Conserv-Marketplace for Ecosystem Restoration, working with The Center for Sustainable Groundwater, and Virginia Groundwater, LLC, have completed the study Underground Albemarle Revisited: The Role of Groundwater Ecosystem Services in Determining an Optimal Sustainable Population Size for the Charlottesville/Albemarle Community. The study was prepared for the non-profit organization, Advocates for a Sustainable Albemarle Population (ASAP).
The purpose of the study is to consider how groundwater management policy impacts optimal sustainable population size (OSPS) in Albemarle County and The City of Charlottesville, Virginia within an ecosystem services framework. The specific research question explored in this paper is – Does groundwater availability impact the determination of an optimal sustainable population size in Albemarle County and the City of Charlottesville and if so, what is that impact? The study embraces a holistic approach to exploring linkages between human population, land use, surface water and groundwater resources.
The Authors conclude with the following Findings:
Findings
1. New language has emerged in recent years to describe responsible stewardship of groundwater resources.
This report introduces and defines the terms:
- Sustainable groundwater management
- Extractive groundwater services
- Non-extractive groundwater services
- Sustainable groundwater extraction.
2. Geophysical images reveal that groundwater is not uniformly distributed throughout the study area. In addition, the images specifically reveal the following:
- Bedrock fractures are not uniformly distributed, even within the same rock-type on a small parcel of land, and are not always interconnected in a horizontal sense.
- Thickness and water storage and transmission capacity of saprolite (the near-surface sponge composed of weather bedrock) vary from place to place, even within the same rock type. In some geologic settings, the only water available for water supply wells exists in the soils and saprolite, above bedrock.
- Recharge to water-bearing zones in the saprolite and the bedrock may be very local in settings where both hydraulic gradient and interconnectivity among fractures are low. This means that in some situations, recharge may be affected much more by land cover changes in the immediate vicinity, than by activities that take place farther away.
3. The conceptual foundation of sustainable groundwater management is that demand for non-extractive groundwater services receives priority over fulfilling demands for extractive groundwater services.
The maximum amount of groundwater that can be sustainably pumped from the ground is the volume left over after non-extractive groundwater needs have been satisfied.
4. The County’s previous groundwater studies and groundwater policy have been focused on extractive groundwater services.
The 2003 availability report (ENSAT Corporation and others, 2003) focused on absolute amounts of groundwater that occur in different parts of the county, capable of being “captured” for human use by drilling a well. It should be noted, however, that language in support of non-extractive groundwater services can be found in non-groundwater specific County policy, such as the Introduction to the Natural Resources Chapter of the Comprehensive Plan (Albemarle County, 1999).
5. Stream ecosystem health can be used as a proxy for non-extractive groundwater services, and an indicator for sustainable groundwater management.
The percentage of impervious land cover that is a threshold for onset of degradation of stream ecosystem health can be used to quantify the percentage of recharge required to supply non-extractive groundwater services. Locally, the degradation threshold appears to be in the range of 5 to 20% impervious land cover. In terms of groundwater recharge, the threshold of degradation to stream ecosystem health can be estimated at diminution of recharge by 5 to 20%. It follows that 80 to 95% of natural recharge is required to fulfill non-extractive groundwater services. This means that 80 to 95% of recharge must be left in the ground, and that a maximum of 5-20% of groundwater recharge in Charlottesville and Albemarle County can be used for extractive groundwater services.
6. The amount of groundwater available on a given parcel to provide for both extractive and non-extractive services varies as a function of hydrogeology, topography and land cover.
There are settings within the study area where groundwater recharge and flow across a given parcel are very large relative to the volume of groundwater needed for non-extractive services. In these settings, it is theoretically possible to sustainably pump significant quantities of water from the ground, and apply this water to a consumptive use where water is transported away from the local watershed. In other areas, groundwater flow and recharge are limited by hydrogeology and other factors. In these areas, the volume of water available for sustainable extraction may be relatively small.
Albemarle County contains two recognizable zones of high potential for significant sustainable groundwater extraction, and one recognizable zone of low potential (Figure 5, above). The remainder of the County and the entire City are within a zone characterized as having mixed potential. Within this area, site-specific study will be required to identify zones of high or low potential, to the extent that such may exist.
