Attachment D Groundwater Level Data, Contour Maps, Area of Impact Delineations

Nobis plotted groundwater levels from test pit monitoring wells (overburden, not bedrock) measured by

CLAWE on March 30, 2015 and provided in a Table in Appendix A to the CLAWE October 2015 EIR (see

CLAWE Table in Attachment D; Nobis performed this analysis prior to receiving the January and February

CLAWE Tables; at the time of Nobis’ initial analysis, the March 30 data set was the most complete water

level data set available). After plotting the water level data, Nobis contoured the water levels, creating

an interpreted potentiometric (water table) contour map for the northern portion of the Site (Attachment

D). Rather than creating artificial data points for the sake of constructing a groundwater contour map

using a software package, Nobis made the standard assumption that the potentiometric surface for an

unconfined aquifer approximately parallels topography. Nobis’ interpretation shows curving contour lines

and a potentiometric surface that generally slopes to the south; the curving contours reflect topographic

ridges and valleys within the Site. The contours are dashed where they are estimated. Nobis’ interpreted

contours do not extend significantly beyond known data points collected on March 30, 2015 (either on-

Site or onto abutting properties).

The resulting groundwater flow directions are generally southward, with local variations. The contours

are closely spaced at SDS1 (using the October 2015 EIR data table for the March 30, 2015 date), indicating

a strong gradient and relatively rapid groundwater flow to the south, assuming that each of the

monitoring wells provides reliable water level data. (Communication with the Town’s peer reviewer,

Steven Smith of Geohydrocycle, indicates, for example that water level measurements in well DHT 2-3 are

suspect; removal for this data point changes the contouring so that the gradient is shallower and the

contours are less arcuate than shown on the working map in Attachment D. CLAWE acknowledged to

BOH on February 22, 2016 that the water level data for DHT 2-3 and DHT 2-1 had been switched in

previous groundwater level data tables after previously asserting that the data were correct.) The blue

arrows on the working map that shows the contoured March 30 data prior to learning of the data error

(map shown in Attachment D) indicate Nobis’ predicted overburden groundwater flow directions,

perpendicular to the groundwater contours, and from areas with higher head to areas with lower head.

Based on the contours and flow arrows on the working map Nobis delineated an Area of Impact (AOI; per

Title 5 Guidelines), from the proposed septic disposal systems to the edge of the “Impacted Wetland”.

Nobis’ AOI for this data set is similar, but not identical to, the AOI delineated by CLAWE in its December

map (Attachment D). Please note that Nobis’ AOI for this data set, which terminates at the edge of the

“Impacted Wetland” is not meant to imply that all groundwater from the proposed septic disposal systems

does or does not discharge to the wetland. As discussed above, Nobis considers this key question to be

unresolved, but understands that water level observations in January 2016 are consistent with the

wetland being connected to the groundwater. Nobis also notes that CLAWE’s more recent (January 2016)

contour and AOI map shows the AOI continuing beyond the “Impacted Wetland”; it is unclear whether

new information on the wetland hydrology has been used to justify this change.

The groundwater potentiometric surface, as interpreted by the contours and groundwater flow arrows in

the working contour map in Attachment D, represents conditions on March 30, 2015, as documented in

the October 2015 EIR table by CLAWE. After construction and when the septic system is in operation,

groundwater mounding is expected at the proposed septic disposal areas, locally changing the

D1-1

groundwater contours, groundwater flow gradient, and possibly local flow directions. Groundwater

mounding is estimated by CLAWE to be a maximum of 0.81 feet, for SDS1 and SDS2, combined. Inclusion

of such mounding in the groundwater contour maps would change the contouring slightly, but because

the southward gradient is so strong for the data set contoured, perturbations to the mapped contours

and the resulting lateral (eastward and westward) flow would likely have been relatively minor for

contours based on the 3/30/15 data reported in the EIR table.

Also, none of Nobis’ contour maps shows the effects that well pumping or stormwater discharge may

have on the overburden potentiometric surface. The stormwater discharges are primarily designed to

occur east of the likely AOI. Although drawdowns in bedrock wells can be relatively large, they are difficult

to predict prior to a pumping test. Further, drawdowns in the bedrock wells will affect the potentiometric

surface for bedrock groundwater and may or may not have noticeable effects on the overburden

groundwater potentiometric surface for the Site. This depends on whether or not a layer of dense glacial

till or other low-permeability deposit separates the bedrock from the sandy overburden.

In its January and February data charts, letters, and emails, CLAWE “corrected” its earlier water level data

for wells STP-5 and STP-7, apparently to account for the stickup height of the well pipes above the ground.

(The top rims of well casing pipes are typically used as measuring points for water level measurements in

this type of investigation.) Further, BOH communicated with CLAWE and determined that the previous

data tables had incorrectly switched data between DHT 2-1 and DHT 2-3. Through discussions, BOH

developed a data table that it believes contains the most reliable of the water level measurements taken

by CLAWE, eliminating those wells for which estimates were made or for which there is more reason to

doubt the data. BOH presented Nobis with a table entitled, “Final as of Feb 22 (based on 10 PM email

from CLAWE.” BOH and Con Comm requested Nobis to use these data to make High Water (4/15/15

measurement date) and Low Water (8/14/15 measurement date) contour maps. The Feb 22 table and

new working contour maps for these dates, using this table, are found in Attachment D.

Using the corrected data from the Feb 22 table resulted in a lesser gradient (less closely-spaced contours)

than the map using the October EIR table for the March 30, 2015 measurement date. As a result of the

greater contour spacing, Nobis believes that including the predicted mound (maximum height of 0.81 feet

per CLAWE calculations) will make a noticeable difference in groundwater contouring and in groundwater

flow directions in the immediate vicinity of SDS-1 and SDS-2. (See red contours on the working contour

maps in Attachment D.)

