Know Your Flood Risk

If you have ever bought a house you should have some idea of what a flood zone is. If the house you bought is within the “100 year flood zone” which is really a 1% annual risk of flooding. It is said to be in Special Flood Hazard Area, SFHA; and requires flood insurance. Moderate flood hazard areas, are the areas between the limits of the base flood and the 0.2% annual chance of flooding (or 500-year) flood. The areas of minimal flood hazard, which are the areas outside the SFHA and higher than the elevation of the 0.2-percent-annual-chance flood, are labeled Zone C or Zone X (unshaded). However, according to FEMA, more than 20% of flood claims come from homes located outside of a high-risk flood zone. Floods can happen anywhere, flood zones just have a higher probability.

FEMA has worked in recent years to update its flood maps, especially in coastal zones, but FEMA’s flood maps are intended for flood plain management, not for mitigation of flood damage for homeowners. The FEMA's maps align with First Street's analysis of current and future flood risk in many areas. However, there are some areas, parts of South Florida and much of the Mid-Atlantic coast, that face higher flood risk than FEMA's maps currently indicate, partly because seas are rising and ocean water is growing warmer, the perfect conditions for more severe storms and hurricanes.

First Street Foundation is a non-profit research and technology group committed to defining America’s flood risk. They have developed a model to evaluate flood risk from multiple sources while also including current and future environmental considerations that may change storm intensity. They have identified this risk on a 1 to 10 scale at the individual property level. This combination of high-resolution scale and national scope brings to homeowners and the public in general a more exhaustive and comprehensive flood risk. According to First Street, FEMA, has undercounted nearly 8 million homes and businesses that face substantial risk of flooding, placing more Americans in jeopardy from coastal storms, rising rivers and flash flooding..

First Street’s Flood Factor model was produced in partnership with researchers and hydrologists from First Street Foundation; Columbia University; Fathom; George Mason University; Massachusetts Institute of Technology; Rhodium Group; Rutgers University; The University of California, Berkeley; and University of Bristol. According to First Street this collaboration makes use of open government data and builds upon decades of research, modeling, and expertise, brought together to develop a high-resolution, property-specific flood risk information at a national scale.

The top five states showing the greatest proportion of properties currently with substantial flood risk* include:

• West Virginia (24.4%),
• Louisiana (21.1%),
• Florida (20.5%),
• Idaho (14.8%) and
• Montana (14.2%),

The states with the lowest proportions of properties that currently have substantial risk are:

• Arizona (3.7%),
• Nevada (3.7%),
• Washington D.C. (5.3%),
• Colorado (5.7%), and
• Maryland (6.2%).

When adjusting for future environmental changes, by 2050 the number of properties with substantial risk across the country will increase by 10.9% to 16.2 million. Louisiana (69.7%), Delaware (21%), New Jersey (19.1%), Florida (18.6%), and South Carolina (16.7%) will see the greatest proportional increase of properties with significant flooding risk over the next 30 years.

The Foundation provides this information for every property in the contiguous U.S., in a format that is publicly and freely accessible via Flood Factor™, (www.floodfactor.com), all you have to do click the link and type in your address or the address of any property you are interested in and the model gives you the flood risk. The tool presents past, present and future flood risk with particular attention paid to recent and projected climate changes that contribute to flood risk. Also, remember that homeowners insurance does not cover damage from flooding, that is a separate flood policy.

Only Rain Should Go Down the Storm Drains

The U.S. Environmental Protection Agency regulates the discharges into the “waters of the United States,” the rivers, streams, estuary and bays, but in the real, everyday world they don’t really work on the local level. In the case of Virginia (and most other states) they actually do this by delegating to the Virginia Department of Environmental Quality the authority to implement the federal Clean Water Act under the Virginia State Water Control Law. While it is the EPA and DEQ who make regulations and inspect for compliance with those regulations, it is the local government, our towns and counties that implements the programs to stop or reduce pollution and encourage compliance with regulations. Prince William County staff translates permits limits and state regulations into action.

