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HomeMy WebLinkAboutSUB200800211 Review Comments Groundwater Assessment 2008-10-20Tier III Groundwater Assessment (Revised) of Jefferson Ridge (Formerly Woodridge) Subdivision Albemarle County, Virginia Prepared For: Barry Meade Homes, LLC 140 South Pantops Drive, Suite 200 Charlottesville, Virginia 22911 Submitted To: Josh Rubenstein, Groundwater Manager Albemarle County Office of Community Development 401 McIntire Road Charlottesville, Virginia 22902 Prepared by: True North Environmental, LLC Charlottesville, Virginia Date: October 14, 2008 Tier III Groundwater Assessment Report (Revised) Of Jefferson Ridge (formerly Woodridge) Albemarle County, Virginia Prepared For Barry Meade Homes, LLC I40 South Pantops Drive, Suite 200 Charlottesville, Virginia 22911 Prepared by: True North Environmental, LLC Analytical Services, Inc. lee Michael Maloy, CPG Analytical Services, Inc. S Vincent L. Day True North Environ tal Date: October 14, 2008 rN v� L. MALOY �Ilp.1424 ��8310, Table of Contents Key Findings 1.0 INTRODUCTION .................................................................. ..............................1 2.0 SITE DESCRIPTION ............................................................. ..............................1 2.1 Topography ....................................................................... ..............................1 2.2 Surface Water Drainage .................................................... ..............................1 2.3 Planimetric Features .......................................................... ..............................1 2.4 Land Use ........................................................................... ..............................1 3.0 PROPOSED DEVELOPMENT LAYOUT AND APPROXIMATE LAND DISTURBANCE..................................................................... ..............................2 4.0 GROUNDWATER AVAILABILITY .................................... ..............................2 4.1 Estimated Groundwater Flow Direction ........................... ..............................4 5.0 POTENTIAL SOURCES OF CONTAMINATION .............. ..............................4 5.1 Site Reconnaissance .......................................................... ..............................5 5.2 Sensitivity Mapping .......................................................... ..............................5 5.3 Regulatory Data Base Review .......................................... ..............................5 6.0 HYDROGEOLOGY ............................................................... ..............................6 6.1 Review of Geologic Mapping ........................................... ..............................6 6.2 Review of Soils Mapping .................................................. ..............................6 6.3 Photolineation Interpretation/Fracture Trace Analysis ..... ..............................7 6.4 Summary of Hydrogeologic Conditions ........................... ..............................7 7.0 BEST MANAGEMENT PRACTICES .................................. ..............................8 8.0 CONCLUSIONS ..................................................................... ..............................9 List of Tables Table 1 Well Data Descriptive Statistics: Well Yield (gallons per minute) Table 2 Well Data Descriptive Statistics: Casing Length (in feet) Table 3 Calculated Ksat Values for each Hydrogeologic Unit Table 4 Well Data Summary List of Figures Figure 1 Site Location Map Figure 2 Site Layout Map Figure 3 Groundwater Availability Map Figure 4 Estimated Groundwater Flow Direction Map Figure 5 Groundwater Sensitive Area Map Figure 6 Geologic Map List of Appendices Attachment A Preliminary Plat (Sheets 2 &3) Appendix B EDR- EnvironmentaURegulatory Records Review Key Findings Based upon the results of the Tier III Groundwater Assessment of the Jefferson Ridge Subdivision, the following key findings can be reported: • Hydrogeologic units: VIII (Piedmont proper) • Groundwater availability zone: Class 1 (lowest relative groundwater availability) • Hydrogeologic conditions favorable to proposed use? yes • Site within groundwater sensitivity zone? no • Groundwater flow pattern: local: southwestward with discharge into Briery Creek • Contamination threats on record: no • Additional contaminant threats observed in field reconnaissance? none • Impacts of proposed use on existing users: none. • BMP recommendations: Maintain undisturbed forest cover as much as possible during development; implement runoff - neutral site plans on individual lots insofar as practicable. Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle County, Virginia October 14, 2008 1.0 INTRODUCTION True North is pleased to submit this Tier 3 groundwater assessment report on the Barry Meade Homes Development Property. The report has been prepared to address the requirements within Section 206 of the Albemarle County Design Standards Manual. The subject property consists of the following tax map parcel identifications as assigned by Albemarle County: TMP 124 -2, TMP 124 -5 and TMP 124 -6 (Attachment A -Sheet 2). The proposed area of development is comprised of approximately 675 acres which will be divided into approximately fifty -five (55) planned residential lots possessing three (3) preservation tracts (Attachment A -Sheet 3). The planned residential development will be serviced by individual well and septic systems. 2.0 SITE DESCRIPTION 2.1 Topography The subject property consists of approximately 675 -acres situated roughly parallel to Route 618 (Figure 1). Topography varies from a high of approximately 520 feet above mean sea level (amsl) near the southwestern property boundary to approximately 390 feet amsl along Briary Creek, which flows (to the south) through the central portion of the property. 2.2 Surface Water Drainage Surface water drainage on the subject property is dictated by the presence of Briery Creek and several associated, unnamed tributaries. Drainage likely flows from greater topographic elevations into the swales formed in association with Briary Creek. Briary Creek flows to the south where it contributes to the Hardware River. 2.3 Planimetric Features The subject property is currently undeveloped (densely wooded) and no planimetric features were identified within the site boundaries (Figure 2). Residential structures are located directly to the north, south, and west of the property boundaries. Areas to the east of the property are forested and assumed undeveloped. 2.4 Land Use True North obtained and reviewed planimetric mapping from Albemarle County to aid in assessing land use in the larger site area. The subject parcel is wooded and currently undeveloped. Adjacent properties are either undeveloped or developed with residential housing. Using the planimetric mapping, True North identified approximately 44 structures within approximately 1000 feet of the site boundary. It is expected that each of these structures are serviced by individual wells and drainfields. The subject site is currently zoned as RA (Rural Area). Page 1 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle County, Virginia October 14, 2008 3.0 PROPOSED DEVELOPMENT LAYOUT AND APPROXIMATE LAND DISTURBANCE The development is composed of approximately fifty -five (55) planned residential lots that include three (3) preservation tracts (Attachment A). Land disturbance will be limited to the individual lots and access roads as indicated on the site layout. This acreage disturbance would be expected to be limited to the vicinity of the residential construction sites including each site's septic drainfield. Care would be taken to limit any unnecessary land disturbance, particularly on steeper sloping topography. Any additional disturbance would be expected to be limited to necessary storm water management and/or recommended BMP structures. 4.0 GROUNDWATER AVAILABILITY The planned residential development will be serviced by individual wells and septic tank drainfields systems. Albemarle County Groundwater Availability Mapping indicates that the entire site lies within the Category 1 (Low) Groundwater Availability Zone Designation (Figure 3). The subject site lies within hydrogeologic unit VIII, which was defined during the Phase II Albemarle County Hydrogeologic Assessment. Hydrogeologic unit VIII, was recognized as the "Piedmont Proper" unit within the Albemarle County Hydrogeologic Assessment Phase II Report. The following description of the mapped hydrogeologic unit, along with pertinent tabulated summaries of well data and Ksat values, has been obtained from the Hydrogeologic Assessment Phase II Report: Piedmont Proper VIII: The Piedmont Proper unit is characterized by gently rolling piedmont topography along the County's eastern border. The bedrock geology underlying the unit is mapped as metagraywacke, quartzose schist and melange. Soils range from shallow and somewhat excessively well drained to deep and well drained. Slopes range from 2 -45 %. Page 2 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle County, Virginia