HomeMy WebLinkAboutCT 14-07; BEACHWALK AT ROOSEVELT; GEOTECHNICAL REVIEW OF BMP DESIGN; 2016-08-09G eoTek, Inc.
1384 Poil\settia Avenue, Suite A Vista, CA 92081-8505
(760) 599-0509 (760) 599-0593 www.geotekusa.com
Vesta Pacific Development
1818 Second Avenue
San Diego, California 920 I I
Attention:
Subject:
Mr. Geoff McComic
Geotechnical Review of BMP Design
Beachwalk at Roosevelt
2685, 2687 and 2715 Roosevelt Street
Carlsbad, California
Dear Mr. McComic:
August 9, 2016
Project No. 3447-SD3
As requested presented herewith is discussion of the planned storm water disposal system
for the subject property. Geo Tek, Inc. (Geo Tek) has performed an infiltration evaluation
at the subject property dated February 27, 2016. The intent of that study was to estimate
the infiltration rate in the proposed infiltration area for the project site as indicated to us
by Pasco, Laret Suitor and Associates. This report is intended to comply with the now current
guidelines as outlined in the Carlsbad BMP Design Manual.
The subject project is located at 2685, 2687 and 2715 Roosevelt Street in Carlsbad, California.
The subject property was occupied by several old bungalow style residential structures. Plans
provided to us indicated that storm water basins are planned along the Roosevelt frontage and
extending along the northern side of the property.
Percolation/Infiltration Testing
Two (2) excavations were dug by hand to a depth of about 3.5 and four (4) feet foot below
existing grade in the area of the proposed storm water basins along Roosevelt Street, as provided
to Geo T ek. Percolation tests were performed in general accordance with San Diego County
DEH procedures. A 6-inch diameter test hole was manually drilled and cleaned using an auger,
the side walls were free from smeared soils, approximately 4 inches of fine gravel was placed in
the hole, a 3-inch perforated pipe was set in the hole and fine gravel placed around the outside
of the pipe. Water was then poured into the pipe to approximately 12 inches above the gravel.
Water fel l to below the top of the gravel. We continued to pour additional water in the gravel
and a total of approximately 200 were used in PI without ever maintaining a head. Approximately
35 gallons of water were used in P2. Water drained from holes completely. Testing was
performed the following day.
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VESTA PACIFIC
Infiltration Evaluation
Beachwalk at Madison. Carlsbad
Project No. 3447-$D3
February 27, 2016
Page 3
Testing (see attached) indicated a stabilized infiltration rate of approximately 3.0
gallons/hr/sf in P2. We were unable to determine an accurate rate in PI , data
suggests a rate exceeding 5.0 gallons/hr/sf. It should be realized that rates should
be expected to vary and may do so significantly.
Over the lifetime of the storm water disposal area, the infiltration rate may be
affected by silt build up and biological activities, as well as local variations in near
surface soil conditions.
Discussion
Appendix C.4 of the Carlsbad BMP Manual outlines guidelines for the Geotechnical and
Groundwater Investigation Report Requirements addressing onsite storm water infiltration.
Below we are providing specific answers/comments the address each section of Appendix C.4.
We quote each section and then provide an applicable comment in italics.
C.4.1 Site Evaluation
Site evaluation shall identify the following:
• Areas of contaminated soil or contaminated groundwater within the site;
There ore no nearby areas of contaminates based on review of Geo Tra cker f,les.
• "Brown fields" adjacent to the site;
There ore no nearby areas of contaminates based on review of Geo T rocker f,les.
• Mapped soil type(s);
Site is underlain by porolic deposits. They ore comprised mainly of sands and silty sands with
varying grovel and small cobble.
• Historic high groundwater (GW) level;
There is limited historic GW data. The best available data suggest a depth of SO~.
• Slopes steeper than 25 percent;
No nearby slopes exceeding 25%.
• Location of water supply wells, septic systems (and expansion area), or underground storage
tanks, or permitted gray water systems within I 00 feet of a proposed infiltration/
percolation BMP.
There is no supply well within that radius in the State Water Doto Ubrory.
There or no UST on the Geo Tracker with that radius.
There ore sewers in the area and hove been for many years it is unlikely that any active septic
systems ore nearby.
We inquired at the City of Carlsbad building deportment regarding permitted groywoter; no
permits were found for addresses from 2653, 2667, 2650-2740 Roosevelt or for 580 Beech.
