The URL can be used to link to this page

Home My WebLink AboutACSA199900003 Correspondence 1999-09-13 William lam L. Hodson 797 Gilliams Mountain Road Charlottesville,VA 22903 Telephone:804-295-8676 Fax:804-295-6991 r"- "" r r-� E-mail:DDI4IMAGE@aol.com PCP 14 i999 PLAN J .3 AND Cc:IMUN)TY 11;EV " September 13, 1999 Wayne Cilimberg Director , Planning & Community Development County of Albemarle 401 McIntire Road Charlottesville, Virginia 22902-4596 Dear Mr. Cilimberg: In our application to Amend the Service Authority Jurisdictional Areas dated July 1, 1999, we promised to amend the application with a report from a Geologist and a Dowser. This correspondence conveys reports from Thomas M. Gathright, II, Consulting Geologist and Robert R. Humphris, Dowser. These reports were promised in our application on page 13. I have been advised by David Hirschman that the next step could be a working session with the Board of Supervisors where we could develop a working relationship and address their concerns. This process seems much more productive rather than a formal presentation at a Board meeting as openers Would you initiate that session? The residents at Peacock Hill are anxious to move the application forward as quickly as possible. Thanks again for your assistance, and those of your staff. Sincerely, William L. Hodson Chairman, Peacock Hill's Comprehensive Water Committee cc: Cindy Perfater, Peacock Hill Manager r OMAS M. GATHRIGHT, I CONSULTING GEOLOGIST P.O. BOX 297 BATESVILLE,VIRGINIA 22924-0297 TELEPHONE(540)456-6462 August 8, 1999 William L. Hodson, Fache 797 Gilliams Mountain Road Charlottesville,Virginia 22901 Dear Mr. Hodson, Fache, I have prepared the following report on the geohydrology of Peacock Hills subdivison and the surrounding area at your request. I used water well data compiled by Dr. Nick Evans from files of the Department of Environmental Quality, the Department of Health, and the Virginia Division of Mineral Resources. I have also compiled a fracture-trace analysis of the Peacock Hills property and the adjacent properties from black and white, stereo-pair, aerial photographs and from MSS (multi-spectral scanner) satellite imagery. The bedrock geology was compiled from The Geology of Albemarle County, Wilbur Nelson, 1959 and The Geology of The Mechums River Belt, personal communication Christopher M. Bailey. A field investigation was made by Dr. Evans and I to confirm the geologic evidence presented in the two reports and to develop an understanding of the fracture (joint)trends in the area. Included in the report are a map defining the fracture traces in the total area, the geologic bedrock distribution,and potential drilling sites that have a good potential for acceptable groundwater yields, and a map of the Peacock Hills subdivision showing the approximate locations of both the producing wells and the dry holes drilled for the subdivision with superimposed fracture traces. The report addresses the general geohydrology of the granitic terrain that Peacock Hills is located on, the locations of significant fracture traces near Peacock Hills, and In And drilling recommendations for sites^near the subdivision that may be accessible. Geohydrology: The Peacock Hills subdivision is underlain by granite and granite gneiss formally of the Lovingston Formation. These rocks have no significant porosity or permeability for storage or transmission of groundwater. Water wells drilled in these rocks must encounter open water-filled fractures that receive adequate recharge to be productive. The fractures are generally of two types; near vertical fractures (joints) that commonly occur in two intersecting sets at large angles to each other, and sub-horizontal fractures (release joints)that occur most commonly in the upper± 50 feet of bedrock. For the fractures to be water-bearing, they must be in a locally low topographic position(valley, hollow, etc.)below the local water table and preferably below 25 feet of saturated soil and weathered rock material. The saturated soil and weathered rock material is critical as it provides the