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Home My WebLink AboutSUB201700011 Assessment - Groundwater Final Plat 2017-05-03 Woodlawn Subdivision TMPs: 44-12W and 44-12F Tier Ill Groundwater Assessment Groundwater Management Plan Prepared For: Woodlawn Development, LLC ATTN: Matthew Gruber 2180 Owensville Road Charlottesville, VA 22901 May 3, 2017 Prepared by: e� e • TIMMONS GROUP YOUR VISION ACHlEVEO THROUGH OURS. John T. Russell, CPG 1001 Boulders Parkway, Suite 300 Richmond, Virginia 23225 KEY FINDINGS Hydrogeologic setting: Located south of a drainage divide in moderate to steep topography (i.e., 2-45%) in the Piedmont Foothills. The site is completely underlain by a porphyroblastic biotite-plagioclase augen gneiss of the Blue Ridge basement complex. Groundwater availability: This site is located in a Class 2 Area of groundwater availability and thus has a moderate potential yield. A total of ten wells have already been installed at the site, of which one was dry and the other nine had yields ranging from 3-60 gallons per minute (gpm) at installation depths of 225 to 405 feet below surface grade with an average yield of 9.6 gpm. Are hydrogeologic conditions favorable to proposed use? Yes Contamination threats on record within 2,000 feet of parcel? Yes. On November 8, 2013, it was reported that there was a release from the farm-use gasoline underground storage tank (UST) at 849 Woodlands Road. In response, Virginia DEQ issued Pollution Complaint (PC) Number 2014-6048 and requested the completion of a Site Characterization Report (SCR), which was submitted on January 13, 2014. A secondary assessment of the home heating oil UST was completed in September 2014 which yielded evidence of a second release from the site into the subsurface. As a result, DEQ requested the preparation of a SCR Addendum to evaluate the extent of semi-volatile hydrocarbons. The SCR Addendum was submitted on October 10, 2014. Following submittal of the October 2014 SCR Addendum, two Post-SCR Monitoring/Sampling Reports were completed for the site in May and September of 2015 with samples collected from the five monitoring wells that had been installed onsite as a result of the SCR process. A series of five samples had likewise been collected from the onsite water supply well over the course of the investigation with no resultant detection of gasoline or heating oil concentrations. DEQ issued a decision in December 2015 to close the Pollution Complaint number, citing the following pieces of evidence: • absence of risk to the site or surrounding area, given the absence of measured contamination in onsite wells, • absence of water supply wells within 2,000 feet of the site, • distance to nearest surface water(approximately 2,600 feet from site). However, evidence at case closure identified the continued presence of low levels of residual contamination in the subsurface. Additional contaminant threats observed in field reconnaissance? None Anticipated impacts of proposed use on existing users of groundwater? Unknown Groundwater management plan: Protect the site during the course of residential construction with appropriate erosion and sedimentation controls. Implement runoff-neutral site development as practicable. Ensure the placement of septic drainfields within the soil/saprolite horizon downgradient of the potable well locations (drainfield permitting and placement have already been approved) .•°�• ' Woodlawn Subdivision Tier III Groundwater Assessment TIMMONS GROUP Page 1 Sample wells prior to occupancy of completed single family residences for concentrations of dissolved phase hydrocarbons. As an added precautionary measure, install carbon filters into each water supply system of the proposed residences prior to occupancy. 4 Woodlawn Subdivision TIMMONS GROUP Tier III Groundwater Assessment Page 2 PROJECT OVERVIEW The proposed development is comprised of two parcels totaling approximately 23.02 acres located south of Route 676 (Woodlands Road) in north-central Albemarle County(Figure 1). The properties have been subdivided for the construction of seven single family homes, in addition to the existing residence. FIGURE 1 mmit� » ,,n arum+els aPai # " � t tai i*.,. .. ,,....„,:t _i,!_.. , I4, , 44;4,4: '.*, ',400''' if 41:„.. . I. ,,,t'ke,N.,=, , , ,,,L.../.4,- it,„4-,, f 3: r' , , a• s. ;�, ,mak. `»' r ' ro n.� °V.0- 4 ..,4;10 4.,„4, .4ail rt , ° /,.,* 1 ,, ,.,,tk.:..1.i, .,„ . ,..,..,,,,.,,,,,,::.,,,z.,;..,..,: .,rt...1.,...0,„,„., .,,,,,,,, ,,,,,,..i.,„:„. „,„,„: , .. _ *.ti, ,,,14,,,,,,, \ 1,''''''''' :! , t, ��`.' R:t 1 � }-� �e'�t � �a�3 a 1 £^�-;4.--.4 '":� '4\41.4',,,r.,/,`41,,,,,94,1,��X �, sxe %��a�g a q�a ,.. „....11 . ,,p„, -, x. '� � '" � S s `��, �' '� r � � � air` �g )�t �+.� #„, � � , , ,,, at + t.r r ;Ait,44.;,:ii;(11')\* c � ,. a , ...:" -.---w'..'„"l� .a '•rr`. ` —:- arx r, '�s.: iv' `Dai.. 