GEOTEK
VESTA PACIFIC
Infiltration Evaluation
Beachwalk at Madison. Carlsbad
C.4.2 Field Investigation
Project No. 3447-$D3
February 27, 2016
Page 4
Where the site evaluation indicates potential feasibility for onsite storm water infiltration BMPs,
the following field investigations will be necessary to demonstrate suitability and to provide
design recommendations.
A field evaluation was performed results were discussed above.
C.4.2.1 Subsurface Exploration
Subsurface exploration and testing for storm water infiltration BMPs shall include:
• A minimum of two exploratory excavations shall be conducted within SO-feet of each proposed
storm water infiltration BMP. The excavations shall extend at least IO feet below the lowest
elevation of the base of the proposed infiltration BMP.
Two tests were performed to evaluate the infiltration test results are included herein. While
several small basins are planned they are nearly contiguous and therefore addressed as one
area.
• Soils shall be logged in detail with emphasis on describing the soil profile.
Logs of soils encountered are presented on the percolation test results.
• Identify low permeability or impermeable materials.
None were encountered.
• Indicate any evidence of soil contamination.
None encountered
C.4.2.2 Material Testing and Infiltration/Percolation Testing
Various material testing and in situ infiltration/percolation testing methods and guidance for
appropriate factor of safety are discussed in detail in Appendix D. Infiltration testing methods
described in Appendix D include surface and shallow excavation methods and deeper subsurface
tests.
Percolation testing in small diameter borings as allowed in the Appendix D.
C.4.2.3 Evaluation of Depth to Groundwater
An evaluation of the depth to groundwater is required to confirm the feasibility of infiltration.
Infiltration BMPs may not be feasible in high groundwater conditions (within IO feet of the base
of infiltration/ percolation BMP) unless an exemption is granted by the City.
Groundwater was not encountered on the site. A 2003 report for a property north of the Carlsbad
Coaster Station (Klienfelder, 2003) and approximately 500ft. west of and roughly 5ft. lower than
this site indicates the depth to groundwater exceeding 50ft. deep.
C.4.3 Reporting Requirements by Geotechnical Engineer
The geotechnical and groundwater investigation report shall address the following key elements,
and where appropriate, mitigation recommendations shall be provided.
A
GEOTEK
VESTA PACIFIC
Infiltration Evaluation
Beachwalk at Madison. Carlsbad
Project No. 3447-SD3
February 27, 2016
Page 5
• Identify areas of the project site where infiltration is likely to be feasible and provide
justificationsfor selection of those areas based on soil types, slopes. proximity to existing
features, etc. Include completed and signed Form 1-8 in Appendix I.
Form /-8 is attached. There is no actual signature block on the form but it is attached to this
signed report.
• Investigate, evaluate and estimate the vertical infiltration rates and capacities in accordance
with the guidance provided in Appendix D which describes infiltration testing and appropriate
factor of safety to be applied for infiltration testing results. The site may be broken into sub-
basins, each of which has different infiltration rates or capacities.
Vertical infiltration rates based on conversion using the Porchet method are attached. The Porchet
method is used to estimate infiltration rates based on percolation tests.
• Describe the infiltration/ percolation test results and correlation with published
infiltration/percolation rates based on soil parameters or classification. Recommend providing
design infiltration/percolation rate(s) at the sub-basins. Use Form 1-9 in Appendix I.
Rates are reasonable for the soil conditions. Sub-basins are not applicable.
• Investigate the subsurface geological conditions and geotechnical conditions that would affect
infiltration or migration of water toward structures, slopes, utilities, or other features. Describe
the anticipated flow path of infiltrated water. Indicate if the water will flow into pavement
sections, utility trench bedding, wall drains, foundation drains, or other permeable
improvements.
Geo Tek performed a Preliminary Geotechnical Evaluation for the project in 20 I 4 which was
updated in 20 I 6.
Recommendations have been provided for structural foundations near the basin (see Updated
Preliminary Geotechnical Evaluation, Beachwalk at Roosevelt· CT 14-07, 2685, 2687 & 2 715
Roosevelt Street, Carlsbad, California by GeoTek, In c. doted April 15, 2016)
There are no significant slopes nearby.
There is some potential for infiltrated water to migrate toward utility trenches. Sewer lines
typically the lowest lines. If water enters the trenches it generally migrates along the pipe bedding.
This would not be expected to be a high volume provided there is reasonable separation between
the Infiltration area and any permeable backfill. We recommend that low permeability material
( e.g. lean slurry) be used as backfiil in any utility within I Oft. of the infiltration basins.
It has previously been recommended to not infiltrate in the basin area above the north retaining
wall. In part to avoid the wall drain in that area.
• Investigate depth to groundwater and the nature of the groundwater. Include an estimate of
the high seasonal groundwater elevations.