October 14, 2008 Table 1 Well Data Descriptive Statistics: Well Yield (gallons per minute) Unit No. Unit Sample Mean Standard Minimum Maximum 1 Name Size Deviation VIII Piedmont 277 11.35 10.97 1.00 75.00 Proper Table 2 Well Data Descriptive Statistics: Casing Length (in feet) Unit No. Unit Sample Mean Standard Minimum Maximum 1 Name Size Deviation VIII Piedmont 310 50.28 24.80 3.00 322.00 Proper Table 3 Calculated Ksat Values for each Hydrogeologic Unit Unit Number Unit Name Mean Ksat (inches per hour) Category Rating VIII Piedmont Proper 0.10 1 True North evaluated available well data from the Albemarle County Well Database to determine casing length and reported yield values for wells in the nearby area. Nearby wells (20), within approximately 2,000 -feet of the property boundaries, were selected and their corresponding data evaluated. Based on the Albemarle County well database shape file, it appears that two (2) of the wells are located within the subject property boundary. However, based on the location of these wells on the map (in densely forested areas), it appears likely that the coordinates provided are slightly erroneous and the wells are associated with two (2) of the forty -four (44) residential structures noted to be present within 1,000 -feet of the property boundaries. Of the twenty (20) wells, casing lengths ranged from 30 feet to 67 feet with an average casing length of 54 feet. Casing length measurements can be used as an approximate indicator to the depth of bedrock and thickness of overburden (soil/saprolite). The total well depths ranged from 50 feet to 230 feet with an average total depth of 105 feet. Of the twenty (20) selected wells, eight (8) did not have any available data for well yield other than a "0" value. Based on our understanding that zeros were previously entered in the database when no information was available, it is unclear as to whether or not these sites represent dry holes with no yield. Of the twelve (12) wells that reported a yield, the Page 3 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle Countv. Virginia October 14. 2008 yield ranged from five (5) to thirty -five (35) gallons per minute. The average yield of the twelve (12) wells was approximately seventeen (17) gallons per minute. The following table summarizes the well data that was evaluated. Table 4 Well Data Summary Well Identification Total Depth (Feet) Casing Depth (Feet) Reported Yield (GPM) 101 -93 -0196 115 165 56 35 101 -93 -0024 115 61 61 0* 101 -93 -0416 115 165 67 0* 101 -87 -0421 124 105 50 10 101 -93 -0015 124 90 40 30 Scottsville -002 (5351) 95 48 15 101 -86 -0336 124 95 48 0* Scottsville -002 (5352) 100 50 10 101 -87 -0352 124 125 62 0* 101 -99 -0163 115 83 58 15 101 -92 -0389 124 60 59 5 Scottsville -002 (5353) 125 62 20 101 -85 -0459 124 72 46 0* 101 -93 -0027 124 125 65 0* 101 -92 -0485 115 55 54 0* 101 -94 -0287 115 80 62 25 101 -88 -0319 124 50 50 0 101 -93 -0454 124 94 49 20 101 -95 -0386 115 130 30 12 101 -97 -0110 115 230 60 8 * Represents potential anomalous data 4.1 Estimated Groundwater Flow Direction Estimated groundwater flow patterns are believed to roughly correspond to site topography. An illustration of the estimated direction of groundwater flow at the site is provided as Figure 4. Drainage divides on the subject property are likely located along areas of greater topographic elevations, between Briery Creek and its associated unnamed intermittent tributaries (Figure 5). 5.0 POTENTIAL SOURCES OF CONTAMINATION True North performed site reconnaissance, reviewed available Sensitivity Mapping from the Albemarle County Phase II Report, and obtained a regulatory database review of the site area (EDR Survey) to identify any potential sources of contamination. Page 4 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle County, Virginia October 14, 2008 5.1 Site Reconnaissance The majority of the property was found to be wooded and relatively undisturbed. During site reconnaissance, no permanent structures were identified within the property boundaries. Several flowing ( unnamed /intermittent) tributaries of Briery Creek (including the creek itself) were noted to be present on the property. Several domestic debris piles, including washing machines, stoves, and lawn mowing equipment were noted to be present along the access road leading through the central portion of the property. A burned down camping trailer was also noted to be present along the property access road, near Route 618. Overhead power lines were observed transecting the southwest and extreme southern portions of the subject site. The approximate locations of the debris piles and burned trailer site have been illustrated in Figure 2. 