CITY OF LACEY WELLHEAD PROTECTION CHAPTER NO. 6 WELLHEAD PROTECTION 6.1 INTRODUCTION The City of Lacey relies on multiple groundwater sources to provide a safe and reliable potable water supply for its growing community (Figure 6.1). The City is committed to protecting the environment and preventing groundwater contamination through a proactive wellhead protection program. Wellhead protection programs are required by the USEPA and the Washington State Department of Health. For a groundwater-supplied water system, required plan elements include: A discussion of the hydrogeologic characteristics of the area; A susceptibility assessment of the sources; Delineation of wellhead protection areas (WHPAs); A contaminant source inventory within defined WHPAs; A contingency plan; Notification to owners/operators of potential contamination sources; Notification to regulatory agencies and local governments of WHPA boundaries and contaminant source inventory findings; Notification to local emergency responders of WHPA boundaries, results of the susceptibility assessment and contaminant source inventory, and contingency plan, and; A spill response plan. The City began implementing its Wellhead Protection Program (WPP) in 1995. In addition to the required elements listed above, over the years the WPP has also included several additional elements including land use restrictions, review of development/redevelopment proposals, site inspections of small quantity generators, groundwater monitoring, and public education. Since the last WHP update in 2003, a number of changes within the city have been considered in this update. This chapter summarizes Lacey’s updated WPP for all the required elements listed above. Most of the technical elements of Lacey’s updated WPP are described in detail in the City of Lacey Wellhead Protection Report that is included in Appendix M of this Water System Comprehensive Plan. CAROLLO ENGINEERS 6-1 February 2013 pw://Carollo/Documents/Client/WA/Lacey/8142A01/Deliverables/Chapters/Ch06.docx Well S15 Well S16 TW-BC3 TW-MR Well S19 TW-HP2 TW-MC Well S29 Well S24 Well S25 Well S07 Well S28 Well S21 Well S22 Well S06 Well S20 Well S01 Well S03 Well S27 Well S02 Well S09 Well S10 Well S04 This figure was originally produced in color. Reproduction LEGEND 0 8000 in black and white may result in a loss of information. Production Well Scale in Feet Map Projection: Test Well Washington State Plane Lacey City Limit South Zone NAD 1983 FIGURE 6-1 Source: CITY OF LACEY PRODUCTION City of Lacey Water Service Area Carollo, WA DNR, AND TEST WELL LOCATIONS Golder Associates Inc. WELLHEAD PROTECTION WSP UPDATE/WA 08393334F35_WellLocations.mxd | 3/15/2010 | THAMMOND CITY OF LACEY WELLHEAD PROTECTION 6.2 SUMMARY OF HYDROGEOLOGIC CONDITIONS 6.2.1 Physical Setting, Climate, and Precipitation The City of Lacey is located in the southern extent of Puget Sound, between the Nisqually River to the east and the Deschutes River to the west (Figure 6.1). The present day land surface is largely the result of erosion and deposition processes that have operated since the last glaciation occurred about 15,000 years before present. The landscape is generally low- lying, with the topography ranging from mean sea level (msl) along the Puget Sound to more than 360 feet above msl (amsl) near Fort Lewis Military Reservation and above 460 feet above msl at Tumwater Hill. Large portions of the region are rural and vegetation consists of coniferous forests and open prairies, as well as urban areas. The climate of northern Thurston County is typical mid-latitude, West Coast marine, characterized by warm dry summers and cool wet winters. During the winter months, rainfall is usually light to moderate in intensity and annual precipitation increases westwards from 40 inches near the Nisqually Delta to 50 inches in East Olympia. Infiltration of precipitation is the primary recharge source for the groundwater system in the region. In general, the portion of the precipitation that is not evaporated, transpired, or subject to surface run-off and overland flow is available to replenish the shallowest aquifer. 6.2.2 Regional Geology and Hydrogeology The understanding of the regional geology and hydrogeology has evolved during the last 40 years as the need to better manage Thurston County’s water resources has increased. The information presented in this section provides a general overview of the geology and hydrostratigraphy of the Lacey area. 6.2.3 Geologic Units The following geologic units in the Lacey area are presented in order of youngest (land surface) to oldest (to depths of up to 1,500 feet). The names and descriptions of these units are based on the most current accepted interpretation of hydrostratigraphy in this region (Borden and Troost, 2001). Additional information on local geology and the evolution of hydrostratigraphy interpretations in this area is provided in the WHP Report in Appendix M. The WHP Report also contains several cross-sections depicting the local variability of the geologic units. A transitional understanding of the