Appendix H: Hydrogeology Study - Monterey County, CA oaks subdivision... · Appendix H:...

Heritage Oaks Subdivison - Draft EIR

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Appendix H: Hydrogeology Study

K L E I N F E L D E R Expect More

64550/HYDRO (SJO7R251) nb Copyright 2007 Kleinfelder West, Inc.

REVISED HYDROGEOLOGIC ASSESSMENT OF THE PROPOSED

HERITAGE OAKS SUBDIVISION AROMAS, MONTEREY COUNTY, CALIFORNIA

For Inclusion in an Environmental Impact Report

To The County Of Monterey Planning and Inspection Department

PREPARED FOR: Michael Brandman Associates Bishop Ranch 3

2633 Camino Ramon, Suite 460 San Ramon, CA 94583 ATTENTION: Mr. Jason Brandman Project Manager

Copyright 2007 Kleinfelder, Inc. All Rights Reserved.

Use or copying of this document is strictly prohibited by anyone other than the client for the specific project.

September 19, 2007 Revised October 10, 2007


64550/HYDRO (SJO7R251) nb Page i of ii September 19, 2007 Copyright 2007 Kleinfelder West, Inc. Revised October 10, 2007

HYDROGEOLOGIC ASSESSMENT OF THE PROPOSED


TABLE OF CONTENTS

1 INTRODUCTION.............................................................................................................1 1.1 SITE DESCRIPTION.................................................................................................2 1.2 PROPOSED DEVELOPMENT, SERVICES AND EASEMENT ............................................3 1.3 PURPOSE AND SCOPE OF SERVICES .......................................................................3

2 PREVIOUS INVESTIGATIONS.......................................................................................5 2.1 SUMMARIES OF PREVIOUS HYDROGEOLOGIC INVESTIGATIONS..................................6

2.1.1 John Kingsley, November 1994................................................................6 2.1.2 Fugro, October 1995 and 1996 ................................................................6 2.1.3 Grice Engineering Inc., April 12, 1999a ....................................................6 2.1.4 Grice Engineering Inc., April 12, 1999b ....................................................7 2.1.5 Grice Engineering Inc., May 7, 1999 ........................................................8 2.1.6 Grice Engineering Inc., September 17, 2000............................................9 2.1.7 Geoconsultants, Inc., October 21, 2000 ...................................................9 2.1.8 Fall Creek Engineering, Inc., March 7, 2007...........................................10

3 GEOLOGIC SETTING...................................................................................................11 3.1 REGIONAL GEOLOGY ...........................................................................................11 3.2 AREA AND SITE GEOLOGY ....................................................................................12

4 HYDROGEOLOGIC EVALUATION ..............................................................................14 4.1 APPROACH..........................................................................................................14 4.2 WELL-DATA SOURCES .........................................................................................15 4.3 AREA RAINFALL ...................................................................................................17 4.4 PROJECT WATER-BALANCE CHECK ......................................................................18

4.4.1 Lot 31 Considerations................................................................18 4.4.2 Storm-Water Infiltration under Pre- and Post-Development

Conditions..................................................................................19 4.4.3 Water Demand...........................................................................20 4.4.4 Well Abandonment ....................................................................21 4.4.5 Project Estimated Change in Water Balance.............................21

5 WATER QUALITY.........................................................................................................23 5.1 SEAWATER INTRUSION .........................................................................................23 5.2 NITRATE LOADING................................................................................................24

6 HYDROGEOLOGIC ISSUES ........................................................................................25 6.1 HYDROGEOLOGIC REPORT-REVIEW SUMMARY ......................................................25


64550/HYDRO (SJO7R251) nb Page ii of ii September 19, 2007 Copyright 2007 Kleinfelder West, Inc. Revised October 10, 2007



TABLE OF CONTENTS

(CONTINUED)

7 ENVIRONMENTAL IMPACTS AND MITIGATION ........................................................27 7.1 SIGNIFICANCE CRITERIA.......................................................................................27

7.1.1 Impact: Interruption of surface water from the Heritage Oaks property to adjoining watersheds...............................................27

7.1.2 Impact: Interruption of groundwater underflow from the Heritage Oaks property to aquifers adjacent to the property....................28

7.1.3 Impact: Negatively impacting the quantity of water in storage beneath the project site .............................................................28

7.1.4 Impact: Substantially increasing overdrafting conditions in the vicinity of the project site............................................................30

7.1.5 Impact: Exacerbating seawater intrusion...................................31 7.1.6 Impact: Contributing to water-quality degradation. ....................31

8 LIMITATIONS ...............................................................................................................33

9 REFERENCES..............................................................................................................34

PLATES Plate 1 Site Vicinity Map Plate 2 Site Aerial Photograph Plate 3 Site Plan with Groundwater Contours (by Grice 1999) Plate 4 Revised Tentative Map (by M.J. Goetz and Associates, 2007) Plate 5 Regional Geologic Map Plate 6 Vicinity Geologic Map Plate 7 Geologic Cross Section Plate 8 Approximate Near-by Well Locations Plate 9 Well Hydrographs (9A through 9C) Plate 10 Chemical Hydrographs (10A and 10B)

ABBREVIATIONS USED IN THIS REPORT: ac. acre APN Assessors Parcel Number ft. feet sq. ft. square feet yr. Year gpm gallons per minute mg/L milligrams per liter


64550/HYDRO (SJO7R251) nb Page 1 of 34 September 19, 2007 Copyright 2007 Kleinfelder West, Inc. Revised October 10, 2007



1 INTRODUCTION

This report presents the results of our revised hydrogeologic assessment for the

proposed Heritage Oaks Subdivision near the community of Aromas in Monterey

County, California. The location of the project site with respect to surrounding cultural

and topographic features is shown on the Site Vicinity Map, Plate 1. A photographic

overview of the property is shown on the Site Aerial Photograph, Plate 2. The proposed

Heritage Oaks Subdivision encompasses 79.47 acres that are proposed to be

subdivided into 32 parcels, ranging in size from 1.1-acres to 15.91-acres (Site Plan with

Groundwater Contours (from Grice. 1999), Plate 3). This revised report incorporates

several changes and assumptions from our original and superseded hydrogeologic

report that include:

• Water for the development will be provided by the Aromas Water District.

• A new Tentative Map of Heritage Oaks, surveyed by Goetz Land Surveyors,

dated June 4, 2007 (Revised Tentative Map, Plate 4).

• Lot 31 is changed from non-residential to residential.

• The location of the well on Lot 31.

• The well on Lot 31, according to the Applicant, will be abandoned in accordance

with County and State guidelines.

• The addition of Lot 32IH and addition of four apartments on this new lot.

• Water demand for the 31 stand-alone single-family dwellings will average no

more than 0.8 ac-ft/yr.



1.1 SITE DESCRIPTION

The project site is located on hilly terrain in northeastern Monterey County near the

community of Aromas. Current site access is by a graded, unpaved drive off San Juan

Road, approximately 600 feet south of the intersection of San Juan Road and Aromas

Road and from Rea Avenue on the east. The irregular-shaped property extends from

Rea Avenue on the east to San Juan Road on the west. Presently, the upland portion of

the property is used for grazing and has several horse trails that meander through the

property. We understand that in the past, portions of the property have been planted in

orchard.