7. The use of groundwater for residential needs in the rural area of Albemarle is non-consumptive, in the sense that most of the water is returned to the ground after use via a sanitary drainfield.
Therefore in most cases, under current 2-acre minimum lot size zoning, domestic groundwater use in the rural areas of the county does not degrade non-extractive services, and is generally sustainable, regardless of hydrogeologic setting.
8. Sustainable groundwater management has implications for sustainable population size.
Under sustainable groundwater management, 80-95% of groundwater recharge is left in the ground to provide for non-extractive groundwater services. Simply stated, this means that under sustainable management, over the long-run, the great majority of groundwater is unavailable for extractive consumption by humans. This would seem to imply that the size of the community’s “sustainable” population may be less than-as presumed in previous assessments of water availability-if all available groundwater were to be extracted to supply human needs.
On the other hand, the impact of sustainable management (or lack thereof) could be particularly significant should Albemarle’s EBRF and MRFZ be utilized for groundwater supply. For example, rather than the 3.9 to 7.8 MGD estimated to be available for extractive services from the EBRF under a sustainable groundwater management regime, approximately 39 to 78 MGD could theoretically be pumped, in the short-term, to facilitate commensurate population growth above and beyond what is sustainable relative to protection of non-extractive groundwater services. The results of unsustainable groundwater mining such as this could be widespread lowering of the water table, causing elimination of base flow in many streams and landscape-scale desertification. Â This has the potential to drastically alter quality of life, and disrupt the local food supply, among other implications for the resident human population.
9. Sustainably managed groundwater could provide a significant proportion of future water needs for the City of Charlottesville and urban areas of the County.
Sustainable groundwater extraction from the Mountain Run Fault Zone (MRFZ) and Eastern Blue Ridge Flank (EBRF) could have a significant impact on maximum sustainable population size for the area. If the County and City were to decide to use groundwater for municipal water supply, a significant portion of the estimated future demand could be supplied via municipal well withdrawals from these two areas.
It should be noted, however, that the County’s longstanding water supply policy is surface-water based. According to Mike Lynn, ACSA Operations Manager, as of August, 2009, the only municipal groundwater system in use by the Authority today is for a small cluster of homes on Red Hill Road.
The following exercise indicates that the EBRF may be capable of supplying from 25 to 49% of the future municipal water demand at build-out:
To estimate the population size at build-out within the County Growth Areas and City combined, we refer to estimates presented in the recent report Estimating Impacts of Population Growth on Ecosystem Services for the Community of Albemarle County and Charlottesville, VA (Jantz and Manual, 2009):
2000 population Build-out population
Charlottesville area                           72,297                                   111,882
Crozet                                               7,101                                     25,106
Rivanna                                             3,960                                     14,205
Route 29Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 12,458Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 60,310
TOTALÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 95,816Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 211,503
(difference between 2000 population and estimated build-out population = 115,687 persons)
According to the ACSA, the average water use for all single family residential customers (persons) is 4100 gallons per month or 137 gallons/day, assuming a 30 day month (Mike Lynn, personal communication, 2009). Applying this figure to the future build-out population of 115,687 persons, an additional 15.8 mgd will be needed.
We estimate the approximate availability of groundwater from the EBRF to be 3.9 to 7.8 MGD. This is equivalent to 25 to 49% of the total future demand needed at build-out of the Growth Areas and City, according to the Jantz and Manual projections.  Additional groundwater capacity of a similar order of magnitude may be available on a sustainable basis from the Mountain Run Fault Zone, and perhaps from other areas yet to be identified within the mixed zone.
10. This study provides a conceptual framework with which to link residential density, stormwater management, impervious land cover, and non-extractive groundwater services in developing growth management strategies (see Recommendation 1 below).
The study can be downloaded from the link below.
A $25.00 donation to Conserv: Marketplace for Ecosystem Restoration or to the Center for Sustainable Groundwater or to Advocates for a Sustainable Albemarle Population is requested from those that intend to use the study for professional purposes.
Please contact Michael Collins at 540-661-7379 or Nick Evans at 434-466-1280 for more information.