Free Appendix - District Court of Delaware - Delaware

_ _~ Case 1 :04-cv-00163-GIVIS Document 212-4 Filed 08/22/2006 Page 1 of 2
, . · G.N. Rrcnartnson & Assocrarrs V
p Engineering and G clcgica|`Sé`rtti¤_éS:*s*?i?fZis"’“{ ·.j‘f;
U January 15, 2004
_ ; Chubb & Sons L
· Attn: Ms. Ellen M. Cavallaro V A yr EXHI '
i [5 Mountarnvrew Road · V
L I Warren, NI 07061 Depenem . . @(2.
RE; City of Newark Water Reservoir Dm$,,w%zlT&m,,.,c,“B
l " Safety of Current Design _
, Dear Ms. Cavallaro:
Per your request, this letter was prepared to concisely present my concerns regarding the
safety of the current reservoir design. My concerns over two design details are the basis
for my opinion that this facility cannot be safely constructed as designed. The two details
and their related concerns are as follows:
1 • The current upper slope design places a fabric formed matting system over the I6 osy
nonwoven cushion geotextile and under a layer of stone. The interface friction
between the fabric formed matting system is dependent of a slight cementing action
resulting from some leakage of fine aggregate concrete through the fabric form. This
cementing bond is essential to the stability of the fabric formed matting system and
; — overlying stone. This cementing bond is not addressed in the current specihcations
1 nor do the testing laboratories feel that they can accurately quantify it. Yet without a
' program to ensure development of the bond between the fabric formed matting
_ 1 system and the cushion geotextile, there is real danger of the upper veneer failing and
‘ _ sliding to the bottom of the slope. This would pose a life threatening danger to
= ‘ workers below the slope or those caught on the upper slope at time of failure.
. . • The current lower slope design uses a silty/sandy soil to ballast and protect the
E i geomembrane liner. This soil ishighly erodible and unstable if even minor pore
* ~ water pressures develop beneath it. While we can protect this layer during
__ construction using temporary tarp covers (rain sheets) if the fabric formed matting
I system is deleted and the bench redesigned, it would not be protected during future
·. maintenance activities. Failure of the soil cover could occur if the reservoir was
lowered too quickly (referred to as rapid draw down condition) or if the layer was
A exposed to even moderate rainfall during the maintenance period. URS has indicated
4 that a maximum draw—down rate of l-ft per day would be used. This _requires
approximately 40-days just to drain the reservoir prior to maintenance. No provisions
g i currently exist for gaining access to the bottom of the reservoir for maintenance over
what would be very weak saturated soils covering the steep slopes. Also note that
i this would preclude a faster emergency draw-down of the reservoir since sliding of
, the soil cover could precipitate a catastrophic failure of the geomembrane liner.
‘ 14 N. BOYIAN AVENUE • RALEIGH, NC 27603 • TEL. 919-828-0577 • FAX 919-828-3899 · WWW.GNRA.COM

» Case 1:04-cv-00163-Gl\/IS Document 212-4 Filed 08/22/2006 Page 2 of 2
i in my professional opinion, these two factors make the current design for the reservoir
UF\SHfC for COl'lS[l'UC[lOl'\ Hlld S€I“ViC€.
Please let me know if these points requireifurther clarihcation.
Z i coidasiiy, -- -
yi GN. Richardson & Associates, [nc.
g chards0n, Ph.D,, P.E.
i
ini


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Case 1:04-cv-00163-GMS

Document 212-4

Filed 08/22/2006

Page 1 of 2

Case 1:04-cv-00163-GMS

Document 212-4

Filed 08/22/2006

Page 2 of 2