20010357 Ver 1_More Info Received_20080821

I BSC GROUP
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TRANSMITTAL
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To: Ms. Annette Lucas Date: 08-21-2008
NC Division of Water Quality Proj. No: 02063.00
2321 Crabtree Boulevard Project: UpChurch Farms
Raleigh, NC 27604-2260
q., tq
We are sending you: AU G 2 1 2008
® Attached ? Under Separate Cover

Via:
pENR -WATER QUlW7Y
V&II NDSANDSTORMWATERBRN
? Overnight Delivery ? To be picked up by Recipient ? Regular Mail
® Messenger ? Direct from printer ? Other:
One 1 Hardco of the Foreba Embankment Plan
One 1 Co of the Design Specification Letter from D. Mlller & Associates dated Jul 18, 2008

This information is:
? For Your Information ? Approved as submitted ? Resubmit _ copies for approval
? Unchecked ? Approved as noted ? Return _ corrected prints
? Preliminary ? Disapproved ? Submit _ copies for
? Revised Plans ? Returned for corrections distribution
® Final Plans ? Sent for your review & comment
Remarks: Annette
Attached is the hardco you requested of the ap proved Foreba Embankment Plan.
Please provide an approval letter at our earliest convenience. Thank you for our
assistance regarding this matter.
BSC File 02063.00
Copy to:

y?
Si gned:
PPtar Frarrarnli P F

CI 701 Corporate Center
Drive, Suite 163
Raleigh, NC 27607
Tel: [phone]
Fax: [phone]

Note: If enclosures are
not as noted, please
contact us immediately.
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mAssiller o?-03?-,
D8. Associates, PA
1000 Bearcat Way, Suite 103
Morrisville, NC 27560
[phone] (Office) [phone] (Fax)
July 18, 2008
Mercury Development
Attention: Michael L. Jones
5660 Six Forks Rd., Suite 202
Raleigh, NC 27609
Phone: [phone]
Fax: [phone]
Emaji:[e-mail]
Re: Engineering Services -Slope Design of the Existing Retention Pond's Forebay
Repair at Upchurch Farms Subdivision
Cary, NC
Project No.: 08-331-0623-01
Mr. Jones:
This letter supersedes our previous letter prepared under project No. 08-331-0623-01, dated
July 1, 2008.
As requested, D. Miller & Associates, PA(DMA) has completed the slope design of the
existing retention pond's forebay repair in accordance with DMA's proposal prepared under proposal
No.1`08-3310141R, dated June 17, 08. It is understood that the existing forebay embankment will be
replaced with a new embankment. The maximum height of the proposed embankment is 3 feet. Based
on the cross-section drawing (Section "A") of the embankment provided by Mr. John Parrish of
Ferguson, the proposed top width of the forebay embankment is approximately 10.5 feet, the bottorn
of the retention pond on the forebay side will be at Elev. 346. The normal pool elevation is at 344.
According to Mr. Peter Fraccaroli, P.E. of BSC Group, the 100 year flood elevation of the pool is at
Elevation 348.38.
On 6-18-08, a representative of D. Miller & Associates, PA visited the subject site for the
purpose of obtaining soil samples within the existing forebay embankment. Two hand auger borings
were advanced each on the up stream and down stream sides of the existing 50 foot long forebay
(please refer to Figure 1 on the attached Project Time Record (PTR) for locations and details). The
soils exposed on the upstream side of the forebay consisted of saturated, orange brown very sandy
clay and the materials exposed on the down stream side of the forebay consisted of gray sand to
possible partially weathered rock. Due to the saturated condition of the soil on the up strearn side and
sandy type soil on the down stream side of the forebay, Shelby tubes could not be obtained for density
testing. Two bulk soil samples were obtained each from both up stream and down stream sides of the
forebay and transported to DMA's Laboratory for Atterberg limits testing (ASTM D4318) and grain
size analysis (ASTM D422). The soil obtained from the down stream side of the forebay embankment
was not utilized for the testing. However, the sample was visually classified as silty sand.
The Atterberg Limits and grain size analysis test results indicate that the soil has the
following properties: liquid limit of 45, plasticity index of 26 and 50% of the soil by weight passing a
No. 200 sieve. The soil classifies as a sandy lean CLAY (CL). Based on the test results, a friction
angle of 25 degrees and cohesion of 200psf were assumed for the stability analysis.
Based on the provided verbal and schematic drawings information, and our laboratory test
results, global stability analysis of the forebay embankment was conducted, Based on the analysis
results, the global stability of the embankment is within tolerable limits. In order to minimize the risk
., - , ,
Mercury Development
Re: Forebay Dam Upchurch Farms
Project No: 08-331-0623-01
July 18, 2008
Page 2 of 2.
of erosion of soils and seepage of water through the embankment, the following points must be
completed for proper construction of the proposed embankment:
1. The side slopes of the embankment should not be steeper than 2(H):l(V), if it is
required to access the forebay for maintenance, 3(H):l(V) or flatter slope is required.
2. The soil fill to be used for the construction of embankment should be impermeable and
the plasticity index of the fill should not be less than 15. Based on the Atterberg limits
test results, the tested material located on the upstream of the existing forebay has a
plasticity index of 26. However; due to the percentage of coarse grained material in
the on-site soils, it is preferable to use silty clays with a plasticity index greater than
15.
3. The permeability of the soil should be 1x1007 cm/sec (3.33X10-09 ft/sec) or less.
4. The soil fill should be placed in 8-inch thick lifts and compacted to a minimum of 95
percent of maximum dry density of the standard Proctor test within 3 percentage
points of optimum moisture content.
5. Based on the global stability analysis results, placement of geosynthetic reinforcement
layers between the lifts is optional. However, the up stream face, down stream face
and the top of the embankment should be covered with high velocity resistant erosion
control mats such as North American Green P550 or equivalent, secured into place per
the manufacturer's specifications.
6. The base of the embankment shall be stripped of all vegetation, stumps, organic matter
and loose and soft soil.
7. A toe drain wrapped in a filter fabric shall be installed at the bottom of the proposed
embankment along the down stream side of the embankment (please refer to attached
drawing for details),
8. All slopes must be overbuilt a minimum of 4 feet and then cut back to the desired final
slope. (please refer to the attached drawing for details)
A rip-rap or gabion wall weir can be considered within the embankment in order to minimize
the overtopping of the pond water. If elected, the inclusion of a weir should be coordinated through
and approved by the engineer of record, Mr. Peter Fraccaroli, P.E. of BSC group. if a weir is planned
for constriction, DMA is available to modify recommendations accordingly. The dimensions of the
weir should be designed by storm water/hydraulics engineer,
The embankment construction should be observed by a qualified geotechnical engineer or his
representative for quality assurance and quality control (QA/QC) purposes. DMA can provide these
services, if desired.
We appreciate the opportunity to assist you during this phase of the project. if you need
further assistance or additional information please do not hesitate to contact us.
Sincerely,
D. Miller & Associates PA O+'••
l 1 A .a nx` l
Phan
Engineer
Kelly P. Flanagan, P.E.
Geotechnieal Dept. Manager
/ G 08-331-0623-01
050 •?<i??l//?.t et i •+?
Photos: patlon?Yes o
Consols /No
PROJECT TIME RECORD
D. NUller & Associates, P.A.
8504 Six Forks Road, Suite 101
Raleigh, NC 27615
Phone; [phone] Fax; [phone]
Attachments
Forensic Form: _
Concrete Form:
Drive Tube Form:
Crack Monitor Form:
Other:
P s DAA6 Job No.: o
roject: Date: . I q. p-,
Pu ose of Visit: DA, e Fax No.;
Client Company: ,l,l Contact No.: 86r. ?za
Contact Name: It4leVAju- Permit No.: ,,,
City /Town: Weather:
StartTime: pw p Sto Time: 'o: Travel Time: -5o Total:
Start Time: Stop Time: Travel Time: Total:
At Subgrade Level: E9 / Fill (circle one)
Fill Controlled? Per Who?
Depth of Overlying Fill:
Soil Description:
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Remarks:
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The above report is a preliminary submittal. All data is subject to technical review and confirmation.
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ASTM D 422 Standard Test Method for Particle-Size Analysis of Soils
Project No.: 08-331-0623 Boring No.: n/a
Project Name: Upchurch Farms Fore Bay Dam Sample No.: 8-1
Client: Mercury Development Depth: n/a
Date: 5/2012008
Sample Weight Before Wash(g) 300.05 Weight Removed with Wash (g) 151
Weight After Wash (g) 149 Assumed Specicif Gravity 2.70
Weight Dry of Hydrometer Sample (g)*
*Silts and Clays 65g Sands 1158
Correted Weight (g) -

