HomeMy WebLinkAboutSDP201600014 Assessment - Groundwater 2016-05-26Wildrock
TMP 6-28B
Tier 3 Groundwater Assessment
Groundwater Management Plan
Prepared for:
Shimp Engineering, P.C.
Charlottesville, VA
Draft submitted April 29, 2016
Modified in response to County Engineering Staff comments May 26, 2016
Nick H. Evans PhD CPG
Virginia Groundwater LLC
PO Box 1424
Charlottesville VA 22902
nick(a)_virginiagroundwater.com
434-466-1280
Key Findings
Hydrogeologic setting: Located in steep topography on the eastern flank of the
Blue Ridge, the property is underlain by fractured charnockite bedrock and thick
deposits of colluvium.
Groundwater availability: Recharge potential to site is excellent. Significant
quantities of groundwater flow through bedrock fracture networks and overlying
colluvium. Wells tapping into bedrock fracture networks beneath colluvium have
potential for significant sustainable yields. A 60+ gallon per minute well has
recently been drilled on the parcel.
Are Hydrogeologic conditions favorable to proposed use? Yes.
Contamination threats on record within 2000 feet of parcel? None.
Additional contaminant threats observed in field reconnaissance? None.
Anticipated impacts of proposed use on existing users of groundwater:
None.
Groundwater management plan:
Protect and expand where possible the amount of forest cover on the property
during construction and beyond.
Implement runoff -neutral development as specified in the development plan, to
include on-site waste disposal through a sanitary drainfield.
2
Project Overview
The proposed development is located on a 28.01 acre parcel in northern
Albemarle (Figure 1), off Rt. 810 about 5 miles northeast of White Hall. The
proposed use is a day camp with 6 primitive overnight camping sites and an
environmental education center.
Figure 1
" Little Flat Mountain
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Albemade GIS. Shimp Engineering
The parcel is located on two unnamed tributaries of Buck Mountain Creek, which
flows into the South Fork Rivanna River upstream from the South Fork Rivanna
Reservoir. The parcel is on the south flank of Little Flat Mountain, which has a
summit elevation, in Shenandoah National Park, of 3125 feet. Elevations on the
parcel range between about 950 feet in the southeast corner to 1200 feet in the
northern corner (Figure 2).
3
Figure 2: TMP 6-28B topography (4 -foot contour interval) and surface water features (blue)
Albemarle GIS; Nick Evans 04/29/2016
Existing land cover on the parcel is open pasture at lower elevations, on the
southeastern portion, and mixed second -growth forest on the remainder. A site
plan showing the existing buildings, proposed development layout and
approximate land disturbance is attached to this report.
Projected maximum water consumption for the facility, based on the VDH-
approved on-site wastewater treatment design capacity, is 765 gallons per day.
A well was recently drilled on the property with a blown yield in excess of 60
gallons per minute (personal communication, Foster Well Company; completion
report attached, p 11 — 14, below).
Surrounding parcels are primarily forested. There are residences on three
adjoining parcels to the west and south. To the north the parcel adjoins the
Patricia Ann Byrom Forest Preserve, owned by Albemarle County and developed
as a park with trails open to hiking and equestrian use.
Hydrogeologic Assessment
Geology
Field mapping indicates that bedrock beneath the parcel is a very coarse-grained
granite, geologically termed charnockite. This bedrock is exposed at the surface
M
in many places in uplands, in the southwest and northern portions of the parcel.
At lower elevations, in the central and eastern portions, bedrock is largely
covered by a thick mantle of colluvium, which is a mixture of rocks and soil that
has been transported down slope by the action of gravity and moving water
(Figure 3).
Figure 3: Site geology showing distribution of charnockite (ch)
and major colluvial deposits (� ) on the parcel
Albemarle GIS; Nick Evans 04;29/2016
Groundwater recharge and flow paths
Recharge for groundwater beneath the parcel occurs both within the parcel and
on about 740 acres of forested land that is topographically up -gradient, to the
north and west, on the south flank of Little Flat Mountain. The entire parcel is
itself a recharge area for groundwater flowing down -gradient to the northeast,
Figure 4: Predicted groundwater flow paths (
and groundwater divides ( ) referred to in text
Albemarle GIS; Nick Evans 0412 912 01 6
into the Buck Mountain Creek drainage. In general, groundwater flow follows
hydraulic gradients that mirror topographic gradients (Figure 4).
Bedrock fracture density and water well productivity
Charnockite bedrock does not contain primary intergranular porosity through
which groundwater might flow. Groundwater flow within the bedrock is confined
to fractures and fissures that can serve as conduits for water. In contrast,
colluvium is very porous, and serves as an ideal conduit for groundwater.
Colluvial deposits on the flanks of Little Flat Mountain above this parcel, and on
the parcel itself, are capable of capturing and transmitting as groundwater,
significant quantities of rainfall. That water is then available to recharge fractures
and fissures where they occur, within underlying bedrock.