stratigraphic sequence has been the generally accepted model for the Lacey area and considers that the strata are relatively continuous across the region, with the few exceptions being the major river valleys. More recent reinterpretations of the hydrostratigraphy have resulted in changes in the previously described hydrogeologic units including removal of some unit names, and incorporating recently identified outwash channels. The hydrostratigraphic units current interpretation are provided in more detail below: Post-Vashon (Holocene) Alluvial and Deltaic Sediments: These sediments exist along the shallow valley bottoms of the main streams, and therefore have relatively CAROLLO ENGINEERS 6-3 February 2013 pw://Carollo/Documents/Client/WA/Lacey/8142A01/Deliverables/Chapters/Ch06.docx CITY OF LACEY WELLHEAD PROTECTION limited areal extent. These units have minimal regional significance in storing or transmitting groundwater. Vashon Recessional Outwash (Qgo, Qgos): This unit consists of poorly to moderately sorted, permeable sand and gravel deposited by streams emanating from the melting and receding glacier. They make up the laterally extensive unconfined water table aquifer and range in thickness of up to 40 feet, supporting small wells for domestic use. The Qgo unit is shallow, unconfined and is substantially influenced by seasonal precipitation; consequently, this unit is very susceptible to contamination from surface activities (PGG 2002). Vashon Glacial Till (Qgt): This unit consists of unsorted sand, gravel and boulders encased in a silt-clay matrix. It is characteristically compact and generally acts as an extensive confining bed. The unit thickness is typically between 20 and 60 feet. Areas where this till layer is absent or discontinuous have been documented immediately west of Long Lake, between Hicks and Southwick Lakes, and in the areas of the County landfill north of Madrona Park and McAllister Park (PGG, 2002). Other areas where till is thin and may be moderately permeable include the vicinities of City of Lacey wells 4 and 7 (PGG, 2002). Vashon Advance Outwash (Qga): This unit consists of fine- to coarse-grained sand and gravel grading upward. It forms the first water-bearing unit of economic value and is the main aquifer for most small-scale, private wells and supplies water and several larger-yielding municipal and industrial wells. It is generally confined by the Qgt unit with a typical thickness between 10 and 65 feet. City wells completed in this unit are wells S01, S04, S15, and S16. This aquifer will be more susceptible to contamination from surface activities in areas where the overlying till layer is absent or discontinuous. Pre-Vashon Glaciolacustrine Deposits (Qpf): This unit consists of laminated clayey and silty sediments deposited in pro-glacial lakes. The soils have a low permeability, and act as a confining unit between the Qga and Qpg and act as a confining unit between the Qga and Qpg when present. However, these sediments are discontinuous in the Lacey area, such as between Lacey wells 6 and 7 (PGG 2002). Pre-Vashon Gravel (Qpg): This unit consists of coarse, stratified sand and gravel. It is laterally extensive, although rarely more than 50 feet thick (between 15 and 70 feet). This unit forms the principal economic (mostly confined) aquifer in the area. City wells completed in this unit are wells S02, S03, S06 (partial), S10, S20, S21, S22, S24, S25, S27, S28, and S29. Although this layer is generally confined by overlying till and the underlying low permeability undifferentiated deposits, the overlying till deposits may be absent or relatively permeable in places (PGG 2002). In these areas, the Qpg could more susceptible to contamination from surface activities. Undifferentiated Quaternary and Tertiary Deposits (TQu): This unit consists of fine- to coarse-grained unconsolidated sediments extending to bedrock. The base of this unit ranges from about 300 feet above mean sea level (msl) in the southeast to more than 1,500 feet below msl along the Puget Sound. It consists of a sequence of aquifers and confining beds; tapped by only a few water wells locally. City wells completed in this unit are wells S06 (partial), S07, S09, and S19. New wells planned for this unit include TW-HP2, TW-MR, TW-MC, and TW-BC3. The depth of this unit and the presence of overlying confining layers will generally protect the saturated portions of this unit from surface contamination. CAROLLO ENGINEERS 6-4 February 2013 pw://Carollo/Documents/Client/WA/Lacey/8142A01/Deliverables/Chapters/Ch06.docx CITY OF LACEY WELLHEAD PROTECTION The bedrock consists of sedimentary sandstone, siltstone and claystone, and some igneous bodies of andesite and basalt. Some private wells produce limited groundwater from the bedrock unit, though it is considered relatively impermeable and does not contribute significantly to the regional groundwater flow system. 6.2.4 Groundwater Flow Regional groundwater flow occurs in the three primary aquifers (Qga, Qpg and TQu), all of which are utilized by the City of Lacey wells.