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Home My WebLink AboutSUB201800177 Other 2018-12-13December 13, 2018 Luke Kitelinger Bella Custom Builder Charlottesville, VA 22902-6348 Kitelingerl@yahoo.com 434-960-3085 IOHydroGeo 418 East Main Street Charlottesville, Virginia 22902 (404) 219-6676 Re: Revised DRAFT Tier III GW Assessment— "Key Findings" for Albemarle Co. Parcel #45-59M HydroGeo Project #18-374 Dear Luke, At your request, HydroGeo Environmental, LLC (HydroGeo) is submitting a DRAFT Tier III Letter Report for Albemarle County Parcel #45-59M (the "Site — see attached figure for Site location). This DRAFT outlines Key Findings of the study, to be included as part of the Special Use Permit application package. The full report will be submitted to Albemade County with the final Site Plan. Key Findings: Albemarle County hydrogeologic unit: Piedmont Foothills (Hydrogeologic Unit III) Groundwater availability zone: Class II (medium relative groundwater availability) Hydrogeologic conditions favorable to proposed use? Yes. See attached calculations for pre- and post development groundwater surplus estimates. Precise well yields will remain unknown prior to drilling. Virginia Department of Health (VDH) has not yet provided well completion reports for nearby properties (FOIA request submitted 12/4/18) — this information will help estimate average well yield in the Site vicinity to refine our recommendations on a groundwater supply development strategy moving forward. Site within groundwater sensitivity zone? No. Review of the Virginia Department of Environmental Quality (VADEQ) Virginia Environmental Geographic Information Systems (VEGIS) viewer and Albemarle County GIS did not identify any open pollution complaint cases within the required 1000-foot search radius. Groundwater flow pattern: Groundwater recharge areas include vegetated land onsite and undeveloped, permeable areas located upgradient of the Site; groundwater discharge areas occur along the southwestern edge of the Site, along the intermittent streambed of the unnamed tributary to Schroeder Branch, a tributary to the Rivanna River South Fork. General groundwater flow in the vicinity of the Site is assumed to be influenced by topography and likely follows a net southwest- to southeast direction toward the unnamed tributary to Schroeder Branch along the southwestern edge of the parcel and then flows southeast to Schroeder Branch. Contamination threats on record: One (1) VPDES outfall was located within the required 1000-foot search radius from the parcel boundaries. Due to its location approximately 950 feet away and downgradient of the Site, and the knowledge that registered VPDES permitted discharge is regulated and monitored by state agencies, HydroGeo does not consider this to be likely contamination threat, nor a reason to place the Site within a groundwater sensitivity zone. Additional contaminant threats observed in field reconnaissance? Field reconnaissance has not been performed at this time. Impacts of proposed use on existing users: Proposed groundwater use should be adequate for the development's needs without unreasonably affecting users offsite. Revised DRAFT Tier III Groundwater Assessment —"Key Findings" HydroGeo Project #18-374 Albemarle County Parcel #45-59M December 13, 2018 BMP recommendations: Maintain vegetated stream buffer as much as possible during development; implement runoff -neutral site plans insofar as practicable. It should be emphasized that these are preliminary and draft findings, thus they are subject to change. Best regards, Ernest Beasley, CPG Geologist c: (404) 219-6676 Enclosures (3): -Site Location Map -Watershed Map -Water Budget Calcs References: Albemarle County GIS Web Viewer: hftp://gisweb.albemarle.org/GISWeb/-Accessed December 4, 2018 Albemade County Hydrogeologic Assessment Summary Report by ENSAT Corporation and Albemarle County Department of Engineering and Public Works (2003) VADEQ VEGIS viewer: hltps://apps.deq.virginia.gov/mapper_ext/default.aspu?service=publicAMmby - Accessed December 4, 2018 Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resource, scale 1:500,000 Site Location Figure Lq �.