Dalecarlia Reservoir

{{Infobox body of water

| name = Dalecarlia Reservoir

| image = {{Location map

| USA District of Columbia#USA

| width = 250

| float =

| border = black

| caption =

| alt =

| relief =

| AlternativeMap =

| label = Dalecarlia Reservoir

| label_size =

| position =

| background =

| mark =

| marksize =

| link =

| lat_deg = 38

| lat_min = 56

| lat_sec = 32.83

| lat_dir = N

| lon_deg = 77

| lon_min = 6

| lon_sec = 37.05

| lon_dir = W

}}

| caption =

| image_bathymetry =

| caption_bathymetry =

| location = Bethesda, Maryland / Washington, D.C., U.S.

| coords = {{coord|38|56|33.0216|N|77|6|36.1548|W|type:waterbody_region:US|display=inline,title}}

| type = Reservoir

| inflow = Washington Aqueduct

| outflow =

| catchment =

| basin_countries = United States

| length =

| width =

| area = {{convert|50|acre|abbr=on}}

| depth =

|pushpin_map=Maryland

| max-depth =

| volume =

| residence_time =

| shore =

| elevation = {{convert|45|m|order=flip|abbr=on}}{{gnis|584007}}

| islands =

| cities =

}}

Dalecarlia Reservoir is the primary storage basin for drinking water in Washington, D.C., and Arlington County, Virginia. The reservoir is fed by an underground aqueduct in turn fed by low dams which divert portions of the Potomac River near Great Falls and Little Falls.{{cite web |title=Washington Aqueduct, District of Columbia, VA and MD; Fact Sheet |url=https://usace.contentdm.oclc.org/digital/collection/p16021coll11/id/647 |date=2023-02-21 |publisher=U.S. Army Corps of Engineers, Baltimore District |location=Baltimore, MD}} The reservoir is located between Spring Valley and the Palisades, two neighborhoods in Northwest Washington, D.C., and Brookmont, a neighborhood in Montgomery County, Maryland.

History

The {{convert|50|acre|m2|adj=on}} reservoir was completed in 1858 by the United States Army Corps of Engineers (USACE) as part of the Washington Aqueduct project.{{cite report |title=Proposed Water Treatment Residuals Management Process for the Washington Aqueduct: Environmental Impact Statement. Vol. 1. |url=http://washingtonaqueduct.nab.usace.army.mil/Residuals/DEIS/Volume1.pdf |date=2005 |publisher=Washington Aqueduct Division, Baltimore District, U.S. Army Corps of Engineers (USACE) |location=Washington, D.C. |page=3-32 |archive-url=https://web.archive.org/web/20130216144647/http://washingtonaqueduct.nab.usace.army.mil/Residuals/DEIS/Volume1.pdf |archive-date=2013-02-16}} It began providing water on January 3, 1859.{{cite book |last=Ways |first=Harry C. |title=Montgomery C. Meigs and the Building of the Nation's Capital |chapter=Montgomery C. Meigs and the Washington Aqueduct |date=2001 |editor-last1=Dickinson |editor-first1=William C. |editor-last2=Herrin |editor-first2=Dean A. |editor-last3=Kennon |editor-first3=Donald R. |publisher=United States Capitol Historical Society/Ohio University Press |location=Athens, Ohio |isbn=9780821413975 |page=34}} Initially the reservoir provided water to the city from the adjacent Little Falls Branch until the aqueduct construction was completed. Regular water service from the Potomac River source through the aqueduct commenced in 1864. The reservoir was modified in 1895 and 1935 to improve water quality and increase water supply.{{cite book |last=Ways |first=Harry C. |title=The Washington Aqueduct: 1852-1992 |url=https://books.google.com/books?id=DSe2RvdI7TsC |date=1996 |publisher=U.S. Army Corps of Engineers, Baltimore District |location=Baltimore, MD}}{{rp|75,99}}