The Prince William County department of Public Works implements a series of programs aimed to reduce the release of pollutants into the local stormwater sewer systems to protect our local waterways from pollution to the greatest extent possible. The Prince William County storm water sewer system consists of man-made components (pipes, ditches, and ponds) and natural components (streams, wetlands, and floodplains) that control the flow of storm water to prevent flooding and minimize pollutants entering our waterways. Prince William like much of Virginia, is also engaged in implementing programs to reduce the nitrogen, phosphorus and sediment pollution from the County to not only protect, but to improve the water quality of nearby streams, rivers, wetlands, the Occoquan Bay and ultimately the Chesapeake Bay.

The Chesapeake Bay and its tidal waters have been impaired by the release of excess nitrogen, phosphorus and sediment. These pollutants are released from waste water treatment plants, agricultural operations, urban and suburban runoff, wastewater facilities, septic systems, air pollution and other sources that enter the tributaries and are carried to the Chesapeake Bay. The EPA has mandated a contamination limit called the TMDL (total maximum daily load for nutrient contamination and sediment) to restore the local waters. The TMDL sets a total Chesapeake Bay watershed limit which is a 25% reduction in nitrogen, 24% reduction in phosphorus and 20 % reduction in sediment from the 2011 levels.

The Prince William County Department of Public Works addresses reducing releases from the stormwater sewer system by a series of programs all paid for by the stormwater fee on your property taxes. I spoke with Robert Jocz who is an Environmental Engineer with the County Department of Public Works, Department of Environmental Services in the Watershed Management Branch. Bobby is in charge of the Dry Weather Monitoring Program for the Prince William County stormwater system. He joined the County Staff in 2013 after receiving a master’s degree in Biological Engineering Systems from Virginia Tech. What Bobby and his inspector do is look for illegal discharges (which the U.S. EPA and the County insist on call illicit discharges) into the stormwater sewer system. We talked about the challenges and the new and improved County program and changes that have been made in response to the new stormwater regulation and tighter permit requirements.

Recently, Prince William County set up a demonstration of our stormwater compliance programs for the EPA to use for training state and regional enforcement inspectors. Bobby set up a demonstration of the Dry Weather Monitoring Program at the landfill. There was also a demonstration by Fleet Management Services of their facilities management programs and Fairfax County set up a demonstration of stormwater programs and VDOT. (See EPA Blog for more details.)

​While stormwater itself can be a problem, according to EPA it is a leading cause of pollution in our rivers and streams. When rain falls the stormwater picks up pollution as it flows across roads, parking lots, and open land, picking up oil and grease, litter, dirt and whatever else is on the ground and carrying the water through stormwater sewer systems which have traditionally been only conveyances. They do not treat the water. So any pollution that enters the system get carried right into our rivers, streams, wetlands and bays and this includes any pollution that was intentionally discharged into the stormwater sewer system. All stormwater programs are intended to reduce the flow of pollutants into the stormwater sewer system. Illicit discharges are intentional discharges into the stormwater sewer system; pouring anything down a storm drain is illegal.

Initially, the EPA regulated only the largest industries and city stormwater sewer systems. As the years have passed, EPA has extended regulation down to smaller and smaller entities. In the last few years as regulations have expanded to include stormwater sewer systems outside the urbanized areas, EPA has worked with many municipalities and counties in the region to improve their compliance with stormwater sewer system regulations and permits. Programs have been tightened and expanded to meet the mandated reductions in stormwater volume and pollutants.

As a result, Prince William County and many other local governments have improved their stormwater management programs to further reduce the contamination of stormwater runoff and prohibit illicit discharges into the system by small businesses and individuals. When small businesses wash their company cars and allow the wash water which contains dirt, grease, gasoline to flow into the storm drain in the parking lot, they are essentially pouring that dirty water directly into the Potomac River and Chesapeake Bay. Likewise, small painting contractors washing their brushes or incorrectly disposing of paint containing water down the storm drain, carpet cleaning companies’ disposal of waste water and cleaning solution into the stormwater sewer system, and others who routinely pour small amounts of waste water into the stormwater system are polluting. All these small pollutants add up. The stormwater system only carries water to our waterways, it does not treat it.