GEOTEK
VESTA PACIFIC
Infiltration Evaluation
Beachwalk at Madison. Carlsbad
Project No. 3447-$D3
February 27, 2016
Page 6
Groundwater was not encountered on the site. A 2003 report for a property north of the
Carlsbad Coaster Station (Klienfelder, 2003) and approximately S00fr west of and roughly
Sfr lower than this site indicates the depth to groundwater exceeding S0fr deep.
Considering the overall geologic conditions significant seasonal GW ffuctuations are not
expected.
• Evaluate proposed use of the site (industrial use, residential use, etc.), soil and groundwater
data and provide a concluding opinion whether proposed storm water infiltration could cause
adverse impacts to groundwater quality and if it does cause impacts whether the impacts could
be reasonably mitigated or not.
The site is proposed for residential use. It is our understanding the bioretention basins are
designed to mitigate the potential contaminants generated by this use. This should be limited
largely to typical waste from roofs, parking and driveway areas. Assuming proper design and
long term maintenance both of which are performed by others then storm water infiltration
should not have a negative impact on GW quality.
• Estimate the maximum allowable infiltration rates and volumes that could occur at the site that
would avoid damage to existing and proposed structures, utilities, slopes, or other features. In
addition the report must indicate if the recommended infiltration rate is appropriate based on
the conditions exposed during construction.
The allowable infiltration rate used in the design is 0.5 inches per hr based on our
recommendation this is considered reasonably conservative based on the testing. The volume
determination is not a function for the geotechnical consultant.
Site construction has not occurred. It is therefore impossible to address the conditions exposed
during construction.
• Provide a concluding opinion regarding whether or not the proposed onsite storm water
infiltration/percolation BMP will result in soil piping, daylight water seepage, slope instability, or
ground settlement.
It is our conclusion that soil piping, daylight water seepage, slope instability, or ground
settlement will not occur as the result of on site infiltration. Provided that recommendations
previously provided for use of filter fabric are followed.
• Recommend measures to substantially mitigate or avoid any potentially detrimental effects of
the storm w ater infiltration BMPs or associated soil response on existing or proposed
improvements or structures, utilities, slopes or other features within and adjacent to the site.
For example, minimize soil compaction.
These were addressed in conjunction with our "Updated Geotechnical Evaluation."
• Provide guidance for the selection and location of infiltration BMPs, including the minimum
separations between such infiltration BMPs and structures, streets, utilities, manufactured and
GEOTEK
VESTA PACIFIC
Infiltration Evaluation
Beachwalk at Madison, Carlsbad
Project No. 3447-SD3
February 27, 2016
Page 7
existing slopes, engineered fills, utilities or other features. Include guidance for measures that
could be used to reduce the minimum separations or to mitigate the potential impacts of
infiltration BMPs.
The locations of basins as currently planned are considered acceptable.
• Provide a concluding opinion whether or not proposed infiltration BMPs are in conformance
with the following design criteria:
• Runoff will undergo pretreatment such as sedimentation or filtration prior to infiltration;
There is planned pretreatment.
• Pollution prevention and source control BMPs are implemented at a level appropriate to
protect groundwater quality for areas draining to infiltration BMPs;
The BMPs appear appropriate to protect groundwater.
• The vertical distance from the base of the infiltration BMPs to the seasonal high groundwater
mark is greater than IO feet. This vertical distance may be reduced when the groundwater basin
does not support beneficial uses and the groundwater quality is maintained;
Criteria is met as basins are currently proposed.
• The soil through which infiltration is to occur has physical and chemical characteristics (e.g.,
appropriate cation exchange capacity, organic content, clay content, and infiltration rate) which
are adequate for proper infiltration durations and treatment of runoff for the protection of
groundwater beneficial uses;
With the treatment as proposed in the BMPs this appears to met
and
• Infiltration BMPs are located a minimum of I 00 feet horizontally from any water supply wells.
There is no record of any well within I 00~ of the site on the California DWR Water Data Ubrary.
LIMITATIONS
The materials observed on the project site appear to be representative of the area; however,
soil materials vary in character between excavations and natural outcrops or conditions exposed
during site construction. Site conditions may vary due to seasonal changes or other factors.
Geo T ek, Inc. assumes no responsibility or liability for work, testing or recommendations
performed or provided by others.
GEOTEK
VESTA PACIFIC
Infiltration Evaluation
Beachwalk at Madison, Carlsbad
Project No. 3447-SD3
February 27, 2016
Page 8
Our conclusions and recommendations are professional opinions that are limited to the extent
of the available data. Observations during construction are important to allow for any change in
recommendations found to be warranted. These opinions have been derived in accordance with
current standards of practice and no warranty is expressed or implied. Standards of practice
are subject to change with time.