groundwater reservoir for the fractures because the fractures have very little volume for groundwater storage. Examination of the 40 water well records for Peacock Hills and the surrounding area that is underlain by the granitic rocks shows that well depths range from 50 to 690 feet, initial yields range from 0 to 38 gallons per minute (gpm) and the median yield and depth is 7.5 gpm and 205 feet respectively. Twenty percent of the yields are 3 gpm or less and 20 percent of the yields are 15 gpm or greater. These data do not include the dry holes that are normally not reported and does not address the accuracy problem with short term yield tests. Generally the long term yield of water wells drilled in fractured rocks is significantly less than those obtained from the 30 minute to two hour tests commonly conducted. Fifty to 75 percent reductions in yield are not uncommon after a few months of continuous use from wells that have high initial yields. This condition indicates that the well site either lacks storage capacity in the overburden or adequate size to the recharge area. The Peacock Hills water system is supplied by six wells that were initially tested at a rate of 38, 28, 17.5, 9, 18, and 12 gpm respectively for wells one through six (Figure 2). This is an aggregate initial yield of 122.5 gpm. A total of 14 wells were drilled to obtain the six productive wells, eight wells being effectively dry holes. The system is capable of supplying a demand of up to about 25,000 gpd(gallon per day) but cannot maintain a supply of 31,000 gpd. A demand of 25,000 gpd is equivalent to an effective aggregate yield of 17.36 gpm or 14 percent of the aggregate initial yield. At 31,000 gpd,the wells cannot maintain an effective yield of 21.5 gpm or 17.6 percent of initial aggregate yield. Assuming there is minimal water loss from the distribution system and that the wells are being pumped on an efficient rotation, the above numbers highlight the low groundwater potential of the Peacock Hills property. Additionally, the fourteen wells drilled on the property have tested virtually all the sites that have any potential or that could be drilled when health department restrictions are considered. Statistically, to add 10 gpm to the long term production to the Peacock Hills water system, eight additional wells averaging at least 500 feet in depth would have to be drilled. Of these wells, three or four would be producing wells and four or five would be dry holes. I do not believe eight drill hole sites are available considering site restrictions. Annual groundwater recharge rates for the upper part of Peacock Hills where the producing wells are located probably ranges between 50 and 100 million gallons. Annual withdrawal rates from the six producing wells probably range up to 10 million gallons at maximum pumping rates. This suggests that the effective recharge area for most of the wells is small and that additional wells could be drilled without approaching annual recharge rates. Fracture trace and lineament study: The generally negative aspects of granitic aquifers can be partially overcome by finding zones of extensively fractured rock that can be intersected by drilling. Fractured rock weathers more rapidly than unfractured rock and if fracture zones are linear, they tend to form linear,topographically low features that are visible on topographic maps, aerial photographs, and satellite imagery. Examination of these images suggests the presence of two significant lineaments in the area. A major lineament parallels Broad Ax, 5-7.4 e( 708 fa 4 />iat w<r t a f"gt 4u.ntR,yar 7-4< seca q J//Hee* -e•rt,4-4e r/tJ P•lra//?