Bobby runs the Dry Weather Monitoring Program. A "dry weather condition" is the period at least 48-hours after the most recent rainfall. If it is not raining, there should be limited flow if any in the stormwater sewer system. Dry weather sampling and monitoring is an effort to isolate potential illegal discharges. Occasionally, people knowingly or unknowingly discharge hazardous waste or other non-storm related waste into the stormwater sewer system. When illicit releases are discovered the first step is education. Bobby and his inspector inform the business or individual that what they are doing is illegal, and though the usual reaction is “it’s only a small amount,” small amounts of pollution quickly add up.

from PW County

If the illicit discharge was by and individual, the first step Bobby and his inspector take is to educate and then get them to agree to comply with the regulations. With small businesses or repeat offenders a “Notice of Violation” is issued that gives them 30 days to come into compliance with regulations of face fines up to $1,000 per day. So far there has been no need to issue fines. Bobby and his inspector revisit the sites to verify continued compliance, but in truth they can only spot check. So far, the largest number of violations have been from washing cars.

To clean up the Chesapeake Bay and meet the requirement of the EPA mandated TMDL we all need to change our behavior to reduce small source of pollution to the stormwater sewer system and our waterways. Individuals are still allowed to wash their automobiles in their driveways, but businesses are not. The car wash that was used as a fundraiser for schools has been banned in many communities and is a source of illicit discharge. You can help clean up our rivers, streams, wetlands and the Occoquan and Chesapeake Bays by not dumping any waste, liquid or trash into the stormwater sewer system or onto the ground that drains to the stormwater sewer system. You can also help Bobby and his inspector protect our waterways by reporting any illicit discharges you observe to the Dry Weather Mentoring Program at Prince William County Department of Public Works (703) 792-7070. Remember, only rain should go down the storm drain.

Stormwater Regulation and the Virginia General Assembly

On Wednesday the Virginia General Assembly opened its 2014 session. Paying attention to what happens in the Commonwealth of Virginia is a good way to understand the forces that are shaping our nation. Among the many items expected to come before the Assembly are several bills to delay the implementation of the Virginia Stormwater Management Program that was planned to finally go into effect on July 1, 2014. On that date local governments were scheduled to become the Virginia Stormwater Management Program (VSMP) authorities and the more stringent stormwater management regulations of the Virginia Stormwater Management Act were scheduled to be implemented. Previously, a less comprehensive set of regulations was managed by the Virginia Department of Conservation and Recreation. Recently, oversight for all water programs has been transferred to the Virginia Department of Environmental Quality (DEQ).

As it stands now, on July 1, 2014 every County, City and Town with a municipal separate stormwater system permit (from the U.S. Environmental Protection Agency) in Virginia needs to implement a Stormwater Management Ordinance that complies with the requirements of Virginia’s stormwater regulations and ensure that any land disturbing activities like construction are incompliance with that Stormwater Management Ordinance, the Virginia Stormwater Management Act and associated regulations. These regulations have been in the pipeline for a while and  until recently, I did not fully appreciate that the regulations would require additional staff and skills to develop and implement and that the regulations require user fees to make the program self-supporting. These regulations mean that the each county would have to have employees with the skills and knowledge to understand and manage stormwater, and the DEQ would have to have a data  and tracking system developed to issue permits and additional bureaucracy to perform its portions of the program such as training, maintaining computer systems, developing handbooks etc. The user fees are supposed to pay for the costs, so the cost of construction in the state will increase. Construction is to a large extent dependent on economic development and growth. In recessions there is and low growth economies there is less construction and without construction there are no fees, but the state needs to pay the employees and maintain the computer systems in good times and bad.

Stormwater regulations ensure the control of stormwater from development sites to slow down the flow of rainwater and snowmelt both during construction and in perpetuity after construction is completed. The collective force of unmanaged stormwater scours streams and erodes stream banks, resulting in large quantities of sediment and other pollutants entering streams, rivers, estuaries and bays every time it rains or snow melts. The US Environmental Protection Agency (EPA) believes that sediment and nutrient pollution contained in runoff from urban/suburban areas is the largest source of water quality impairments to estuaries (areas near the coast where seawater mixes with freshwater) in the United States and has turned its water quality focus on these areas starting with the Chesapeake Bay Watershed and the pollution diet the EPA has imposed on Virginia and the other Chesapeake Bay states.

