1 TO: City Council
FROM: Ryan Smoot, City Manager
PREPARED BY: Carla Dillon, P.E., Public Works Director
MEETING DATE: November 7, 2023
SUBJECT: Groundwater Well Feasibility Study
RECOMMENDATION
Receive and file the final report, a New Groundwater Well Feasibility Study.
BACKGROUND
The New Groundwater Well Feasibility Study was included as part of the City of Lomita CIP Master Plan 2022-2027. The purpose of the study is to evaluate and determine a suitable location for a new groundwater production well.
The Lomita Water System is somewhat unique among water agencies in that it holds significant adjudicated water rights to pump local groundwater, but currently has only one (1) groundwater source well from which to produce that groundwater. The City’s only groundwater well (Well No. 5), with approximate production capability of 1,500 gallons per minute (GPM), is a main component of the Cypress Water Production Facility (CWPF). Due to the detection of benzene at Well No. 5, both the well and the CWPF have been offline since May 2019 in order to install a granulated activated carbon treatment system. During the construction period, the City has been forced to rely on more costly and less reliable water sourced from other parts of the State and the Colorado River. Well No. 5 and the CWPF are expected to be returned to service in early 2024.
In 2018, the most recent full year of production for Well No. 5, the well provided approximately 28% of total water volume delivered to City residents and customers and the remaining 72% was imported from Metropolitan Water District (MWD). The 28% pumped groundwater represents approximately 561 Acre Feet of water produced locally. In recent years, the City has discussed ways to increase its production of local groundwater and reduce its dependance on more costly and less reliable imported Item No. 7j
CITY OF LOMITA
CITY COUNCIL REPORT
2 water sources while maintaining and improving overall water quality throughout the City.
The upgrades to the CWPF are part of these efforts and are expected to allow the City to increase groundwater production from Well No. 5. But, even with this increased local production, the City will continue to be reliant upon water imported from other sources and will not uses its full allowable pumping rights.
In order to maximize the production of water from local sources and thereby increase the City’s projected reliability in normal operations as well as during emergencies, and to decrease the total costs of water production, the City has explored siting a secondary sources of groundwater beyond Well No. 5. A secondary production well would minimize the City’s long-term reliance on imported water and provide an additional level of contingency in case of future operational impacts to Well No. 5.
The City currently holds 1,352-acre feet (ac-ft) of adjudicated groundwater rights in the West Coast Basin. In its last year of normal operations, CY 2018, Well No. 5 produced 561 ac-ft of groundwater, though in the past, CWPF blended treated groundwater with imported water at ratios averaging approximately 40%-50%, or approximately 800 to 1000 ac-ft, still well below the City’s available pumping rights. Additionally, CWPF currently only supplies Zone 1 of the city’s water system, approximately 66% of the city’s customers. Future studies may consider the feasibility of additional local reliance efforts for Zones 2 and 3, but these efforts were not included in this study.
In February of 2023, the City awarded a contract to Stetson Engineers, Inc. (Stetson) to identify best possible well locations. In October, Stetson prepared the final report with three possible areas to consider for siting another groundwater well. All three locations are on the eastern side of the City. Stetson also provided recommendations for next steps and cost estimates. The next steps would include an exploratory program to field verify the water quality and production conditions.
FISCAL IMPACT
None for this action.
OPTIONS
1. Approve staff’s recommendation.
2. Provide alternative direction.
ATTACHMENTS
1. New Groundwater Well Feasibility Study Final, October 2023 3 Reviewed by: Approved by:
_____________________
Gary Y. Sugano Ryan Smoot
Assistant City Manager City Manager
Prepared by:
_______________________
Carla Dillon, P.E.
Public Works Director
NEW GROUNDWATER WELL
FEASIBILITY STUDY
FINAL
PREPARED FOR:
CITY OF LOMITA
OCTOBER 2023
PREPARED BY:
STETSON ENGINEERS INC.
Attachment No. 1
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TABLE OF CONTENTS
Section 1 – Introduction
Section 2 – Hydrogeologic Review
2.1 Regional Geology
2.2 Cross Section
2.3 Hydrogeologic Units
2.4 Well Capacity and Specific Capacity
2.5 Water Quality
2.6 Water Level
2.7 Well Interference
2.8 Summary of Hydrogeologic Review
Section 3 – Constructability
3.1 Land Availability
3.2 Theoretical Well Yield Capacity
3.3 Design and Constructability Constraints
3.4 Estimated Life Cycle
3.5 Permitting Requirement and Regulations
3.6 Operation and Maintenance Considerations
3.7 Treatment Technology Recommendations
Section 4 – Conclusions and Recommendations
References
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LIST OF FIGURES
Figure 1 New Groundwater Well Feasibility Study Flow Chart Figure 2 General Location Map
Figure 3 Geology Map
Figure 4 Cross Section A-A’
Figure 5 Cross Section B-B’
Figure 6 Cross Section C-C’
Figure 7 Thickness Contour of the Silverado Aquifer
Figure 8 Depth from land surface to the Base of Water Bearing Units Figure 9 Specific Capacity
Figure 10 GAMA Well Location
Figure 11 Total Dissolved Solids (TDS) Contour Map
Figure 12 Hydrographs for Lomita #1 (WRD 100818, 100819, 100820, 100821, 100822, 100823)
Figure 13 Figure 13 Hydrographs for Carson #2 (WRD 101787, 101788, 101789, 101790, 101791)
Figure 14 Water Level Contour Map (October 2011)
Figure 15 Schematic Site Layout of Well Construction
Figure 16 Ranking of Potential Well Sites
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LIST OF TABLES
Table 1 Geologic Formation, Aquifers, and Properties within the West Coast Basin Table 2 Maximum Annual Production of Wells in the West Coast Basin near the City of Lomita
Table 3 Water Quality Data from Selected Production Wells and Monitoring Wells Table 4 Well Construction Data (USGS, 2002; WRD; https://gis-apps.wrd.org/) Table 5 Well Design and Construction Cost Estimate
Table 6 Preliminary List of Required Permits and Approvals Table 7 Operation Cost Estimate
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SECTION 1 INTRODUCTION
Currently, the City of Lomita (City) has groundwater rights of 1,352 acre feet (AF) in the West Coast Basin. Due to the detection of benzene, the City’s only groundwater source well, Well No. 5, has remained offline since May 2019. Well No. 5 is anticipated to resume operation in late 2023. In calendar year 2018, Well No. 5 produced 561 acre-feet of groundwater. To form a basis of a long-term reliable water supply, the City is considering developing a new municipal water supply well within the City limits or in neighboring cities in the West Coast Basin (Study Area).
Stetson has prepared this Feasibility Study for a New Groundwater Production Well in the Study Area. The general methods utilized to perform the study are shown schematically in Figure 1. The purpose of this report is to summarize the findings of the feasibility study regarding potential well locations in the Study Area.