/ 1r:4e-titrc Tr.tct.t °//&"vs Creek frommState Road 61'Z and crosses I-64 and Broad Ax Creek with 682. Both of these lineament are in drainages that may be affected by runoff or groundwater migration from the Albemarle County landfill. Many shorter linear fractures are in and around Peacock Hills but they lack the systematic orientation or the suggestion of a rectilinear pattern that would connect them genetically to a specific tectonic stress event. The accessible sites in Peacock Hills provided by these linears have been drilled including the sites for five of the eight dry holes. Also, two of the producing wells were not drilled on suspected fractures. All this indicates that the short(less than 2000 foot long) linears may not be very meaningful. Examination of the property across State Road 708 and adjacent to Peacock Hills property two areas appear to have characteristics indicating a greater potential for groundwater development than is available at Peacock Hills. Field examination and fracture trace analysis verified the presence of a north trending diabase dike on the property and a long parallel fracture trace in the drainage to the east of the dike. The dike is about 800 feet east of the southeastern corner of Peacock Hills and the fracture trace is about 500 feet east of the dike. Both features are positioned to take advantage of a large recharge area unlike the well sites in Peacock Hill that are close to the foot of Gilliam mountain. The importance of these two features is their probable age. The dike is typical of other Triassic or Jurassic dikes in Virginia which are much younger than the granitic rocks they intrude. The dikes were intruded during a period of extensional (tensional) faulting and commonly are accompanied by brittle fracturing in the adjacent bedrock. The parallel fracture trace to the east of the dike may be a parallel fracture zone or fault developed at the time the dike was intruded and may represent an extensive open fracture system. If drilling on the property east of State Road 708 is possible,the first site should be located close to but upstream of the point where the stream crosses the dike. Drilling depths should be less than 300 feet but if water is being encountered near that depth, drillings should continue at least another 50 feet. Dr. Evans or I should be on site if a drill hole site is to be selected. Recommendations: There are four options available to a private water supply system. 1) brill more wells on the property: Considering Healthy Department restriction there may be several areas available for drilling even though those areas may not have the theoretically best hydrogeologic characteristics for a well site. Geologists have a limited number of tools to use in the search for water. It is always possible to find useable supplies of water at unlikely sites but the probability is not great. Possibly deepening the dry holes or drilling deeper wells near some of the dry holes where drilling can be approved would provide useable quantities of water. As I have no information on the depth of these wells this approach may be futile since they may already be very deep. 2) Drill very deep wells: There is very little data on wells deeper than about 500 feet. We know there are fractures and faults that extend to great depths in the Blue Ridge Complex which include the rock units at Peacock Hills. I am aware of open water- bearing fractures(200 gpm) as deep as 4,200 feet in a deep hole drilled in the Blue Ridge. The probability of encountering such a fracture system within the drilling capabilities of most drilling machines seems very small as most are limited to less than 1000 feet. Also, we do not have any data that deep fracture systems are present below the property although we know there are major faults less than two miles to the west. Those faults are probably too old to be water-bearing. 3) Acquire additional property specifically for groundwater development: The potential for groundwater development on the property across State Road 708 to the east of Peacock Hills has already been addressed. Possibly a portion of that property large enough to protect a well site located near the intersection of the diabase dike and the local stream course can be obtained. Certainly an option to buy the property should be acquired dependent on finding an adequate water supply. 