The opportunity to be of service is sincerely appreciated. If you should have any questions,
please do not hesitate to call our office.
Respectfully submitted,
GeoTek, Inc.
Attachment: Infiltration Test Data
Figure I -Infiltration Test Location Map
Form 18
Distribution: (I) Addressee via email (PDF file)
GE O TE K
Senior Project Engineer
GEOTEK, INC.
PERCOLATION TEST DATA SHEET
TEST HOLE NO. P ----------------DEPTH OF TEST HOLE: 4 ft TEST HOLE SIZE: 6inch ----------------S O1 L CLASSIFICATION: Light red Brown, sl moist, clean SAND (SW)
START
STOP
PRESOAK PERIOD
TIME INTERVAL
10:50 AM
9:15 AM
2/19/16
AMOUNT OF WATER USED
200 Gallons
2/20/16 (no water left in test hole) Unable to fill hole
TEST PERIOD
Initial Water Final Water _6.in Water Percolation Calculated
Time Time Interval (min) Level (inches) Level (inches) Level Rate Infiltration
(inches) (min/inch) (gal/hr/sf)
9:20 AM Attempted to fill test hole unable to obtained a 10 inch head 10:00 AM
TECHNICIAN: WD/TM DATE: 2/20/2016 -------------
TEST HOLE NO. p 2
DEPTH OF TEST HOLE: 4 TEST HOLE SIZE: 6inch -,----,,----------------,---SOIL CLASSIFICATION: Red Brown, Slightly Clayey Sand, Moist (SC)
START
STOP
PRESOAK PERIOD
TIME INTERVAL
11:30 AM
10:15 AM
2/19/16
AMOUNT OF WATER USED
35 Gallons
2/20/16 (no water left in test hole)
TEST PERIOD
Initial Water Final Water ~n Water Percolation Calculated
Time Time Interval (min) Level (inches) Level (inches) Level Rate Infiltration
(inches) (min/inch) (gal/hr/sf)
10:20 AM
10:30 AM 10 10.0 1.9 8.1 1.2 3.0
10:32 AM
10:42 AM 10 10.0 1.8 8.2 1.2 3.1
10:45 AM 10 10.0 1.8 8.2 1.2 3.1 10:55 AM
10:58 AM 10 11 :08 AM 10.0 1.8 8.2 1.2 3.1
TECHNICIAN: WD/TM DATE: 2/20/2016 -------------
Roosevelt
Not to
Scale
Geotechnical Legend
$ Percolation Test Location
P-2
All locations approximate
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Figure 1
Appendix I: Forms and Checklists
Part 1 -Full Infiltration Feasibilicy Screening Criteria
Would infiltration of the full design volume be feasible from a physical perspective without any undesirable
consequences that cannot be reasonably mitigated?
Criteria Screening Question
Is the estimated reliable infiltration rate below proposed
facility locations greater than 0.5 inches per hour? The response
to this Screening Question shall be based on a comprehensive
evaluation of the factors presented in Appendix C.2 and Appendix
D.
Provide basis:
Yes No
□
Pursuant to the letter report dated February 27, 2016 prepared by Geotek, Inc.
which summarized the results of their infiltration analysis for the project, a
percolation test was performed which showed an infiltration rate of 1.7 in/hr. Refer
to the letter report for more details.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
2
Can infiltration greater than 0.5 inches per hour be allowed
without increasing risk of geotechnical hazards (slope stability,
groundwater mounding, utilities, or other factors) that cannot
be mitigated to an acceptable level? The response to this
Screening Question shall be based on a comprehensive evaluation of
the factors presented in Appendix C.2.
Provide basis:
□
The site is underlain by paralic deposits (GeoTek, 2014) which is generally dense granular material and are not
subject to the following: Hydro collapse and calcareous soils; Expansive soils; Frost heave (due to climate);
Consolidation; and Liquefaction. There are no nearby slopes to consider for stability issues. The groundwater
depth in the downtown Carlsbad area can vary although depths on the order of 30 feet are typical. Groundwater
mounding could potentially occur for brief periods however this would be a localize issue an and quickly
dissipate due to the generally high permeablility of the paralic deposits. The water potential could enter Utility
trench backfills however it should quickly disapate. No long term concerns are anticipated. Locally deepened
foundations are appropriate based on proximity of foundatiojns and basin.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/ data source applicability.
