17040_Stanhope Center_Pre-Occupancy Report_20150722

July 22, 2015

Mr. Tony Duque, Project Manager
NCDENR Brownfields Program
217 West Jones Street
Raleigh, North Carolina 27603

Subject: PRE-OCCUPANCY TESTING REPORT
STANHOPE CENTER II
3001 HILLSBOROUGH STREET
RALEIGH, NORTH CAROLINA
MID-ATLANTIC PROJECT NO. 000R2490.04
BROWNFIELDS PROJECT NUMBER 17034-13-92

Dear Mr. Duque:

Mid-Atlantic Associates, Inc. (Mid-Atlantic) is providing this Pre-Occupancy Testing Report
for the Stanhope Center II for your review and approval.

BACKGROUND INFORMATION

The site is currently being developed as a mixed-use redevelopment with residential
and retail components. A 3.31-acre portion of the subject property is subject to an
existing Brownfields Agreement (BFA) between the North Carolina Brownfields Program
(NCBP) and Hillsborough Ventures, LLC and is identified by the Brownfields Program
as Project No. 06011-02-92. The presence of historical soil and groundwater
contamination is documented in this BFA. A Brownfields Property Application (BPA)
for the subject site was received by the NCBP and was deemed eligible for entry
into the Program for continued evaluation for a BFA as stated in an October 16, 2013
Letter of Eligibility. Additional lots have been included in an updated BFA that, in
addition to the original 3.31 acres, comprise the entire 4.28 acre site (subject site).
The subject site is now listed as NCBP Project No. 17040-13-92. On November 15,
2013 the NCBP approved an Environmental Management Plan (EMP) for the subject
property, and on March 24, 2014 the NCBP approved a Vapor Intrusion Mitigation
System (VIMS) design and specifications document for use at the subject property. The
NCBP-approved EMP and VIMS enabled the redevelopment of the subject site to
occur under the existing BFA while the new BFA was being developed.
Pre-occupancy Report
Stanhope Center II
Raleigh, North Carolina
July 22, 2015
Page 2

Five buildings (discrete building sections) and a parking deck are being developed
as the Stanhope Center II. A vapor intrusion mitigation system (VIMS) was designed
for each of the five buildings by Mid-Atlantic, and the design was approved by the
NCBP. The VIMS design incorporates seven zones with uninterrupted sub-slab
venting layers and active sub-slab depressurization in each zone. The VIMS zones
layout is depicted in Drawing 1.

Contaminants of Concern (COC’s) on the site identified in groundwater depicted in Exhibit
2 of the draft Brownfields Agreement are as follows:

Benzene, Toluene, Ethylbenzene, Xylenes, Naphthalene, Tetrachloroethylene,
Trichloroethylene, 1,2-Dichloroethane, 1,2,4-Trimethylbenzene,Isopropylbenzene.

INITIAL VIMS EFFECTIVENESS TESTING

Mid-Atlantic has completed initial VIMS effectiveness testing at Stanhope Center II for
VIMS zone A (March 3, 2015), zone B (March 11, 2015) and zone C (August 1, 2014).
For the remaining VIMS zones (zones D, E, F and G), sub-slab pressure monitoring was
conducted following permanent blower installation during pre-occupancy testing. For
initial VIMS effectiveness testing Mid-Atlantic temporarily connected and operated a
RadonAway XR-261 blower (e.g., low energy, 100-watt, 120-volt radon type fan, with 6
inch inlets) at each of the vertical riser stubs. During testing vacuum was only initiated at
one riser at a time. The blower depressurized the sub-slab venting layer beneath the floor
slab per the VIMS design/horizontal vent layout. Mid-Atlantic installed vapor pins into the
floor slab sections at approximate locations depicted in Drawing 1 in order to measure the
indoor/sub-slab pressure differentials and evaluate the influence being obtained by the
sub-slab depressurization system.