In this geologic setting, drinking water wells are normally constructed with
sufficient casing to exclude water that exists within near -surface colluvial
0
deposits. This is because colluvium is readily vulnerable to contaminants
introduced at the surface. Hence water wells are drilled targeting bedrock
fracture networks deep enough that recharge water from the overlying colluvium
has had enough travel time and distance through the rock to be cleansed of
contaminants.
Successful water wells have both a reliable source of recharge (in this setting,
colluvial material), and an open network of bedrock fractures that connect with
the recharge source. TMP 6-26B has both of these ingredients. In addition to
the mantel of colluvium, field observations indicate there are abundant north-
northwest trending fractures present within the bedrock. The reported capacity of
the well recently drilled on the property (60+ gallons per minute) is consistent
with these conditions, and far exceeds the needs of this project.
Water budget estimate for site
It is instructive to review the proposed use of water relative to the amount of
water available to the site from natural recharge.
Annual regional precipitation: 44 inches
Conservative estimate for the percentage of precipitation contributing to
groundwater recharge, subtracting runoff and evapotranspiration:
15%
Annual regional groundwater recharge: 6.6 inches
Average regional daily groundwater recharge- .0181 inches = .0015 feet
Daily recharge per acre: .0015 feet X 43560 square feet per acre = 65.6
cubic feet recharge per acre
Gallons recharge per day per acre: 65.6 cubic feet X 7.48 gallons per
cubic foot = 491 gallons per day per acre
Gallons per day recharge on parcel: 491 gallons per acre X 28.01 acres
= 13,753 gallons per day
Gallons per day recharge to the parcel plus up -gradient forested acreage
off -parcel to the north: 491 gallons per acre X 735 acres =
360,885 gallons per day
Predicted maximum daily groundwater withdrawal on site: 765 gallons*
*a significant portion of daily withdrawal to be returned as recharge
via an onsite drainfield
These numbers indicate that the proposed use of groundwater is negligible
relative to the abundance of groundwater that naturally occurs on the parcel.
7
Potential for proposed use to affect existing users of groundwater
There are 3 residences on adjoining parcels that rely on their own water wells
(Figure 5). TMP 6-28A and TMP 6-35 have reported yields of 2 and 3 gallons
per minute, respectively. No records were found for a well on TMP 6-35A. It is
not anticipated that the proposed use on TMP 6-28B will impact any of the wells
on adjoining parcels or elsewhere, for the following reasons:
Figure 5: Existing wells and drainfields o
(locations approximate) within 1000 feet of TMP 6-28B
Albemarle GIS; Nick Evans 04/29/2016
1) Recharge to each of the wells on adjoining parcels is estimated to come
from a different source from that on TMP 6-28B. In the case of TMP 6-
28A, it appears the well is receiving recharge primarily from the south and
west, southwest of a groundwater divide between 6-28A and 6-28B
(Figure 4).
In the case of 6-35 and 6-35A, both parcels are southeast of the principal
northeast trending drainage (a groundwater divide) that parallels Rt. 810
0
and crosses the eastern margin of 6-28B. Both 6-35 and 6-35A receive
recharge from the south (away from 6-28B; Figure 4).
2) The proposed peak groundwater usage of 735 gallons per day is very
modest relative to available groundwater. Furthermore, this proposed
withdrawal is not consumptive, to the extent that much of the water will be
returned to the ground as recharge via the drainfield. It is not anticipated
that this withdrawal will impact existing groundwater users on adjoining
parcels or elsewhere.
There are no public water supply wells within 2000 feet of the parcel.
Contaminant threats
There are no reported contaminant spills or other documented threats to
groundwater in current County, State and Federal databases, within 2000 feet of
the TMP 6-28B.
There are three existing drainfields inferred within 1000 feet of TMP 6-28B
(Figure 5). None of these is up gradient from the parcel; none poses a threat to
groundwater quality on the parcel.
The proposed use as a day camp with primitive campsites and education center
does not involve activities that pose a threat of toxic spill under normal
circumstances.
Reserve wellfield
Due to the size and hydrogeologic setting of TMP 6-28B, there are ample
favorable locations for a replacement well in the event that the primary well fails
due to contamination, lack of water or other issues .
Groundwater management plan
Protect and expand where possible the amount of forest cover on the property
during construction and beyond.
Implement runoff -neutral development as specified in the development plan.