Figure 1 New Groundwater Well Feasibility Study Flow Chart
1. Review regional hydrogeologic conditions
• Characterize aquifers
• Evaluate well capacity, water quality
• Determine density of existing wells
2. Identify project boundaries and constraints
• West Coast Basin
• City of Lomita
• Near existing distribution mains (12-inch or larger)
3. Constructability
• Land availability
• Cost estimate for design, construction, operation, and maintenance
• Construction constraints
The first part of this study reviews the geology and hydrogeology of the West Coast Basin in the vicinity of the City. Next, project boundaries and constraints are identified to determine the initial target area to be considered for potential sites. This target area is refined into a smaller, final target area by assessing hydrogeologic conditions, distance from existing infrastructure, and other project constraints. The study will conclude with recommendations of three general areas for a well site in the West Coast Basin.
Hydrogeologic
Review
Project
Constraints
Constructability
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SECTION 2 – HYDROGEOLOGIC REVIEW
The City is located in the southwestern part of Los Angeles County, 26 miles south of downtown Los Angeles. The City is bounded by the City of Torrance to the north and west, the Harbor Region of Los Angeles to the east, the City of Rolling Hill Estates to the southwest; and the City of Rancho Palos Verdes and an unincorporated Los Angeles County area to the southeast. The City’s limits along with the Skypark Commercial Properties, nested monitoring well Lomita #5 and the City’s groundwater production Well #5 are shown in Figure 2.
This section summarizes hydrogeologic conditions in the Study Area as indicated in Figure 2. Areas that have favorable hydrogeologic conditions within City limits and neighboring cities in the West Coast Basin will be identified. Favorable hydrogeologic conditions for siting a productive extraction well include:
• Potential for high well capacity
• Water quality that requires minimal or no treatment
• Relatively shallow static water level or piezometric surface • Adequate distance from existing extraction wells to reduce well interference The Water Replenishment District of Southern California (WRD) in cooperative with the United States Geological Survey (USGS) has constructed 50 deep, nested monitoring wells throughout the Central and West Coast Basins. The nested monitoring wells include four to six small diameter casings installed at different depths in the same borehole.
WRD’s database of well construction, water level, well production, and water quality for all monitoring wells and production wells throughout the Central and West Coast Basin was utilized for this study. In addition, the City provided lithology well logs for Lomita #2 and Lomita #5.
Borehole geophysical logs, including logs for the Lomita #1, Carson #2, Madrona Marsh and Wilmington_2 wells, were obtained from the USGS GeoLog database:
https://webapps.usgs.gov/GeoLogLocator/#!/.
Water level, water quality, well construction and well production reports for public water wells within the WRD service area were downloaded from the link:
https://gis-apps.wrd.org/Html5Viewer/Index.html?viewer=Well_Search.Well_Search.
Well completion reports (lithology logs) for all wells within and in the immediate periphery of the Study Area were downloaded from the California Department of Water Resources’ (DWR’s) web mapping application:
https://water.ca.gov/Programs/Groundwater-Management/Wells/Well-CompletionReports. 3 | P a g e
Since part of the Study Area overlays active and abandoned oil fields, locations, lithology and borehole geophysical logs are obtained from the California Geologic Energy Management Division’s (CalGEM) Well Finder program:
https://www.conservation.ca.gov/calgem.
The above data provides key insights into important hydrogeological conditions including underlying aquifer structure, specific capacity, and water quality.
2.1 Regional Geology
The Los Angeles physiographic basin is divided into two distinct groundwater basins by the Newport-Inglewood uplift (Poland et al., 1959; Yerkes et al., 1965). On the northeast side is the Central Basin; and on the southwest is the West Coast Basin. Located in the southwestern part of the West Coast Basin, the Study Area is bordered by the Torrance plain to the north, the Newport-Inglewood uplift to the northeast and the Palos Verdes Hills to the south and southwest (Figure 3).
Major structures in the study area include the buried northwest-trending anticlinal arches in the basement rock, the southwest-dipping Palos Verdes Fault, and the west-northwesttrending oblique-slip Pacific Coast Highway Fault. The Pacific Coast Highway Fault was identified from borehole and gravity data and the north side was inferred to have a maximum down throw of approximately 800 feet (Paulinski et al., 2021).
In the Study Area, thick Tertiary and Quaternary marine and continental sediments have been deposited on a basement of pre-Tertiary metamorphic and igneous rocks (Poland et al., 1959). The basement rocks are exposed on the north slope of the Palos Verdes Hills in the southwestern corner of the Study Area. These rocks have been encountered in many oil wells drilled throughout the whole Study Area at an elevation between 5,000 and 14,000 feet below mean sea level and generally slope northeast (Yerkes et al., 1965).
These basement rocks are pre-late Cretaceous in age. These basement rocks and the overlaying late Cretaceous to pre-Pliocene deposits do not contain productive aquifers.
Almost half of the Quaternary deposits in the study area are coarse-grained gravel and sand of the Pleistocene age. These coarse deposits are almost entirely of littoral or shallow marine origin. Overlying the coarse deposits are fine-grained deposits of sand, silt, sandy clay, and clay. The fine-grained deposits are of lagoonal and continental origin, but to a lesser extent of marine and littoral origin (Poland et al., 1959).
2.2 Cross Section
More than 1,000 lithologic logs, well completion reports, and borehole geophysical logs were reviewed and analyzed with approximately 25 well logs selected to create three cross sections: A-A’ through C-C’. An oblique view of the land surface is included in each cross-section. Figure 3 shows the extent and location of these three cross sections.
Patterns and color fills are used to illustrate lithology. Horizontal hatched lines indicate screen interval. Resistivity logs are displayed in blue curves. Red-dashed lines indicate 4 | P a g e
faults and black arrows point to the relative movement direction of the faults. Question marks show areas of questionable interpretation.
Cross section A-A’ (Figure 4) trends southwest to northeast. Wells No. 3705507, 3705645, 3717336 and 3717073 are oil and gas wells drilled to depths of 4,212, 3,395, 4,066 and 4,346 feet below ground surface (bgs), respectively. Only the shallow segment (<1,600 feet of depth bgs) of the well logs are shown on the cross section. At Well No. 3705507, coarse-grained gravel and sand dominate the depth interval between 100 and 380 feet bgs. Following a suite of sandy shale, shale, and shells at a depth from 380 to 1,014 feet bgs is a coarse-grained layer having a thickness of approximately 44 feet.
Underneath this coarse-grained layer is an assemblage of shale dominated deposits from 1,058 to 1,280 feet bgs. Between the depth of 1,280 and 1,594 feet bgs is an alternative layer of brown shell, sand, shale, gravel, and sandy shell. The bottom section of this borehole consists of brown shale.
Located at 1,320 feet to the northeast is another oil and gas well (3705645), where beneath the surface layer, a thick clay layer was deposited between the depth of 16 and 85 feet bgs. From 85 to 360 feet bgs, fine to coarse-grained sands are encountered. The following 89 feet is composed of blue clay with layers of sand and clayey sand. The section between 449 and 543 feet bgs consists of sand with a thin layer of shell.
Interbedded sticky blue clay and fine sand can be found from 543 to 655 feet bgs. Fine sand dominates the depth interval from 655 to 1,215 feet bgs. The bottom section consists of two shale and sandy shale layers with a thick sand layer sandwiched in between.
