2906_DavidsonMSW_HydroReview_DIN28688_20170108

S t a t e o f N o r t h C a r o l i n a | E n v i r o n m e n t a l Q u a l i t y | W a s t e M a n a g e m e n t
1 6 4 6 M a i l S e r v i c e C e n t e r | 2 1 7 W e s t J o n e s S t r e e t | R a l e i g h , N C 2 7 6 9 9 -1646
9 1 9 7 0 7 8 2 0 0
ROY COOPER
Governor
MICHAEL S. REGAN
Secretary

MICHAEL SCOTT
Director
January 8, 2018

Sent via email – [e-mail]

Mr. Rex Buck
Public Services Director
PO Box 1067
Lexington, NC 27293

RE: Design Hydrogeologic & Monitoring Reports Technical Review
Davidson County MSWLF Phase 2 - Area 3
Permit No. 2906-MSWLF-2008
Davidson County, North Carolina
DIN 28710

Dear Mr. Buck:

The Division of Waste Management, Solid Waste Section (Section) has reviewed the design hydro report and
monitoring plans for the proposed Phase 2 – Area 3 landfill expansion at the Davidson County MWS facility.
These documents were included as attachments in a permit to construct application (DIN 28523) submitted
by Smith+Gardner Inc (S+G) on behalf of Davidson County in October 2017. The Design Hydro report
(Attachment I) addresses regulatory requirements for a proposed 14.6-acre expansion of the existing active
MSW landfill. The proposed Water Quality and Landfill Gas monitoring plans (Attachments J and K) are
updates to the current monitoring plans for the MSW landfill.

Design Hydrogeologic Report – ref 15A NCAC 13B .1623(b)
Upon our review, we have determined that the Design Hydrogeologic Report for Phase 2 – Area 3 expansion
meets the criteria required in .1623(b), including top-of-bedrock datum and seasonal high groundwater table
determinations for vertical separation requirements for construction [15A NCAC 13B .1624(4)]. As noted in
Table 8 and in Figure 6 cross-section A-A’, a rock pinnacle near well PZ-11 will be removed during
construction by excavation or, if necessary, by blasting to meet the minimum four-feet vertical separation
between bedrock and base grade. If blasting is needed, the owner shall submit a blasting plan for Section
review prior to execution of the work.
The Design Hydrogeologic Report (Attachment I of DIN 28523) is approved.
Page 2

Water Quality Monitoring Plan – ref 15A NCAC 13B .1623(b)(3)
The current groundwater monitoring well network for the Phase 2 MSW consists of nine (9) shallow wells
monitoring the upper saprolite aquifer and three (3) bedrock wells. The three bedrock wells are used only to
collect water level measurements. Additionally, surface water samples are collected at two (2) locations to
monitor Richland Creek just west of the Phase 2 landfill. Leachate samples are also collected from the onsite
leachate storage tanks. Groundwater, surface water, and leachate sample collection and analyses are
performed semi-annually and reported to the Section in accordance with the approved plans.
For the Phase 2 MSW expansion, S+G has proposed converting four (4) existing piezometers for monitoring
purposes. Three shallow piezometers (PZ-45, -46, &-51) will be converting to compliance monitoring wells
MW-11s, MW-12, & MW-13, respectively. One bedrock piezometer (PZ-45D) will be converted to bedrock
monitoring well MW-11D, which will be used only for collection of water level measurements. Prior to
approval of the proposed WQ plan, please address the following items:
• Section 2.2 Monitoring Network & Analytical Parameter – Four pre-existing piezometers (PZ-45s,
PZ-45d, PZ-46 & Pz-51) are proposed for converting to monitoring wells. Text states “Five
piezometers are proposed for conversation to monitoring”. Please correct.

• Section 2.2.1 Modifications to Monitoring Network (MW-11D) – MW-11D is a bedrock well nested
with a shallow well MW-11S, which will be part of the regular detection monitoring network. The
plan proposes sampling well MW-11D for Appendix I constituents only during the initial Spring
2018 semi-annual monitoring event and then use the well only for water level measurements
thereafter, unless required otherwise. Additionally, both filtered and unfiltered samples will be
analyzed for inorganic constituents due to possible sample turbidity.

As stated in rules .1623(b)(3)(C) and .1631(a), the ground-water monitoring network or system is
designed to provide for early detection of a possible contaminant release from the landfill to the
uppermost aquifer. Unless site-specific hydrogeologic conditions indicate otherwise, monitoring of
the deeper bedrock aquifer wells, such as MW-11D, would only be required in the case where
contaminants are detected in the shallow wells, which monitor the uppermost aquifer at the site. For
the Phase 2 MSW, there does not appear to be any regulatory reason for monitoring the bedrock
aquifer at this time. As such, the Section is not requiring any bedrock aquifer sampling and
monitoring (via the proposed well MW-11D or other bedrock wells) for the Phase 2 MSW
expansion. For this reason, the facility may want to consider maintaining the proposed MW-11D as
a piezometer for water level monitoring only. However, should the facility decide to collect
groundwater samples from this well for Appendix I analysis, the results must be reported to the
Section. Please advise on how you plan to proceed.

• Figure 1 – revise the water quality monitoring network map to also show surface water sampling
locations, streams, and general ground-water flow contours (this could also be a separate
potentiometric map with well/surface water locations).

Landfill Gas Monitoring Plan – ref 15A NCAC 13B .1626(4)
The existing LFG monitoring network for Phase 2 MSW consists of nine (9) LFG wells located around the
perimeter of the landfill unit. LFG is also monitored within the scale house located to the northeast of the
landfill. No additional monitoring locations are proposed for the Phase 2 – Area 3 expansion.

The proposed LFG monitoring plan meets all the all the requirements [per .1626(4) and Section guidance] for
monitoring of explosive gases at the facility. The Section approves the LFG Monitoring Plan (Attachment K
of the application package DIN 28523).
Page 3

Well Abandonment
Any existing piezometers and/or monitoring wells within the footprint of the proposed Phase 2 Area 3
expansion must be properly abandonment prior to construction activities commencing for the landfill
expansion. (Piezometers, groundwater monitoring wells, and borings, located in proposed expansion may be abandoned now or
after a Permit‐to‐Construct is issued by the Section). Please adhere to the following conditions:

Prior to construction of cell(s), all piezometers, ground‐water monitoring wells, and borings, located in the
proposed cell(s), shall be properly abandoned by over drilling first (exception for non‐cased borings) and
sealed with grout in accordance with 15A NCAC 2C .0113, entitled “Abandonment of Wells”.

a. In areas where soil is to be undercut, abandoned piezometers, monitoring wells, and borings must
not be grouted to pre‐grade land surface, but to the proposed base grade surface to prevent having
to cut excess grout and potentially damaging the wells.

b. Well abandonment records (GW‐30 form) for each decommissioned piezometer, boring, and
groundwater monitoring well must be certified by a Licensed Geologist in accordance with rule
.1623(b)(2)(I) and submitted to the Solid Waste Section in accordance with 15A NCAC 02C
.0114(b).

NOTE: The Permit-to-Construct to be issued later will include Ground Water and other Monitoring
Requirements.

If you have any questions or need further assistance on this review, please contact me via email at
[e-mail] or by phone at [phone].

Sincerely,
Perry Sugg, PG
Permitting Hydrogeologist
Solid Waste Section

Cc: Ed Mussler, PE - SWS Permitting Branch Head
Ming Chai, PE – SWS Permitting Engineer
Steven Sink – Davidson County
Madeline Germane, PG – Smith+Gardner Inc.