An occupied, single-family residence is located on a ridge crest along the north property

line on proposed Lot 31. Other improvements on the property include dirt roads and

wire fences. A well is located at approximate elevation 178 feet in the east portion of

Lot 31 (Plate 4). The well provides irrigation water for a truck-garden located adjacent

to San Juan Road. Water from the well is also pumped to a storage tank located

upslope from the residence. A second well, reported by Grice to be dry, is located in

the northeast corner of the property (Grice, 1999). A concrete spring tank is located on

the eastern portion of the Spring Lots (Plate 3 and 4). An unused, locked access gate

is located at the project’s access at Rea Avenue.

Land surrounding the project site is rural and includes farms, ranches, and large-lot,

single-family homes. Property elevations range from 150 feet in the western portion of

the site to 450 feet at the east corner. Approximately 22 acres of the project site

consist of slopes ranging from 20 to 30 percent and approximately 16 acres of the

project consists of slopes greater than 30 percent.

Native vegetation on the property consists of grassland, coast live oak forest, and

northern mixed chaparral. Forested areas cover approximately 50 percent of the

property, generally following the slopes. Chaparral borders and mixes with forested

areas on the western portion of the property, with the remaining, flatter potions of the

property in grassland and shrubs.



1.2 PROPOSED DEVELOPMENT, SERVICES AND EASEMENT

The Heritage Oaks property is currently proposed to be subdivided into 31 single-family

residential parcels, and one parcel with four-unit inclusionary apartment housing (Lot

32IH). Development of the project site will require the extension of public services and

utilities including gas, electricity and water. The revised Tentative Map (Plate 4) shows

that access to the subdivision will be via Rea Avenue. The proposed average density of

the property is to be 2.56 acres per single-family residence not including the

apartments. Dwelling units will be served by individual septic systems. Approximately

16 acres of the property, including oak groves and areas with slopes greater than 30

percent, are proposed to remain undeveloped scenic easement.

1.3 PURPOSE AND SCOPE OF SERVICES

The purposes of this hydrogeologic assessment are to review previous studies provided

by the County of Monterey, in order to assess whether conclusions reached in these

studies adequately describe hydrogeologic conditions at the project site, and to assess

the water balance for the property. Our study consisted of applying hydrogeologic

information, compiled for previous investigations, to the area of the project site to

assess groundwater conditions specific to the site and, based on this information,

assess possible change in aquifer storage at the site.

A hydrogeologic study of the proposed Heritage Oaks Subdivision is to be included in

an Environmental Impact Report prepared for the County of Monterey Planning and

Inspection Department by Michael Brandman Associates. Our scope of services for

this study included the following:

• Research and review hydrogeologic reports pertaining to the Heritage Oaks

Subdivision that have been provided by the County of Monterey and the

Applicant;

• Research and review readily available regional hydrogeologic reports to assess

groundwater conditions at the project site;



• Review aerial photographs covering the site for the presence of geomorphic

features relating to geologic structural and hydrogeologic conditions at the site;

• Conduct a geologic reconnaissance of the site by a Certified Engineering

Geologist and Certified Hydrogeologist;

• Meet with County Planning personnel and the Applicant to discuss parameters to

be used in the hydrogeologic analysis; and

• Assess the researched data and prepare this report with conclusions regarding

groundwater conditions at the site.

A Certified Engineering Geologist and Certified Hydrogeologist visited the site on

December 19, 2005 and July 26, 2007 to observe surface geologic conditions.



2 PREVIOUS INVESTIGATIONS

Several reports pertaining to hydrogeologic conditions at the Heritage Oaks Subdivision

site have been provided by the County of Monterey for our review and evaluation. The

reports and documents reviewed for this hydrogeologic assessment include the

following:

REVIEWED DOCUMENTS Report title Author Date

Geologic Hazard Report, Dodge Subdivision, A.P.N. 267-051-014, 267-06-11 and 267-123-031, Aromas, California

John Kingsley November 1994

North Monterey County Hydrogeologic Study, Volume I, Water Resources Fugro October 1995

North Monterey County Hydrogeologic Study, Volume II, Critical Issues Report and Interim Management Plan

Fugro May 1996

Geotechnical Soils-Foundation and Geological Hazards Report for the proposed Heritage Oaks Subdivision, Aromas, California A.P.N. 267-051-014 + 267-123-031

Grice Engineering Inc. April 12, 1999a

Percolation & Groundwater Study with Septic System Design Recommendations for the proposed Heritage Oaks Subdivision, Aromas, California A.P.N. 267-051-014 + 267-123-031

Grice Engineering Inc. April 12, 1999b

Addendum No. 1, Percolation & Groundwater Study with Septic System Design Recommendations for the proposed Heritage Oaks Subdivision, Aromas, California A.P.N. 267-051-014 + 267-123-031

Grice Engineering Inc. May 7, 1999

Memorandum, Monterey County Health Department, Heritage Oaks 980503

Mr. Jerry Lemoine, Supervising Environmental Health Specialist

March 1, 2000

Water Balance Evaluation and Report Heritage Oaks Subdivision Rea Avenue Aromas, California A.P.N. 267-051-014 + 267-123-031

Grice Engineering Inc. September 17, 2000

Hydrogeologic Considerations, Proposed Heritage Oaks Subdivision A.P.N. 267-051-014 and 267-123-031, Monterey County, California

Geoconsultants, Inc. October 21, 2000

Drainage Analysis and Preliminary Drainage Plan, Heritage Oaks Subdivision, Aromas, California, APN 267-051-014 and 267-123-031

Fall Creek Engineering, Inc. March 7, 2007



2.1 SUMMARIES OF PREVIOUS HYDROGEOLOGIC INVESTIGATIONS

2.1.1 John Kingsley, November 1994

The Kingsley report is a geologic hazards study that makes minor mention of

groundwater. According to Kingsley, water percolating downdip along the upper

surfaces of clay layers, impermeable duripans, and oxidized zones may create

undesirable seepage downslope from the water sources. Resistant paleosols at the

site, also called duripans, range between 10 and 60 feet thick and commonly contain

perched water tables due to low permeability.

2.1.2 Fugro, October 1995 and 1996

The North Monterey County Hydrogeologic Study - Volume I and II reports by

Fugro were intended to evaluate groundwater conditions throughout the north

Monterey County region. The reports redefine the hydrogeologic area units

from previous work by the U.S. Geological Survey and designate the area

occupied by the proposed Heritage Oaks Subdivision as “Highlands North.”

The study draws on historical groundwater elevations and discusses seawater

encroachment toward the Heritage Oaks project site.

The Fugro reports conclude that water demand in the North County study area

far exceeds supply and the area is in a state of chronic overdraft. The Fugro

reports summarize possible long-term solutions to the overdraft conditions but

offers little hope for a solution in the near future.

2.1.3 Grice Engineering Inc., April 12, 1999a

The 1999a geotechnical and geologic hazards report prepared by Grice Engineering

summarizes the results of 37 soil borings including depths to groundwater. (However,

the table is missing from Kleinfelder’s copy of the report. Because the groundwater text

is the same as in the Grice 1999b report, we assume the water depth measurement

and elevation data are the same in both reports).



2.1.4 Grice Engineering Inc., April 12, 1999b

The April 1999b Grice Engineering study examined the proposed subdivision

relative to on-site disposal of effluent from single-family residences. The study

consisted of determining the subsurface soil profile, presence or absence of

groundwater, testing for soil percolation rates and evaluation for the

subsurface disposal of septic leachate. A table giving a partial list of soil

boring data is presented in the report and is reproduced below.