To reduce the damage caused by stormwater and reduce the contamination carried to our rivers and streams and ultimately the Chesapeake Bay, Virginia developed the Virginia Stormwater Management Act and associated regulations to improve stormwater management often using natural processes. These natural processes manage storm water runoff in a way that maintains or restores the site’s natural hydrology, allowing groundwater to recharge. Low Impact Development, LID, is the term for the site level actions and strategies to do this. LID is a strategy of stormwater management emphasizing conservation and natural features combined with small scale stormwater controls to mimic as closely as possible the natural hydraulic properties of a site. The idea is to move water slowly through open conveyance systems and use distributed stormwater retention in open unpaved areas to allow infiltration of rain water into the earth. This reduces the quantity and velocity of stormwater as it leaves a site reducing the damage that uncontrolled stormwater runoff can cause. The stormwater management program is a key portion of the plan Virginia submitted to the U.S. Environmental Protection Agency (EPA) to meet the mandated reductions in pollution under the Chesapeake Bay TMDL imposed on the state by the EPA.

Under the new regulations the counties or cities are required to:

1. Review and approve Stormwater Pollution Prevention Plans (SWPPP) for all construction and land disturbance of more than an acre within the county. These plans need to contain an Erosion and Sediment Control Plan, a Stormwater Management Plan, any additional control measures necessary to address requirements under the TMDL  and appropriate management and control of any on-site chemicals and fuels. 
2. Review and approve registration statement, to obtain the VSMP permit from the state DEQ.
3. Inspect construction sites to ensure activities conform to the approved SWPPP and permit.
4. Enforce the stormwater regulations by having specific violation criteria and a process for the imposition of penalties.
5. Oversee a maintenance program that ensures the ongoing functioning of stormwater management control.

It is likely that the regulations will be delayed because at the last meeting of the Virginia Association of Counties  in the fall, it became apparent that the smaller and more rural counties were not ready to implement the regulation. In addition, many counties were not fully embracing the need or importance of the required stormwater fees that were intended to fund the training and staffing necessary to review plans and ensure that stormwater management strategies work and remain in operation forever. A significant portion of the stormwater fee is intended to go to the state to track data, develop and deliver training both on the basics of the regulations and enforcement of the regulations as well as maintain handbooks and operate the program.

Some of the counties out and out rejected the fee for the state services. Clearly, these communities were not embracing or fully understanding the regulations or simply did not feel that regulatory schemes intended for urban areas should apply to them. Compliance with regulations designed for communities with hundreds of thousands or more than a million residents do not fit well into communities with tens of thousands of residents and is a fundamental problem in the regulated world we live in. In addition, the DEQ itself is not ready, they have not completed the handbook nor completed developing all the training necessary for implementation of the programs. At this time it appears as if a delay of one year will be put into the legislative package.

Until I examined the requirements of the Virginia Stormwater Management Act and associated regulations I did not appreciate how large a challenge it was going to be to meet the current timeline or what the true demands on our communities were going to be from this regulation. Not all areas of the state are Fairfax, Loudoun or Prince William counties and the smallest communities do not have technical expertise to develop and operate these programs or even know how to go about it.

Though regulatory development, oversight and enforcement are costly, they also generate benefits. Regulations protect our health and safety. They preserve the quality of the environment and facilitate efficient operation of markets (real estate, natural resource, financial, commodity- all competitive markets). They protect ownership rights and enforce contractual agreements. We need to be diligent in determining and constantly reevaluating the right balance of regulation, reporting and oversight that produces the desired benefits for society while limiting costs to all of us. Determining the right balance between regulatory cost and benefit is largely based on values and world view. Let your state representatives know your values and views.

Hetch Hechy Valley Restoration Plan on Ballot for November

Picture from SF PUC web site

The Hetch Hetchy Valley is a glacier-carved granite canyon located in Yosemite National Park. Though once described by John Muir as a smaller version of the Yosemite Valley it is currently dammed and used as a reservoir and hydroelectric generator by the City of San Francisco. After obtaining more than 15,000 signatures, a group whose ultimate goal is to restore the Hetch Hetchy Valley has put an initiative on November’s ballot. The initiative would require the city to create a new master plan for their water system based on draining the reservoir and returning Hetch Hetchy to the national park service.

The initiative requires that the water plan include water recycling, water reclamation, conservation, improved storm water capture and increased development, including recharge capability, of groundwater sources and replacing the hydropower from the loss of the dam with solar and wind renewable sources of power. In addition, the plan would have to develop other sources of water supply because all the studies cited on both sides of the argument indicate that the water supply will fall short.