In the 1920s a water purification plant was built adjacent to the reservoir. The rapid sand filter plant began operation in 1927.{{rp|101–105}} {{cite book |last=Scott |first=Pamela |year=2007 |title=Capital Engineers: The U.S. Army Corps of Engineers in the Development of Washington, D.C., 1790-2004 |chapter=Chapter 5. The Expanding City, 1915-50 |url=http://140.194.76.129/publications/eng-pamphlets/ep870-1-67/toc.htm |pages=204–205 |location=Washington, D.C. |publisher=U.S. Army Corps of Engineers |isbn=978-0160795572 |archive-url=https://web.archive.org/web/20090722205704/http://140.194.76.129/publications/eng-pamphlets/ep870-1-67/toc.htm |archive-date=2009-07-22 |access-date=2023-03-24 |id=Publication No. EP 870-1-67}}

In 1942, the headquarters of the Army Map Service was established on the grounds adjacent to the reservoir; several buildings constructed in the 1940s still exist. In 1946, its headquarters moved to the nearby Sumner Site, which is today the Intelligence Community Campus-Bethesda.{{Cite web |url=https://mht.maryland.gov/secure/medusa/PDF/Montgomery/M;%2035-133.pdf|title=Army Map Service Historic District |last=Horton |first=Barbara |date=2004-02-02 |website=Maryland Historical Trust |pages=1–3|url-status=live |access-date=2019-10-15|archive-url=https://web.archive.org/web/20170203000220/https://mht.maryland.gov/secure/medusa/PDF/Montgomery/M;%2035-133.pdf |archive-date=2017-02-03}}

Until the early 21st century, the semi-solid residuals (sludge) produced by the treatment plant were periodically discharged to the Potomac River. The U.S. Environmental Protection Agency (EPA) required USACE to halt most of these discharges, and a residuals handling facility was built on site, which went into operation in 2012.{{cite web |title=Water Treatment Residuals Management Project |url=https://www.nab.usace.army.mil/Missions/Washington-Aqueduct/Ongoing-Projects-Studies/ |website=Washington Aqueduct |access-date=2023-03-30 |publisher=USACE}}{{cite web |title=Fact Sheet: NPDES Permit No. DC0000019 |url=https://www.epa.gov/sites/default/files/2021-04/documents/aqueduct_final_fact_sheet_april.11.2021.pdf |date=2021-04-13 |publisher=U.S. Environmental Protection Agency |location=Philadelphia, PA}}

Current operation

The reservoir and water treatment plant are operated by the Washington Aqueduct, Baltimore District, U.S. Army Corps of Engineers.{{cite web |title=Washington Aqueduct |url=https://www.nab.usace.army.mil/Missions/Washington-Aqueduct/ |publisher=U.S. Army Corps of Engineers |location=Baltimore, MD}}

Climate

File:Residuals processing facility - Dalecarlia Reservoir - Washington Aqueduct - 2011.jpg

According to the Köppen Climate Classification system, the area has a humid subtropical climate, abbreviated "Cfa" on climate maps. The hottest temperature recorded at Dalecarlia Reservoir was {{convert|105|F|C|1}} on August 17, 1997, while the coldest temperature recorded was {{convert|-11|F|C|1}} on January 21, 1985.

{{Weather box

|location = Dalecarlia Reservoir, Maryland, 1991–2020 normals, extremes 1948–present

