINGER AV E EDINGER AV WALNUT AV S BRISTOL ST W WARNER AV S MAIN ST S STANDARD AV E WARNER AV S GRAND AV 13-OW-1A 13-OW-1B 55 NEWPORT AV VALENCIA AV 1 73 EXPLANATION Proposed Existing Groundwater Sampling Location Document Path: C:\Users\SLP\Documents\In-Box\OCWD SB NCP\GIS\Application\2018_01_SouthBasinGW_FSPAddendum.mxd W SEGERSTROM AV PAULARINO AV S FLOWER ST W MACARTHUR BLVD SUNFLOWER AV W DYER RD MAIN ST S MAIN ST 5-MW-42B SAM-7 SAM-13 MACARTHUR BLVD MAIN ST 405 E DYER RD SAM-8 5-MW-43B SAM-12 RED HILL AV SAM-lO SAM-9 7-MW-8A 7-MW-8B SAM-ll VON KARMAN AV BARRANCA PKWY ALTON PKWY JAMBOREE RD JAMBOREE RD WARNER AV HARVARD AV Proposed OCWD Monitor Well Cluster OCWD Monitor Well Cluster installed in 2017 Study Area Source Sites 0 1,000 2,000 4,000 Groundwater Sampling Locations FIGURE 1 Feet Regarding basemap features and information from THOMAS BROS. MAPS, reproduction with permission granted by THOMAS BROS. MAPS. Some information on this map is copyrighted by THOMAS BROS. MAPS. It is unlawful to copy or reproduce all or any part therof, whether for personal use or resale, without prior, written permission of THOMAS BROS. MAPS. ORANGE COUNTY WATER DISTRICT SOUTH BASIN GROUNDWATER PROTECTION PROJECT FOUNTAIN VALLEY, CALIFORNIA

5 TABLE 1 HANDLING PROTOCOL FOR INITIAL GROUNDWATER SAMPLES ANALYTE METHOD OCWD LABORATORY METHOD SAMPLE CONTAINER OTHER REQUIREMENTS PRESERVATION METHOD* MAXIMUM HOLDING TIME GROUPING FIELD PARAMETERS ph SM 4500 H + B -- Field TEMPERATURE SM 2550 B -- Field 1 X 1 LITER HDPE NA 15 MINUTES TOTAL RESIDUAL CHLORINE SM 4500 Cl -- Field DISSOLVED OXYGEN SM 4500 O -- Field ORGANIC COMPOUNDS VOLATILE ORGANIC COMPOUNDS + OXYGENATES 8260B CHLOROETHYL VINYL ETHER, ACROLEIN & ACRYLONITRILE 8260B -- 1,4-DIOXANE 8270C OR Modified SEMI-VOLATILE ORGANICS 8270C X 40 ml VOA VIAL, TEFLON 3 X 40 ml VOA VIAL, TEFLON VIALS FILLED COMPLETELY, NO HEAD SPACE VIALS FILLED COMPLETELY, NO HEAD SPACE FILLED TO NECK FILLED TO NECK HCl, 14 DAYS COC 3 DAYS COC N-NITROSO-DIMETHYLAMINE (NDMA) 521 OCWD NDMA Test Method ORGANOCHLORINE PESTICIDES 8081A ocwd TOTAL ORGANIC CARBON SM 5310B SM 5310B TOTAL PETROLEUM HYDROCARBONS 8015B X 40 ml VOA VIAL, TEFLON 3 X 40 ml VOA VIAL, TEFLON FILLED TO NECK FILLED TO NECK FILLED TO NECK VIALS FILLED COMPLETELY, NO HEAD SPACE FILLED TO NECK VIALS FILLED COMPLETELY, NO HEAD SPACE Na 2 S 2 O 3, COOL TO <10 o C 1 YEAR EXTRACTION / 1 YEAR AFTER EXTRACTION COC H 2 SO 4, 28 DAYS HCl, 14 DAYS GENERAL INORGANIC PARAMETERS TOTAL ALKALINITY SM 2320 B SM 2320 B 14 DAYS BICARBONATE/ALKALINITY SM 2320 B SM 2320 B 14 DAYS TDS SM 2450 C SM 2450 C 7 DAYS TSS SM 2450 D SM 2450 E 7 DAYS UNPRESERVED, COOL ELECTRICAL CONDUCTANCE SM 2510 B SM 2510 B 2 X 1 LITER HDPE FILLED TO NECK TO 4 o C 28 DAYS INORGANIC ANIONS (CHLORIDE NITRATE, NITRITE, SULFATE) HOURS HEXAVALENT CHROMIUM HOURS COC METHYLENE BLUE ACTIVATED SUBSTANCES SM 5540C SM 5540C 48 HOURS / SM / SM Required for total inorganic AMMONIA 4500-NH NH 3 1 LITER PLASTIC nitrogen H 2 SO 4, TOTAL PHOSPHORUS , 4500-PF 28 DAYS TOTAL PHENOLS LITER AMBER GLASS H 2 SO 4, SULFIDE (TOTAL) SM 4500-S 2 SM 4500-S 2 -D 500 ml PLASTIC 1 ml ZINC ACETATE AND NaOH, COOL TO 4oC 7 DAYS PERCHLORATE X 1 LITER HDPE 28 DAYS COC OIL & GREASE 1664A -- CYANIDE SM 4500 CN / SM 4500 CN / REQUEST HEM AND SGT HCl, 28 DAYS 1 X 1 LITER HDPE NaOH, COOL TO 4oC 14 DAYS 1170_H01_2018-1_FSPadd1_Tbl_1 Page 1 of 3