Sieve Sieve Opening
mm Weight per
Sleve Cumulative
Weight Percent
Retained % Percent
Passing %)
3in. 75,0 0 - 100
2 in. 50.0 0 - 100
1-1/2 in. 37.5 0 - 100
1 in. 25.0 0 - 100
3/4 in, 19.0 0 - 100
112 in 12,5 5,70 5.7 2 98
318 in 9.5 5.7 2 98
114 in 6.25 5.7 2 98
No.4 4.8 2.02 7.72 3 97
No.8 2.36 7.72 3 97
No. 10 2.0 6.53 14.25 5 95
No. 14 1.4 8.52 22.77 8 92
No. 16 1.18 22.77 8 92
No. 40 0.425 59,71 82.48 27 73
No. 100 0,150 82,48 27, 73
No. 200 0.075 66.65 149.13 50 50
Pan -- 149.13
Elapsed

Time (min)
Temperature (°F) Hydrometer

Reading Corrected
Hydra
ea i % Total in

Suspension
K Effective
Length
c Particle
Diameter
mm
2 -0.002 #DIV101 #N/A #N/A #NIA
5 -0.002 #DIV/01 #N/A #N/A #NIA
15 -0,002 #DIV101 #N/A #N/A #N/A
30 -0.002 #DIV/01 #NIA #N/A. #N/A
60 -0.002 #DIV101 #N/A #N/A #NIA
E 250 -0.002 #DIV/01 #NIA #NIA MIA
1440 -0.002 #DIV/0I #N/A #NIA #N/A