GROUNDWATER TABULATION

Project: Heritage Oaks Subdivision

Elev. Top Of Hole

Depth Of Hole

Elev. Bottom Of

Hole

Depth To Ground Water

Elev. Ground Water

feet feet feet feet feet Boring No. 1 362.39 11.94 350.45 2.34 360.05

Boring No. 2 295.03 15.68 279.35 15.04 279.99

Boring No. 3 388.59 49.31 339.28 36.78 361.81

Boring No. 4 330.90 21.00 309.90 14.92 315.98

Boring No. 5 384.94 32.78 352.16 DRY DRY

Boring No. 6 397.40 28.38 369.02 DRY DRY

Boring No. 7 430.99 28.21 402.78 DRY DRY

Boring No. 8 370.77 30.20 340.57 25.36 345.41

Boring No. 9 439.35 33.18 406.17 DRY DRY

Boring No. 10 368.94 31.34 337.60 26.76 342.18

Boring No. 14 336.83 28.94 307.89 19.31 317.52

Boring No. 16 327.61 31.34 296.27 30.37 297.24

Boring No. 17 377.52 37.43 340.09 26.03 351.49

Boring No. 19 362.38 27.92 334.46 16.86 345.52

Boring No. 21 333.58 25.23 308.35 15.71 317.87

Boring No. 22 333.45 38.79 294.66 32.45 301.00

Boring No. 24 375.35 39.50 335.85 37.58 337.77

Boring No. 26 442.57 51.46 391.11 DRY DRY

Boring No. 27 474.39 32.39 442.00 DRY DRY

Boring No. 35 270.00 54.79 215.21 DRY DRY



The locations of the borings are shown on the Site Map with Groundwater

Contours (from Grice, 1999), Plate 3. Grice Engineering approximated lines of

equal groundwater elevation for the eastern portion of the property. The

results of their water-elevation interpolation are shown on the Site Map with

Groundwater Contours. The groundwater equipotential lines are constructed at

approximate 10-foot intervals on the free water surface. A second set of lines

on the Site Map with Groundwater Contours indicates the approximate depth

to groundwater at intervals of 10 feet as calculated by Grice Engineering.

2.1.5 Grice Engineering Inc., May 7, 1999

Grice’s May 1999 addendum report references the April 12, 1999b percolation

and groundwater study and addresses comments by the Monterey County

Health Department. The report gives results of percolation testing and

“groundwater determination” associated with Heritage Oaks Lots 1, 7, 10, 12,

and 16. The report includes boring logs for soil borings 38 through 46. The

report does not contain a summary table of the borings with water elevations.

The following table is complied for this review report based on information

presented on Grice’s borehole logs.

GROUNDWATER TABULATION

Date Of Measurement: 05/06/99

Elev. Top Of Hole

Depth Of Hole

Elev. Bottom Of Hole

Depth To Ground Water

Elev. Ground Water

feet feet feet feet feet Boring No. 38 348 11.12 336.88 4.80 343.20

Boring No. 39 378 23.70 354.30 18.72 359.28

Boring No. 40 372 9.92 362.08 Dry Dry

Boring No. 41 374 13.63 360.37 8.51 365.49

Boring No. 42 328 17.04 310.96 13.26 314.74

Boring No. 43 302 16.98 285.02 12.03 289.97

Boring No. 44 300 10.22 390.20 Dry Dry

Boring No. 45 345.0 51.5 293.99 Dry Dry

Boring No. 46 366.0 7.45 358.55 6.59 359.41



2.1.6 Grice Engineering Inc., September 17, 2000

This report, titled “Water Balance Evaluation and Report” presents a water

balance summary table in front of the first page of the report. The summary

table provides estimates of available collected water for percolation from

proposed residential roof areas, hardscape, storm drainage, and cropland

abandonment and concludes that there will be a net increase to groundwater

storage at the Heritage Oaks site of 5.15 ac. ft. per year. The Grice 2000

water balance summary table is reproduced below.

Residence roof area = 4.65 ac.ft. Gross

Equal area undeveloped = 0.31 ac.ft. Existing

Net to groundwater 4.34 ac.ft.

Residence hardscape = 6.20 ac.ft. Gross


Net to groundwater 5.58 ac.ft. Development storm drainage

= 15.91 ac.ft. Gross


Net to groundwater 3.67 ac.ft. Cropland abandoned (current)

= 3.60 ac.ft. Gross


Net to groundwater 3.96 ac.ft.

Total Net to groundwater 17.55 ac.ft.

Development Demand 12.40 ac.ft.

Net increase to groundwater

5.15 ac.ft.

2.1.7 Geoconsultants, Inc., October 21, 2000

In its review of Grice’s September 17, 2000 “Water Balance Evaluation and

Report,” Geoconsultants (2000) generally concurs with the methodology used

in the analysis and the report’s findings. In its discussion of the existing on-site

well, Geoconsultants states:



”The Monterey County Environmental Health Department has approved this source of supply per their letter of March 1, 2000 (not provided for Kleinfelder’s review). The well produced 40 gallons per minute on a 7-hour test, with a pumping level of 11 feet below the static level, for a specific capacity of 4 gpm/ft of drawdown, which is generally efficient considering the well is 40 years old. It is of interest to note that the static level has declined from 118 feet in 1960 to 153 feet in February 2000, an average of about 1 foot per year or about 15 percent of the total well depth. Considering the relatively shallow depth of the well (252 feet) even with a continuing, decline of the static water level, there should be many years of service life left.”

2.1.8 Fall Creek Engineering, Inc., March 7, 2007

The Fall Creek drainage-analysis letter report states that "Each lot will include a

subsurface infiltration system to capture and retain runoff from the roof and driveway

areas." However, it should be noted that the Fall Creek report does not provide site-

specific layouts of the subsurface infiltration system and no indication is given in the

report that there is sufficient room on each lot to accommodate the proposed drainage

system.



3 GEOLOGIC SETTING

3.1 REGIONAL GEOLOGY

The Heritage Oaks Subdivision area, situated adjacent to Pajaro Valley near the north-

most portion of Monterey County, lies within the Coast Ranges Geomorphic Province.

The Coast Ranges Geomorphic Province is a discontinuous series of northwest-

southeast trending mountain ranges, ridges, and intervening valleys characterized by

complex folding and faulting. The general geologic framework of the Central Coast

Area of California is illustrated in studies by Page (1965), as well as in Jennings and

Strand (1958), and the CGS (2002) included as the Regional Geologic Map, Plate 5.

Geologic structures within the Coast Ranges Province are generally controlled by a

major tectonic transform plate boundary. This right-lateral strike-slip fault system

extends from the Gulf of California, in Mexico, to Cape Mendocino, off the coast of

Humboldt County in northern California and forms a portion of the boundary between

two global tectonic plates. In this portion of the Coast Ranges Province, the Pacific

plate moves north relative to the North American plate, which is located east of the

transform boundary. Deformation along this plate boundary is distributed across a wide

fault zone, which includes the San Andreas, Hayward, Calaveras, and San Gregorio

faults. Together, these and other faults are referred to as the San Andreas fault

system. The general trend (about N30 to 45W) of the faults within this system is

responsible for the strong northwest-southeast structural grain of most geologic and

geomorphic features in the Coast Ranges Province.

The large wedge of geologic material west of the San Andreas fault that generally is

underlain by Cretaceous Age (about 140 to 65 million years old) granitic basement rock

is referred to as the Salinian block (Regional Geologic Map). The Heritage Oaks

property is included within the Salinian tectonic block. The Salinian Block is bounded

by the San Andreas fault on the east and the Sur-Nacimiento fault zone on the west.

