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Home My WebLink AboutARB202000104 Groundwater Assessment 2020-10-05Ivy Proper TMP58A-14 & 20 Tier 3 Groundwater Assessment Groundwater Management Plan Prepared for: Building Management Company 400 Locust Avenue, suite 3 Charlottesville VA 22902 Draft submitted September 3, 2020 Nick H. Evans PhD CPG Virginia Groundwater LLC PO Box 1424 Charlottesville VA 22902 nick(a)viroiniagroundwater.com 434-466-1280 Key Findings Hydrogeologic setting: Located in the valley of Little Ivy Creek just above the flood plain, the site is underlain by deep and well -drained soils that overlie fractured crystalline porphyroblastic biotite gneiss bedrock. Groundwater availability: Soils and bedrock are favorable to water well construction. Recharge potential from onsite soils is excellent, and there is likely to be significant recharge from off site. Bedrock fracture potential is favorable. Are Hydrogeologic conditions favorable to proposed use? Yes. Contamination threats on record within 2000 feet of parcel? Yes. Due to the proximity of open LUST cases to the site, it is advisable to test any new well on the property for possible contaminants. Additional contaminant threats observed in field reconnaissance? None. Anticipated impacts of proposed use to existing users of groundwater? None Anticipated impacts of proposed use to impact sustainability of groundwater resources? None Groundwater management plan: Offset groundwater recharge lost due to impervious surface created during development by infiltrating runoff on site to the extent possible. Project Overview The proposal is to construct a 6500 square foot office building to include a veterinary clinic and general office space, on TMP58A-14 & 20, which comprise 0.87 acres on the north side of Ivy Road at Ivy (Figure 1). New impervious surface area created by the project will total 0.466 acres. A conceptual site plan showing the project layout and area of land disturbance is provided with this report. Figure 1: Site location map _t{olk� sS a m ' 3 -4e C At, 9 Ivv Rd 4 e = ', assme� Asa O,OOmt�e\� Rd mPiy. �1 scale N 2000 feet Projected maximum water consumption for the facility is 875 gallons per day, based on usage by the veterinary clinic and office employees using restroom facilities. Water will be supplied by a well to be drilled on site. Waste water will be disposed of through an on -site drain field that has a permitted capacity of 875 gallons per day. Adjoining parcels are in a mix of uses (Figure 2). While all adjoining parcels are within the Albemarle County Service Authority service area (water only), not all are connected to the system, and all use on -site drain fields for waste disposal. Figure 2: location detail with nearby land usage • residential ® commercial o church ■100-year flood plain I, Hydrogeologic Assessment Topography and hydrology The parcels to be developed are located within the Little Ivy Creek watershed. Site elevations range between about 516 feet above sea level on the southeast edge along Ivy Road, to about 537 feet in the northeast corner at the rear of the property (Figures 2 and 3). The southern portion of the property slopes gently south toward the alluvial flood plain Little Ivy Creek. The western edge of the 100-year flood plain is about 100 feet south of the property. Slopes are steeper along the northern edge of the property. The landscape slopes upward to the north and west of the site, toward a drainage divide defined by Turners Mountain. To a first approximation groundwater flow directions within a few hundred feet of the surface may be predicted to be down a hydraulic gradient that mimics surface topography. On this basis overall groundwater flow beneath the project site is predicted to be south to southeast, toward discharge in Little Ivy Creek. Figure I Topography, watershed drainage divides, and predicted groundwater flow directions in the vicinity of TMP 58A2-14 & 20 i Allechurns River watershed f y Ivy Creek watershed � r n TM 58A2-14 & 20 watershed drainage divide predicted groundwater flow direction scale 2000 feet N Hydrogeology In central Virginia, the physical characteristics of soils and the underlying bedrock are critical to the suitability of a given site to water well construction. Soils and weathered rock close to the surface serve as a "sponge" that captures rainwater, then feeds water downward to recharge fractures in the bedrock. Drinking water wells are normally constructed to tap water from deep bedrock fractures, while excluding potentially contaminated water that may exist in soils and weathered rock close to the surface. Groundwater becomes cleansed by passing downward through deeper soils and bedrock fissures. While the soils provide an excellent medium for recharge and groundwater storage, a successful well must intersect deeper water -bearing fracture networks in the bedrock that are interconnected with the soils as a source for recharge. The soils on this site are classified as Yadkin clay loam, deeply eroded. These are described in the USDA Soil Survey as deep and well -drained, with moderate water storage capacity and moderate to high capacity to transmit water. These attributes are favorable for storage and transmission of groundwater. There is significant acreage up hydraulic gradient from the site to the north and west, which suggests potential for significant groundwater recharge from off site. The crystalline bedrock beneath the project site is called porphyroblastic biotite gneiss. There is an exposure of this rock on the northern edge of the site in an erosion ditch on the slope leading up to the railroad bed (image left). This type of rock is very widespread in western Albemarle County. The bedrock does not contain primary intergranular porosity through which groundwater might flow. Rather, groundwater flows in fractures and fissures, where such occur. The reported yields from drilled wells are a good proxy for assessing the degree of bedrock fracture density, which has a direct correlation with the magnitude of yields of wells drilled into that rock. Of 1536 database wells constructed in the