HomeMy WebLinkAboutSDP200900080 Assessment - Groundwater 2009-09-11South Plains Presbyterian Church
Tier 3 Groundwater Assessment
Groundwater Management Plan
Prepared for:
South Plains Presbyterian Church
410 Black Cat Road
Keswick, Virginia 22947
David Garth, Pastor
September 11, 2009
Nick H. Evans PhD CPG
Virginia Groundwater LLC
PO Box 1424
Charlottesville VA 22902
Key Findings
Hydrogeologic units: VI (Candler)
Groundwater availability zone: Class 3 (lowest groundwater availability)
Hydrogeologic conditions favorable to proposed use? Yes
Site within groundwater sensitivity zone? Yes: LUST sites and public water supply
well located within 1000 feet
Contamination threats on record: Petroleum releases documented within 1000 feet
of property
Additional contaminant threats observed in field reconnaissance? No
Projected maximum groundwater withdrawal: 163 gallons per day (average); 810
gallons maximum daily
Estimated average groundwater recharge to site: 2651 gallons per day
Anticipated impacts of proposed use on existing users: None
Groundwater management plan: Preserve existing forest cover where possible;
implement runoff - neutral technology to whatever extent practicable.
Overview
This groundwater assessment relates to a proposal to construct a fellowship hall
adjacent to South Plains Presbyterian Church. The church is situated on a 4.95 -acre
parcel, TMP 80 -116, located immediately south of the intersection of Black Cat Road
and Virginia Route 22 in Keswick (Figure 1). The church cemetery is located on an
adjoining parcel, TMP 80 -116A, less than 1 acre in size. The church has been in
existence since the early nineteenth century; no other historic uses are known. The
church parcel is partially wooded; surrounding land uses are rural residential and
agricultural.
The church parcels is situated at the head of a small unnamed tributary of Carroll
Creek, which flows south into the Rivanna River (Figure 1). Topographically, the parcel
is on a low northeast - trending ridge created by the underlying metasiltones at the
stratigraphic base of the Candler Formation. There are no streams, springs or other
surface water features on the property.
The church sanctuary seats 80 people; the proposed fellowship hall will have a capacity
of 200. There is an existing well on the property with a reported yield of 8 gallons per
minute (GPM). Peak water usage is predicted to be 810 gallons per day (GPD) on
Sundays when the facilities are at full capacity: on weekdays, water usage is estimated
to be 55 GPD (overall average 163 GPD). A site plan showing the proposed
development and extent of land disturbance is included with this report (Attachment A).
Hydrogeologic Assessment
Bedrock geology
The site is located within metamorphosed sedimentary rocks mapped as laminated
metasiltstone (Cas, 1993 Geologic Map of Virginia; Figure 2). These rocks are
stratigraphically at the base of the Candler Formation. The contact between
metasiltstone and underlying hyaloclastite breccia of the Catoctin Formation is located
about 100 feet northwest of the church parcel. The contact with overlying phyllites of
the Candler Formation is about 100 feet southeast of the parcel
The property is within the Candler (VI) hydrogeologic unit, with Class 3 (lowest) relative
groundwater availability, as defined in the Albemarle County Hydrogeologic Assessment
Summary Report of 2003. No bedrock exposures were observed on the property during
field reconnaissance.
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Bedrock fracture density and water well productivity
Candler Formation metasiltstone bedrock that underlie this parcel does not contain
primary intergranular porosity through which groundwater might flow. Groundwater flow
is confined to bedrock fractures and fissures. No significant linear features, fracture
traces or structural features were identified on air photos or other maps in this study that
would be useful indicators of bedrock fracture orientation on this parcel.
In the absence of good bedrock exposures with which to directly observe bedrock
fractures, the yields of randomly -sited water wells can be used as a proxy for fracture
density. Table 1 (below) summarizes county -wide data from the 25 wells in the county
database that were constructed in Candler metasiltstone bedrock, a geologic setting
identical to the church parcel.
Table 1: domestic water well statistics from Albemarle County database
Geologic map unit yield total well depth casing length Count
gallons per minute)feet)feet)
Cas average: 14 Average: 215 Average: 40
25
laminated metasiltstone)maximum: 75 Maximum: 405 Maximum: 84
The existing well on the church parcel has a reported yield of 8 GPM, total depth of 160
feet, and casing length of 61 feet (personal communication, Lanny Moore, 8/13/2009).
These figures are below average relative to wells with a similar hydrogeologic setting in
the County database. However, the 8 GPM reported yield is more than adequate to
supply the proposed use.
There are four wells in the Albemarle County database that are within 3000 feet of TMP
80 -116 (Figure 3). Data from these wells are reported in Table 2 (below). Numerous
other wells are inferred to be present within this radius on the basis of air photos and
site reconnaissance, although not in the county database. Overall, the data indicate the
geology is favorable for groundwater development in terms of fracture density.
However, the success of a water well drilled at a given location still depends on whether
or not the well intersects water - bearing fractures. A dry hole results if no water - bearing
fractures are encountered at the chosen drilling site.
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Total depth gallons per Casing lengthWelluse
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Public well (Little not in database not in database not in database not in database
Keswick School)
Public well 340 22 60 10
Keswick Hall)
Private well 125 2 23 12
TMP 80 -117)
Private well 300 1 35 30
TMP 80 -126)
Soils and saprolite
Soils on the church parcel are dominantly Nason and Tatum silt loam (Figure 4). These
soils are deep and well- drained, with moderate permeability and water capacity. With
an average thickness (casing length) of about 40 feet, this soils - plus - saprolite column is
well suited to groundwater storage and transmission to bedrock fractures.