- I�J S FORDIF ,ch«rorr �uat�Q►na�, J 1 r r ` r HydroGeo ENVIRONMENTAL !��.� �v+i' 1, Hollyrnead 38006'57"N, 78028'13"W (WGS 1984) ' jf �� SITE 'per l y� �__ 1 , _ South Fork (J. Fot w Rivanna'Riirer v Reset-wir �. Albemarle County Parcel #45-59M J Earlysville, Virginia 22936 ;- HydroGeo Environmental, LLC 'Val", 418 East Main St. Charlottesville, VA i l�� 29 rf �.� ' `i�y ^� ``, (� NORTH Scale: Date: C'� �=, �1 c. T , i -0.7 mi 10/30/2017 BASEMAP: USGS — The National Map 2018 -r J OWN Revised DRAFT Tier III Groundwater Assessment — "Key Findings' HydroGeo Project #18-374 Albemarle County Parcel #45-59M December 13, 2018 Attachment: Water Budget Calculations for DRAFT Tier 3 GW Assessment (Albemarle Co. Parcel #45-59M) Quantitative analysis helps evaluate the impact to local groundwater resources due to creation of impervious surface and increased groundwater pumping as a result of site development. Existing recharge to the site's local watershed (38.9 acres of undeveloped forest and cleared residential land) can be modelled as follows (see attached figure for delineated watershed boundary): Annual regional precipitation: 43 inches Conservative estimate for the percentage of precipitation contributing to groundwater recharge, subtracting runoff and evapotranspiration: 15% Annual regional groundwater recharge: 6.45 inches Average regional daily groundwater recharge:.0179 inches = .0015 feet Daily recharge per acre:.0015 feet X 43560 square feet per acre = 66.6 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 natural recharge to site: 491 gallons per acre X 38.9 acres = 19,100 gallons per day (gpd). Gallons per day recharge lost due to existing impervious cover: 491 gallons per acre X 2.28 acres = 1,120 gallons per day. Existing recharge = 19,100 gpd — 1,120 gpd = 17,980 gpd And considering current withdrawals from existing residences: Average water usage per day: 100 gallons per day Average People Per Household: 4 people Current Households in watershed: 5 households 100 gallons per day per person X 4 people x 5 households= 2,000 gallons per day Based on these calculations, the current (pre -development) groundwater surplus for the local watershed can be expressed as: Inputs (recharge) — Outputs (GW pumped) = Surplus 17,980 gpd — 2,000 gpd = 15,980 gpd surplus (pre -development) Revised DRAFT Tier III Groundwater Assessment — "Key Findings' HydroGeo Project #18-374 Albemarle County Parcel #45-59M December 13, 2018 Post -Development Calculations: Our current estimate is that the project will result in a net increase of impervious surface of 1.5 acres. The impact on post -development groundwater recharge is estimated below: Annual regional precipitation: 43 inches Conservative estimate for the percentage of precipitation contributing to groundwater recharge, subtracting runoff and evapotranspiration: 15% Annual regional groundwater recharge: 6.45 inches Average regional daily groundwater recharge:.0179 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 lost due to new impervious cover: 491 gallons per acre X 1.5 acres = 736 gallons per day. Existing recharge — Recharge Lost Due to New Impervious Surfaces = Post-Dev. Recharge 17,980 gpd - 736 gpd = 17,244 gpd And considering projected withdrawals from new and existing residences: Average water usage per day: 100 gallons per day Average People Per Household: 4 people Current Households in watershed: 5 households Proposed Households in watershed: 5 households 100 gallons per day per person X 4 people x 10 households= 4,000 gallons per day Based on this set of calculations and assumptions, the estimated post -development groundwater surplus for the local watershed can be expressed as: Inputs (recharge) — Outputs (GW pumped) = Surplus 17,244 gpd — 4,000 gpd = 13,244 gpd surplus (post -development) Relative to the proposed usage of groundwater post development, overall recharge post -development will be more than adequate to supply groundwater usage without long-term degradation of groundwater resources.