Geologically, the study area has a crystalline basement of Upper Cretaceous granitic



rocks of the Salinian block and older metasedimentary rocks of the schist of the Sierra

de Salinas of probable pre-Cretaceous age.

Resting nonconformably upon these basement rocks in the Monterey area is a

sedimentary section that ranges in age from middle Miocene to Holocene (about 24

million years ago to present) and has a composite thickness of as much as 3,600 feet.

The Miocene rocks record quiet marine waters with abundant microscopic lifeforms

(forams and diatoms). Later, in the Pliocene and Pleistocene, the ocean retreated and

non-marine fluvial environments abound. These Cenozoic age rocks are typically

folded and faulted into a series of generally northwest-southeast trending folds and

faulted blocks, largely as a result of predominantly right-lateral strike-slip stresses

related to movement along the San Andreas fault system. The inland valleys, including

the valley along San Juan Road along the west margin of the Heritage Oaks property

and the internal valley of the property west of Rea Avenue, are filled with

unconsolidated to semi-consolidated alluvium (stream channel and over-bank deposits)

of Quaternary age (about the last 1.6 million years).

3.2 AREA AND SITE GEOLOGY

Sand deposits of the Aromas Formation underlie most of the Heritage Oaks property

(Vicinity Geologic Map, Plate 6 and Geologic Cross Section, Plate 7). The Aromas

Sand generally is composed of well-sorted, medium-grained brown to red quartzose

sand with silt and clay lenses that varies from being uncemented to weakly cemented

by iron oxide. The Aromas Sand was deposited by both wind and river processes, with

water deposition occurring near the coast in a lagoonal or shoreline environment and

wind-born deposition occurring further inland forming sand dunes. Several sequences

of sand dune deposits are present in the area, each sequence generally is separated

by oxidized water-laid sequences.

The presence of clay layers and low permeability lenses suggest that there are areas of

very little vertical flow through the layered aquifer systems in the Highlands North area.



The confining aquitards are laterally extensive but may be missing in places owing to

stream erosion or offsetting by fault movement.

Geomorphically, the project site is on a highland area surrounded by lowland streams.

The geomorphic configuration is the result of complex interaction of active faulting and

stream erosion. Tectonic deformation of the area is suggested by the apparent capture

by the Pajaro River drainage of the old stream drainage that is located along San Juan

Road. From the topographic expression of this stream deposit, it appears that the

stream channel north of the Heritage Oaks property has recently (in geologic terms)

been captured by the Pajaro River drainage while the portion south of the Heritage

Oaks drains to Elkhorn Slough.



4 HYDROGEOLOGIC EVALUATION

4.1 APPROACH

To evaluate the change in groundwater storage of a study area, most investigators

calculate the hydrologic water balance of a selected area and for a specific time of

interest. A hydrologic budget (or water budget) is an equilibrium equation that

describes the balance of atmospheric moisture, surface water, and groundwater in a

defined area over a time frame of interest under inferred or measured conditions. The

generalized equation for the groundwater budget is:

Where dtdS

is the change in storage of groundwater over the period of interest, Gin and

Gout are groundwater flow rates in and out of the control volume over the period of

interest, Qg is groundwater rate of flow into or out of surface streams, Eg is surface

evaporation rate, Tg is plant transpiration rate of surface moisture, I is infiltration rate.

This equation is expressed in terms of volumes per unit time. Using net mass

exchanges and simplifying for the project conditions, the equation can be presented as:

Where S∆ is the change in total water storage over the period of interest, P is

precipitation over the period of interest, Ro is the combined effect of water flow across

and through the area of interest. ETo is a combined evapotranspiration term which

represents an estimate of evapotranspiration from an extended surface of 3 to 6 inch

tall green grass cover of uniform height, actively growing, completely shading the

ground, and not short on water. The solution to the hydrologic equation gives the net

change in water storage for the study area. The accuracy of the solution is dependent

on the thoroughness applied to collection and the reliability of the input data.

gggoutin TEQGGIdtdS −−−+= −

oo ETRPS −−=∆



The above approach was generally followed by Fugro (1995) in its North Monterey

County Hydrogeologic Study. In our review of the study, we found Fugro’s assumptions

and conclusions to be generally representative of the study area. We have used

Fugro’s values where appropriate in our analysis.

Given the relatively small watersheds that contribute water to the aquifers by deep

percolation on the Heritage Oaks property, we assume that regional stratrigraphic units

lying beneath the Quaternary deposits are the sources of water to the on-site well

although this is not discussed in the Grice reports. The major watersheds at Heritage

Oaks are shown on Plate 1. The watershed near the west end of Rea Avenue provides

water to the alluvial valley fill in the east portion of the property. The watershed at San

Juan Road, also shown on Plate 1, that contributes water to the alluvium along the

property’s west margin, is also small. None of the reports provided for our review give

aerial measurement of these watersheds nor do they provide estimates of the quantity

of groundwater that can be held in storage in the alluvial deposits. The alluvial stream

deposits near the intersection of San Juan and Aromas Roads appear to have been

tectonically uplifted so that surface drainage north of Heritage Oaks has been captured

by the Pajaro River drainage system shutting off a large portion of an ancient

watershed. These issues are not investigated in the reports provided for our review and

may not have significant impacts on groundwater conditions at the site because of the

overshadowing affect of the area-wide stressed aquifers.

4.2 WELL-DATA SOURCES

Water-level data are sparse in the area of the proposed Heritage Oaks project.

Readily available data for known water wells in the vicinity of the site are listed in the

following table.



Well Id. (Plate 8)

State Well No. Use

Ground-Surface

Elev. (ft.)

Depth (ft.)

Perforation Depth (ft.)

Change in Water Depth

(ft.) / Years Monitored

Avg. Rate of Change (ft. / yr)

1 12S/03E-21B01 Indust. 390.5 450 322-442 65/15 +4.33

2 12S/03E-18E04 Dom. 60.5 --- --- 19/31 -0.61

3 12S/03E-18D01 Dom. 60.5 172 125-160 21/21 -1.00

4 12S/03E-30A01 Irr. 100 225 141-225 27/27 -1.00

5 12S/03E-29H01 Irr 141 169 106-130 8/16 -0.50

6 12S/03E-19M01 Irr 115 161 100-161 26/30 -0.87

7 On-site well Irr 168 252 --- 35/40 -0.88

Indust. = Industrial, Dom. = Domestic, Irr.= Irrigation

Data for wells 1 through 6 in the above table selected for this analysis are derived from

Fugro (1995). The approximate well locations are shown on Plate 8. Hydrographs of

these wells are presented on Plates 9A through 9C. Well number 7 (Plate 8 and the

above table) is an on-site well that is described by Geoconsultants as producing 40

gpm during a seven-hour pumping test.

The wells in the above table are all within two miles of the project site, appear to be

screened in the Aromas Sand Formation that underlies the Heritage Oaks property, and

are inferred to represent groundwater conditions at and in the vicinity of the Heritage

Oaks property. With the exception of well 12S/03E-21B01 (number 1 on Plate 8), all of

the wells in the above table have demonstrated a drop in water elevation over each

respective period of monitoring. We found no information specific to the 12S/03E-

21B01 well other than its use is listed as industrial. The general trend of groundwater



depletion, shown in six of the seven wells in the vicinity of the project, appears to

confirm Fugro’s conclusion that the Highlands North subbasin and the area of the

proposed Heritage Oaks subdivision is in chronic overdraft and that the groundwater

table is declining by as much as one foot per year.