The center of cross section A-A’ is dominated by coarse-grained sand and gravel. Nested monitoring well Lomita #1 (100820) was drilled by the USGS in cooperation with WRD to a depth of 1,340 feet bgs. At 100820, gravelly, clayey fine sands are exposed at land surface to a depth of 20 feet bgs. From 20 to 60 feet bgs, sandy clays and fine sands are encountered. Following a suite of sand, gravelly sand, and silty sand from 60 to 340 feet bgs is a thick layer of very coarse sandy granular to pebble gravels with wood fragments from 340 to 620 feet bgs. The bottom section consists of alternative layers of silty sand and sandy silt. Large resistivity spikes in the geophysical logs correlate with coarsegrained deposits from 340 to 620 feet bgs.
Separated at less than 300 feet apart, both the lithology log at Well No. 3717073 and resistivity log at Well No. 3717336 are shown on cross section A-A’. At Well No. 3717073, coarse grained sand and boulders exposed at land surface to a depth of 195 feet bgs.
From 195 to 220 feet bgs, the section consists of blue clay and gravel. Corse-grained deposits dominate the depth interval from 220 to 950 feet bgs. Underneath a 10-feet layer of sand and shale, the material grades up to coarse sand and boulders from 960 to 1,437 feet bgs. The bottom section is composed of sticky clay, shale, sandy shale and shell. In Well No. 3717336, the resistivity log indicates high resistivity values, which generally correlates to coarse-grained deposits, from 270 to 660 feet bgs. 5 | P a g e
At the eastern end of cross section A-A’, the resistivity log for well 101787 indicates a high resistivity value section, which generally correlates to coarse-grained deposits, from 220 to 910 feet bgs.
Trending northwest-southeast, cross section B-B’ (Figure 5) is roughly perpendicular to cross section A-A’. Three deep oil and gas well logs and 5 shallow well logs are included in cross section B-B’. At the northwestern end, the geology consists of sand and gravel from land surface to a depth of 940 feet bgs, followed by a thick layer of blue shale from 940 to 1,657 feet bgs. The bottom section is composed of hard sand.
Cross section B-B’ slices through the northwest corner of Skypark Properties. The middle part of cross section B-B’ is a heterogeneous unit dominated by sandy silts and silty sands with a few clay lenses. Reportedly, Lomita #5 is screened in the Silverado aquifer. The lithology log at Lomita #5 indicates coarse-grained deposits from 350 to 660 feet bgs.
South of the Palos Verdes Fault line, Well No. 1097997 was drilled to a depth of 220 feet.
Here, sand and gravel are present from land surface to a depth of 94 feet bgs. The bottom section consists of black sandy clay. At the southeastern end of cross section B-B’, Well No. 717414A was drilled to 65 feet bgs and below a surface fill of 10 feet, brown clay was deposited.
Cross section C-C’ is roughly parallel to cross section B-B’. Deep boreholes are concentrated in the center. Both Well No. 3717213 and Well No. 3717926 are oil and gas wells. At Well No. 3717213, the lithology log indicates sand and streaks of shale from land surface to a depth of 581 feet bgs. The bottom section was logged as sand and shale to a total depth of 1,650 feet bgs.
Both lithology and resistivity logs at Lomita #1 have been discussed in the above section.
Deposits at Well No. 3717926 consist of sand from land surface to 50 feet bgs.
Underneath is a thick layer of red clay. The middle section, from 110 to 1,013 feet bgs, is dominated by coarse-grained sand, gravel and boulders. The bottom section, from 1,013 to 1,642 feet bgs, is composed of shale and sandy shale with streaks of hard sand.
2.3 Hydrogeologic Units
Previously, the Central and West Coast Basins were grouped into five hydrogeologic units: the Recent, Lakewood, Upper San Pedro, and Lower San Pedro Aquifer systems and the non-transmissive Pico unit by Poland et al. (1959), the California Department of Water Resources (1961) and later slightly modified by Reichard et al. (2003). These aquifer systems are summarized in Table 1.
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Table 1
Geologic Formation, Aquifers, and Properties within the West Coast Basin (Modified after Reichard et al., 2003)
Age Formation Aquifer Systems Thickness
(ft)
Holocene
Active dune sand Semi-perched Recent Aquifer
System Alluvial sediments varied
and marine deposits Gaspur/Ballona
Upper
Pleistocene
Palos Verdes sand
Lakewood
Aquifer System 150-400 Unnamed Upper
Pleistocene
(Poland et al., 1959)
Gardena
Gage
(200-foot sand)
Lower
Pleistocene San Pedro Formation
Lynwood Upper San
Pedro Aquifer
System
Silverado 500-700
Sunnyside
(Lower San
Pedro)
Lower San
Pedro Aquifer
System
>600
Upper Pliocene Pico Formation Does not contain productive aquifers >1,000
Poland et al. (1959) reported that the upper division of the Recent Aquifer was tapped by a very few domestic wells because it is composed chiefly of fine texture. Though the lower division (Gaspur Aquifer) is highly permeable, it has been contaminated by sea water intrusion.
According to Poland et al. (1959), the Pleistocene deposits are chiefly unconsolidated and consist of cross-bedded sand, gravel, silt, and clay. The upper Pleistocene deposits (Lakewood Aquifer System) vary considerably in lithology and the upper half is generally fine grained, while the lower half is chiefly sand (Poland et al., 1959). Termed as the Palos Verdes sand by Poland et al. (1959), it is continental in origin and its base is marked by a shell layer. Ranging in thickness from a few inches to less than 15 feet, the Palos Verdes sand generally consists of coarse-grained sand and gravel. Due to its thickness and depth of deposition, the Palos Verdes sand has little importance as an aquifer.
The lower section of the upper Pleistocene deposits is a productive aquifer in the study area. It is noted that the Lakewood Aquifer System is in physical and hydraulic continuity with the underlying San Pedro formation. Based on a shift in the spontaneous potential (SP) geophysical log and a change in the character of both the gamma and resistivity logs, Reichard et al. (2003) identified the boundary between the Lakewood Aquifer System and the Upper San Pedro Aquifer System.
The San Pedro formation is of early Pleistocene age. Poland et al. (1959) divided the San Pedro formation into the upper San Pedro sand and two basal members. In the type area in and near San Pedro, the San Pedro sand mainly consists of stratified and cross-bedded 7 | P a g e
sand. The top basal member is composed of brownish to yellowish sandy silt and silty sand. The underlying basal member consists chiefly of marl and calcareous sand.
In the West Coast Basin, the Lynwood and Silverado Aquifers are the lowermost aquifers within the Upper San Pedro Aquifer system (Poland, 1959; DWR, 1961; Reichard et al., 2003). As indicated by upward-increasing resistivities, the Lynwood Aquifer is identified as an upward-coarsening sequence (Reichard et al., 2003). The Silverado Aquifer produces the most water in the study area. Reichard et al. (2003) reported that the resistivity log for the Silverado aquifer indicates a fining-upward package.
Except for the southwest corner of the study area (Palos Verdes Hills), the Silverado aquifer underlies throughout. Its thickness varies from less than 100 feet along the Palos Verdes fault to more than 700 feet in the southeast corner of the area (Figure 7). Poland et al. (1959) reported that with an average thickness of approximately 500 feet, the upper 300 feet of the aquifer is highly permeable clean sand and gravel, while the lower 200 feet is chiefly coarse sand.
Recently, Paulinski et al. (2021) developed a groundwater-simulation model in the Los Angeles Coastal Plain, Los Angeles County, California, where 15 chronostratigraphic units were defined. These chronostratigraphic units are mapped and defined based on bounding unconformities, while previous hydrogeologic units were defined based on lithologic characteristics and inferred depositional environments (Paulinski et al., 2021).