|single line = Yes

|collapsed = Yes

|Jan record high F = 79

|Feb record high F = 82

|Mar record high F = 91

|Apr record high F = 95

|May record high F = 98

|Jun record high F = 100

|Jul record high F = 103

|Aug record high F = 105

|Sep record high F = 99

|Oct record high F = 95

|Nov record high F = 87

|Dec record high F = 82

|Jan avg record high F = 65.7

|Feb avg record high F = 68.0

|Mar avg record high F = 77.9

|Apr avg record high F = 87.1

|May avg record high F = 91.9

|Jun avg record high F = 96.0

|Jul avg record high F = 98.0

|Aug avg record high F = 96.6

|Sep avg record high F = 92.1

|Oct avg record high F = 84.4

|Nov avg record high F = 75.3

|Dec avg record high F = 67.2

|year avg record high F = 99.3

|Jan high F = 42.9

|Feb high F = 46.4

|Mar high F = 54.8

|Apr high F = 67.6

|May high F = 75.7

|Jun high F = 84.0

|Jul high F = 88.2

|Aug high F = 86.2

|Sep high F = 79.4

|Oct high F = 68.0

|Nov high F = 56.4

|Dec high F = 46.9

|year high F =

|Jan mean F = 34.2

|Feb mean F = 36.8

|Mar mean F = 44.2

|Apr mean F = 55.6

|May mean F = 64.7

|Jun mean F = 73.4

|Jul mean F = 78.1

|Aug mean F = 76.3

|Sep mean F = 69.3

|Oct mean F = 57.4

|Nov mean F = 46.4

|Dec mean F = 38.3

|year mean F =

|Jan low F = 25.5

|Feb low F = 27.3

|Mar low F = 33.5

|Apr low F = 43.6

|May low F = 53.7

|Jun low F = 62.8

|Jul low F = 68.0

|Aug low F = 66.3

|Sep low F = 59.2

|Oct low F = 46.8

|Nov low F = 36.4

|Dec low F = 29.6

|year low F =

|Jan avg record low F = 9.2

|Feb avg record low F = 13.2

|Mar avg record low F = 18.5

|Apr avg record low F = 29.0

|May avg record low F = 39.2

|Jun avg record low F = 50.1

|Jul avg record low F = 57.6

|Aug avg record low F = 55.3

|Sep avg record low F = 45.6

|Oct avg record low F = 31.9

|Nov avg record low F = 22.4

|Dec avg record low F = 16.3

|year avg record low F = 7.8

|Jan record low F = -11

|Feb record low F = -1

|Mar record low F = 5

|Apr record low F = 17

|May record low F = 23

|Jun record low F = 30

|Jul record low F = 42

|Aug record low F = 41

|Sep record low F = 31

|Oct record low F = 16

|Nov record low F = 8

|Dec record low F = -2

|precipitation colour = green

|Jan precipitation inch = 3.32

|Feb precipitation inch = 3.24

|Mar precipitation inch = 4.15

|Apr precipitation inch = 3.53

|May precipitation inch = 4.44

|Jun precipitation inch = 4.24

|Jul precipitation inch = 5.11

|Aug precipitation inch = 4.42

|Sep precipitation inch = 4.54

|Oct precipitation inch = 4.40

|Nov precipitation inch = 3.32

|Dec precipitation inch = 3.81

|year precipitation inch =

|unit precipitation days = 0.01 in

|Jan precipitation days = 10.0

|Feb precipitation days = 9.3

|Mar precipitation days = 11.5

|Apr precipitation days = 11.1

|May precipitation days = 11.7

|Jun precipitation days = 10.1

|Jul precipitation days = 10.3

|Aug precipitation days = 9.5

|Sep precipitation days = 9.5

|Oct precipitation days = 9.4

|Nov precipitation days = 9.4

|Dec precipitation days = 11.0

|Jan snow inch = 2.9

|Feb snow inch = 1.4

|Mar snow inch = 0.7

|Apr snow inch = 0.0

|May snow inch = 0.0

|Jun snow inch = 0.0

|Jul snow inch = 0.0

|Aug snow inch = 0.0

|Sep snow inch = 0.0

|Oct snow inch = 0.0

|Nov snow inch = 0.0

|Dec snow inch = 0.8

|year snow inch =

|unit snow days = 0.1 in

|Jan snow days = 1.5

|Feb snow days = 1.1

|Mar snow days = 0.5

|Apr snow days = 0.0

|May snow days = 0.0

|Jun snow days = 0.0

|Jul snow days = 0.0

|Aug snow days = 0.0

|Sep snow days = 0.0

|Oct snow days = 0.0

|Nov snow days = 0.0

|Dec snow days = 0.7

|source 1 = NOAA

{{cite web

|url = https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-monthly-1991-2020&stations=USC00182325&format=pdf&dataTypes=MLY-TMAX-NORMAL,MLY-TMIN-NORMAL,MLY-TAVG-NORMAL,MLY-PRCP-NORMAL,MLY-SNOW-NORMAL

|publisher = National Oceanic and Atmospheric Administration

|title = U.S. Climate Normals Quick Access – Station: Dalecarlia RSVR, MD

|access-date = February 20, 2023

}}

|source 2 = National Weather Service

{{cite web

|url = https://www.weather.gov/wrh/climate?wfo=lwx

|publisher = National Weather Service

|title = NOAA Online Weather Data – NWS Baltimore

|access-date = February 20, 2023

}}