Grice (1999a, 1999b, and 1999) describe drilling 46 boreholes and measuring depth to

groundwater ranging from 2.3 feet to greater than 54 feet below the ground surface.

Contours of groundwater elevation and depth to groundwater are shown on Plate 3

modified from Grice 1999a. The depth to groundwater is shown graphically on the

Cross Section, Plate 7. Given that the regional elevation of groundwater, projected

beneath the project site from data from Fugro (1995), is about 50 feet above mean sea

level, we infer that the water measured in the site borings is perched on the resistant

duripan-paleosols described by Kingsley (1994). This perched groundwater is inferred

to be the source for the springs on the Spring Lots in the west, downslope portion of the

Heritage Oaks property. Groundwater sourced from such limited and seasonal

reservoirs may not provide a long-term sustainable water supply. Therefore, the water

observed by Grice (1999) in the soil borings is not considered as source water in this

study.

4.3 AREA RAINFALL

The Western Regional Climate Center (http://www.wrcc.dri.edu/index.html) references

two weather stations within a ten-mile radius of the Heritage Oaks area. The Gilroy

station is 9.6 miles to the northeast of the site and shows an annual precipitation of

21.4 inches averaged over a 38-year period. The other station, the Watsonville

Waterworks, is located about 6.6 miles northwest of the Heritage Oaks project site.

Recorded rainfall quantities at both stations are similar, however, the Watsonville

Waterworks station is inferred to more closely reflect climate conditions in the Heritage

Oaks area and is used in our analysis.

The following table shows average rainfall by month at the Watsonville Waterworks

from 1971 to 2000.



Average monthly rainfall at Watsonville Waterworks from 1971 to 2000 Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

average Average 4.72 4.45 3.92 1.62 0.51 0.12 0.08 0.07 0.29 1.06 3.00 3.41 23.25

The average rainfall from 1971 through 2000 was 23.25 inches or 1.94 ft./yr. This

volume of precipitation is inferred to be representative of that in the vicinity of the

Heritage Oaks property and is used in the following analyses.

4.4 PROJECT WATER-BALANCE CHECK

The Grice (2000) water-balance summary suggests that there will be a net annual

increase of 5.15 ac-ft to the groundwater after the Heritage Oaks project is developed

as proposed. This conclusion is based on the proposed collection of surface water

from residential roofs, hardscape, developed storm drainage, and reduction in

agricultural use of the land and to recharge the collected water through infiltration

facilities. However, no data are presented by Grice or other readily available sources

that give information about the design of the infiltration facilities, efficiency or rates, or

describe the construction, maintenance or other required features of the facilities.

Because of the absence of data provided for our review relating to design and

associated infiltration parameters, we assume that the County will require confirmation

of appropriate infiltration design and maintenance plans before permitting the project.

Design, construction, and maintenance of the infiltration facilities may require site-

specific percolation-rate studies including soil borings, logging and sampling of the

boreholes, laboratory testing, and engineering design along with implementation of a

thorough maintenance program.

4.4.1 Lot 31 Considerations

Lot 31 is a proposed 15.91-acre parcel located in the west portion of the property

adjoining San Juan Road. An occupied residence is located near the north-central



portion of this lot. We understand that the Applicant has indicated that the well on Lot

31 will be abandoned and that all lots, including Lot 31, will be limited (presumably by

permitting process) to the use of no more water than 0.8 ac.ft./yr.

4.4.2 Storm-Water Infiltration under Pre- and Post-Development Conditions

The surface area of the project property is 79.47 acres. Based on the topographic

setting of the Heritage Oaks property, it is inferred that increases of water volume in the

aquifer system beneath the property prior to site development is the result of

precipitation. According to Fugro (1995), recharge to groundwater from precipitation for

the Highlands North subbasin ranges from 1.3 to 1.8 inches per year. Assuming the

average recharge of this range for the Heritage Oaks area, the existing or pre-

development recharge for the property is: 79.47 acres of property X 1.5 inches/yr / 12

inches/ft. = 9.93 ac.ft./yr.

In the absence of test data showing that water collected from post-development hard

surfaces can be appropriately recharged and the presence of evidence that there are

infiltration barriers (duripans) present at the site, no infiltration of water collected from

hard surfaces is included in the water balance presented here.

It should be noted that storm-water infiltration may potentially include the introduction of

surface contaminants to shallow groundwater. The shallow soil borings by Grice

(1999a, 1999b, 1999) indicate that shallow groundwater (probably perched on

impermeable lenses) is present at the site. Consideration should be given to monitoring

the quality of storm water that is directed to infiltration facilities. If unacceptable levels

of contaminants are found in the recharge water, treatment may be needed.

The creation of infiltration facilities should be implemented with the understanding that

they are storm-water recharge facilities, and should not be considered to be engineered

wetlands. These features, however designed, should not be construed as ecologic

sanctuaries that the property owner(s) might have to maintain once implemented. Such



change in purpose may cause more water to be needed for their maintenance than

might be estimated to accomplish the calculated infiltration at the project site.

4.4.3 Water Demand

The proposed average density of the project site is 2.56 acres per single-family

residence. Considering possible future uses of the property including small orchards,

landscaping, and animal husbandry, gross water use could be over 2 ac-ft/yr. for each

parcel, if not limited by the development permitting process or other means.

After discussions with the project Applicant and Monterey County Planning personnel in

a meeting at the County’s office on August 31, 2006, the quantity suggested by the

Fugro study (1995) for rural dwelling units occupying one to ten acres with no allowance

for croplands or pasture irrigation was used for each of the 31 single-family residences

in this study. The Fugro study suggests that water demand at suburban residential

dwellings of one to ten acres per dwelling unit may be about 0.8 ac-ft per year. For the

four apartments proposed for Lot 32IH, we use the Fugro study suggested water

demand of 0.7 ac-ft per year for suburban residential dwellings of less than one acre

per unit.

The estimated water use for the residential development would also increase recharge

from effluence at each residential unit. This recharge is expected to be about 0.4

ac.ft./yr. for stand-alone houses and 0.38 ac.ft./yr for the four apartments assuming

return flow from leach fields and irrigation of minor residential landscape. That is, about

half of the water used on each lot would be expected to return to the water table1. The

total additional net demand on groundwater at the Heritage Oaks property based on the

proposed 31 residential parcels and four apartments is therefore estimated to be about

13.9 ac-ft./year.

Our estimate of water demand assumes that no additional wells will be drilled on the

Heritage Oaks property. For the water balance described in this report to remain

1 This simplified assumption ignores soil-moisture holding capacity and subsequent evapotranspiration.



applicable, permit restrictions or other limitations that restrict drilling additional wells on

site should be placed by the County.

4.4.4 Well Abandonment

In the absence of verifiable pumping and water-use data from the well located on Lot

31, no groundwater withdrawal or recharge is considered for that well in the water

balance presented in this report.

We understand that the Applicant intends to abandon the Lot 31 well in accordance

with state and county well-abandonment requirements. An alternative to abandoment

of the well on Lot 31 would be to convert it to a non-pumping monitoring well. The

pump and plumbing would be removed and the well could be fitted with a pressure

transducer and with monitors to measure temperature and salinity. This alternative

would have the advantage of providing real-time groundwater conditions for long-term

monitoring and would demonstrate that the well is not being pumped.