Without delving into much detail how the chronostratigraphic units were defined, depth from land surface to the base of water-bearing units (base of Long Beach C chronostratigraphic unit) is digitized and shown in Figure 8. It shows that the bottom of water-bearing zone varied in depth from 800 feet to over 950 feet throughout the study area.
2.4 Well Capacity and Specific Capacity
In order to evaluate the production capacity of existing wells in the selected areas in the West Coast Basin, the monthly production rates of known active and inactive wells were gathered from the WRD Website (http://gis.wrd.org/wrdmap/index.asp). Well identification (ID) and maximum annual production rate of existing wells are summarized in Table 2.
These well locations are shown in Figure 9. Nested monitoring well Lomita #1 is included for reference. The symbol size and color on Figure 9 indicates maximum annual production rate of each production well, the larger the symbol size and the darker the color shade, the higher the production rate. Among the 12 production wells investigated, Well Nos. 200648, 200649, 200671, 200806, 201100 and 201946 are inactive. The maximum annual production rate among these wells for which records are available is 4,074 acre-feet per year (AFY), which equates to a constant pumping rate of 2,526 gallons per minute (gpm).
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Specific capacity is short term sustainable discharge divided by the drawdown yielding the discharge (Q/Sw). The units of specific capacity are gallons per minute per foot of drawdown (gpm/ft). A high specific capacity value indicates a relatively productive well with less drawdown. In general, areas with higher specific capacity are preferable to site a production well because they will permit greater production rates and lower associated pumping costs.
Table 2
Maximum Annual Production of Wells in the West Coast Basin near the City of Lomita
State ID WRDID
Maximum
Production
Rate (AFY)
Record
Period
Water
Quality Owner Status
4S/13W31E01 200648 4,074.15 1970-
2020 No Inactive
4S/13W31N03 200649 2,539.2 1979-
2007 No Los Angeles Inactive
4S/13W31N04 200650 2,730.27 1990-
2022 No Los Angeles Active
4S/14W14K01 200671 2,655.24 1997-
2001 Yes Torrance Inactive
4S/14W35E06 200675 436.4 1970-
2022 Yes Rolling Hills Estates Active
4S/14W35E07 200676 653.1 1978-
2021 Yes Lomita Active
4S/14W35F02 200677 128 1970-
2022 Yes Rolling Hills Estates Active
4S/14W28J01 200806 25.92 1970-
1974 No Torrance Inactive
4S/13W31P01 201100 1,919.81 1970-
1975 No Los Angeles Inactive
4S/14W24A01 201946 20.74 1970-
1972 No West Carson Inactive
4S/13W31P03 203174 2,605.75 2012-
2022 No Los Angeles Active
4S/14W34H02 203993 289 2019-
2022 No Rolling Hills Estates Active
WRD estimated the specific capacity for 328 wells in the study area. Figure 9 is a map of specific capacity in the general area of the City of Lomita, which indicates that the southwest area of the City of Lomita has the highest specific capacity value. The map shows that the northern 75% of the City, from just south of the Pacific Coast Highway to the northern City limit has a specific capacity larger than 100 gpm/ft. A zone of higher specific capacity value (> 200 gpm/ft) is located to the southeast of the City limits. 9 | P a g e
2.5 Groundwater Quality
The City’s only production well, Lomita #5, was offline due to detection of VOC contamination (TCE, PCE) a few years ago. The City conducted a study that evaluated Skypark Commercial Properties’ (SCP) impact on groundwater contaminants migrating to Lomita Well #5. The study concluded that the benzene impacting Lomita Well # 5 originated from a near surface source and the chlorinated volatile organic compounds (cVOCs) could potentially impact downgradient aquifers. It was noted that groundwater flow and the contamination plume outside of the SCP area have not been identified.
Water quality and well location data for more than 538 monitoring wells and production wells (Figure 10) within the Study Area were downloaded from the Groundwater Ambient Monitoring and Assessment (GAMA) Program website at:
https://gamagroundwater.waterboards.ca.gov/gama/gamamap/public/.
Note that except the two nested monitoring wells Lomita #1 (WRD 100818, 100819, 100820, 100821, 100822, 100823) and Carson #2 (WRD 101787, 101788, 101789, 101790, 101791), all the monitoring wells within the Study Area have a depth of less than 200 feet, while most production wells were perforated deeper than that depth. Including well construction data, 8 constituents (Arsenic, Chloride, Iron, Manganese, TDS, Color, TCE and PCE) have been reviewed and analyzed. All TCE and PCE concentrations were below their respective Detection Limit for purposes of reporting (DLR), which is 0.5 micro gram per liter.
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Table 3
Water Quality Data from Selected Production Wells and Monitoring Wells Site
Well ID
(Map
Label)
As
(mg/L)
Cl
(mg/L)
Fe
(mg/L)
Mn
(mg/L)
TDS
(mg/L)
Color
(ACU)
TCE
(mg/L)
PCE
(mg/L)
Chandler_1 100080 6.9 68.4 26 1500 650 5 <0.5 <0.5
Chandler_2 100081 1.6 221 60 1,740 5 <0.5 <0.5
Chandler_3_1 100082 5.2 195 350 140 740 15 <0.5 <0.5
Chandler_4 100084 1.7 111 120 18 580 3 <0.5 <0.5
Lomita #1
100818 16 860 550 520 2,500 18 <0.5 <0.5
100819 14 800 460 450 2,300 25 <0.5 <0.5
100820 8.9 440 440 440 1,200 30 <0.5 <0.5
100821 7.5 490 430 530 1,600 35 <0.5 <0.5
100822 16 1100 740 520 2,900 10 <0.5 <0.5
100823 3.6 213 95 980 <0.5 <0.5
Carson #2
101787 1.2 23 45 4 278 45 <0.5 <0.5
101788 23 11 32 322 25 <0.5 <0.5
101789 1.3 24 150 29 314 40 <0.5 <0.5
101790 28 25 31 290 10 <0.5 <0.5
101791 1.7 23 63 67 340 10 <0.5 <0.5
Border Ave.
Well #7 200671 153 261 44 512 15 <0.5 <0.5
Lomita Well 5 200676 2.5 212 1630 90.3 820 40 <0.5 <0.5 MCL 10 250 300 50 500 15 5 5
The groundwater quality within the Study Area is generally good, except for high TDS, manganese, iron, arsenic and color at Lomita #1 and shallow contamination from the SCP. Total dissolved solids (TDS), arsenic, and general mineral concentrations are documented as the most common water quality problems by the USGS and WRD (http://gis.wrd.org/wrdmap/index.asp). A few selected constituents of groundwater quality data for production wells and monitoring wells are shown in Table 3. Locations of these wells are shown in Figure 11. The following section provides a narrative summary of the selected constituents listed in Table 3.
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• Arsenic concentrations ranged from 1.2 to 16 micrograms per liter (µg/L). Three sample results at Lomita #1 (100818, 100819 and 100822) are above the State MCL of 10 µg/L for this constituent. The detected arsenic concentrations at all the other wells are below the State MCL of 10 µg/L.
