4.1 Water Supply Sources
The City's water supply system consists of three sources: the Dungeness River Infiltration Gallery, the Silberhorn Wellfield, and the Port Williams Wellfield. Prior to construction of the Infiltration Gallery, the City diverted water directly out of the Dungeness River. In 1953 the City was authorized to withdraw water from the infiltration gallery, and in 1954 a second surface-water diversion was authorized to convey water from the river to the infiltration gallery. Groundwater withdrawals from the Silberhorn Wellfield were authorized in 1975, and pumping from the Port Williams wellfield was authorized in 1996.

The Infiltration Gallery is located east of the Dungeness River in the NE ¼ of the NW ¼, Section 12, Township 29N, Range 4W. It consists of a large-diameter collection well located east of the river, from which horizontal interception pipes extend to about 150 feet from the current stream channel. The interception pipes are buried and set in gravel pack. Until the mid 1980's, the City used to supplement Infiltration Gallery yield by diverting surface water from the Dungeness River into the gravel pack surrounding the laterals. Now that this practice is discontinued, discharge from the Infiltration Gallery flows via gravity to a treatment plant for chlorination. Gravity flows are taken on-demand at rates of about 200 gpm (0.45 cfs).

The Silberhorn Wellfield is located in Doctor James Standard Memorial Park, 750 feet west of the intersection of Silberhorn and River Roads (NE ¼, NW ¼, Section 25, Township 30N, Range 4W). Three production wells were constructed between 1975 and 1985; however, Well #1 is no longer in production and is currently used for groundwater level monitoring. Well completions range from 132 to 220 feet below land surface (bls), and instantaneous pumping rates range from about 300 to 370 gallons per minute (gpm) on demand. Drilling information and pumping responses indicate that groundwater occurs under confined conditions at the wellfield. The three wells are tentatively identified as completed in a confined portion of the Shallow Aquifer (PGG, 1996). Occurrence of glacial till above the completion intervals and the confined nature of the aquifer conform to the USGS description of the Shallow Aquifer summarized above.

The Port Williams Wellfield is located just north of Port Williams Road, about 500 feet west of its intersection with Brown Road (SE ¼, NW ¼, Section 17, Township 30N, Range 3W). Two production wells were installed in 1995 and 1998, and are both completed in the Lower Aquifer. Well completions range from 284 to 411 feet bls. While maximum well yields range from 635 to 800 gpm, the wells are currently pumped on demand at instantaneous rates between 550 to 625 gpm. The Port Williams wellfield was constructed in order to shift a portion of the City's pumping withdrawals away from the Silberhorn Wellfield and the Dungeness River Infiltration Gallery towards a deeper groundwater source that has less hydraulic connection with the Dungeness River. Reduced withdrawals from the Infiltration Gallery are beneficial in that they leave more flow in the Dungeness River to benefit fish habitat, and were agreed upon between the City and Ecology in 1997 (Ecology, 1997). Reduced withdrawals at the Silberhorn Wellfield serve to reduce pumping stress on an aquifer with a history of local groundwater level decline (see Section 7.2), and may also benefit Dungeness River streamflow.

4.2 Water Use
The City monitors water use from all three of its sources, with available records beginning in 1978. Figure 7 shows that average annual water use has increased from about 0.4 million gallons per day (mgd) in the early 1980's to about 0.8 mgd in 2001. Most of the increase occurred between 1982 and 1989, with only minor increases noted after 1990 except for two peak years (1994 and 1995) when average water use reached about 0.9 mgd. While annual precipitation plotted on Figure 7 shows that 1994 corresponds to a low precipitation year, relatively high pumping in 1995 cannot be similarly attributed to low rainfall.

Prior to 1992, water-use records only provide total pumping from the Infiltration Gallery and Silberhorn Wellfield combined. After 1992, the records show a reduced reliance on these two sources and an increased reliance on the Port Williams Wellfield. In the past four years (1998-2001), water use from the City's three sources was divided as follows:

Seasonal patterns of water use are shown on Figure 8, a chart of monthly pumping from the City's three sources. Water use is relatively low between November and April, with values on the order of about 0.6 mgd. Beginning in April or May, water use begins to climb to maximum values of about 1.0 to 1.4 mgd in July and August. Water use remains relatively high in September and then declines back down to the relatively low winter rates observed in November through April. Relative to other areas on the Olympic Peninsula, water use near Sequim is higher due to low rainfall in the rain shadow of the Olympic Mountains.