The Hetch Hechy system consist of much more than the reservoir created by the O’Shaughnessy Dam. The system consists of Hetch Hechy Reservoir, Cherry Reservoir and Eleanor Reservoir a portion of the New Don Pedro Reservoir as well as other small surface reservoirs of various size and significance and five groundwater basins.  The stored water in the system is transported to the cities, towns and farms supplied by the system via the Hetch Hetchy Aqueduct, the California Aqueduct, the Delta Mendota Canal, the South Bay Aqueduct, and the Pacheco Tunnel. 

Taken from BAWSCA

Now developing a plan for removing O’Shaughnessy Dam to restore Hetch Hetchy Valley is on the ballot. While many will dismiss the idea as preposterous, enough studies have been done and computer models created that it is fairly certain that the idea is only extremely costly and will reduce somewhat the reliability of the water supply. Billions upon billions of dollars depending on how certain you want your water supply to be, and remember these are costs that would have to be borne by San Francisco water rate payers not the state taxpayers or national taxpayers.

First of all, the inescapable regulatory costs- these costs are certain. While O’Shaughnessy Dam has storage capacity of 360 thousand acre-feet (taf) and the Hetch Hetchy system stores 2,000 taf of water a year, its value is more than that modest amount of water storage. The O’Shaughnessy Dam and Hetch Hechy reservoir provides water storage, hydropower generation, and some flood control, but primarily its value is that water from O’Shaughnessy Dam has filtration avoidance status. Without O’Shaughnessy Dam, the San Francisco Public Utilities System, SFPUC, would have to build a water treatment plant for filtration. New York is currently completing the construction of a new filtration facility to treat the water from the Croton Water System. Though it was originally estimated to cost $950 million, to date its cost has been $2.8 billion. This would translate to a cost of $5-$6 billion to build a filtration plant for SFPUC. Then on top of the construction costs and interest payments, there are the operating costs. Estimates have ranged from $13 million (estimated in 2000) to $20 million annually.

In addition, to replace the storage various solutions have been suggested the most obvious one being increasing the height of the Don Pedro Reservoir to increase its storage. This would require a major construction project. I could find neither feasibility studies nor estimates on the costs associated with that project- the dam cost about $100 million in 1967. Would it cost five times, ten times to expand it now? There is very little recent dam expansion or building data to use to estimate the cost.  However, to effectively replace the Hetch Hetchy storage an inter-tie linking the New Don Pedro Reservoir to the Hetch Hetchy Aqueduct would be necessary to avoid releasing the water through the Delta (and we know how that works out). It would probably cost a couple of billion or more to take care of those two items.

The ballot measure calls for including water recycling, water reclamation, and improved storm water capture in the plan. The reason is there is virtually no other way to obtain enough water for the Bay Area without it. It should be noted that at some time in the future these water reuse strategies will be necessary if the population of the Bay Area continues to grow. There are 993 miles of combined sewers in San Francisco, which collect sanitary sewage from toilets and drains in apartments, homes, schools, offices and other businesses, and street runoff throughout the city. The Water Sustainability and Environmental Restoration Plan would require rebuilding the sewer system to separate the storm water system from the sanitary sewer system and improving the water treatment and recovery of the wastewater treatment plants in San Francisco.

The two major waste water treatment plants that serve the city of San Francisco are the Southeast Water Pollution Control Plant in Bayview built in 1950’s and the Oceanside Water Pollution Control Plant built in 1993. On a dry day the San Francisco combined sewage system treats about 80,000,000 gallons a day of sanitary sewage.   The San Francisco Wastewater Treatment plants are not designed to do any more than screen out trash, skim off scum and grease and use bacterial action to digest toilet paper and bio-solids. Pharmaceuticals, pesticides, hydrocarbons and anything else the residents can think to pour down the drain or dump into the storm drains will either clog the system or be released into the Bay or Ocean. If we are to reuse this water additional treatment would be necessary. Pharmaceuticals, pesticides and other chemicals pass through the system untreated at this time additional treatment and control would be necessary to reuse this water. The cost of these systems would be dependent on the level of treatment desired to drink that water. Washington DC is currently engaged in a plan to upgrade their Blue Plains Wastewater Treatment system that discharges to the Potomac their program is estimated to cost $7.8 billion.