• Chloride was detected in concentrations ranging from 23 to 1,100 mg/L. All samples at Lomita #1 (100818 through to 100822) were detected to have a chloride concentration above the State Secondary MCL of 250 mg/L for this constituent. The detected chloride concentrations are below the State Secondary MCL of 250 mg/L at all other well locations.
• Iron concentrations ranged from 11 to 1,630 µg/L. Almost half of the sample results are above the State Secondary MCL of 300 µg/L for iron. • Manganese was detected in concentrations ranging from 4 to 1,500 µg/L. Ten out of 16 sample results are above the State Secondary MCL of 50 µg/L for manganese. • TDS concentrations ranged from 278 to 2,900 mg/L. Within the City boundary, high TDS values were measured at Lomita #5 and the nested monitoring well Lomita #1 in Lomita Park.
• Color was detected ranging from 3 to 40 units. Note that the State Secondary Standard for color is 15 Units.
To avoid pumping poor quality water from the shallow aquifer, it is recommended the proposed well be sited an adequate distance from the contaminated SCP area or located in an area that has a groundwater flow barrier (fault) between the site and the SCP.
Isolated aquifer zone testing is recommended in the pilot hole to test groundwater quality when a well is constructed.
2.6 Water Level
A high groundwater level or piezometric surface requires a lower lift for a well pump which decreases the cost associated with production. Each aquifer can have an independent static water level. To evaluate water levels in each aquifer, the USGS has installed nested monitoring wells at several locations in the West Coast Basin. Nested monitoring wells consist of two or more casing strings within the same borehole separated by impermeable seals. The screened interval of each casing string is designed to obtain water from different aquifers or water-bearing zones.
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Table 4 Well Construction Data
(USGS, 2002; WRD; https://gis-apps.wrd.org/)
Name WRD_ID
Land
Surface
Elevation
(ft amsl)
Depth to Top
of Perforation
(ft)
Depth to
Bottom of
Perforation
(ft)
Aquifer System
Lomita-1 #1 100818 79.48 1,240 1,260 Lower San Pedro
Lomita-1 #2 100819 79.48 700 720
Lomita-1 #3 100820 79.48 550 570 Upper San Pedro
Lomita-1 #4 100821 79.48 400 420
Lomita-1 #5 100822 79.48 220 240 Lakewood Lomita-1 #6 100823 79.48 100 120 Carson-2 #1 101787 43.04 1,230 1,250 Lower San Pedro
Carson-2 #2 101788 43.04 850 870 Upper San Pedro
Carson-2 #3 101789 43.04 600 620 Upper San Pedro
Carson-2 #4 101790 43.04 450 470 Upper San Pedro
Carson-2 #5 101791 43.04 230 250 Lakewood
Torrance Tank Farm
Well 201862 74.3 188 300
Rolling Hills Estates 2 200675 180.3 300 600
There are two USGS nested wells located in the study area. Nested monitoring well Lomita #1 is in Lomita Park, City of Lomita, and nested monitoring well Carson #2 is in Veterans Park in Carson. In addition, the Torrance Tank Farm well and Rolling Hills Estates 2 well are also used as monitoring wells. Well construction data for these wells are summarized in Table 4.
Analysis of lithology and downhole geophysical logs at Lomita #1 shows that the Upper San Pedro aquifer system (Lynwood and Silverado aquifers) from 400 to 1,200 ft bgs is well defined at the well location. If a production well is proposed near Lomita #1, the target depth would be 1,200 ft bgs and the screen interval would be from 400 ft to 1,200 ft bgs.
The earliest water level observation at the Torrance Tank Farm Well (WRD-201862) dates back to the late 1940s. WRD has regularly monitored the groundwater levels and water quality of these wells since August 2000. Hydrographs for Lomita #1 and Carson #2 are summarized in Figure 12 and Figure 13, respectively.
As shown in Figure 12, it appears that the groundwater levels in the individual piezometers at Lomita #1 were generally grouped at three depths before 2008, where water levels in the shallow monitoring wells Lomita_1_5 were among the highest, water levels in the deep monitoring wells Lomita_1_1 the lowest, while water levels in the other 4 piezometers were in between. After 2008, however, the highest water levels are observed at the two shallow wells Lomita_1_5 and Lomita_1_6 and at the mid-level well Lomita_1_3. A slight separation of water levels is observed between Lomita_1_2 and Lomita_1_4. The groundwater levels in all the piezometers rose steadily from 1999 to 2010 and then remained stable until 2015. Following a period of steady rise, a slight water level drop has been observed since 2022.
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At Carson #2, water levels are generally grouped at four depths, and a downward gradient is observed. The lowest water levels are observed in the lowest monitoring well Carson_2_1. Groundwater levels in the two medium level monitoring wells Carson_2_2 and Carson_2_3 are almost identical and are consistently about 5 feet higher than in the lowest monitoring well.
At Carson #2 (Figure 13), water levels in all aquifers rose steadily from 2000 to 2006 and stayed stable for three years. This was followed by a continuous water level rise from 2009 to 2020. Water levels have dropped slightly since 2021.
Contours of equal groundwater elevation are shown in Figure 14. Groundwater levels are below mean sea level throughout the study area. One groundwater mound is centered in the SCP area. Within the City’s boundaries, groundwater flows east, southeast, and south. Figure 14 shows that along the eastern City boundary groundwater levels rage from -26 ft above mean sea level (amsl) in the northeastern corner and its surrounding area to -46 ft amsl at the intersection of 263rd Street and South Western Avenue. Land surface elevation in the northeastern corner is approximately 72 ft amsl. To the south at the intersection of 263rd Street and South Western Avenue, land surface elevation is approximately 160 ft amsl. Thus, the approximate depth to groundwater water in this area is expected to be in the range of 98 ft bgs in the north to 206 ft bgs in the south.
2.7 Well Interference
A cone of depression is a cone-shaped lowering of the water table centered around a well that typically occurs when a well is pumped. When two wells are close together, their cones of depression may intersect. This intersection is known as well interference, which increases the drawdown in both wells. Well interference is possible in confined and unconfined aquifers. For some wells, this additional drawdown may not affect well yield, but will lead to higher pumping costs because the water must be lifted a greater distance.
For other wells, the additional drawdown may lower the water level in the well below the pump intake causing the well to go “dry”. To minimize well interference, new wells should be sited at an adequate distance from existing production wells to minimize well interference.
The Theis equation is a widely used method for estimating the drawdown at a distance from a production well given certain properties of an aquifer. Figure 9 indicates that the majority of the Study Area has a specific capacity value of more than 100 gpm/ft. To estimate transmissivity of the aquifer, an equation from Driscoll (1986) for unconfined aquifers is used; T = 1,500 (Q/Sw), where T is the transmissivity in gallons per day per foot (gpd/ft), Q is the constant discharge rate in gallons per minute (gpm), and Sw is the drawdown in the pumped well after one day in feet. Transmissivity is estimated to be 150,000 gpd/ft. Assuming a storage coefficient of 0.15 and a flow rate of 2,500 gpm for a period of one year and using the Theis equation, the calculated drawdown at a distance of 3,000 feet from the proposed well is approximately 5 feet. Thus, to minimize drawdown 14 | P a g e
interference to less than 5 feet, the proposed well should be located at a distance of at least 3,000 feet from any existing production wells.