9
Submitted by Nicholas H. Evans, CPG # 2801 001041
May 26, 2016 ff
DEPARTLENT OF PROFESSIONAL ANO OCCUPATIONAL REGULATION
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Attachment:
Form G-2
Ruwived 71112015
Page 1 of
1_ Cants t Infnrmnfinn
COMMONWEALTH OF VIRGINIA
UNFORM WATER WELL COWLETION REPORT
USGS Local #
V DH HDfN # l� -1 - V VTV
VDH PWSID f
Contact:
Name Address
Phone
Owner
l an etude:
'Food Processing ElCooling(Reating
Datum Soares I 13orizont2l: ❑ WGS84 D NAD83 ❑ NAD27
Driller
taster Welt 6 Nmp
❑ Survey ❑ LTtagery ❑ WASS
Location Information Collected .By :
Fire Safety ❑ Geothermal
co_, Ioe_
W I= 260. ;aa+17e, Va, 22936
(434) 973-9079
system
-
Provider '
Hole Size (Hucrude rearmed zoates): 10 inches from 0 to 4 f ft,
1, Inches from
2.. Well Location
Physical Address: 60T
I Cauary/cky:
subdivision Name: _ Section: Block: Lot=
Talc M2pIGPIN #: 1 'Weil DcsiguadUn ar Number:
Latitude: l
l an etude:
'Food Processing ElCooling(Reating
Datum Soares I 13orizont2l: ❑ WGS84 D NAD83 ❑ NAD27
1 Vertical: ❑ NOVD29 Ll NAVD98--
11LatUu Source Check One). ❑ Map D GPS ❑ PPDGP5
❑ Survey ❑ LTtagery ❑ WASS
Location Information Collected .By :
Fire Safety ❑ Geothermal
Physical Ltion Daerf ption.
1- Parllifv & II.I;c
Type of p ill ebeck One):
Type of Use
Check All That A
❑ Waterworks
DriukingjDomestic Use U
'Food Processing ElCooling(Reating
EI bsmvationl onitoring Well
I
❑ Agricultural 0
Manufacturiag ❑ Injection
Private Well
❑ Irri ation 17
Fire Safety ❑ Geothermal
4. Well Coustruetian
Well designation, Name or Number,
-
Date Started: Y Date Cum let d. i'9A Ile,
I,TypwPU : a, -
Clam Well (Check One): 0 1 ❑ r IIS n IIIA ❑ 1118 ❑ !lit~ ❑
HID LITE ❑
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Construction T Check One): New d Existing -Modified
Well Depth: . d -s ft. I Burehale Depth: d ft.
Depth to Bedrock: Fd f1.
Hole Size (Hucrude rearmed zoates): 10 inches from 0 to 4 f ft,
1, Inches from
(L/ to &J5
Height Of CREWR shove Land Surface: .i fl. d inches
Casing Size (7.D.) and Materia€s. (below) Total Depth ofCasing:
fk.
inches from #;L, to Ise l ft- Mate,—jai , ,gfro
Wei ht per (I-
or weIl thickness
in-
' iaclteS front Oo D fk, material 2&f
Weight per fl.
or wall thickness
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inches from to ft. Material _
Inches from to ft- Material
Screeti Size & Mesh:
Weighl per Ct.
Wei ht per F[.
Wei hter !Tor
- �'----�—.-.,
or waII Th k;kness
or wall thickness
wa 11. thickne.5s
in,
in.
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inches from to ft. Mesh Size
inches from to ft- wesh Size
inches from to R- Mesh size
Water Zones: from 7 W 7y ft. from
Gravel Puh. From to ft. _ from
G_raut Tyke: fromD to3p ft- Groi
This Information was collected by Ca Survey:
Additional Well Construction Form Information Atte
Type
Type
_ to 9H fi" From to IO ft -
to ft. From to fl,
ming Method: TvDe ofcal: .
❑ Yes R No I Dare Couduekd:
cared: ❑ Yes LI No
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Form GW -2 COMMONWEALTH OF V aGMA DEQ Well #
Revised 7/112015 iI ORM WATER WELL CON9LETION REPORT u5ti
Fvrrn GVH -2 COM ON TALTH OF VIRG1NtA DEQ Well 41 .—
e ise IJ20t5 UNIFORM WATER WELL C01WLETiON REPORT USG5 Local #
Page 3 of 4
V DH HDIN # [ ,
VDH PWSfD #
10. Driller's 1, se additional sheets ifnec
)
VVeH designation, Name or Number -
Depth (feet)
Type aRock or Soil
Rana&
twilling
Diagam cFf Noll Construction (with
Time
dioiensions)
(]4tJrs.}
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To
(Ca6oQ, Mamial, fnr hardness er')
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to+laies s�.
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J Ce'dify [hal the information corltainod herein is true arrd correv and tha[ this well an&or sys[em has been installed and consinwt-ed in
:k Wvrddnr't• with the lippli-qaA. pGrMk and further thal [he well complies with all applicable Federal, slue and local regulatiors,
ordinances and laws -
Signature; _ 1.14 �
Date;
[ACMIM NCFrhber: 2705015945
13
Form OW -2 COMMONWEALTH OF VERGINIA
Revised 71113015 UNLFOit M WATER WELL COM-PLET[ON REPORT
Page 4 #{ d
Additional Well Construction Data
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DEQ WA 4 _
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14