Table 1 shows data from effectiveness testing from VIMS zones A, B and C. The column
heading shows the riser location and the rows are sub-slab vapor pin identification
numbers. At each vapor pin Mid-Atlantic documented at least 15 pascal (Pa) sub-slab to
indoor pressure differential with the blower operating. Pressure differentials were also
measured at distant pin locations (pins that had other risers that were closer) with the
pressure differential decreasing with increased distance from the riser.

PRE-OCCUPANCY TESTING METHODS

On June 17, 2015 Mid-Atlantic conducted pre-occupancy sub-slab pressure differential
monitoring to demonstrate that the operating VIMS was adequately interrupting the vapor
exposure pathway. Our methods for assessment for final pre-occupancy assessment
were described in a May 26, 2015 Pre-Occupancy Testing Work Plan provided to the
NCBP and approved on May 27, 2015. We conducted the testing following completion of
vertical construction, and installation and start-up of all permanent blowers using the full
Pre-occupancy Report
Stanhope Center II
Raleigh, North Carolina
July 22, 2015
Page 3

extent of the VIMS piping network in order to assess as–built system performance.
Heating, ventilating and air conditioning systems have been installed and were operating
in VIMS zones A and C.

After it was determined that all roof-top VIMS blowers were functioning, monitoring points
were identified in the VIMS zones. A rotary drill was used to penetrate the slab and vapor
barrier and a vapor monitoring pin with an air sealed fitting was driven into the slab
penetration. A tube leading to a “DP Calc” micromanometer was connected to the vapor
pin fitting so that the indoor to sub-slab pressure differential could be measured (Photos 1
and 2).

Pressure differential testing was conducted in two to six locations in VIMS zones A, and C
through G for a total of 17 monitoring locations. Approximate monitoring pin locations are
depicted on Drawing 1. Pre-occupancy VIMS testing was not conducted in VIMS Zone B
because post tension cables in the slab of that section precluded drilling in the floor for
placement of monitoring probes.

Permanent blower operation was verified by recording pressure readings on magnahelic
pressure gauges mounted on permanent risers on the roof of the buildings (Photo 3).
Magnahelic gauges were not yet operational on June 17, 2015 when pressure monitoring
was conducted. Mid-Atlantic returned to the site on July 9 following notification that
gauges were functional to record gauge static pressure. Spot sub-slab pressure
measurements were collected on that date to assure that sub-slab depressurization was
similar to that measured on June 17.

PRE-OCCUPANCY TESTING RESULTS

Mid-Atlantic observed that all permanent roof mounted VIMS blowers were operational
on June 17, 2015. On that date we measured sub-slab to indoor pressure
depressurization that ranged from 54 to 221 pascals (Pa) at 17 locations in VIMS zones A
and C through G. Results are depicted on Table 2 and Drawing 1. The mean
depressurization in Zone A was 178 Pa. (six locations). In Zone C the mean
depressurization measured was 72 Pa (two measurements). In Zone D the mean
depressurization measured was 74 Pa (two measurements). In Zone E the mean
depressurization measured was 191 Pa (three measurements). In Zone F the mean
depressurization measured was 185 Pa (two measurements). In Zone G the mean
depressurization measured was 199 Pa (two measurements).

On July 9, 2015 static fan pressure readings were collected from each of the 15
magnahelic gauges installed on the risers just beneath the roof mounted VIMS blowers
(Photo 3). Static pressure measurements ranges from 0.9 to 1. 7 inches water gauge
(inches WG) (Table 3). According to the fan manufacturer’s specifications the resulting
volumetric flow rate for those static pressure results is approximately 110 cubic feet per
minute (cfm) at 1.7 inches WG and 200 cfm at 0.9 inches WG (Attachment 1).
Pre-occupancy Report
Stanhope Center II
Raleigh, North Carolina
July 22, 2015
Page 4

Selected sub-slab pressure measurements collected on July 9 were similar to those
collected on June 17. Sub-slab depressurization measured at 11 of the 17 points
measured on June 17 ranged from 64 to 239 PA. Six of the monitoring points were
inaccessible on July 9. Ten of eleven measurements collected on July 9 were higher
(greater depressurization) than they were on June 17.