4.4.5 Project Estimated Change in Water Balance

We have evaluated the change in water balance at the Heritage Oaks project site

based on the information described above and by assuming the following:

• Thirty-one stand-alone residences will be located on the property (including one

residence on Lot 31) and four apartment buildings.

• No pasture, crops, or other irrigation-intense use will be made of the parcels

(water demand of the 31 single-family lots will be limited to 0.8 ac.ft./yr).

• The well on Lot 31 will be abandoned and no new wells will be drilled.



Inflow Outflow Change Table 4.4.5 ac-ft/yr ac-ft/yr ac-ft/yr Description Recharge - natural conditions pre development 9.93

79.47 total property acres X 1.5 inches of recharge (Fugro) / 12 in/ft

Reduction in natural recharge at post-development from homes -0.75

6 acres (31 houses + 4 apts. roofs and hardscape) X 1.5 inches of recharge / 12 in/ft

Reduction in natural recharge at post-development from roads -0.21 1.66 ac x 0.125 ft/yr

Depletion via Spring Lots 0 Pipelines from spring are not presently flowing

Suburban residential demand (1 to 10 ac each) 24.8

31 houses X 0.8 ac-ft demand per home (Fugro)

Residential house recharge 12.4 above demand X 0.5

Apartment demand 2.80 4 apts X 0.7 ac-ft demand per home (Fugro)

Residential apt. recharge 1.54 above demand X 0.55 22.9 27.6 -4.7

This evaluation suggests that the net change in water to the area beneath the property

would decrease by about 4.7 ac-ft per year after the Heritage Oaks project is developed

if the assumptions described in this report are incorporated into the project

development.



5 WATER QUALITY

5.1 SEAWATER INTRUSION

Using the inland migration of seawater suggested by the Fugro (1995) study and

assuming uninterrupted progression, groundwater in the vicinity of the Heritage Oaks

property may be adversely affected by saline influence in the future. Figure 15 of Fugro

(1995) graphically shows inland migration of seawater resulting from over-drafted

aquifer conditions in the North County area. The rate of inland migration of the saline

front is irregular but, based on the limited number of observation points shown on

Figure 15 (Fugro, 1995), the seawater front (100 mg/L) appears to have been moving at

about ½ mile per year between 1979 and 1993. At this estimated rate, deterioration of

groundwater could be expected at this time in the vicinity of the Heritage Oaks property.

Chemical Hydrographs (Plates 10A and 10B) derived from Fugro (1995) show changes

in chloride concentrations in groundwater near the project site. The highest increases

in concentration of chloride appear to be in wells located in alluvial stream deposits

north and south of the site. However, without additional chemical data, it is difficult to

correlate chloride concentrations with seawater intrusion, since chloride can be from

other sources, as well. We cannot verify the present location of the seawater front, but

assume it is closer to the project site then observed in 1993. Increase rates of

ovedrafting the basin would be expected to increase the rate of seawater intrusion in

the Highlands North area.

The potential intrusion of seawater caused by water withdrawal in the Highlands North

area may be less beneath the Heritage Oaks property than in surrounding areas based

on the presence of the large reservoir defined by the thick water-bearing strata at depth

underlying the site. Groundwater elevation generally follows ground-surface

topography and because the Heritage Oaks property is on a topographic high

surrounded by lowland streams, groundwater should remain at a higher elevation

beneath the property than at the surrounding streams (Geologic Cross Section,

Plate 7). This “mound” of water beneath the property should act to prevent seawater



from intruding the higher portions of the property at Heritage Oaks. However,

continued pumping in the Highlands North area at current or increased rates will

maintain or accelerate over-draft conditions and will allow seawater to continue its

inland migration.

5.2 NITRATE LOADING

Figure 22 in the Fugro (1995) report shows the area of the proposed Heritage Oaks

subdivision to not have nitrate loading. The Fugro report also presents graphs

depicting changes in nitrate concentrations in wells near the project site (Plates 10A

and 10B). The following table lists the wells with measured nitrate concentrations near

the site. Again, as with chloride, nitrate concentrations are highest in the wells located

in alluvial stream deposits. No information was made available to us for chemical

analyses of the well located on the Heritage Oaks property.

Well Id. (Plate 7)

State Well No. Use

Nitrate

(mg/L) / years monitored

Avg. Rate of Change

(mg/L/ yr)

1 12S/03E-21B01 Indust. --- ---

2 12S/03E-18E04 Dom. 200/14 +14

3 12S/03E-18D01 Dom. -25/14 -1.8

4 12S/03E-30A01 Irr. -300/32 -9.4

5 12S/03E-29H01 Irr. --- ---

6 12S/03E-19M01 Irr. 25/32 0.8

7 On-site well Irr. --- ---

Indust. = Industrial, Dom. = Domestic, Irr. = Irrigation,



6 HYDROGEOLOGIC ISSUES

6.1 HYDROGEOLOGIC REPORT-REVIEW SUMMARY

Our comments regarding the reviewed reports follow:

• The October 2000 Geosciences report describes production of an on-site well.

However, no description is given by Geoconsultants (2000) or Grice Engineering

(2000) of the well’s design or other production factors. Geoconsultants states

that the on-site well produced 40 gpm during a seven-hour pumping test. No

confirmed data of water production from this well has been made available to us

for review. Because the estimates that the Applicant has provided for well

production have not been confirmed, they are not used in the present water-

balance analysis.

• Grice Engineering’s report does not address the overall stress to the aquifer

system caused by the existing wide-area overdraft. Geoconsultants (2000)

indicates that the static water level of the on-site well declined about 35 feet in

40 years suggesting overdraft of the local groundwater reservoir. This is

confirmed by at least six other wells within a two-mile radius of the site. It is our

experience that the County of Monterey Water Resources Agency does not

consider “overdraft pumping” to be an acceptable long-term, sustainable water

source. Our water-balance analysis is based, in part, on the following: 1) the

Aromas Water District will provide water for the development, 2) water use at

each lot will be limited to 0.8 ac-ft/yr, and 3) the well on Lot 31 will no longer be

pumped.

• The Site Plan provided in the Grice reports, and reproduced in this report as

Plate 3, shows “Existing Spring Lots” that are “not included in this subdivision.”

The Grice Site Plan shows a pipeline easement leading from the spring lots off

the plan to the northwest. During our site visit of July 26, 2007, we observed

that the concrete spring tank was empty and, based on the condition of the tank

and plumbing, it appears to not have been used for several years. Ms Star, the

current tenant of the portion of the Heritage Oaks property near the spring lot,



stated that she believes that her neighbor who owns the spring lot has connected

to Aromas Water District water supply and no longer uses the spring water. The

watershed above the “Spring Lots” is relatively small. Flow from the springs

would be expected to be small and seasonal which may have contributed to the

spring lot owner no longer maintaining the spring or its infrastructure.



7 ENVIRONMENTAL IMPACTS AND MITIGATION

7.1 SIGNIFICANCE CRITERIA

The following significance criteria for the hydrogeologic project setting were formulated

based on the findings of this investigation, State CEQA Guidelines, professional

judgment, and knowledge of the project area. From a perspective of hydrogeologic

conditions specifically related to this study, the proposed project would result in a

significant effect on the environment if it would result in:

• Interruption of significant amounts of surface water from the Heritage Oaks

property to adjoining watersheds;

• Interruption of groundwater underflow from the Heritage Oaks property to

aquifers adjacent to the property;

• Negatively impacting the quantity of water in storage beneath the project site;

• Substantially increasing over-drafting conditions in the vicinity of the project site;

• Exacerbating seawater intrusion; or

• Contributing to water-quality degradation.