4) Revamp the existing water system if necessary: Many water systems, even those as young as the Peacock Hills System, may be experiencing devastating leaks or inefficient pumping schedules. Water flow needs to be metered at the well head, at the input to storage tanks, and at the points of consumption. If this is not done, leaks will go undetected. Considering the disparity between the initial yield tests and the apparent maximum production rates, there is a possibility of significant water loss in the system. As I do not know how the system is monitored, this option may already be in place. Of these options, I believe the one most likely to be successful is option three if the property can be obtained. I am not optimistic about the other options. I believe this report will answer some of your questions on groundwater availability in the area and I will be glad to answer any other questions that I can. Very truly yours, Thomas M. Gathright II . 1CP/t/ll.tf/d17: 6?:141!\:?.. w• l l� �� \ i i •y' -.i)/ f •_, \�.,/ -�, +/ mil; �) r,%. 1 `- `s \� ' •A./ • • + K I -Q•- L � C_' ,V/ , `�V tit —._ � ,,/ ��clrx►n J Rl vcr Irk .� ' ` ), VJ,5 Z t .�:_' � �j/ ---,L of tra ( j., _ tZPOnj � -� ` ( C= �\�frgr I Cvit it , 1 S . .''' "- (- . • fi ., , -irt__,_„... ... \` ---\-- i / ("\--, ' c.---, -.--2 • --- 1: dc-7--_ --., , i/A/ . c......)), . "� ... .,.. .. . .4). ‘i--nghoge _.,_, s-- , 7-A..,f, . (--,-__-:._,Th .4;-, ,-..,_ .„.___, ,,. , ,r-- \ ."'" 1 / - '--\--- ' . );(„?..;,,d,‘ .....__.....) , mGFu.trft Gre♦Ifs i 1., f� 4A • �'r'r� i `�' +r) '.6 ✓,�?/, 1 \� �1 I T •C - — -a a -�_.)7 •N` (,-•r I �C 'may".: 1N) �`► ` _ k' /�� -�i9T_ I _,, +iv ` 1 . � .. . ......----1(4•••"" -2 'gill' (...1V-Laft," 2,1r . I'"; 1,."---/N. ) ' 1*. Sid es e ✓ 0 " _ , , , . •w�i. ' _g p ' ,�`�) 0 r wJ � t pkig.eAt, '..-� l ►•/`' • C <0 I ,• ,�Ji �r`� . ram`\l T h•C, �,iiipatmewt .,.." �L� •� �1 '_ � / 1 ` _ —• � �: ,..jr....iv7 .. ),7-,tom. ` � 1! ' tl �1 �, 1:44 r�a ct 1L1141' �1 )it'o7eu fi.t. () .""'N/kV ...„7 ji(-) fir-, r `, ,t� ,,?] �' �-- : * . 1IP ' iri( -� ,� -H. fic. r TpAC..e --.11-10.,6447......,--.,-- „A\.4,.,:, r"\\,;...•) f - ..,"---.... .)ry/ ' IISV 7 . - -7--_. ----•,..........,'•••••=1.4f, (Praia ble) 11111 , c.. "`\\\\s',\E'r„--:11/4,--'rcc:\j„... ••••-•,.--' ... ., rr-----,7 ,,,,,,,, ' _ 4, cc-_-:,...-...•\••=. -;,-,..„\v,-----\_--- - , - 4 li________„(2e : -..:i, O pr.G41 c(K 9 wall 1 ?, ,_ ^ r .. , k7,,,//, • .3 •(, --No.0ftv.:.i0. • ,74., sacs . (,_.-. ,•\k_..,!.,,.__-- .-7,"7.. .v.-it S/l'z{ yjJ � • , li`mil`` / ` y ,..4 {�/ „�^�� 4 J;�/ ••�� ' -- ,‘. .1-it ,\ - ' --.:. /-'it - • . 'N---/typi i-\,) , -!4.,/-- __J , 1 1 .,i ,__z- ,2,,_ Ji .:.-"r J. 1 L.,,,-----,---— e_,--,,x v 0 • ,ip /- ,,, il\1, 1 .' ,, , , .„.f. i ,..,__ . i 0/12:-\'4_,-,. A i ' - ----, - -',.*=--- . det: / „...,L_____ l7 KsS N S! /Q•f q / ,`j('--4 .,\ cern. ' 1 ' 7,1 .'s.- r." -."-, .( '-...c-9" ---)1 -: : ,, ,....-/,,-, . #. 1 ,1\7-,-7:i '-•' """" 1.._— ^ {//��1 J • •,' �:, ,c.„.. ,...i• .,, .v.• . I �' •'" al { //\ 1 r-.. v , //J/�� r7... i ...f "=3`�l 117,/rtJ 1 '� ' / / 1 /V \\ J (� I 1�/�` �r �'.1:�'��? �. ;{f i'j /�'a /�1 • �J�! +\�,� a{r `.••`^� /�tl,%/// C//+tC to C.to Pi A c.e is il;11 S ci ip 4 4, ^ t1 er Si m s A c B a v e b.t z s,TQ*� 'rank . ` r,.- Peacock lilt - 44°4 ,,,, .. , .., Ory iA1EBER pt.P.►T/cD 1 \ .:"... ,-A i0 0. vh '..J s T! - oft_. : -` =J - •, 6'pp.iIT! PEAesLtc 1,14 •t, 4.4/I £Owir N-3 .<../". _`3 + --, .i- - Ad1.y- �r—r' , )% Not check:4 s.d I T.. /YI. Tit `•- }�. _ ;f. 'r .... �\ ! fS4 R g rt ram-+ • + f J`"'* �' '",--s< ,,. - - �' — . N\I 1 4.,.. ,4' --1-- 3 :-,.: It1411"111E147 . , 79i is ir _.: - t , . - sa ' dell l - t k ,bl % `� a/a// �* t , • Ao. Ni.at ra. � t .. , - 7---''.- '--"'N. , I r - . '. -- leg 6 c -,.%4- --------Th ' t i. Pr l 'far �oJrAiJCiA� \ , 'r��.iirtijoa.,t• , 1" • 3 4 • erwirt �'I!/e 1 I it f aefire .rie- f.::'' .r J1i i • / 4440le/ , -_• Z. AI 0 4, s , . 1f,,A, ,, 44 ir ..ii.. - ., . lig J/ a u,Q, Y , >, (I r t,. 13 ,.a 1 t.,,..t:A fla '. ' ,, : ' • ' ,,,,' ill /000-...,..„,„ .. .0. , • a 6 _ . = Ire • .-r7l- - _.- -. ?_•::s 0 ..... 3 10oi 3 ..... 9-11C)spw, Dim:eda a Wee 1.64 Wee to Ivy Foci.Leh an 437.Right on 708 Peacock Kill on let.Twelve minutes tram tJJNn, 2 5 TRtAMs 2 0 rR 4AAA*