CONCLUSIONS AND RECOMMENDATIONS

Mid-Atlantic measured adequate sub-slab depressurization across the Stanhope Center II
building slabs to effectively interrupt the vapor intrusion pathway. In a 2008 Engineering
Issues Report the US EPA states that “… the average range of soil/building
depressurization is on the order of 4-10 Pa. Thus, a mitigation system that compensates
for a minimum of 4-10 Pa everywhere under the slab should adequately mitigate vapor
intrusion.” 1 The measured depressurization at the subject site of approximately 50 to 240
Pa will adequately compensate for building use, climate and other variables that could
have some impact on sub-slab depressurization levels.

Although we were unable to collect sub-slab depressurization measurements in VIMS
zone B during pre-occupancy testing on July, 2015, data collected during system
effectiveness testing in March 2015 indicated that there is adequate depressurization
across the slab in VIMS zone B to interrupt the vapor intrusion pathway. Additionally, the
permanent blowers provide greater fan capacity than those used for effectiveness testing.
As was the case in each of the other VIMS zones it is likely that sub-slab depressurization
is greater with as-built conditions than it was during effectiveness testing.

Magnahelic gauge readings may be used to indicate that adequate depressurization is
present in the sub-slab at Stanhope Center II. Mid-Atlantic recommends that monthly fan
pressure readings be taken to insure that the blowers are operational and providing
adequate fan ventilation to depressurize the building sub-slab. These readings should be
documented and kept on site. In the event a fan(s) burns out, malfunctions, or if pressure
readings are recorded outside of the observed range, we recommend that repairs and/or
adjustments be initiated immediately.

1 US EPA. Engineering Issues: Indoor Air Vapor Intrusion Mitigation Approaches. EPA/600/R-08-115
October 2008.
Pre-occupancy Report
Stanhope Center II
Raleigh, North Carolina
July 22, 2015
Page 5

CLOSING

Mid-Atlantic appreciates the opportunity to submit this report to the NCBP for review and
comment. If you have any question please feel free to contact us at 919-250-9918.

MID-ATLANTIC ASSOCIATES, INC.
William Service
Environmental Toxicologist

Darin McClure, P.E.
Principal Engineer

Attachments: Drawing 1
Tables 1-3
Photographs
Attachment 1

WS/DMM/bro/bj

DRAWING

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DRAWN BY: DATE: JULY 2015 DRAFT CHECK BY: JOB NO.: 000R2490.04 ENGINEER CHECK BY: GIS NO.: 03G-R2490.04-2 APPROVED BY: DRAWING NO.: 1
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DRAWINGS FOR ALL CON STRUCTION RELATED DETAILS

TABLES

TABLE 1
EFFECTIVENESS TESTING DATA 
STANHOPE II CENTER 
3001 HILLSBOROUGH STREET 
RALEIGH, NORTH CAROLINA 
BROWNFIELDS PROJECT NUMBER 17034‐13‐92 
MID‐ATLANTIC ASSOCIATES PROJECT NO. R2490.04
VIMS Zone A Vent Riser ID
3/3/2015 A1 A2 A3 A4

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A‐1 ‐‐‐11 ‐‐‐45
A‐2 ‐‐‐14 ‐‐‐37
A‐3 ‐‐‐20 ‐‐‐29
A‐4 ‐‐‐21 ‐‐‐22
A‐5 ‐‐‐29 ‐‐‐16
A‐6 ‐9 ‐27 ‐‐‐3.9
A‐7 ‐10 ‐16 ‐‐‐‐
A‐8 ‐15 ‐3.5 ‐1.9 ‐‐
A‐9 ‐15 ‐‐‐17 ‐‐
A‐10 ‐11 ‐‐‐36 ‐‐
A‐11 ‐‐‐‐‐49
VIMS Zone B Vent Riser ID
3/11/2015 B1 B2

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B‐1 ‐58 ‐10
B‐2 ‐42 ‐16
B‐3 ‐22 ‐33
B‐4 ‐8.5 ‐22
VIMS Zone C Vent Riser ID
8/1/2014 C1 C2 C1+C2