'it ,i The topography along which Woodlands Road extends along the northern property boundary is a watershed divide from which the site is identified within the Ivy Creek Water Supply Watershed (Figure 2). Furthermore, an unnamed tributary of Jumping Branch extends southward from the site with another unnamed tributarylocated approximately 900 feet to the west. Jumping Branch flows eastward approximately 6,200 feet before discharging into Ivy Creek which flows into the South Fork Rivanna River Reservoir. FIGURE 2 Water Resources Map r �. FomRIbE 9Cwrk �UYJ1l ,:-../,,,i4',„.,--:,-, yz,, $�"" 3: 4 C 1 Sou"'For4 Rtvesaos jw@wvw?e ,,,oi) � '-WMst 5oppty iveteyattM tA`�, # �" ' 4353+Xf y�'9tXq IC a Wats SuyytY WetcFshM � _� -. ` 't \ , 'r t ' t r / 1, n r t i -1 i aP �L '') r *s i IFacll .. ....0.4Woodlawn Subdivision Tier III Groundwater Assessment TIIMMONS GROUP Page 3 Elevations across the site range from approximately 588 ft at the northernmost property corner to approximately 500 feet at the southernmost corner(Figure 3) FIGURE 3 t_ r 4-Foot Contours and Surface'Ittaters ' •'; /P ti t �� r 1 _!r. Vr i ✓ f r ; i— - y Sa ER Fcrr ft RerrnrtA a lx4ae x esvi Vmr1 -•' /:' r t s, g r r � wnra g, t fNRYa;P^lee 3Fdmte'rR k,+ed .n - e— ! f ! rl� \ p( .,'W .. "ice /'�0��'i.�;�. ...-f.✓JriS Existing land cover across the contributing parcels is mostly open pasture with mixed growth forest at the southernmost extent along the unnamed tributary of Jumping Branch. Sparse tree cover extends along fence lines in the northern area of the site and around the existing single family residence. Based on the Commonwealth of Virginia Private Well Regulations, daily demand (usage) is derived from design criteria for the onsite sewage disposal system (septic) which is 150 gallons per bedroom per day with no cap or daily withdrawal limit. Presently, no design details have been offered for the proposed residences. HYDROGEOLOGIC ASSESSMENT Geology The site is underlain by a porphyroblastic biotite-plagioclase augen gneiss of the Blue Ridge basement complex (Figure 4) with no surface exposure. From the boring logs for the recently installed residential wells, depth to bedrock beneath the site ranges from 38-55 ft below surface grade. Groundwater Recharge and Flow Paths The majority of recharge to the unconfined and bedrock aquifers occur within the parcel; however, the degree of bedrock fracturing is unknown but nonetheless anticipated to provide a means for offsite recharge beyond the limits of the Ivy Creek Watershed. Groundwater contained within the unconfined saprolite aquifer is expected to flow southward as able toward Jumping Branch. •` ' Woodlawn Subdivision Tier Ill Groundwater Assessment TIMMONS GROUP Page 4 FIGURE 4 Geology of Albemarle County Target Property is located•a:Ybg-Porphyroblastic Biotite-Plagioclase Augen Gneiss • • N:z.tt'1cta�li,i 7. a,y r i• „ • ,..13 3 , f IZil' ' s?t c�c7z( earth is Bedrock Fracture Density and Water Well Productivity The underlying bedrock formation does not contain primary intergranular porosity through which groundwater might flow. Groundwater flow within the bedrock aquifer is therefore resolved to occupying and flowing through fractures and fissures under confined conditions. The mantle of weathered rock, which overlies the bedrock interface, and the lower levels of the saprolite horizon (collectively referred to as regolith) maintains a higher degree of porosity and therefore groundwater retention. As a result, the regolith layer serves as either a shallow source of groundwater or as a source of recharge for the underlying fractured bedrock aquifer. Although generally more plentiful, the groundwater from an unconfined Piedmont aquifer in the mantle of regolith has a greater susceptibility to contamination from surface and near-surface sources. In this hydrogeologic setting, domestic water supply wells are constructed with a casing set through the regolith horizon to the bedrock interface with further advancement into the bedrock aquifer and the intent of penetrating as many fracture zones as possible to provide sufficient volumes of generally higher quality groundwater. Although the fracture density within the underlying bedrock is unknown, the drillers logs from the installation of the onsite wells details almost unanimously that the elevation of the potentiometric surface lies above that of the bedrock interface. These measurements suggest that groundwater recharge is occurring from potentially .