Thursday, March 15, 2012

Raspberry Falls Bearing the Cost of Water Problems in Karst Terrain

The karst area of Loudoun County is contained within the limestone overlay district that was created in 2010 when Loudoun County Board of Supervisors approved the re-adoption and re-enactment of the Limestone Overlay District (LOD). This district is the area of the county generally north of Leesburg and east of the Catoctin Mountains which is underlain by limestone conglomerate bedrock and runs north along Route 15. The LOD is really an amendment to the zoning to try and address the ecological and environmental challenges associated with karst terrain. The LOD attempts to ensure that the groundwater supply is capable of supporting needs of the eventual inhabitants of new subdivisions and the land can support the septic needs of current and future residents without impacting the water supplies of existing residents and creating sinkholes that could endanger their properties. Karst terrain is fragile and ignoring the limits of natural systems can have serious consequences.

Raspberry Falls is a clustered development around a golf course in the LOD of Loudoun County. While clustered development usually involves fewer disturbances to natural landscape, and is encouraged in low impact development designs, golf courses are not a low impact design feature. The groundwater pumping to feed the homes and water the golf course may create or exacerbate problems in karst terrain, especially during droughts. The turf management herbicides can also be a problem. The Raspberry Falls development was originally approved for 206 homes and currently has, I believe, 134 homes that are served by a community water system consisting of two wells built out by the developer and operated by Loudoun Water. The system has been plagued by the bacterial problems that are a common problem with karst terrain. Fractures in the overlying limestone become enlarged over time and provide a direct route of surface water to groundwater. Sinkholes proved another direct path for surface contaminants to enter the groundwater as do sinking streams and rivers. The faster water moves into the ground the higher the likelihood that bacteria will remain alive and nitrate is not going to denitrify. When that happens the groundwater is deemed to be, Groundwater Under is the Direct Influence of Surface Water or GUDI. A water source is determined to be GUDI if more than 10% of total coliform numbers exceed 100 cfu/100 mL.

One of the water supply wells for Raspberry Falls was determined to be GUDI by the Department of Health and taken out of service and replaced this past year by a new well at a cost of almost a million dollars. Replacing the well solved the problem for the short term, but experience in the western third of Virginia has demonstrated that the GUDI condition could impact the other wells. Local septic systems did not appear to be the source of bacterial contamination, but E coli numbers were not broken out in the raw water data by Loudoun Water, only total coliform. However, wastewater in Raspberry Falls is collected and treated to a at the community wastewater treatment plant (WWTP). Most organic material and nutrients are removed through biological treatment before being disinfected and discharged to an unnamed tributary of Limestone Branch.

Though the GUDI well was replaced with a new well (and right now the water meets all the standards of the Safe Drinking Water Act), additional treatment beyond the current chlorine disinfection of the drinking water is being considered because of the relatively easy connection of surface water to groundwater, the unconfined nature of the groundwater aquifer and probably the immediate problems with turbidity that the new well experienced. Two options were considered and studied by Hazen and Sawyer (Loudoun Water’s consultant): the extension of municipal water from Leesburg into the Rural Policy Area that encompasses Raspberry Falls or the installation of membrane filtration for all Raspberry Falls water supply wells as an additional water treatment step. The extension of the municipal water pipeline would involve an amendment to the Loudoun County Revised General Plan to authorize extending the pipeline and the Town of Leesburg would need to accept ownership and operation of the Raspberry Falls Community Water System.

The costs associated with the installation of membrane filtration and operation were $4 million for purchase and installation and $67,000 additional in annual operation costs for Raspberry Falls only. Loudoun Water estimates that the cost per lot would be an additional $1,830/year for membrane filtration. The Town of Leesburg estimated the construction cost of the pipeline at $7.5-$8 million, with annual operating costs of $418,000 and an annual cost per lot of $4,260/year. The recent water rate increase does not take into consideration either of the options under consideration. The membrane filtration was the cheaper option, and would still carry significant costs that would ultimately be paid for by the water system customers. Loudoun Water appears to prefer the cheaper membrane filtration system, and though residents might suspect business concerns took precedence over water quality issues, it may be an excellent solution given what is known about the source water quality. Loudoun Water has requested that Loudoun County and the Town of Leesburg decide whether to pursue the pipeline extension no later than May 2012 otherwise they will proceed with installation of membrane filtration at Raspberry Falls.