The City currently reuses a portion of its treated municipal wastewater for irrigation purposes. In 1998 the City upgraded its wastewater treatment to meet Class "A" surface water standards for reclaimed water, with the goal of achieving 100% reuse. The wastewater treatment plant produces about 0.5 mgd of reclaimed water. Initially, the reclaimed water was used only for irrigation of ornamental roadside vegetation, the Highway 101 rest area, the yard at the City Shop, and for various City Shop operations. The City's Reuse Demonstration Site, located immediately north of Carrie-Blake Park, was constructed in 1999-2000 and has since been used to demonstrate reclaimed water irrigation of fields and gardens. It is one of the first sites of its kind, and includes data collection to evaluate hydrologic responses to the irrigation applications. Irrigation at the site began in the summer of 2000, and the City began augmenting streamflow in Bell Creek with 0.1 cfs (0.07 mgd) of reclaimed water in December 2001. The remaining reclaimed water is available for other certified uses, but is currently discharged to a new outfall in Sequim Bay a quarter mile northeast of Washington Harbor (at a water depth of 53 feet). Guidance for the City's program of water reuse was provided by the Water Reuse Task Force, a group composed of community members, tribal representatives, and agency staff from Washington Departments of Ecology, Health, and Fish & Wildlife (among others). Although the water savings associated with reuse of reclaimed water currently represents only a small portion of the area's overall water budget, the potential for water savings associated with developing new uses is significant.

Other pumping withdrawals in the vicinity of the City's two wellfields are taken by the PUD #1 of Clallam County, various other water systems, and individual private wells. East of the Dungeness River, the PUD operates the Loma Vista Wellfield (its largest source) and several small satellite systems. The Loma Vista wellfield is located about one mile east of the Silberhorn Wellfield. Between 1995 and 2001, the Loma Vista Wellfield had an average withdrawal of 94,000 gallons per day (0.094 mgd), down from a prior average of 154,000 gallons per day (0.154 mgd) between 1992 and 1994. Some of the later pumping was shifted to the PUD's Holgerson Well on the same water system (Evergreen System), where average annual pumping ranged from 38,000 to 45,000 gallons per day (0.038 to 0.045 mgd) between 1999 and 2001. Other major water systems east of the Dungeness River include: Sunland Water District, Parkwood Mobile Home Community, and Dungeness Meadows Homeowner's Association. As a rough measure of the relative groundwater withdrawals, in 1996 these three systems had 630, 210, and 200 total connections, respectively (1,040 connections total). Several other water systems with between 50 and 100 total connections exist east of the river. In comparison, in 1996 the City had 1,086 total connections and the PUD's Evergreen System had 280 total connections.

Increases in the number of private domestic wells can be reasonably approximated by increases in the total number of wells for a given area. Based on a well database maintained by Clallam County Natural Resources Division (Soule, pers. comm., 2002), Figure 9 presents charts of the annual numbers of total wells from 1950 onwards for three areas² :

1. The northern half of the Sequim-Dungeness Peninsula east of the Dungeness River;
2. Within approximately one mile of the Silberhorn Wellfield, and
3. Within approximately one mile of the Port Williams Wellfield.

In the overall Sequim vicinity, the increase in consumptive use by domestic wells between 1990 and 2001 is estimated to be approximately 0.32 mgd, and is predominantly associated with irrigation for landscaping. Over the same period, the total increase in total pumping from domestic wells (including the non-consumptive portion of use) is likely to be at least 0.58 mgd³ . The sub-area immediately surrounding the Silberhorn Wellfield accounts for about 14 percent of this increase, and the sub-area immediately surrounding the Port Williams Wellfield accounts for about 16 percent of the increase. Increased total pumping from the City's two wellfields is estimated to be approximately 0.38 mgd over the same 11-year period and 0.48 mgd since the late 1970's⁴ . A portion of the City's pumpage increase is non-consumptive and is returned to shallow groundwater via residential irrigation applications and (limited) portions of the City's service area without sewer coverage. Thus, increases in consumptive groundwater use estimated for domestic wells and the City's two wellfields are of similar magnitude between 1990 and 2001. It should be noted that the City's withdrawals are localized to its wellfield locations, whereas domestic withdrawals are spread out over larger areas.

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²The first (and largest) area includes all square-mile sections north of Township 29, west of Sequim Bay, south of the northern coast, and east of a north-south section line 1 mile west of Range 3W (approximate course of the Dungeness River). The areas within a mile of the two wellfields are based on quarter-quarter sections within a mile radius of the productions wells.  Return

³ Based on the assumption that residential irrigation efficiency (plant requirement divided by irrigation application) is about 75 percent. If actual efficiencies are lower, total estimated pumping would be higher.  Return

⁴ While data are generally lacking for the distribution of pumping between the Infiltration Gallery and the Silberhorn Wellfield prior to 1992, discussions with the City indicate that withdrawals were approximately divided as 30% from the Silberhorn Wellfield and 70% from the Infiltration Gallery. Assuming this to be the case, analysis based on Figure 7 yields the above numbers.  Return