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Comments
by Nick Evans on the Rivanna Water & Sewer Authority's The VHB report evaluates more than 30 alternatives that could be included in long-range planning to meet a projected water supply shortfall for Charlottesville and urban Albemarle of about 15 million gallons per day (mgd) by the year 2050. Some of the alternatives involve costly new infrastructure, some involve costly modifications to existing infrastructure. Some are environmentally and culturally disruptive; others, relatively benign. The VHB study attempts a rigorous cost-benefit analysis of each alternative independent of the others; it does not attempt to analyze the implications of coupling alternatives or phasing various alternatives in over time. This quickly becomes a very complex game. We can simplify the matter of sifting through all of this if we recognize, first, that several alternatives included in the report are clearly impractical or unworkable, and can be discarded outright. These include such notions as conventional groundwater withdrawal, aquifer storage and recovery, and conversion of either Chris Greene Lake or the South Fork Rivanna Reservoir to pumped storage facilities. Next we can recognize that a few of the alternatives should be integral to whatever plan we come up with, and should not considered optional. Water conservation…. Our community needs to become aware that water is not an unlimited resource, and that during times of drought we all need to do our share to conserve water. A combination of conservation pricing structure, designed to reduce discretionary water use during peak use periods, and public education on water conservation should be a part of the program. According to VHB, these actions can buy us 1.67mgd increased safe yield in the year 2050. Are we prepared to write-off the South Fork Rivanna Reservoir (SFRR)? We live in a throw-away society where many things from cars to computers are considered disposable when they break. Have we evolved to a point where it's acceptable to throw away our reservoir? We either need to decommission the SFRR and remove the dam (a process that would be neither inexpensive nor environmentally inconsequential), or we need to plan on performing necessary, if costly maintenance on the reservoir, and do what we can to reduce maintenance costs in the future. This means removing (dredging) the silt and sand that have partially filled the reservoir (reducing its capacity to store water), and taking steps to reduce the amount of sediment that enters the reservoir in the future. Several alternatives described in the VHB report are contingent on utilizing the existing (or in some cases expanded) raw water intake and treatment plant located at the SFRR dam. If there is no dredging program, and if sediment influx to the reservoir is allowed to continue unabated, it is only a question of time before we have a big swamp in our collective back yard, and a silted-up water supply intake facility. Any analysis of costs / benefits of dredging the reservoir must consider the costs of "no action"…..in reality, "no action" is not an option. VHB says dredging the SFRR can gain about 7.2 mgd increased safe yield in the year 2050. How can we keep the sediment from getting into the reservoir in the first place? The County has been in the business of protecting the SFRR from sedimentation and other threats since the early 1970's. These efforts culminated in the 1998 Albemarle County Water Protection Ordinance, which is aimed squarely at erosion and sediment control and stormwater management. In the years to come, the County is going to be applying increasing amounts of resources to enforcing the ordinance, and maintaining/upgrading stormwater management structures. On the agricultural side, the Thomas Jefferson Soil & Water Conservation District will continue to administer programs such as the VA Agricultural Best Management Cost-Share Program, which assist farmers in implementing farming practices that minimize sediment run-off into streams and rivers. Unfortunately, there are indications that to date these activities have achieved only marginal success in reducing sediment load in rivers and streams. Recent figures on sediment loading in the James River show only a 2 percent reduction following a decade of work and millions of dollars spent regionally on erosion & sediment control and agricultural BMP's. It may be time for us to reconsider our approach to this problem…...simply put, we need to rethink where the sediment is actually coming from and target our strategies accordingly. Most of our efforts to date have been directed toward preventing sediment from being washed overland through the riparian zone (strip of land bordering the stream), and into the stream. These efforts have not been misguided and should continue, but we need to recognize that there are huge volumes of sediment in the bottoms and sides of the stream channels themselves, ready and waiting to be plucked into suspension during periods of high stream flow. We need to be implementing strategies to stabilize banks and channels, targeting large pockets of unconsolidated sediment (alluvial material in flood plains) on the two major contributors of sediment to the reservoir, Mechums River and Ivy Creek. Given the likelihood that we are never going to totally eliminate influx of sediment into the reservoir, we should be looking into installing sediment traps in the upper reservoir (and/or lower Mechums River and Ivy Creek), that could be cleaned out on a periodic basis. Could the projected demand be met with modifications to our existing infrastructure? The answer is yes. Dredging the reservoir and managing sediment load are necessary components of a long-term water supply plan, but they will not of themselves enable us to meet the projected 2050 demand. Two of the other alternatives involve modifications to both the SFRR and to Chris Greene Lake. One would raise the elevation of the pool on the SFRR by four feet; the other involves constructing a pipeline in order to utilize water from Chris Greene Lake (to a maximum draw down of 5 feet) via an existing treatment facility on the North Fork of the Rivanna River. Not only do these two alternatives make practical sense in that they take advantage of existing infrastructure, but they also entail manageable levels of adverse environmental and societal impact. And they are relatively inexpensive. In concert, these two alternatives increase the safe yield of the system by about 9.9 mgd, or 66% of the projected demand in the year 2050. While projected increases in safe yield for various alternatives are not additive in a simple sense, the VHB numbers imply that these two alternatives plus water conservation, dredging and aggressive sediment control could more than satisfy projected demand in 2050. What if we still come up short……do we need to build another reservoir? The answer is no. Of the alternatives that involve major investment in new infrastructure, there is one that stands out from all of the others as being consummately sensible and environmentally sustainable. This alternative involves enhancing the wastewater treatment facility at Moore's Creek, and pumping treated water westward through a pipeline adjacent to Interstate 64, to a discharge point in the Mechums River (or, at additional expense, the Moormans). The water would then flow downstream into the SFRR, and recycle through the system. This proposal is far less environmentally or culturally disruptive than any of the alternatives involving new dams and reservoirs. It may actually be beneficial to the ecology of whichever stream receives the recycled water. By way of comparison, the projected dollar cost of the pump-back/recycle alternative is about the same as the projected dollar cost for the Buck Mountain reservoir alternative. Pump-back/recycle is a long-term strategy that theoretically could be developed to serve a demand far greater than that projected by VHB for 2050, and beyond the long-term safe yield of any new reservoir alternative. Nick H. Evans, PhD PG
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