There appears to be many residents who strongly support the pipeline/ Leesburg water solution despite the higher cost. Appropriately, many residents are only concerned about obtaining the best water supply possible, but the pipeline may not be that answer. Personally, after reviewing the US Geological Service (USGS) raw water studies and the USGS and US Fish and Wildlife (USFW) studies into skin lesion on bass in the southern branch of the Potomac River, I would hesitate to pay extra to drink water sourced from the Potomac River without advanced nanomembrane filtration. The USGS found fish suffering from a variety of lesions. Some fish had bacterial lesions, some fungal lesions, and some fish had parasite. The USGS concluded that there was no specific cause of the lesions and that the fish appeared to be immunosuppressed so that any pathogen in the water could attack the fish. A series of studies were performed over a period of years. During the investigation it was discovered that male fish had immature female egg cells in their testes and the females had lowered levels of an essential protein in the formation of eggs. The bass suffering from lesions were intersexed.

It had previously been demonstrated that estrogen and estrogen mimicking compounds can cause intersex. The occurrence of intersex among the lesioned fish prompted further studies. The study found the problem of endocrine disruption in fish to be widespread in the limited study area of a portion of the Chesapeake Water Shed and Potomac River, but increased in proximity to and downstream of the waste water treatment plants. Chemical sampling that took place along with the fish sampling found higher concentrations of waste water chemicals near the waste water plants. Pesticides, herbicides and their breakdown products currently used in agriculture were detected at all locations. Hormones were not detected in the samples, but analysis using yeast screening assays found estrogenic endocrine-disrupting chemicals at all locations their specific source is not yet known. None of these chemicals are currently regulated under the Safe Drinking Water Act, SDWA, and so would not be tested for or treated by the Leesburg town water treatment system except by happy coincidence.

Before the residents of Raspberry Falls choose a solution to their water problems they should consider carefully the quality of the source water and finished water. USGS groundwater source studies have also found the presence of the gasoline additive MTBE, the solvent 1,1-dichloroethane, and the herbicide breakdown products from alachlor and atrazine in a significant percentage of groundwater supply wells in unconfined aquifers. The herbicide degradates are not regulated by the USEPA in drinking water under the SDWA, so these contaminants are not tested for in drinking water and there are no known health screening levels. Though these herbicides are widely used in agriculture and turf management for golf courses and the herbicide degradates may be regulated by USEPA under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Though whatever solution Loudoun County Supervisors and the residents of Raspberry Falls choose will have additional costs associated with it, this is a rare opportunity to select your source water and potentially your treatment method after purchasing your home. Performing extensive source and finished water analysis before making a final decision might be very worthwhile in this instance.

1 comment:

  1. Good advice. Performing a comprehensive "source water" assessment is a logical next step. As a karst hydrogeologist who is very familiar with the Raspberry Falls and Selma situation, a geotechnical fix to the problem of bacterial contamination to the local groundwater is very real possibility. Cost-wise, a geotechnical fix would most likely fall in the $500K to $1million dollar range, based upon similar fixes that have been implemented at other sites. A karst hydrogeologic assessment would be designed and implemented to locate and characterize conduits through which bacteria are transported to the water supply wells of Loudoun Water. Karst aquifers are unique in that water flows through discrete "pipe-like" features in the bedrock. Those specific "pipes" that are transporting contaminated water could potentially be sealed with impermeable materials, rendering the remaining water flow to the wells as non-contaminated. Thus, eliminating the need for (expensive) pipelines and membrane filtration, and the associated long-term operating costs. Sincerely, Jim L. Lolcama, KCF Groundwater, Inc.