1-3 February 2016
Appendix I: Forms and Checklists
,. . ;. \.
Criteri
a
3
·, ..
• '· ;=· Form 1-8 ~age 2 <>f 4
Screening Question
Can infiltration greater than 0.5 inches per h our be allowed
without increasing risk of groundwater contamination (shallow
water table, storm water pollutants or other factors) that cannot
b e mitigated to an acceptable level? TI1e response to rJ1is
Screening Question shall be based on a comprehensive evaluation of
rJ1e factors presented in Appendix C3.
Provide basis:
Yes No
□
The rapid infiltration rate is based on the sandy nature of the soils encounter these sandy zones are typical
within the paralic deposits although they are neither laterally nor vertically continuous due to the lensing and
layering. Much cleansing action of these basins takes place in the man made bio-filtration materials so that the
underlying paralic deposits provide secondary cleansing . The water potentially could enter Utility trench
backfills however it would be expected to dissapate rapidly. No long term concerns are anticipated. Based on
reveiw of records through the Geo Tracker system there does not appear to be any active remediation either up
or down gradient that need be considered. There is no indication of seasonal groundwater within 20 feet of the
ground surface. No nearby water well records are indicated on the DWR Water Data Library
Swnmarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/ data source applicability.
4
Can infiltration greater than 0.5 inches per hour be allowed
without causing potential water balance issues such as change
of seasonality of ephemeral streams or increased discharge of
contaminated groundwater to surface waters? The response to
this Screening Question shall be based on a comprehensive
evaluation of rJ1e factors presented in Appendix C3.
Provide basis:
□
There are no nearby stream or surface waters in close proximity to the site. The Pacific Ocean is the nearest
surface water is roughly 2000 feet to southwest
Swnmarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
Part 1
Result
*
If all answers to rows 1 -4 are ''Yes" a full infiltration design is potentially feasible.
The feasibility screening category is Full Infiltration
If any answer from row 1-4 is "No", infiltration may be possible to some extent but
would not generally be feasible or desirable to achieve a "full infiltration" design.
Proceed to Part 2
*To be completed using gathered site information and best professional judgment considerii1g rJ1e definition of l'vIEP in
the MS4 Permit. Additional testing and/ or studies may be required by the City to substantiate findings.
I-4 February 2016
Appendix I: Forms and Checklists
Part 2 -Partial Infiltration vs. No Infiltration Feasibility Screening Criteria
Would infiltration of water in any appreciable amount be physically feasible without any negative
consequences that cannot be reasonably mitigated?
Criteria
5
Screening Question
Do soil and geologic conditions allow for infiltration in any
appreciable rate or volume? The response to th.is Screening
Question shalJ be based on a comprehensive evaluation of the
factors presented in Appendix C.2 and Appendix D.
Provide bas.is:
Yes No
□ □
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability and why i1 was not feasible to mitigate low infiltration rates.
6
Can Infiltration in any appreciable quantity be allowed
without increasing risk of geotechnical hazards (slope
stability, groundwater mounding, utilities, or other factors)
that cannot be mitigated to an acceptable level? 'The response
to this Screening Question shall be based on a comprehensive
evaluation of the factors presented in Appendix C.2.
Provide basis:
□ □
Summarize findings of studies; provide reference to studies, calculations, maps, da ta sources, etc. Provide narrative
discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates.
1-5 February 2016
..
Appendix I: Forms and Checklists
'. • ... ·•
Criteria
7
Screening Question
Can Infiltration in any appreciable quantity be allowed
without posing significant risk for groundwater related
concerns (shallow water table, storm water pollutants or other
factors)? 111e response to this Screening Question shall be based
on a comprehensive evaluation of the factors presented in
Appendix C.3.
Provide basis:
Yes No
□ □
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates.
8
Can infiltration be allowed without violating downstream
water rights? The response to this Screening Question shall be
based on a comprehensive evaluation of the factors presented in
Appendix C.3.
Provide basis:
□ □
Summarize findings of srudies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/ data source applicability and why it was not feasible to mitigate low infiltration rates.
Part 2
Result*
If all answers from row 5-8 arc yes then partial infiltration design is potentially feasible.
The fcasibili ty screening category is Partial Infiltration.
If any answer from row 5-8 is no, then infiltration of any volume is considered ro be
infeasible within the drainage area. 111e feasibility screening category is No Infiltration.
*'fo be coinpleted us111g gathered sue mfonnat:ton and best professional Judgment consJdering the definition of ~fEP 1n
the MS4 Permit. Additional testing and/or studies may be required by the City to substantiate findings.
1-6 February 2016