5.2 Sensitivity Mapping Based on a review of the County Sensitivity Mapping, two (2) areas mapped as sensitive were recognized within proximity to the subject site (Figure 6). A former leaking underground storage tank site assigned Virginia Department of Environmental Quality (DEQ) Pollution Complaint Numbers (PC# 1993 -0705 and PC# 1993 -0919) is located near Woodridge, Virginia, and is identified as the Woodridge Market. The two (2) releases of petroleum were reported on October 2nd and November 4th of 2002. Both pollution complaint cases are reported as closed by the DEQ. The site lies greater than one -mile from the subject property. Review of the mapping indicates the 2000 -foot radius sensitive areas associated with the leaking underground storage tank site lies well to the north/northeast of the subject property. No other identified sensitive areas were noted to be within close proximity to the subject property. 5.3 Regulatory Data Base Review As part of this assessment, True North reviewed information sources to obtain existing information pertaining to a release of hazardous substances or petroleum products on or near the subject property. True North obtained an ASTM site search report from Environmental Data Resources (EDR), Incorporated (Appendix B). The subject property was not listed in any of the federal or state databases reviewed. No sites with environmental concerns were listed within the minimum search distances specified in ASTM E1527 -00. The database search also provides a list of orphan sites occurring in the general vicinity of the subject site. However, orphan sites do not have sufficient address information to be accurately located on the site map. The Woodridge Market site was listed in the EDR report's orphan summary. Page 5 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle County, Virginia October 14, 2008 6.0 HYDROGEOLOGY 6.1 Review of Geologic Mapping According to the Albemarle County Geologic map, the subject site is underlain by Cambrian aged stratified rocks of the Western Piedmont Province (Figure 6). The rock types are described as metagraywacke, quartzose schist, and melange. The following descriptions of the bedrock and soils were provided within the Albemarle County Phase II Hydrogeologic Assessment Report. The Piedmont Proper unit is characterized by gently rolling piedmont topography. The bedrock geology underlying the unit is mapped as Metagraywacke, quarttoze schist and melange. Soils in the unit area are dominated by the Nason and the Manteo in nearly equal percentages. Although these same soils also dominated the Candler unit, it should be noted that the Manteo soils were nearly twice as prevalent as compared to the Nason. Manteo soils are shallow and somewhat excessively drained. The Manteo soils are formed in the weathered products of sericitic schists/phyllites on uplands and range in slope from 2 -45 %. The Nason soil series are deep and well drained and are also formed in the weathered products of sericitic schist. The Nason soils are formed on uplands and range in slope from 2 -25 %. No appreciable bedrock exposures were observed during the site reconnaissance. Quartz - rich metamorphic rock fragments and boulders were identified within the unnamed tributaries of Briary Creek. The majority of the rocks observed most closely resembled diabase with distinct foliation patterns. 6.2 Review of Soils Mapping True North has reviewed the Soil Survey of Albemarle County for the purposes of this report. Five different soil series were mapped within the site's property boundaries. A copy of the soils map for this area, including detailed descriptions of the five (5) identified soil series, have been included in Appendix D. The lowest topographical areas (along Briery Creek and its' unnamed tributaries) are predominantly characterized by the presence of the Wehadkee (95) soil series. The Wehadkee series is characterized as deep, nearly level, poorly drained silt loam soils. Slopes where the Wehadkee is dominant typically range from 0 to 2 percent. The portions of the site where intermittent drainages extend the furthest from Briery Creek are characterized by the presence of the Lignum (46B) soil series. The Lignum series is characterized as deep, moderately well drained to somewhat poorly drained silt loam soils. Slopes where the Lignum is dominant typically range from 2 to 7 percent. Page 6 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle County, Virginia October 14, 2008 Areas surrounding the Wehadkee soil series are characterized by the presence of the Manteo (5113, 51C, and 51D) soil series. The Manteo series is also sparsely present on and along minor ridgetops. Manteo channery silt loam soils are generally described as shallow and somewhat excessively drained. Slopes vary from 2 to 7 percent (51B), 7 to 15 percent (51C), and 15 to 25 percent (51D) respectively. Estimated Ksat values for the Manteo, as illustrated in the Phase II Albemarle County Hydrogeologic Assessment Report, ranged from 0.006 inches/hour to 0.39 inches/hour. The most abundant soil type identified at the site is the Nason (62B & 62C) soil series. The Nason series is characterized as deep, well drained silt loam soils. The 62B Nason soils are located on the gently rolling topography (2 to 7% slopes) whereas the 62C soils are located on the site's steeper slopes (7 to 15% slopes). Estimated Ksat values for the Nason, as illustrated in the Phase II Albemarle County Hydrogeologic Assessment Report, ranged from 0.007 inches /hour to 0.02 inches /hour. Soils from the Tatum (80B) series are noted to be sparsely present along ridgetops located within the property boundaries. Tatum silt loam soils are generally described as deep and well drained. Slopes vary from 2 to 7 percent. Estimated Ksat values for the Tatum, as illustrated in the Phase II Albemarle County Hydrogeologic Assessment Report, ranged from 0.00 inches/hour to 0.03 inches/hour. 6.3 Photo Lineation Interpretation/ Fracture Trace Analysis Stereoscopic analysis of aerial photographs was performed for the purpose of identifying fracture traces or lineaments across the site area. A stereo pair of photographs (NAPP, 40000 scale) were obtained from the United States Geological Survey (USGS). The photographs were dated March 24, 2000 and were representative of leaf -off conditions. The aerial photographs were stereoscopically analyzed with a stereoscope for the presence of straight -line features representative of zones of fracture concentration or lineaments. Seven (7) prominent, or primary fracture traces were observed from the USGS photographs in the area of the site. The majority of these lineations lie along Briery Creek and its' unnamed intermittent tributaries. These observed lineations were transferred to a USGS topographic base map and are presented graphically in Figure 1. The lineations were noted to generally lie in a west - northwest orientation. 6.4 Summary of Hydrogeologic Conditions Based on the findings of this report, the site characteristics appear to conform to the Relative Groundwater Availability Rating as published for the site in the Phase II Albemarle County Hydrogeologic Assessment Report. The site is underlain by Cambrian aged stratified rocks of the Western Piedmont Province. The rock types are described as metagraywacke, quartzose schist, and melange. The site would appear to have somewhat favorable conditions for groundwater wells for individual residential supply, although the presence of dry wells is entirely possible. Page 7 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle County, Virginia October 14, 2008 The bulk of the development is slated to occur in areas dominated by the Nason soil series. The Nason is generally characterized by the Soil Survey of Albemarle County as deep and well drained. Development is also slated to occur in areas where the Tatum, Manteo, and Lignum soil series are present. Generally, the Lignum and Tatum soils are described as deep and well drained whereas the Manteo soils are described as shallow and somewhat excessively drained. It appears that primary lineations are somewhat limited in number across the site area. However, the fracture trace analysis conducted for the site indicated the presence of several prominent linear features which follow the tract of Briary Creek and its' associated unnamed tributaries. The presence of these features indicates that a potential does exist for the completion of suitable individual domestic supply wells at the site. 7.0 BEST MANAGEMENT PRACTICES The Albemarle County Design Standards Manual offers the following advice for coordinating groundwater and stormwater Best Management Practices: If the site also requires a stormwater management/BMP plan in accordance with the Water Protection Ordinance (WPO), then, to the extent feasible, the groundwater BMPs and management plan can be incorporated into the stormwater plan. This would be especially relevant for the use of "non - structural measures" as outlined in Section 17 -313 