CALVIN (CALifornia Value Integrated Network) is an economic-engineering optimization model of California’s inter-tied water management system. It was developed by Jenkins et al. at the University of California, Davis and has been used to make many of the estimates for feasibility for removal of the O’Shaughnessy Dam and restoration of the Hetch Hetchy valley. CALVIN uses 72 years of monthly historical data to represent future hydrology. They use data from water year 1922 to water year 1993. This period includes the droughts of, 1929-1934, 1976-1977, and 1987-1992, which were some of the worst on record. However, this period of time may not be representative of the severity and duration of droughts and what rainfall will look like in the next decades. Australia’s experience with drought duration last decade should have taught us that.  The driest year in the data was 1924 when the state average rainfall was only 10.50 inches, but in that year the San Francisco Bay region was drier than the rest of the state. The future might hold a worse or longer drought or a regional drought.

An important limitation with CALVIN is perfect foresight; CALVIN knows when the droughts are going to happen and how long the droughts will be. This allows the model to be proactive in preparation for droughts, reducing water scarcity and associated costs. In addition, the model assumes that unlimited amounts of water can be purchased from others (farmers) to make up any shortfall and that there exists a pipe linking the New Don Pedro Reservoir to the Hetch Hetchy Aquitard.

This ballot measure is for the development of the Water Sustainability and Environmental Restoration Plan. This plan has the potential to be forward looking and develop an integrated and robust design for the water and wastewater systems of the Bay Area for the next century. The cost of developing this plan is limited to 0.5% of funds previously authorized by voters for the Water System Improvement Program, WSIP. That translates to $23 million dollars of the $4.6 billion WSIP just to develop a plan that must be completed by November 2015 “in time for the San Francisco Board of Supervisors or a group of citizens to propose a charter amendment to be voted on at the November 2016 election, which if passed would authorize implementation of the plan.”

Even this ballot measure is a significant decision for the residents of San Francisco, and about much more than restoring the Hetch Hetchy Valley. This is a first step on the road towards rebuilding the entire, water storage, treatment and sewer system for the Bay Area  as well as replacing the hydroelectric power from O’Shaughnessy Dam with other (hopefully) renewable power. The full implementation of the plan could easily cost San Francisco rate payers $10-$20 billion for infrastructure. I assume that funds to restore the Hetch Hetchy Valley would come from donations or the federal park service. The $23 million that the ballot measure authorizes for the study may not be enough to develop a fully integrated and workable plan, for transport, sewers, water treatment, water recycling and power generation let alone hold the necessary public hearings and outreach in San Francisco.    

The Rural Crescent, the Occoquan and the Water Supply

The Board of Supervisors of Prince William County have allocated $60,000 to engage a study to examine if the goals desired from the creation of the Rural Area of the county have been met through the implementation and management of the Rural Crescent. In addition, the study is to identify other rural preservation tools that would allow the elimination of the Rural Crescent restrictions on development density. This is a direct result of a motion by Supervisor Martin Nohe at the regular March meeting of the Prince William County Board of Supervisors.

The Rural Crescent was created in 1998 and originally intended as an urban growth boundary for the county designed to preserve the agricultural heritage and force redevelopment along the Route 1 corridor rather than development in the remaining rural areas. This was to be accomplished by limiting development to one home per 10 acres with no access to public sewers. The Rural Crescent has been chipped away at for years, but still contains 80,000-acres; however, active farming in Prince William continues to decrease.  To adequately judge the utility of the Rural Crescent the study must consider its impact on water resources and water ecology. While the Rural Crescent may have been the wrong policy to preserve our agricultural heritage, it has been a success at preserving water resources, protecting our groundwater and supporting the ecosystem of our estuary. In addition, continued redevelopment of areas with preexisting infrastructure will allow Prince William County to improve storm water management in those areas and score nutrient points for the EPA mandated TMDL as well as revitalize older areas of the county and support of sustainable development. The Rural Crescent is about water, specifically groundwater.