2.8 Summary of Hydrogeologic Review
Analysis of lithology and downhole geophysical logs of nested monitoring wells, deep oil and gas wells and groundwater production wells shows that the Lynwood and Silverado Aquifers are well defined in the majority of the Study Area and the depth interval of the target water bearing zone is from approximately 400 ft to over 1,200 ft bgs. These are the target aquifers for the proposed well.
The northwest trending Palos Verdes fault and the Pacific Coast Highway fault are inferred to have vertical separation of up to 800 ft. It is postulated that these two fault segments are a groundwater flow barrier.
The City conducted a study that evaluated Skypark Commercial Properties’ impact on groundwater contaminants migrating to Lomita Well #5. The study concluded that the benzene impacting Lomita Well #5 originated from a near surface source and the chlorinated volatile organic compounds (cVOCs) could potentially impact downgradient aquifers. The groundwater level contour map shows that water levels are below mean sea level throughout the study area and one water mound is centered in the SCP area.
Groundwater flows east, southeast, and south within the City’s boundaries.
Along the eastern City boundary, water level rages from -26 ft amsl in the northeastern corner and its surrounding area to -46 ft amsl at the intersection of 263rd Street and South Western Avenue. Land surface elevation in the northeastern corner is approximately 72 ft amsl. To the south at the intersection of 263rd Street and South Western Avenue, land surface elevation is approximately 160 ft amsl. Thus, the approximate depth to groundwater in this area is expected to be in the range of 98 ft bgs in the north to 206 ft bgs in the south.
The groundwater quality within the Study Area is generally good, except for high TDS, manganese, iron, arsenic, benzene, and color at Lomita #1 and shallow contamination from the SCP. To avoid pumping poor quality water from the shallow aquifer, it is recommended the proposed well be sited an adequate distance from the contaminated SCP area or located in an area where there a groundwater flow barrier (fault) exists between the well site and the SCP area. Isolated aquifer zone testing is recommended in the pilot hole, if a production well is constructed, to test groundwater quality. 15 | P a g e
SECTION 3 – CONSTRUCTABILITY
Section 2 identified favorable areas for well siting from a purely hydrogeologic perspective. This section focuses on discussions of logistical considerations for the construction of a new well aside from hydrogeologic conditions. The following criteria are considered:
• Land availability for potential well sites
• Potential pipeline alignment and connection between proposed well sites and the existing distribution system
• Estimated costs for the proposed well sites for design, construction, and operation and maintenance
3.1 Land Availability
During well construction, one drill rig with trailer, two mud tanks, one air compressor and an electricity generator are set up at the well site (Figure 15). In addition to the space for temporary storing construction materials, such as casing, gravel and bentonite etc., a working area is required. In practice, a minimum size for well construction must be no less than 50 feet by 100 feet, approximately 1/8 of an acre. Although the actual area needed for a well site would be much smaller, purchase of this area of land would allow for future maintenance and installation of treatment facilities if needed or improvements to the site which provide benefit to the surrounding community such as a small park or picnic area.
Based on the above hydrogeological analysis, three areas were identified to have favorable hydrogeologic conditions. As shown in Figure 16, the three areas ranked based on hydrogeologic conditions:
• Area 1 includes the northeastern corner of the City and the Walnut Sump in the City of Torrance. The Walnut Sump site was identified as a potential well site, although it is outside of the City. The Walnut Sump is a stormwater basin (23845 Walnut St, Torrence, California). At present, it is inactive. Four ultimate receiving waters of Torrance storm drainage can be found at:
https://www.torranceca.gov/home/showpublisheddocument/59759/63729019127 1470000
• Area 2 is an elongated area along the eastern City boundary between the Pacific Coast Highway to the south and 247th Street to the north. • Area 3 includes Lomita Park and its vicinity.
Rationale for ranking Area 1 (Figure 16) is as follows:
• Medium high productivity
• TDS concentration could be below 500 mg/L
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• Fault line as a downgradient barrier from the SCP (Figure 3) Area 2 (Figure 16) is ranked second. Rationale for ranking this area is as follows:
• High productivity
• TDS concentration could be below 500 mg/L
• Distance downgradient from the SCP. Being a sufficient distance downgradient from the SCP provides some protection from contaminated groundwater at the SCP but the fault in the northeaster portion of the City (Figure 3) potentially provides greater protection, which is why the northeast corner area of the City is ranked higher than this eastern boundary area.
The third ranked potential area is Lomita Park (Area 3). Rationale for ranking this area is as follows:
• Medium high productivity
• TDS concentration could be higher than 1000 mg/L
• Distance downgradient from the SCP
3.2 Theoretical Well Yield Capacity
It is estimated that a 16-inch diameter well drilled to a depth of 1,250 feet below ground surface in any of the three recommended areas would be able to yield 2,500 gpm.
3.3 Design and Constructability Constraints
Potential construction constraints that should be considered and avoided or minimized at any potential well site include insufficient space for well drilling equipment for construction and future maintenance of well, presence of overhead power lines, proximity of residences or other nearby land uses that may be sensitive to construction or operations noise, conflicting underground utility lines, and access issues. Sites with fewer constraints would be assigned higher scores.
Table 5
Well Design and Construction Cost Estimate
Well
Size
(inch)
Well
Depth
(foot)
Casing Well
Construction
Design
& CMS Total
16 1,250 HSLA $1,500,000 $300,000 $1,800,000
16 1,250 Stainless Steel $2,812,500 $562,500 $3,375,000 17 | P a g e
The design and construction cost (Table 5) is estimated based on recently completed well construction projects. High-strength low-alloy steel (HSLA) is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. Design and construction management services (CMS) are assumed to be 20% of the total cost of the well construction.
3.4 Estimated Life Cycle
The projected service life of water distribution system facilities can vary depending on the equipment type (i.e., well casings, pipelines, storage reservoirs, pumps, etc.). The California Public Utilities Commission’s (CPUC) “Standard Practice for Determination of Straight-Line Remaining Life Depreciation Accruals”, provides average ranges of equipment service life for different types of utilities, including water systems. These service life ranges are based upon factors such as the future effect of wear and tear, decay, action of the elements, inadequacy, and public requirements.
Based upon these CPUC ranges, the initial service life for a well casing is estimated to be 40 years and the initial service life for a well pump is estimated to be 25 years. These initial service life estimates are only applied to new equipment. Service life estimates can change once the equipment is in operation. The CPUC relies on various “Iowa Curves”, or Survivor Curves, to determine the remaining service life of equipment that has been in operation. The remaining service life estimate is based on the age of the facility divided by the initial service life estimate and applying that percentage to the corresponding survivor curve tables to obtain the percentage of probable life remaining. The percentage of probable life remaining is multiplied by the initial service life estimate to estimate the remaining service life. Iowa Curves are also used to determine the remaining service life of operating equipment that has already exceeded its original estimated service life. For example, a 50-year-old well casing has exceeded its initial service life estimate of 40 years. However, if the well casing is currently still in relatively good operating condition, the Iowa Curve analysis will show that the well casing will have an estimated additional 9 years of service life remaining.