These potential effects are addressed in the following Sections.

7.1.1 Impact: Interruption of surface water from the Heritage Oaks property to adjoining watersheds

Groundwater that is not consumed by plants, infiltration, or evaporation at the Heritage

Oaks property currently flows overland from the property’s highlands predominately

toward the south. However, based on observation of minimal stream-channel incision

on the property, it is inferred that only minor quantities of surface water complete the

journey offsite. Because only small amounts of surface water would, under natural

conditions, leave the site, as observed from geomorphic evidence inferred to cover a

period of more than the last 11,000 years (Holocene Age), and based on Fall Creek’s

assessment of reduction of drainage flow using appropriate BMPs from the 100-year to



10-year storm event, the potential for a decrease of offsite recharge due to

development of the project site is considered less than significant.

Mitigation: None required

7.1.2 Impact: Interruption of groundwater underflow from the Heritage Oaks property to aquifers adjacent to the property.

Relatively high permeability Aromas Sand, exposed over the surface of the Heritage

Oaks property, generally allows groundwater to quickly infiltrate. This flow may be

interrupted by duripan-paleosol aquicludes that either retain the water in perched

reservoirs or direct the flow to deeper aquifers removed from the locus of infiltration.

This condition is cause by subsurface soils that may extend to several tens of feet

below the ground surface that are generally not expected to be affected by the

proposed development. Based on the above, the potential for added degradation of

groundwater sources for adjacent aquifers due to development of the project site is

considered to be minimal and not significant.


7.1.3 Impact: Negatively impacting the quantity of water in storage beneath the project site

Previous investigations and data provided by the Monterey County Water Resources

Agency (MCWRA) indicate that the overall trend of groundwater elevation has been in

decline for the past 40 years. This decline appears to be as great as one foot per year

in the area of the proposed Heritage Oaks subdivision.

Our evaluation suggests that post-development change to the amount of water that

enters the aquifer system beneath the property will decrease if the water-use

requirements presented herein are implemented in the development. Water demand

for each of the stand-alone residential parcels (averaging 2.56 acres) can range from

more than 2 ac-ft/yr (if portions of the parcels are used for pasture) to as little as 0.8 ac-

ft/yr (if only the house and a small amount of landscaping is considered at each parcel).



Discussions with the project Applicant and Monterey County Planning personnel

concluded that a water demand of up to 0.8 ac-ft/yr for each stand-alone residential

parcel was to be used in this assessment. 0.7 ac.-ft./yr water demand is used in this

study for each of four proposed apartments.

For the assumption that 0.8 ac-ft/yr represents an accurate upper-limit water-use

volume for the stand-alone dwellings for the water-balance evaluation for the project,

some restrictions must be applied to the new residents so that average water use per

parcel will stay within the assumed demand. The Applicant should provide

documentation to the County of appropriate controls and means of long-term

confirmation that will assure that future water demand at the Heritage Oaks project will

be maintained at or below the average of 0.8 ac-ft/yr per parcel. Water demand for the

development should be measured from all water sources including from the Aromas

Water District and any other sources that may become available. The same conditions

apply to the applications of BMPs to storm-water infiltration. The County shall assure

that appropriate storm-water recharge facilities and maintenance protocol are

incorporated into the permitted design for development. Alternatives to the water-

balance model described in this report (e.q. methods of increasing recharge, water

sourced from outside the basin, confirmed well discharge and water use, etc.) may be

considered when such methods are shown to be viable.

The results of the water-balance evaluation presented in this report suggest that there

will be an decrease of about 4.7 ac-ft/yr at post development. To minimize additional

adverse impact to the quantity of water held in storage beneath the project site, the

Applicant must assure County-permitting agencies of certain requirements that can be

sustained over the useful life of the proposed subdivision project. These requirements

include:

• Water demand for stand-alone dwellings shall be maintained at an average of

not more that 0.8 ac-ft/yr per residential parcel.



• Irrigated pastures or other irrigation-intense use of the parcels shall not be

allowed unless pre-approved by the County. Such restrictions should be

specified in deed documents or other appropriate form.

In addition to the above long-term development requirements, the Applicant has stated

that the well on Lot 31 will be abandoned. Alternatively, this well may be converted to a

non-pumping monitoring well.

The creation of BMP infiltration facilities should be implemented with the understanding

that they are storm-water recharge facilities, and that they are not engineered wetlands.

These features, however designed, should not be construed as ecologic sanctuaries

that the property owner(s) might have to maintain once constructed. Such a change in

purpose may cause more water to be needed for their maintenance than may be

estimated to accomplish the calculated infiltration at the project site.

The County shall determine that the above requirements are met or that appropriate

alternatives are met prior to issuing grading permits for the project. Because the

County shall assure that the above requirements are in place prior to issuing applicable

permits, this impact is considered less than significant.


7.1.4 Impact: Substantially increasing overdrafting conditions in the vicinity of the project site

The Highlands North subbasin as well as the other subbasins within the Monterey north

county area are in chronic overdraft. Any additional water removed from the subsurface

reservoirs, if not replaced in like quantity, will increase the overdraft conditions of the

basin. The proposed Heritage Oaks subdivision will withdraw additional water from the

system (albeit from off-site wells operated by the Aromas Water District). Therefore,

this impact is considered less than significant and should be mitigated. Mitigation of

this impact should rest with the Applicant.



Mitigation: Mitigation required

7.1.5 Impact: Exacerbating seawater intrusion

Seawater is reported to be migrating landward as groundwater is being overdrafted

(Fugro 1995) from the Highlands North subbasin. The potential acceleration of

seawater intrusion that may be caused by water withdrawal at the Heritage Oaks

property is considered to be minimal based on the presence of large reservoir defined

by the thick water-bearing strata at depth underlying the site. Because the Heritage

Oaks property is on a prominent high surrounded by lowland streams, groundwater

should remain at a higher elevation beneath the property than at the surrounding

streams (Geologic Cross Section, Plate 7). This “mound” of water beneath the property

will act to prevent seawater from intruding the area. Because development of the

Heritage Oaks property should not exacerbate seawater intrusion at the project site, this

impact is considered less than significant.


7.1.6 Impact: Contributing to water-quality degradation.

Storm-water infiltration potentially could include the introduction of surface

contaminants to shallow groundwater. The County shall require, as needed, that

recharge water, and, if applicable, the well at Lot 31, be monitored and tested for

possible contaminants. If unacceptable levels of contaminants are found in the

recharge water, some treatment may be required by the County. Because recharge

water will be required by the County to be treated prior to infiltration, if unacceptable

contaminant levels are found, this impact is considered less than significant.

According to Fugro (1995) there presently is no nitrate loading at the Heritage Oaks

site. It is inferred that development of the subdivision as planned should add no more

organics from effluent that has been present at the site from past grazing operations.

The likelihood that nitrate loading resulting from residential development reaching the



deep aquifers beneath the site is low. Because the planned project should not increase

nitrate loading at the site, this impact is considered less than significant.