•�'� Woodlawn Subdivision TIMMONS GROUP Tier III Groundwater Assessment ”, e Page 5 higher elevations or otherwise areas that create pseudo-artesian conditions relative to the elevation of the bedrock interface. Although one of the ten wells installed at the site was dry and two yielded only three gpm, the overall median yield of 9.6 gpm with a high yield of 60 gpm indicate that the underlying bedrock maintains sufficient fracture density to enable the installation of successfully yielding water supply wells. Water Budget Estimate for Site The below, although approximate, is intended to review the proposed groundwater usage relative to naturally occurring volumes. Average annual regional precipitation = 47.68 inches Estimated percentage of precipitation contributing to groundwater recharge = 30%* Annual regional groundwater recharge = 14.3 inches Average regional daily groundwater recharge: 0.039 in = 0.0033 feet Daily recharge per acre: 0.0033 ft x 43,560 sq ft/acre = 142.21 cubic feet of recharge per acre Gallons recharge per day per acre: 143.75 cubic feet x 7.48 gallons per cubic foot = 1,063.19 gallons per day per acre Gallons per day recharge on parcel: 23.02 acres x 1,075.25 = 24,488.19 gallons per day Gallons per day recharge from offsite: Unknown to minimal based on position of property relative to drainage divide Predicted maximum daily groundwater withdraw per day based on Commonwealth of Virginia Private Well Regulations (based on assumed eight x four-bedroom homes) = 4,800 gallons** Although approximate, the calculations above nonetheless indicate low to moderate usage of naturally occurring groundwater. * Swain, L.A., Mesko, T.O., and Hollyday, E.F., 2004. Summary of the hydrogeology of the Valley and Ridge, Blue Ridge and Piedmont Physiographic Provinces in the Eastern United States: U.S. Geological Survey Professional Paper 1422-A, 23p. ** a significant portion of daily withdrawal to be returned to recharge through the onsite drainfields. ••' 't Woodlawn Subdivision Tier III Groundwater Assessment TIMMONS GROUP Page 6 Potential for Proposed Usage to Affect Existing Users of Groundwater The single family residence currently occupying the site and which is scheduled to remain has been factored into the projected groundwater usage calculations above. No additional residence are located between the site and Jumping Branch located to the south. To the best of knowledge no public water supply wells are located within 2,000 feet of the site. Contamination Risks Previously stated, the Virginia DEQ previously issued Pollution Complaint (PC) Number 2014- 6048 to the site(849 Woodlands Road)following the report and confirmation of a gasoline release from the farm-use gasoline UST on November 8, 2013. In response, DEQ requested the completion of a Site Characterization Report which was submitted on January 13, 2014. A secondary assessment of the home heating oil UST was completed in September 2014 which yielded evidence of a second release from the site into the subsurface. As a result, DEQ requested the preparation of a SCR Addendum to evaluate the extent of semi-volatile hydrocarbons. The SCR Addendum was submitted on October 10, 2014. Following submittal of the October 2014 SCR Addendum, two Post-SCR Monitoring/Sampling Reports were completed for the site in May and September of 2015 with samples collected form the five monitoring wells that had been installed onsite as a result of the SCR process. A series of five samples had likewise been collected from the onsite water supply well over the course of the investigation with no resultant detection of gasoline or heating oil concentrations. The PC Number was closed in December 2015 citing an absence of risk to the site or the surrounding area given the absence of measured contamination in the onsite wells, the absence of water supply wells within 2,000 feet of the site, and the nearest surface water to the site being approximately 2,600 feet from the site. However, evidence at case closure identified the continued presence of low levels of residual contamination in the subsurface. Additional risks may exist as related to the associated usage of drain fields with each proposed residential parcel; however, based on the measured depths to bedrock across the site, this potential risk is anticipated to be minimal. Reserve Wellfield Based on the size of the overall property and the hydrogeologic setting, an adequate number of favorable/alternative locations for replacement wells are located across the site in the event that a primary well fails as a result of contamination, insufficient yields of groundwater, or other issues. ...0. # Woodlawn Subdivision Tier III Groundwater Assessment TIMMONS GROUP Page 7 Submitted by: John T. Russell, CPG#2801 001550 May 3, 2017 DEPARTMENT OF PROFESSIONAL AND OCCUPATIONAL REGULATION COMMONWEALTH OF VIRGINIA ( EXPIRES ON NUMBER M 9960 aytand Dr.,Suite 400,Richmond,VA 23293 08-31-2017 2801001550 Telophons (804)3818500 BOARD FOR PROFESSIONAL SOIL SCIENTISTS,WETLAND PROFESSIONALS&GEOLOGISTS CERTIFIED PROFESSIONAL GEOLOGIST JOHN THOMAS RUSSELL 3519 GROVE AVENUE RICHMOND,VA 23221 t )44 TRAMON AN,A" DOCLAAANA,yEE Ar'EL,EXAM/MON OR USE EY POMMES OR PRUE CAmeAl MAN MOM NAMED MAY REAM.Ai CFAMINAt PRO66C1MNON UNDEA CODE Of WOW. it .04 Woodlawn Subdivision TIMMONS GROUP Tier Ill Groundwater Assessment Page 8