An important factor in determining the service life of a well casing is the ability of the casing to resist corrosion, which can cause holes to develop in the well casing and cause screen/perforation slot sizes to increase, allowing sand, fines, and gravel pack to enter the well. Typically, the area of a well casing most vulnerable to corrosion lies between the static water level and pumping level, due to the alternating wet and dry conditions.
Greater than average corrosion occurs in this area for steel casing. Doubling the wall thickness may extend the life of a well casing four or more times. The use of copper bearing material in a well casing can increase corrosion resistance by approximately two times.
Although a standard method has not been developed to determine the life of a well based on water quality constituents, it is generally accepted that the presence of bicarbonate retards corrosion and chloride accelerates corrosion. Groundwater containing calcium 18 | P a g e
carbonate (alkaline waters), which is present in the City’s wells, tends to encrust, rather than corrode, which promotes well casing longevity. Because encrustation tends to reduce production capacity, it must be removed periodically to restore the production capacity of the well.
Well casings should be inspected with video equipment (i.e., video logging or surveying) whenever the pump is pulled to visually inspect the need for remedial work. Several maintenance and rehabilitation techniques can maintain or restore the well casing effectiveness including redevelopment (sand pumping, swabbing, air lift pumping, and surging and backwashing), chemical redevelopment (acid treatment and dispersing agents), mechanical redevelopment (wire brushing and high-pressure water jetting), screen cleaning (vibratory explosives), structural repairs (liners, complete relining, and screen replacement), and well deepening. The appropriate technique can be determined from the video survey.
A major cause of deterioration in well pump performance is damage resulting from cavitation, pumping of air or sand, encrustation, corrosion, rust, normal wear, or any combination of these conditions. Cavitation occurs when gas bubbles in the water collapse under high pressure, which can cause severe vibration of pump components.
Air intrusion reduces pump capacity and efficiency due to the volume the air occupies.
Sand pumping wears down the impeller, bearings, and pump bowl, making them less efficient. Encrustation can plug the impellers, bowls, and even the pump head. Corrosion of the impellers, bowls, or column pipe may increase the wear and failure of pump components. Rust on pump components can increase friction losses and decrease operating efficiency.
Refurbishment and replacement can be considered maintenance options to increase the service life and efficiency of a well or well pumps. Replacement consists of replacing the existing pump and/or motor. Refurbishment activities include motor repairs, rebuilding of the motor, head shaft replacement, trimming the pump impellers, and re-setting of bowl depth (to prevent pumping of air or sand).
3.5 Permitting Requirements and Regulations
A preliminary listing of required approvals and permits is shown in Table 6. If needed, treatment facilities may trigger additional permitting requirements. In addition, easements may be required. Potential environmental impacts must be reviewed prior to construction, including aesthetics and noise during construction.
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Table 6
Preliminary List of Required Permits and Approvals
Permit Agency
NPDES Permit for Well discharge California Regional Board Permanent and Temporary Discharge
Permits LA County Flood Control District
Well Construction Permit LA County Department of Public Health, Environmental Health Division
Drinking Water Source Assessment
-50-foot Radius Map
-Minimum Horizontal Distance Table
-Permit Amendment
State Water Resource Control Board-Division of Drinking Water
3.6 Operation and Maintenance Considerations
Integration of the well with distribution system and potential impacts to neighbors are among the operation and maintenance considerations for this well feasibility study.
Integration With the Distribution System – Since the potential new well will be delivering water to the City’s distribution system, higher scores should be assigned to potential well sites located near existing reservoirs and larger diameter pipelines. Segments of 10-inch diameter pipeline and interconnection WB-7 are located in Area 3, therefore, a higher objective priority was given to Area 3. While Area 2 has the medium range priority, the lowest priority was given to Area 1, where some of this area is located outside of City limits, which would require additional pipe construction to connect to the water system, and the existing distribution system consists of segments of 6-inch diameter pipeline in the area within City limits.
Impacts to Neighbors – Among the three areas, Area 2 is a built out residential area.
Operation and maintenance of a groundwater production well in this area would cause a higher impact to neighbors. If a well is located in Area 3, much less impact would be caused to neighbors.
The cost of energy to pump water from a well is calculated using the following equation:
𝐸𝑛𝑒𝑟𝑔𝑦 𝑐𝑜𝑠𝑡 𝑝𝑒𝑟 ℎ𝑜𝑢𝑟 =
(𝑔𝑝𝑚) × (𝑇𝐷𝐻) × (0.746) × (𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦 𝑐𝑜𝑠𝑡 𝑖𝑛 $ 𝑝𝑒𝑟 𝑘𝑊ℎ) (3960) × (𝑝𝑢𝑚𝑝 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦) × (𝑚𝑜𝑡𝑜𝑟 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦)
Table 7 summarizes operating cost based on assumptions listed in the table. Assuming a flow rate of 2,500 gpm, a total discharge amount of 11.05 acre-feet per day (AF/day) is calculated. It is assumed that the static water level is 150 ft bgs and pumping water level is 200 ft bgs. Thus, a 50-feet of drawdown is calculated. A well’s specific capacity equals 20 | P a g e
the flow rate (2,500 gpm) divided by the water level drawdown (50 feet). A system pressure of 90 psi is assumed. The total dynamic head (TDH) is calculated by converting the system pressure to head in feet and adding the pumping water level. The City’s electricity bill dated 05/09/2023 indicates the per kilowatt-hour rate is $0.14104 and the monthly customer charge is $10.82. For future operation, a per kilowatt-hour rate of $0.15 is assumed. Assuming the wire to water efficiency is 0.63, energy cost per hour of operation is calculated using the formula described above and the calculated amount is $45.75.
Assuming the well is pumping two thirds of the time during the year; Southern California Edison (SCE) monthly customer charge is $10.82; O & M labor cost is 60$/Hr; and total annual O & M labor is 600 hours, including the electricity cost of operation, the customer charge and operation and maintenance, the total annual cost is $303,310. The total amount of water pumped would be 2,688 AF. The cost per acre-foot to pump water would be $112.80.
Table 7
Operation Cost Estimate
Flow Rate (gpm) 2,500
Static Water Level (ft bgs) 150
Pumping Water Level (ft bgs) 200
Drawdown (ft) 50
Specific Capacity (gpm/ft) 50
System Pressure (psi) 90
TDH (feet) 408
Electricity ($/KWHr) 0.15
SCE Monthly Customer Charge $10.82
Wire to Water Efficiency (-) 0.63
Cost per Hour of Operation $45.75
AF/day 11.05
O & M Labor Cost ($/Hr) 60
O & M Labor (Hr/Yr) 600
3.7 Treatment Technology Recommendations
Review and analysis of existing water quality data indicates that the following five (5) constituents are of concern:
• TDS
• Arsenic
• Manganese
• Iron
• Color
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In general, less TDS is expected in the north-northeast area, while high TDS is expected to the south-southwest area. Colored water comes from depth. Arsenic, manganese and iron concentration varies from location to location, though correlated to TDS to a certain degree. Related treatment technologies are summarized below:
Conventional treatments will remove a variety of secondary contaminants. Coagulation (or flocculation) and filtration removes metals like iron and manganese, and arsenic.
Aeration removes odors, iron, and manganese. Granular activated carbon will remove most of the contaminants which cause odors, color, and foaming.
Non-conventional treatments like distillation, reverse osmosis, and electrodialysis are effective for removal of chloride, total dissolved solids, and other inorganic substances.