Figure 4: Soils in the vicinity of South Plains Church
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Groundwater flow, recharge and discharge
Groundwater flow in the vicinity of the parcel is estimated to be generally in a southerly
direction (Figure 5), with recharge on the slopes of the Southwest Mountains, and
discharge into tributaries that flow into the Rivanna River. Regional flow is driven by a
strong topographic gradient on the flank of the Southwest Mountains. On the parcel
itself, at relatively shallow levels of the crust, there is a southwestward component to
flow, toward an unnamed tributary of Carroll Creek.
Groundwater sensitivity
Contaminant threats
TMP 80 -116 is situated within an area of recognized groundwater sensitivity according
to the County study and databases that were assembled during the 2003 Albemarle
County Hydrogeologic Assessment, Phase II (Figure 6). Releases of petroleum from
underground storage tanks within 2000 feet have been documented on several parcels
in the vicinity of TMP 80 -116, including the church parcel itself (Table 3, below):
Table 3:
VADEQ ID Name address date status
20086036 Oak Hill Farm 4125 Louisa Rd Keswick 10/24/2007 Open
20066143 South Plains Presbyterian Church 410 Black Cat Rd Keswick 5/22/2006 Closed
20016098 Susan Jones Property 483 Black Cat Rd Keswick 12/18/2000 Closed
20006057 Susan Jones Property 483 Black Cat Rd Keswick 10/11/1999 Closed
19975091 Keswick Post Office Rt. 22 Keswick 1/28/1997 Open"
19943850 Rivanna Volunteer Fire Dept.Rt. 22 Keswick 5/11/1994 Closed
19943757 Rivanna Volunteer Fire Dept.Rt. 22 Keswick 5/4/1994 Open*
County database status
The most recent case, Oak Hill Farm, is classified as an open case in the DEQ
database as of September 6, 2009. This means that cleanup and mitigation are
ongoing at this site, and have not yet been approved as complete. Other cases that
have occurred within the past ten years are classified by the Virginia Department of
Environmental Quality as "closed ", meaning that clean -up and mitigation activities have
been carried out in accordance with DEQ standards. Two older cases are still classified
as "open" in the County database, although not apparently carried as such by Virginia
DEQ.
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The church parcel appears to be up hydrologic gradient from all documented petroleum
releases in terms of surface topography. This plus limited development of extensive
fracture networks in the underlying bedrock suggests it is unlikely that any residuum
from petroleum releases on nearby parcels will impact groundwater on the church
parcel. Testing of the church well for possible contamination Is the only way to be
certain that there has been no impact.
There are numerous existing drainfields inferred from air photos and field
reconnaissance within 3000 feet of TMP 80 -116 (Figure 3). All of these are either down
hydrologic gradient from the parcel, or hundreds of feet away. None is predicted to
pose a contamination threat under normal usage.
No other contamination threats were identified during field reconnaissance.
Water budget estimate
It is instructive to evaluate the proposed use within the context of a theoretical water
budget:
Annual precipitation: 44 inches
Conservative estimate for percentage of precipitation contributing to groundwater
recharge: 15%
Annual groundwater recharge: 6.6 inches
Daily groundwater recharge: .0181 inches = .0015 feet
Daily recharge per acre: 0015 feet X 43560 square feet per acre = 65.6 cubic feet
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 over entire site: 491 gallons per acre X 5.4 acres =
2651 gallons per day
Predicted groundwater withdrawal on site: 163 gallons per day (average), 810 gallons
maximum.
Groundwater withdrawals for the proposed use at South Plains Church appear to be
well within the amount of theoretical daily recharge to the site.
Potential for proposed use to affect existing users of groundwater
The proposed use anticipates pumping an average of 163 gallons per day of
groundwater. This withdrawal would not be consumptive, to the extent that much of the
water would be returned to the ground as recharge via a sanitary drainfield. It is not
likely that existing users of groundwater down - gradient will be impacted by the proposed
use. No negative long -term impacts are anticipated for regional groundwater resources
from development of the proposed fellowship hall.
There is one public water supply well, serving Little Keswick School, within 1000 feet of
the church parcel. This well is situated on the opposite side of the unnamed tributary to
Carroll Creek from the church. To the extent that this tributary serves as a groundwater
divide, it is not likely that there will be mutual interference between the Little Keswick
School well and the church well.
The proposed use does not involve activities that pose a threat of toxic spill under
normal circumstances.
Reserve well field
The parcel is of sufficient size to allow for construction of a third well in the event that
the two existing wells fail or become contaminated.
Dedicated Monitoring well
The parcel is of sufficient size to allow for construction of a dedicated monitoring well if
the County deems this to be an appropriate site.
Groundwater management plan
Existing forested land cover is favorable in terms of groundwater recharge, and should
be preserved wherever possible. Implementing runoff - neutral development practices,
such as a "green roof" and porous pavement technology would help mitigate runoff and
enhance onsite groundwater recharge.
Submitted by Nicholas H. Evans, CPG # 2801 001041
September 11, 2009
oEFARTVEw7OPpROFE8GiONAL AND OCCupA/Ou=L RESULAT0m
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1408-31-2011 7°*r^"=`»wz5c 2801 001041
BOARD FOR GEOLOGY
CERTIFIED AS A PROFESSIONAL GEOLOGIST
NICHOLAS H EVANS
4609 BURNLEY STATION ROAD
i BARBOURSVILLE, VA 22923