The Rural Crescent in Prince William aligns roughly with the Culpeper groundwater basin, one of the more important watersheds in Virginia and essential to the health of the Occoquan Reservoir which in turn is an essential element in the drinking water supply of Fairfax Water - Prince William Service Authority, PWSA, obtains most of the drinking water they distribute in the county wholesale from Fairfax Water. Besides purchased water from Fairfax Water, PWSA operates the Evergreen water wells that draw water directly from the Culpeper Basin and thousands of home owners have private wells that also draw from the aquifer. The Virginia-American Water Company also distributes water purchased from Fairfax Water. Any changes in land use have the potential to negatively impact groundwater, the watershed and the Occoquan Reservoir and should be considered in the study of “other preservation tools.”  

The Rural Crescent is located within the northeast quadrant and eastern quadrant of the Culpeper basin and consists of an interbedded sequence of sedimentary and basaltic that is highly fractured and overlain by a thin cover of overburden. While ground water flows generally speaking west to east, the fractures within the rock run predominately north south. Contaminants can enter the groundwater at these fractures and zigzag through the aquifer, but these fractures also serve as recharge areas. Groundwater is typically protected against contamination from the surface by the soils and rock layers covering the aquifer, but there is inadequate overburden in much of the Rural Crescent. Once contaminated, groundwater is very difficult to clean and in a fractured rock system there is limited if any natural attenuation and the aquifer could be polluted beyond our ability to remediate.

Generally, groundwater in the Culpeper Basin is replenished each year through precipitation. Groundwater recharge through precipitation requires adequate area for infiltration of rainwater, control of sheet flow created by roads and paved areas, as well as protecting the most geologically favorable infiltration points. Precipitation and snow melt flows over the ground as surface runoff. Not all runoff flows into rivers, much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes the saturated subsurface rock of the aquifer, which store huge amounts of freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into rivers, creeks, and ponds as base flow for the rivers, and some ground water finds openings in the land surface and emerges as fresh water springs.

According to the U.S. Environmental Protection Agency, impervious cover levels of 10% can significantly impact watershed health increasing stormwater runoff. When runoff volume increases, runoff velocity increases, and peak storm flows causes flooding and erosion.  Increased stormwater velocity increase soil erosion, increases nutrient contamination and reduces water infiltration into groundwater. The groundwater is essential as the base flow to the streams and rivers that feed the Occoquan Reservoir during the dry months. The groundwater stored in the watershed can supply adequate water to maintain river flow during droughts. Maintaining open areas provides areas of groundwater recharge and controls runoff. Decisions about the fate and management of the Rural Crescent will impact groundwater quantity and quality and in turn will impact water flows to the Occoquan Reservoir during dry periods.  Flow to the Occoquan Reservoir is essential in managing the drinking water withdrawals from the Potomac River.  The Interstate Commission on the Potomac River Basin, ICPRB, manages the Potomac River drinking water allocations for the entire region by “suggesting” the quantity that Fairfax Water draw from the Occoquan and Potomac daily.  Prince William County’s decision on the fate of the Rural Crescent could impact drinking water supplies in Fairfax, Maryland, and DC as well as our own county.

 

The “rural preservation tools” to be investigated as part of the study are sustainable community concepts, high density communities utilizing the strategies of Low Impact Development, LID, which include dedicated open space. While high density communities built adjacent to dedicated open space of cute community farms as is being done in Loudoun might preserve our agricultural heritage, it will not guarantee the preservation of our ecosystem and water. When development disturbs more than 10% of the natural land by covering surfaces with roads, driveways, walkways, patios, and homes the natural hydrology of the land is disturbed, irreparably disturbed. These developments while much better than traditional developments still disturb more than half the land area by significantly increasing building density. 

The lack of overburden limits natural protection to the aquifer, but has allowed easy infiltration. The sedimentary rocks of the Rural Crescent are productive aquifers and feed not only the groundwater wells that provide drinking water to Evergreen and other communities, but also feeds the tributaries to Bull Run assuring the base flow to the rivers and streams that feed the Occoquan. Our freshwater resources need to be managed as a whole. Development that will impair the recharge of the aquifer can result in impacts to the entire region, including the decrease in water level and aquifer storage, reductions in stream base flow and lake levels, loss of wetland and riparian ecosystems, saltwater intrusion and changes in groundwater quality. Our future and our children’s future is our water. We can’t allow it to be destroyed  in paving roads and building houses for short term gain.