D1-2

5

247A Washington Street

Groundwater Monitoring

Site: 247 Washington Street, Sherborn, MA

Date: 4/14/2014 4/18/2014 4/23/2014 6/3/2014 6/10/2014 6/30/2014 11/8/2014 12/24/2014 1/16/2015 1/29/2015 3/30/2015 diff Perc rate

Location

Standing

pipe

Rim or

Well Top

Ground

surface

Depth to

Bottom

Depth to

water

Depth to

water

Depth to

water

Depth to

water

Depth to

water

Depth to

water

Depth to

water

Depth to

water

Depth to

water

Depth to

water

Depth to

water

TP# ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft mpi

DHT 1-1 4.11 197.31 193.2 19.98 19.54 19.08 18.89 19.15 19.71 22.84 20.8 20.19 20 20 3.95 <2

DHT 1-2 196.6

DHT 1-3 196.3

DHT 2-3 3.5 190.6 187.1 20.00 19.68 19.46 18.74 18.92 19.40 21.97 20.08 20.05 19.87 19.52 3.23 <2

DHT 2-2 197.6

DHT 2-1 3.6 193.6 190 17.05 16.98 16.74 16.55 16.68 16.95 18.97 17.31 17.3 17.23 17 2.42 <2

A3 1.7 182.8 181.1 12.06 12 11.89 11.87 12.02 12.55 13.52 12.08 12.45 12.57 11.24 2.28

A4 1.3 170.3 169 2.47 2.35 2.48 2.68 2.8 3.18 3.92 2.6 2.92 2.92 2.12 1.8

STP-1 1.25 182.45 181.2 13.62 13.58 14.19 14.26 0.68

STP-2 3.47 189.17 185.7 22.35 21.92 0.43

STP-3 2.1 178.7 176.6 10.39 8.83 1.56

STP-4 3.5 171.8 168.3 8.11 6.58 1.53

STP-5 2.3 171.8 169.5 7.99 6.86 1.13

STP-6 0.99 171.79 170.8 8 8.56 0.56

STP-7 1 172.2 171.2 7.28 6.67 0.61

STP-8 1.84 173.74 171.9 5.67 4.37 1.3

STP-9 1.06 185.16 184.1 17.43 15.85 1.58

Date: 4/14/2014 4/18/2014 4/23/2014 6/3/2014 6/10/2014 6/30/2014 11/8/2014 12/24/2014 1/16/2015 1/29/2015 3/30/2015

Location

Standing

pipe

Rim or

Well Top

Ground

surface

Depth to

Bottom

Water

Table

Water

Table

Water

Table

Water

Table

Water

Table

Water

Table

Water

Table

Water

Table

Water

Table

Water

Table

Water

Table Max WL

GS to

HGW Corrected

TP# ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft HGW, ft

DHT-1-1 4.11 197.31 193.2 177.33 177.77 178.23 178.42 178.16 177.6 174.47 176.51 177.12 177.31 177.31 178.42 -14.78 179.36

DHT 1-2 196.6

DHT 1-3 196.3

DHT-2-3 3.5 190.6 187.1 170.6 170.92 171.14 171.86 171.68 171.2 168.63 170.52 170.55 170.73 171.08 171.86 -15.24 172.4

DHT 2-2 197.6

DHT-2-1 3.6 193.6 190 176.55 176.62 176.86 177.05 176.92 176.65 174.63 176.29 176.3 176.37 176.6 177.05 -12.95 177.7

A3 1.7 182.8 181.1 170.74 170.8 170.91 170.93 170.78 170.25 169.28 170.72 170.35 170.23 171.56 171.56 -9.54

A4 1.3 170.3 169 167.83 167.95 167.82 167.62 167.5 167.12 166.38 167.7 167.38 167.38 168.18 168.18 -0.82

STP-1 0.25 182.45 181.2 168.83 168.87 168.26 168.19 168.87 -12.33

STP-2 3.47 189.17 185.7 166.82 167.25 167.25 -18.45

STP-3 2.1 178.7 176.6 168.31 169.87 169.87 -6.73

STP-4 3.5 171.8 168.3 163.69 165.22 165.22 -3.08

STP-5 2.3 171.8 169.5 163.81 164.94 164.94 -4.56

STP-6 0.99 171.79 170.8 163.79 163.23 163.79 -7.01

STP-7 1 172.2 171.2 164.92 165.53 165.53 -5.67

STP-8 1.84 173.74 171.9 168.07 169.37 169.37 -2.53

STP-9 1.06 185.16 184.1 167.73 169.31 169.31 -14.79

Stormwater: Depth Soil Perc rate date DEP allowed Test based (estimate) Half rate to apply times of DEP rate

TP-STP1 14 m.s. 11 spi 1/17/2014 8.27 iph 1.62E-03 ft/s 34.99 iph 4.23

TP-STP2 12 m.co. s 16 spi 1/17/2014 8.27 iph 1.27E-03 ft/s 27.43 iph 3.32

1.45E-03 ft/s Infiltration

1/19/2015 constant head test 1.55E-03 ft/s Design rate (1/2 tested): 13.72 iph

160

165

170

175

180

3/1/2014 5/27/2014 8/23/2014 11/18/2014 2/14/2015 5/13/2015

Wa

ter

Ele

v.,

ft

Date

Groundwater Table ChartWashington Street, Sherborn, MA

DHT1-1

DHT2-3

DHT2-1

A3

A4

D-2: soil and groundwater evaluation 4-8-2015

D3:

D4