of the WPO. (DSM, page 2 -25). In general, the BMP plan for the site may consist of the following measures, referenced to the Albemarle County Design Standards Manual, Section 206.2.C.3 — Best Management Practices for Groundwater. • Site Design & House Construction — Locating houses and septic drainfields in a way that does not interfere with or enhances groundwater recharge. Preserving trees and forest cover to promote recharge. The property is currently forested. During development of the property, tree cover will be preserved to the extent feasible. See below under "Landscape & Land Cover" for more detail on the riparian protection strategy. In addition, other measures associated with road and lot drainage may be incorporated to promote groundwater recharge. These may include stormwater measures that are modified to promote recharge. For instance, the standard "Silt Trap Retrofit to Biofilter" design (DSM, figure WR -9) can have a gravel "sump" below the underdrain pipe to allow exfiltration back into the ground. Final decisions on the use of these types of measures will be included with the final plan package. • Landscape & Land Cover — Preserving and restoring trees and forest cover during and after construction, especially in areas likely to be important for recharge. Please Page 8 of 9 Tier III Groundwater Assessment True North Environmental Jefferson Ridge Subdivision Project No. 05 -090 Albemarle Countv. Virginia October 14. 2008 reference the preliminary plat (Attachment A- Sheets 2 & 3) regarding required stream buffers, set -backs from streams and additional mitigation measures. • Education & Outreach — Distribute educational materials for homeowners on the value and use of groundwater, pollution prevention, and water conservation. An educational brochure could be distributed to each lot buyer. This task may be coordinated with any County plans in the works to provide such materials for building permit applicants. The DSM suggests that easements may be provided for long -term monitoring wells (DSM, page 2 -26) with guidance provided by the County monitoring plan. However, the county does not seek an easement at this time. 8.0 CONCLUSIONS True North Environmental, LLC concludes the following: 1. The project site is located in a groundwater availability zone where successfully placed wells possess an average yield of nearly 7 gallons per minute (gpm) (Phase II Albemarle County Hydrogeologic Assessment Report). 2. Based on the subdivision layout, it appears that the highest density of building sites will take place within areas where the Nason soil series is dominant. The Nason series is characterized as being deep and well drained. Other areas of proposed development are underlain by the Tatum and Lignum series, which are also characterized as being deep and well drained. Limited areas of proposed development are underlain by the Manteo series, a shallow and somewhat excessively drained soil. 3. Based on the fracture trace analysis conducted for the site, it appears that primary lineations are relatively limited in number at the site. However, several prominent lineations are present along Briery Creek and its' associated unnamed tributaries. The well yield data utilized from the Phase II Albemarle County Hydrogeologic Assessment Report indicates that wells completed within a relatively close proximity to the site have typically provided a sufficient yield for domestic consumption. The proposed lots are large enough, and topography sufficiently gentle that it should be possible to locate multiple drilling sites on each lot, if the first attempt at constructing a well is unsuccessful, or if a well fails sometime in the future. Page 1 of 1 FIGURES Z_ N b FIGURE 1: SITE LOCATION MAP WITH FRACTURE TRACES �� n 7% �/ /� dle Oa r ~ 532 r• \ Cn New thel 'k t - ' +Ch t fd 581 1 � f i \, fit `:'r; �J / /' � - � `L _ - •.� C"-- 11 BM f 5 535 Y 6�` — — 346 ! r BM �• 512 . f r. f _41.• G 1 i + _ �� • ,ter r TRUE WH i ` LEGEND D Site Boundary �, '- Fracture Trace } o— 1 � � �,1 � d Base Map Source: USGS Albemarle County opograp is Q 0 TRAILER SITE ➢EBRIS--\o PILE DEBRIS (STOVE/ LAWNMOWERS) DEBRIS (LAWNMOWERS) SITE: WOODRIDGE PROPERTY I FIGURE 2: SITE LAYOUT MAP I ENN 1 4 -19 -05 SCALE JOBS' ' =1000' AD5 -24D9 A052409.DWG I MLM 0 1DOC 2000 FEET LEGEND: SITE BOUNDARY 1000' PERIMETER ARUUND SITE Bdundaries TSite Boundary Availability Rating Class 1: Lowest Relative Availability Class 2: Medium Relative Availability Class 3: Highest Relative Availability 12000 Feet Base Map Source: USGS Albemarle County Topographic Map