6 TABLE 1 HANDLING PROTOCOL FOR INITIAL GROUNDWATER SAMPLES ANALYTE METHOD OCWD LABORATORY METHOD SAMPLE CONTAINER OTHER REQUIREMENTS PRESERVATION METHOD* MAXIMUM HOLDING TIME GROUPING METALS TOTAL & TOTAL RECOVERABLE METALS TOTAL ARSENIC TOTAL ANTIMONY 6010B TOTAL BERYLLIUM 6010B TOTAL RECOVERABLE SELENIUM TOTAL RECOVERABLE CADMIUM 6010B TOTAL RECOVERABLE CHROMIUM 6010B TOTAL RECOVERABLE COPPER 6010B DAYS TOTAL RECOVERABLE LEAD 6010B X 1 LITER HDPE FILLED TO NECK HNO 3, TOTAL RECOVERABLE NICKEL 6010B TOTAL RECOVERABLE SILVER 6010B TOTAL RECOVERABLE THALLIUM 6010B TOTAL RECOVERABLE ZINC 6010B TOTAL CALCIUM 6010B TOTAL MAGNESIUM 6010B TOTAL MERCURY DAYS HARDNESS SM 2340C CALC TRIVALENT CHROMIUM CALC -- DISSOLVED METALS DISSOLVED COPPER 6010B EPA DISSOLVED LEAD 6010B EPA FIELD FILTERED, HNO 3, 1 X 1 LITER HDPE FILLED TO NECK 180 DAYS DISSOLVED ZINC 6010B EPA DISSOLVED MANGANESE 6010B EPA DIOXINS & FURANS 1613B -- FILLED TO NECK 1 YEAR EXTRACTION 40 DAYS AFTER EXTRACTION COLIFORMS TOTAL & E. COLI SM ml HDPE STERILE Must use sterile bottle provided by lab Na 2 S 2 O 3, COOL TO <10 o C 8 HOURS ASBESTOS X 1 LITER HDPE 48 HOURS 1170_H01_2018-1_FSPadd1_Tbl_1 Page 2 of 3

7 TABLE 1 HANDLING PROTOCOL FOR INITIAL GROUNDWATER SAMPLES ANALYTE METHOD OCWD LABORATORY METHOD SAMPLE CONTAINER OTHER REQUIREMENTS PRESERVATION METHOD* MAXIMUM HOLDING TIME GROUPING ADDITIONAL MONITORED NATURAL ATTENUATION PARAMETERS DISSOLVED OXYGEN FIELD METER -- Field OXIDATION-REDUCTION POTENTIAL FIELD METER -- Field ph FIELD METER -- FLOW CELL OR TRANSFER Field NA NA ELECTRICAL CONDUCTIVITY FIELD METER -- Field TEMPERATURE FIELD METER -- Field TURBIDITY FIELD METER -- Field DISSOLVED GASES (METHANE/ETHENE/ETHANE) RSK175 3 X 40 ml VOA VIAL, TEFLON 7 DAYS DISSOLVED IRON EPA ML PLASTIC FIELD FILTERED, HNO 3, 180 DAYS FOOTNOTES ( * ) = Additional preservative may be required if residual chlorine is contained in water, contact laboratory with questions. (<) = Less than o C = degrees Celsius H 2SO 4 = Sulfuric Acid NA = Not applicable COC = Compounds of concern HCI = Hydrochloric Acid HPDP = High Density Polyethylene HNO 3 = Nitric Acid Lab = Laboratory HEM = N-Hexane Extractable Material ml = Millileter Na 2S 2O 3 = Sodium thiosulfate HNO 3 = Nitric Acid OCWD = Orange County Water District NaOH = Sodium Hydroxide PCBs = Polychlorinated biphenyls SGT = Silica Gel Treated TDS = Total Dissolved Solids TSS = Total Suspended (non-filterable) Solids VOA = Volatile Organic Analysis 1170_H01_2018-1_FSPadd1_Tbl_1 Page 3 of 3

8 TABLE 2 PROPOSED EXISTING MONITOR WELL SAMPLING LOCATIONS AND RECENT CONTAMINANTS OF CONCERN IN GROUNDWATER Well ID Facility Recent Sample Date Screen Interval (feet below land surface) micrograms per liter 1,1-Dichloroethene (1,1- DCE) 1,4-Dioxane Tetrachloroethene (PCE) Trichloroethene (TCE) Perchlorate OW-1A Bell Industries 3/10/ < NA OW-1B Bell Industries 3/10/ < NA MW-42B* MW-43B* Holchem/Former Service Chemical Holchem/Former Service Chemical 7/10/ ,500 NA 7/13/ ,400 NA MW-8A GE Plastics 2/22/ NA NA NA NA 66 MW-8B GE Plastics 10/19/ NA NA NA NA 3.2 * Either MW-42B or MW-43B will be sampled based on accessibility NA = Analyte not analyzed 1170_H01_2018-1_FSPadd1_Tbl2 1 of 1