As a consequence of proposed Heritage Oaks project development, there are several

hydrogeologic issues that will be required to be addressed by the Applicant before the

project should be allowed to move forward. In our opinion, except for the chronic

overdrafting of the Highlands North basin, these specific issues can be mitigated by

project design, agreements with future residents, and implementation of long-term

maintenance and testing program. The above impacts analysis may change should

modifications of the proposed project change or become inconsistent with County,

State or other regulations.



8 LIMITATIONS

This investigation excludes the assessment of environmental, geotechnical, or geologic-

hazard characteristics at or in the vicinity of the project site. Services such as chemical

analysis of soil or groundwater or evaluation of development characterization including

independent groundwater research was not included in our scope of services.

This report may be used only by Michael Brandman Associates and by members of the

project design team, and only for the purposes stated, within a reasonable time from its

issuance but not more than three years from the date of the report issuance. Land use,

site conditions (both on site and off site) or other factors may change over time, and

additional work may be required with the passage of time. Any party other than Michael

Brandman Associates and the project design team who wishes to use this report shall

notify Kleinfelder of such intended use. Based on the intended use of the report,

Kleinfelder may require that additional work be performed and that an updated report

be issued. Non-compliance with any of these requirements by the clients or anyone

else will release Kleinfelder from any liability resulting from the use of this report by any

unauthorized party.

The conclusions in this report are intended only for inclusion in the EIR report for the

Heritage Oaks Subdivision. Our field reconnaissance does not provide a warranty as to

the conditions that may exist across the entire site. It is possible that variations in soil

conditions and depth to bedrock and groundwater could exist at the site and may

require additional studies, consultation, and possible design revisions.



9 REFERENCES

Monterey County, December 2000, Monterey County Code Title 19, Subdivision Ordinance

Reports and documents provided by the County for our review are listed and described in the text of this report.

PLATE

1Site Vicinity Map and Vicinity Watersheds

Compiled by: M. SwankReviewed by: M. Clark Revision date:© 2006, by Kleinfelder, Inc.

2011 N. Capitol AvenueSan Jose, California 95132

Ph. (408) 586-7611 Fax. (408) 586-7688

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PROJECT NO.: 64550

Site

Heritage Oaks SubdivisionAromas, Monterey County, California

0 1 2 3 4 5

Scale (hundred feet)

N

Heritage Oaks property

Watersheds showing direction of surface-water flow

Line of Cross Section

A

A’

A’

Base Photo: GlobeXplorer - August 1, 2000 used with permission.

PLATE

2Aerial Photograph

Reviewed by: M. Clark Revision date:

0 50 100

Scale (feet)

© 2006, by Kleinfelder, Inc.


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Heritage Oaks property

��

��

PLATE

3Site Plan


0 20 40 60 80 100

Scale (feet)

Drainage divide(Arrows indicate general surface-water flow direction)



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Base Map Source: Tentative Map of Heritage Oaks, by Grice Engineering, Inc., surveyed by Goetz Land Surveyors, dated April 12, 1999

Groundwater depths and elevations by Grice Engineering, Inc. shown on this plan are measured from soil borings. See report text for discussion of the possible accuracy of these measurements.

N

PLATE

4Revised Tentative Map (June 4, 2007)


0 20 40 60 80 100

Scale (feet)



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Base Map Source: Revised Tentative Map of Heritage Oaks, by Goetz Land Surveyors, dated June 4, 2007

N

PLATE

5Regional Geologic Map

Reviewed by: M. ClarkRevision date:



Ph. (408) 586-7611 Fax. (408) 586-7688Date: 03/27/06

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SCALE MILES

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EXPLANATIONof units in SF Bay Area

Cenozoic nonmarine Mesozoic Granitic rocks

Cenozoic marine Mesozoic Ultramafic rocks

Late Mesozoic shelf and slope

Late Mesozoic of the Franciscan FormationFault, dotted where concealed, arrows indicate direction of

movement

Map source: California Geological Survey, 2002, Geologic Map of California, California Department of Conservation. Use with permission.

PLATE

6Vicinity Geologic Map


N Base Map, Portion of: Wagner, D.L., Greene, H.G., Saucedo, G.J., and Pridmore, C.L., 2002, Geologic Map of the Monterey 30’ X 60’ Quadrangle and adjacent areas, California Geological Survey, Map No.: 1, scale: 1:100,000

0 1 2 3 4 5

Scale (thousand feet)



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EXPLANATIONHolocene DepositsFlood Plain

Alluvium

Alluvial fan

Terrace (undivided)

Watsonville terrace

Aromas Sand (undivided)

Aromas Sand fluvial

Fault (dashed where uncertain, dotted

where concealed)

Proposed Heritage Oaks Subdivision

Line of Cross Section

QflQ QfQtQtwQarQaf

A’

A A’

PLATE

7Geologic Cross Section

Compiled by: M. SwankReviewed by: M. Clark Revision date:© 2006, by Kleinfelder, Inc.


Ph. (408) 586-7611 Fax. (408) 586-7688

Date: 01/18/06

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Vertical scale = 5 X Horizontal scaleLine of section shown on Plate xx

0 5000 10000 15000

500500

400

300

200

100

0

-100

-200

-300

-400

-500

-600

-700

-800

Pajaro RiverCreek that flows to Elkhorn Slough

??

?

???

???

?

? ? ?V

V

V V

V

V

V

V

V

VV

V

V

V

V

V

V V

V

V

V

V

V

Zayante-Vergeles fault

QarQar

Bedding

EOsjOrb OvqOvqKgr

QflQtQt

Q

Qar

1983 G.W. level est.

1994 G.W. level est.

On-site well (dry?)Heritage Oaks Property

Mv

Distance (feet)

Ele

vatio

n (fe

et)

ASouthwest

A’Northeast

?

???

San Juan Road

Quarry Road and SP Railroad

Aromas Road

Water table from Grice, April 12, 1999

ExplanationQ Stream alluvium (Holocene) Eosj San Juan Bautista Formation (Eo-Oligocene)Qt Terrace deposits (Holocene) Mv Unnamed volcanics (Miocene)Qfl Flood plain deposits (Holocene) Kgr Granitic Rocks (Cretaceous)Qar Aromas Sand Formation (Pleistocene) Geologic contact (queried where uncertain)Ovq Vagueros Sandstone (Oligocene) Fault (dashed where uncertain, dotted where concealed)

Orb Red Beds (Oligocene) Groundwater

Unnamed pre-Quaternary inactive fault

PLATE

8Approximate Well Locations




Ph. (408) 586-7611 Fax. (408) 586-7688Date: 03/27/06

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2-mile radius1

23

4

5

6

On-site well7

12S/03E-19M016

12S/03E-29H015

12S/03E-30A014

12S/03E-18D013

12S/03E-18E042

12S/03E-21B011

State Well No.Map ID

7

Map source: Fugro 1995

N

PLATE

8AWell Hydrographs




Ph. (408) 586-7611 Fax. (408) 586-7688Date: 03/27/06

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Average change over period of measurement: +4.33 ft/yr

Average change over period of measurement: -0.61 ft/yr

Graph source: Fugro 1995

PLATE

9BWell Hydrographs




Ph. (408) 586-7611 Fax. (408) 586-7688Date: 03/27/06

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PLATE

9CWell Hydrographs




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Average change over period of measurement:-0.50 ft/yr

Average change over period of measurement:-0.87 ft/yr


PLATE

10AChemical Hydrographs




Ph. (408) 586-7611 Fax. (408) 586-7688Date: 03/27/06

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PLATE

10BChemical Hydrographs




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