porphyroblastic biotite gneiss bedrock present on this site, the average yield is 8.4 gallons per minute (GPM), and the average well depth is 218 feet. These numbers suggest that on average this type of rock is favorable in terms of fracture density. G9 Of 23 database wells in the vicinity of the site (Figure 4) in the County database, the average yield is 10 GPM, with a low of 0 GPM and a high of 60 GPM. Although 5 wells are reported as zero yield (dry holes), the numbers imply that overall bedrock fracture density is favorable to water well productivity in the vicinity of the project site. The existing well on the property is in the database as a zero yield well (drilled 1961, 122 feet deep). The applicant plans to abandon that well. Figure 4: Existing wells in the County database in the vicinity of TMP 58A2-14 & 20, also showing ACSA service area extent TMP 58A2-14 & 20 • existing domestic well 15 in County database, location approximate, yield, gallons per minute existing public supply 0 well in County database 7 I ACSA service area VA Water budget analysis of project impact It is instructive to use quantitative water budget analysis to evaluate the proposed use of groundwater relative to natural groundwater recharge. (data source: Sanford, W.E. and others, 2011, Quantifying components of the hydrologic cycle in Virginia using chemical hydrograph separation and multiple regression analysis: USGS Scientific Investigations Report 2011-5198) Annual precipitation, Albemarle County: 46.8 inches --normal year 25.7 inches --drought year (d) Percentage of precipitation contributing to groundwater recharge, subtracting runoff and evapotranspiration: 32% Annual regional groundwater recharge: 14.98 inches 8.39 inches (d) Average regional daily groundwater recharge:.04104 inches = .00342 feet .02299 inches = .00192 feet (d) Daily recharge per acre: (.00342 feet) X (43560 square feet per acre) = 149 cubic feet recharge per acre 84 (d) Gallons recharge per day per acre: 149 cubic feet X 7.48 gallons per cubic foot = 1115 gallons per day per acre 682 (d) Recharge area available on project site: (0.87 acres) — (0.466 acres new impervious surface) = .404 acres Gallons per day natural recharge to site post development: (1115 gallons per acre) X (.404 acres) = 450 gallons per day 275 gallons per day (d) Predicted maximum daily groundwater withdrawal post development: 875 gallons per day Estimated proportion of daily withdrawal that is consumptive (water not returned to the ground on site through the drain field, for example water carried off -site in containers, or water lost to evaporation): 5%, or 43.8 gallons per day. The proposed consumptive usage of groundwater amounts to about 10% of daily recharge to the site post development under normal precipitation, and about 16% during drought years. Potential for proposed use to affect existing users of groundwater While the County database contains records for many wells in the vicinity of the proposed project site (Figure 4), it is not clear which of these are still in service due to expansion of the ACSA service area. Regardless, TMP58A-14 & 20 is down hydraulic gradient from all existing wells on record. The water budget analysis, above, suggests that a well drilled on this site and pumped to supply the modest demands of the proposed use would have no foreseeable impact on existing users of groundwater on nearby parcels. Potential for proposed use to impact sustainability of groundwater resources The proposed withdrawal of 875 GPD, of which roughly 844 GPD are returned to the ground as recharge through the drain field, would have no foreseeable impacts on regional groundwater resources in the long term. Contaminant threats affecting the proposed site A Phase 1 Environmental Assessment of the property was conducted in 2019 by ECS Mid -Atlantic LLC (attached to this report). This assessment found four documented LUST (leaking underground storage tank) cases within 1000 feet of the site. (Figure 5). In reviewing these cases, none appear to pose potential impacts to the project Figure 5: LUST sites on record within 1000 feet of TMP58A-14 & 20 and predicted groundwater flow directions LUST site, case closed LUST site, case open y predicted groundwater flow direction site. The two sites listed as "closed" are hydraulically up gradient from the property. Neither is considered a potential threat to groundwater quality on TMP58A-14 & 20 because of their "closed" status and relative distance from the site. The two "open" cases are closer to the site, but both are down gradient hydraulically from the site, and not likely to impact a well drilled on site. A comprehensive study was conducted at the Scott's Exxon LUST site, located 300 feet southeast of the project site (Sullivan International Corporation, 2013, attached to this report). The data from this study confirm that groundwater flow in the area is toward the south-southeast, which would carry contaminants away from TMP58A-14 & 20. A domestic well on 58A2-20A, which is between the Scott's Exxon site and the proposed development site, was tested and found to be impacted by MBTE contamination from the spill. It is advisable that any well drilled on the proposed development site be tested for possible contaminants. Threats of contamination by proposed Droiect There are no perceived threats to groundwater quality by the proposed use. Reserve wellfield The limited size of the property poses potential challenges to siting a replacement well if the supply well for the project becomes compromised in some way. Groundwater management plan Offset groundwater recharge lost due to impervious surface created during development by infiltrating runoff on -site to the extent possible. Submitted by Nicholas H. Evans, CPG # 2801 001041 September 3, 2020 i U:VIXIONAVEALTH of VIRGE T A EzwnEs Ekpamnent of Professional and Occupational Regaulation - _ - 9960MaylendDrive.Suitei , Richmond. VA LIM 08-31-2021 TO,Pp ,ne.(804)36]-SM0 2801001041 BOARD FOR PROFESSIONAL SOIL SCIENTISTS, WETLAND PROFESSIONALS 8 GEOL CERTIFIED PROFESSIONAL GEOLOGIST ?i NICHOLAS H EVANS 4609 BURNLEV STATION ROAD ^� BARBOURSVILLE. VA 22923 CP