However, these are expensive technologies and may be impractical for smaller systems.
Source: https://www.epa.gov/sdwa/secondary-drinking-water-standards-guidancenuisance-chemicals As can be seen by the above general descriptions of conventional and non-conventional treatment processes, the appropriate treatment technology depends on which constituent of concern or combination of constituents of concern are present. The following general recommendations for selected combinations of the potential constituents of concern are provided.
Arsenic, Iron and Manganese
If arsenic and/or Iron and Manganese are present, a coagulation and filtration treatment process is recommended. Including wellhead equipping, a well site having a size of 50’ by 100’ would be able to accommodate an arsenic treatment system. If treatment of manganese is needed, additional space of 1,800 square feet is required.
TDS and Any of the Other Constituents for Concern
If TDS is present at elevated amounts, reverse osmosis treatment is recommended. It is estimated an area of 2,000 square feet would be required to construct a reverse osmosis treatment system for a flow rate of 2,500 gpm.If any of the other constituents of concern are present in combination with TDS, additional treatment may be required. 22 | P a g e
SECTION 4 – CONCLUSIONS AND RECOMMENDATIONS
Based on the above hydrogeological analysis, three areas were identified to have favorable hydrogeologic conditions. These three areas in ranking order are listed as follows and shown in Figure 16.
• Area 1 includes the northeastern corner of the City and the Walnut Sump in the City of Torrance. The Walnut Sump site was identified as a potential well site, although it is outside of the City. The Walnut Sump is a stormwater basin (23845 Walnut St, Torrance, California). At present, it is inactive. Four ultimate receiving waters of Torrance storm drainage can be found at:
https://www.torranceca.gov/home/showpublisheddocument/59759/63729019127 1470000
• Area 2 is an elongated area along the eastern City boundary between the Pacific Coast Highway to the south and 247th Street to the north. • Area 3 includes Lomita Park and its vicinity.
Recommended field testing needed at each site
As discussed in the above sections, there are potential water quality concerns in all three areas. An exploratory program is recommended, wherein an exploratory borehole would be drilled to a depth of 1,250 feet bgs and three isolated aquifer zone tests would be conducted in the drilled borehole to determine the site-specific productivity and water quality characteristics in either all three areas or in the area ranked most favorable. A planning level cost estimate is summarized in Table 8 for the drilling of an exploratory borehole and three isolated aquifer zone testing in the drilled borehole. If test results indicate both productivity and water quality are acceptable, the City may continue to complete the exploratory borehole into a production well. If the test results indicate otherwise, the City may abandon the borehole or convert it into a monitoring well.
Table 8
Planning Level Cost Estimate
Item No. Description Quantity Unit Unit
Price Total
1 Mobilization and
demobilization 1 LS $100,000 $100,000
2 Conductor Casing 1 LS $25,000 $25,000
3 Exploratory Borehole 1,200 VF $100 $120,000
4 Geophysical logs 1 LS $5,000 $5,000
5 Isolated aquifer zone testing 3 Zone $25,000 $75,000
TOTAL $325,000
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In addition, all three areas are located in a seismic hazard zone for liquefaction potential as mapped by the State of California. Prior to designing any improvements at a well site, at least one (1) boring to at least 50 feet below the existing grade would need to drilled at each site as part of a geotechnical evaluation of the sites. Prior to drilling, Dig Alert or approved equal shall be called to locate known municipal and private utilities, easements, or piping in the area of the proposed drilling.
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REFERENCES
Advisian, 2022, High-Level Evaluation of Potential Impacts from Chlorinated Solvents on Lomita Well #5.
California Department of Water Resources, 1961, Planned utilization of the ground water basins of the coastal plain of Los Angeles County, Appendix A, Ground water geology: California Department of Water Resources Bulletin 104, 191 p., http ://wdl.wat er.ca.gov/ waterdatalibrary/ docs/ historic/ Bulletins/ Bulletin_ 104/ Bulletin_ 104- A_ _ 1961.pdf
Driscoll, F.G. (1986) Ground Water and Wells. 2nd Edition, Johnson Division, St. Paul.
DUDEK, 2022, Water Master Plan, Summary Report, prepared for: City of Lomita.
Paulinski, S., ed., 2021, Development of a groundwater-simulation model in the Los Angeles Coastal Plain, Los Angeles County, California: U.S. Geological Survey Scientific Investigations Report 2021–5088, 489 p., https://doi.org/ 10.3133/ sir20215088.
Poland, J.F., Garrett, A.A., and Sinnott, Allen, 1959, Geology, hydrology, and chemical character of ground waters in the Torrance - Santa Monica area, California: U.S. Geological Survey Water-Supply Paper 1461, 437 p., https://pubs.er.usgs.gov/publication/wsp1461.
Reichard, E.G., Land, M., Crawford, S.M., Johnson, T.D., Everett, R.R., Kulshan, T.V., Ponti, D.J., Halford, K.L., Johnson, T.A., Paybins, K.S., and Nishikawa, T., 2003, Geohydrology, geochemistry, and groundwater simulation-optimization of the Central and West Coast Basins, Los Angeles County, California: U.S.
Geological Survey Water-Resources Investigations Report 2003–4065, 196 p., https://doi.org/ 10.3133/ wri034065.
Yerkes, R.F., McCulloh, T.H., Schoellhamer, J.E., and Vedder, J.G., 1965, Geology of the Los Angeles Basin, California—An introduction: U.S. Geological Survey Professional Paper 420–A, 57 p., https://doi.org/ 10.3133/ pp420A.
Figure 4 Cross Section A-A’
Figure 5 Cross Section B-B’
Figure 6 Cross Section C-C’
Figure 12 Hydrographs for Lomita #1
(WRD 100818, 100819, 100820, 100821, 100822, 100823)
-45
-40
-35
-30
-25
-20
-15
-10
-5
0 Jan-99Jan-00Jan-01Jan-02Jan-03Jan-04Jan-05Jan-06Jan-07Jan-08Jan-09Jan-10Jan-11Jan-12Jan-13Jan-14Jan-15Jan-16Jan-17Jan-18Jan-19Jan-20Jan-21Jan-22Jan-23 Groundwater Elevation (ft amsl)
Lomita_1_1 (Screen: 1,240-1,260)
Lomita_1_2 (Screen: 700-720)
Lomita_1_3 (Screen: 550-570)
Lomita_1_4 (Screen: 400-420)
Lomita_1_5 (Screen: 220-240)
Lomita_1_6 (Screen: 100-120)
Figure 13 Hydrographs for Carson #2
(WRD 101787, 101788, 101789, 101790, 101791)
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0 Jan-99Jan-00Jan-01Jan-02Jan-03Jan-04Jan-05Jan-06Jan-07Jan-08Jan-09Jan-10Jan-11Jan-12Jan-13Jan-14Jan-15Jan-16Jan-17Jan-18Jan-19Jan-20Jan-21Jan-22Jan-23 Groundwater Elevation (ft amsl)
Carson_2_1 (Screen: 1,230-
1,250)
Carson_2_2 (Screen: 850-870)
Carson_2_3 (Screen: 600-620)
Carson_2_4 (Screen: 450-470)
Figure 15 Schematic Site Layout of Well Construction