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C‐1 ‐60 ‐108 ‐196
C‐2 ‐70 ‐100 ‐189
C‐3 ‐70 ‐85 ‐177
C‐4 ‐60 ‐62 ‐150
* All values are in Pascals 
‐‐None measured at this location

TABLE 2
PRE‐OCCUPANCY TESTING DATA 
STANHOPE II CENTER 
3001 HILLSBOROUGH STREET 
RALEIGH, NORTH CAROLINA 
BROWNFIELDS PROJECT NUMBER 17034‐13‐92 
MID‐ATLANTIC ASSOCIATES PROJECT NO. R2490.04
VIMS Zone A Vent Riser IDs : A1, A2, A3, and A4
6/7/2015 7/6/2015

Vapor Pin ID
VP‐121 ‐221 ‐229
VP‐132 ‐194 ‐202
VP‐129 ‐190 ‐196
VP‐142 ‐123 ‐‐
VP‐141 ‐172 ‐‐
VP‐145 ‐171 ‐‐
VIMS Zone C Vent Riser IDs : C1 and C2
6/7/2015 7/6/2015
Vapor Pin ID VP‐158 ‐54 ‐64
VP‐161 ‐90 ‐‐
VIMS Zone D Vent Riser IDs : D1 and D2
6/7/2015 7/6/2015
Vapor Pin ID VP‐D1 ‐81 ‐97
VP‐D2 ‐68 ‐‐
VIMS Zone E Vent Riser ID : E1
6/7/2015 7/6/2015
Vapor Pin ID VP‐E‐1‐E ‐191 ‐188
VP‐E‐1‐W ‐157 ‐180
VIMS Zone F Vent Riser IDs : F1 and F2
6/7/2015 7/6/2015

Vapor Pin ID
VP‐F1 ‐182 ‐220
VP‐FC ‐189 ‐230
VP‐F2 ‐203 ‐232
VIMS Zone G Vent Riser IDs : G1 and G2
6/7/2015 7/6/2015
Vapor Pin ID VP‐G1 ‐207 ‐239
VP‐G2 ‐191 ‐‐
* All values are in Pascals 
‐‐Not measured on this date

TABLE 3
VIMS BLOWER STATIC PRESSURE GAUGE READINGS 
PRE‐OCCUPANCY TESTING 
STANHOPE II CENTER 
3001 HILLSBOROUGH STREET 
RALEIGH, NORTH CAROLINA 
BROWNFIELDS PROJECT NUMBER 17034‐13‐92 
MID‐ATLANTIC ASSOCIATES PROJECT NO. R2490.04
VIMS Zone A GAUGE READINGS
7/9/2015

Riser / Blower ID
A1 1.5‐1.6
A2 1.5‐1.7
A3 1.5
A4 1.7
VIMS Zone B GAUGE READINGS
7/9/2015
Riser / Blower ID B1 1.5
B2 1.5‐1.7
VIMS Zone C GAUGE READINGS
7/9/2015
Riser / Blower ID C1 1.3‐1.4
C2 1.4‐1.5
VIMS Zone D GAUGE READINGS
7/9/2015
Riser / Blower ID D1 1.1‐1.2
D2 0.9‐1.0
VIMS Zone E GAUGE READINGS
7/9/2015
Riser / Blower ID E1 1.5‐1.6
VIMS Zone F GAUGE READINGS
7/9/2015
Riser / Blower ID F1 1.5
F2 1
VIMS Zone G GAUGE READINGS
7/9/2015
Riser / Blower ID G1 1.6
G2 1.6
* All values are in inches H2O

PHOTOGRAPHS

STANHOPE CENTER II 
PRE‐OCCUPANCY REPORT 
PHOTOS 

Photo 1. Slab Penetration and Vapor Pin Prior to Installation 

Photo 2. Micromanometer Connected to Vapor Pin Measuring Sub‐Slab to Indoor Pressure Differential 

Photo 3. Magnahelic Gage Installed Beneath Roof –Mounted VIMS Blower 

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